KTBB News|Sports|Talk - AskWx

Dr. Bob, has it ever snowed on Christmas Eve or day in Tyler?

Dr. Bob, has it ever snowed on Christmas Eve or day in Tyler? (Posted by Administrator)

ANSWER

Snow--none; sleet--yes, in 1975 and 1991 there was snow on the ground in
Tyler, in 1929 (from a December 21 snow), and in 1963 (from a December 22
snow.) I don't think we'll be numbering 2007 among the above list.
RKP

This morning you said that our recent weather temperature was very similiar to the years of 1954 and 1969 (I believe those were the dates). Does this also mean that the rainfall amount could be similiar as well, and, if they are similiar, what would be a prediction for the rainfall amounts for this summer? Thank you.

This morning you said that our recent weather temperature was very similiar to the years of 1954 and 1969 (I believe those were the dates). Does this also mean that the rainfall amount could be similiar as well, and, if they are similiar, what would be a prediction for the rainfall amounts for this summer? Thank you. (Posted by Administrator)

ANSWER

Sir, I said that today's weather map was similar to that of June 2, 1969 and
May 21, 1954. As things turned out, 1969 was dry during the first half of the Summer, and wet in its second half; in 1954, rainfall was below normal throughout the Summer.

The 90-day outlook for the Summer is calling for below normal rainfall. Normal rainfall between June 1 and August 31 is about 8 inches. I would expect rainfall this Summer to run around 6 inches, and temperatures to run slightly above normal.

One qualifier: we have had a rather wet Spring. Though it is uncomfortably warm and humid out there right now, I would expect the wet soils to hold down temperatures somewhat through at least the middle of June.
RKP

With the clear and dry conditions we have been experiencing you would think the barometric pressure would be higher than it has been the past couple of days.

With the clear and dry conditions we have been experiencing you would think the barometric pressure would be higher than it has been the past couple of days. (Posted by Administrator)

ANSWER

Yesterday and today, we had a thermal low--the result of heating. Also, there is a surface low pressure area to our northwest running from Eastern Kansas into Southwest Texas. This is being intensified by a strong storm system over the Northern and Central Rockies.

And, yes, you are right in thinking the pressures later in the Summer would have been higher.

RKP

About 20 years ago, the "northern lights" were visible in this area for one or two evenings. I know you will remember the exact date and would you again explain what occurred for this to be visible so far south.

About 20 years ago, the "northern lights" were visible in this area for one or two evenings. I know you will remember the exact date and would you again explain what
occurred for this to be visible so far south. (Posted by Administrator)

ANSWER

It was in March 1989. The vertical air column was extremely dry above us
and well northward up the Plains; it was just prior to the Vernal Equinox,
and the Northern Hemisphere was still pointing away from the sun; there
was a maxima of solar activity, which increased the number of ionized
particles in the atmosphere.

We, thus, got to see something which comes along once every
half-century or so this far south--the Northern Lights.
RKP

When you say "moderate to fresh" winds--what does that mean?

When you say "moderate to fresh" winds--what does that mean? (Posted by Administrator)

ANSWER

About two centuries back, a Royal Navy officer (captain or admiral or something) named Sir Francis Beaufort came up with a scale for measuring wind velocity without requiring an instrument. This is known as the "Beaufort Scale", and is still in common usage.

What is both the meaning and origin of the "Red Flag Warning" I saw in the forecast today?

What is both the meaning and origin of the "Red Flag Warning" I saw in the forecast today? (Posted by Administrator)

a) Red flag warning: This is a term which the Weather Service took a
while coming to. The idea of "warning" suggests an existing weather
condition directly threatening life and property. A tornado warning means
there is one--and you'd better do something.

I'm looking for a scale that describes the terminology used with wind velocity ranging from 1 mph to 35 mph. Light,moderate strong, etc..

I'm looking for a scale that describes the terminology used with wind velocity ranging from 1 mph to 35 mph. Light,moderate strong, etc.. (Posted by Administrator)

ANSWER

You are looking for the Beaufort scale, which can be found at Wikipedia. Use the link below to view that article.

RKP

Beaufort Scale

Why is it windy the day after it rains?

Why is it windy the day after it rains? (Posted by Administrator)

Rain most often results from the passage of a storm system (surface and
upper air low pressure area.) High pressure builds in behind the departing
low. Air moving from the high into the low causes the winds. The deeper
the low, the stronger the wind. RKP

Dr. Bob , what is your opinion of "global warming"?

Dr. Bob , what is your opinion of "global warming"? (Posted by Administrator)

ANSWER

Sir,
I believe global warming is happening. Insofar as its cause, there are
two possible answers:
a) variations in solar activity, and
b) increase in greenhouse gasses in the atmosphere.
The latter has been occurring for about 200 years, with a sharp increase
since about 1950.

Over what period of past years is "average precipitation" computed?

Over what period of past years is "average precipitation" computed? (Posted by Administrator)

ANSWER

The term "average" refers to the present standard climate period of
1971-2000; in May 2011, we will go to the new period, 1980-2010.
RKP

What is DIRUNAL CONVECTION? My dictionary didn't have it and the online definition leaves me scratching my head. Could you define in layman's terms?

What is DIRUNAL CONVECTION? My dictionary didn't have it and the online definition leaves me scratching my head. Could you define in layman's terms? (Posted by Administrator)

ANSWER

Yes, Sir. "diurnal" refers to the day/night swing; thus, "diurnal
convection" is convection which enhances during the afternoon in the period
of maximum daytime heating, and collapses with nightfall. "Convection", of
course, is the fancy word for thunderstorm development.
RKP

How does the angle of the Sun affect the temperature of the Earth?

How does the angle of the Sun affect the temperature of the Earth? (Posted by Administrator)

ANSWER

The higher the sun angle, the greater the amount of heat it can impart to the Earth. At the Winter Solstice in Tyler, Texas, the sun angle at noon is about 35 deg. above the horizon at noon; at the Summer Solstice, the angle is about 80 deg. above the horizon. Thus, the higher the angle--the greater the heat. About six weeks after the sun angle begins to decline, temperatures begin a cool-down. The lag-time (which also exists after the Winter Solstice) is because of the ability of the earth to store heat. I hope this helps.

RKP

What is the average yearly rainfall for Tyler, Texas?

What is the average yearly rainfall for Tyler, Texas? (Posted by Administrator)

ANSWER

The average precipitation based on the 1971-2000 Standard Climatic Period is 45.27 inches; this is a slight increase over the 1961-1990 Standard Climate, when the amount was 45.12 inches. The average annual precipitation has increased by about one inch over the 1931-1960 Standard Climate--when I first began reporting weather.

RKP

Dr. Bob, What is the difference in a cyclone and a hurricane?

Dr. Bob, What is the difference in a cyclone and a hurricane? (Posted by Administrator)

ANSWER

In the Northern Hemisphere, an anti-cyclone is a high pressure center; a cyclone is a low pressure center.

RKP

Is it true that when you count to 5 the rain storm is 1 mile away?

Is it true that when you count to 5 the rain storm is 1 mile away? (Posted by Administrator)

ANSWER

Yes, if you're talking about the time lapse between seeing lightning and hearing thunder. Light travels at 186,275 miles per second; sound at about 739 mph--or about one mile in every five seconds. Actually the speed of sound fluctuates with air pressure and altitude, but not so much as to make a difference in the five-second rule.

RKP

A professor (years ago) told us that a 50% chance of precip means that on like days with similar conditions, that there was a 50-50 probability of precip. What's the real deal?

A professor (years ago) told us that a 50% chance of precip means that on like days with similar conditions, that there was a 50-50 probability of precip. What's the real deal? (Posted by Administrator)

ANSWER

Actually, neither is correct--though your geography professor was somewhat closer. This, also, explains why I never use them in broadcast, and place them in brackets in writing--so very few understand the concept. The POP (probability for measurable precipitation) is the likelihood that a given location will receive 0.01 inch of precipitation or greater. Thus, the POPs do not refer to areal coverage or amount.

RKP

What causes the sound that thunder makes?

What causes the sound that thunder makes? (Posted by Administrator)

ANSWER

The sound of thunder is caused by the superheating of the atmosphere by lightning, and the rapid expansion of the air molecules due to the heating.

RKP

What is the difference between isolated thunderstorms and scattered thunderstorms?

What is the difference between isolated thunderstorms and scattered thunderstorms? (Posted by Administrator)

ANSWER

The difference is the proportion of the forecasting zone which the thunderstorms are expected to cover; typical forecasting blocks are about 5,000 square miles. Isolated suggests 5-10 percent of areal coverage; scattered suggests upwards of 25 percent areal coverage.

RKP

How does snow occur?

How does snow occur? (Posted by Administrator)

{answer
occurs when moisture vapor condenses through cooling into droplets in the atmosphere; if those droplets--and they are extremely tiny--freeze, then the droplets become very small ice crystals. If enough of these bump together, they stick to one another, and eventually become heavy enough to fall to earth as snowflakes.

RKP

Why is it that the further you get from Earth the colder it gets?

Why is it that the further you get from Earth the colder it gets? (Posted by Administrator)

ANSWER

The heating of the earth is due to its atmosphere. When you go farther away from the surface of the earth, the atmosphere thins. Thus, the ability of the atmosphere to retain heat decreases. This phenomenon reverses at about 40 miles above the surface, and then resumes. Outside the earth's atmosphere, the sun's ability to heat is very much limited, so it is quite cold.

RKP

What is the eye of the storm? How is it created?

What is the eye of the storm? How is it created? (Posted by Administrator)

ANSWER

The "eye" of the storm is the area at its center; it is usually free of cloud, and has light winds; it is created by the strong winds whirling around its vortex; the upward forcing of this air when the vortex narrows creates the "eye", which is cloud-free and has little surface wind.

RKP

Could you please answer below questions as equation?

Could you please answer below questions as equation? (Posted by Administrator)

Could you please answer below questions as equation?
1-The relationship between daily average temperature, relative humidity
and saturation vapor pressure?

ANSWER

The higher the relative humidity, the higher will be cool-season
average temperatures, and warm-season temperature averages will be lower.

What is the conversion factor to convert millibars to inches and inches to millibars?

What is the conversion factor to convert millibars to inches and inches to millibars? (Posted by Administrator)

ANSWER

This is an approximation: 33.87; millibars to inches would be divided by the coefficient; inches to millibars, you would multiply the inches by the coefficient.

RKP

What causes frost to form? If washed off a plant before the sunlight hits it is there any damage to the plant?

What causes frost to form? If washed off a plant before the sunlight hits it is there any damage to the plant? (Posted by Administrator)

ANSWER

Sir, Frost forms when the water vapor in the air condenses and freezes since the air temperature is 32 deg. or lower, and it collects on exposed objects. In order for this to happen, there must be:

* light winds
* a dew point temperature not much lower than 28 deg.

The observed air temperature may be higher than 32 deg., since observations are taken at 5 feet above ground level. Cold air, being heavier, the temperature at the actual surface may be a few degrees colder than the reported temperature. Insofar as plant damage: I'm not into horticulture; it strikes me that the primary benefit for getting it off before sunlight strikes the plant is that the plant was ice-coated for a shorter period of time.

RKP

I saw the term "WETBULBING" in one of your reports. What is "WETBULBING?"

I saw the term "WETBULBING" in one of your reports. What is "WETBULBING?" (Posted by Administrator)

ANSWER

"Wetbulbing" means the cooling of the atmosphere through evaporation of precipitation as it falls.

The term comes from one of the two thermometers on a psychrometer. A
psychrometer is the instrument we used to use to determine dew point and
humidity. It is, essentially, two thermometers on a chain which is twirled
about the head. One of the thermometers is a "dry bulb"; the other has a
piece of gause over its base which is dipped in water, and called the "wet
bulb". The "wet bulb" registers a lower temperature than does the dry bulb
because of evaporation. The difference is the "depression"; that yields the
dew point and hence the relative humidity.

When rain falls through the atmosphere, some of the moisture from the
drops evaporate, and cool the atmosphere. We call it "wet bulbing".

RKP

How much easier is it to prepare a weather forecast these days compared to when you started in the business?

How much easier is it to prepare a weather forecast these days compared to when you started in the business? (Posted by Administrator)

I would be very curious as to the most significant changes to the industry - like equipment, internet access, etc.... And - if applicable at all - how much more accurate are the present day forecasts?

ANSWER

Sir,
I'm glad you asked this. I have spent some time thinking about this
before I replied, and here goes:

Forecasting is much easier in every sense of the word but one since I
started. In 1962, the Weather Bureau (as it was then called) issued a
forecast for East Texas--which ran from Bonham on the northwest to Bay City
on the southwest, and along the Louisiana border. Also, we got one forecast discussion, out of Meacham Field in Forth Worth. Thus, if you disagreed, you had only one office with which to disagree. Nowadays, we have access to every National Weather Service, and everything they publish. So, when two nearby forecast offices disagree--as they frequently do, you can adopt the reasoning of the one with which you agree, and go from there.

I did this on the onset of the recent cold event--I believed Fort Worth and not Shreveport, and on the icing--I believed Lake Charles and not Houston,
Shreveport, or Fort Worth. Maybe it is 45 years of doing this, but I chose
right on both occasions.

Insofar as the amount of information--well, it is incredible. When I
started, we had access to an "8028 teletype.) This operated at 100 words
per minute, and spent the first half of each hour printing out observations
in the old Surface Airways code. (At least they weren't doing it in Celsius then.) The last half of the hour they put in whatever they had room for--which were usually printed in the meteorological code--lots of
abbreviations and contractions. I could read them, but it was a rather
arcane specialty. Now, most of it is sent in clear--though the stuff out of the national offices still comes in code.

The Internet has made a world of difference. This is why we have as
much as we have. Insofar as instrumentation: well, to my left is a remote reading thermometer, and to my right is an automated rain gauge. In 1962, we had a wooden shelter (outside), and a direct reading rain gauge (outside), which I had to go outside to read. I got the indoor equipment about fifteen years ago. I still have to use the direct reading rain gauge for frozen precipitation, and for the actual daily observation on rainfall, as the automated gauge is still not quite perfected. Mine does well on light rain; in heavy rainfall, it reads about 25 percent high.

Insofar as accuracy of forecasting: we are better at the analysis of
severe weather and potential heavy rainfall events. I'm not sure we're that much better at sky cover, temperature, and wind forecasting. What we can now do, which 45 years ago we could not begin to do, is to forecast with any degree of accuracy beyond about 72 hours. The cold event we forecast 12 days out; the current rain event 13 days out, and we are expecting significant precipitation and cold temperatures to continue well into March. That is something which, 45 years ago, would have been little more than an educated guess.

I hope this answered your question; again, I'm glad to have been made to
think about it.

Two more comments:
a) There is one thing I absolutely do not like--the inclusion of
POPS--"probabilities for measurable precipitation". I place them in
parentheses in written forecasts, and do not use them in spoken forecasts.
Most people haven't the foggiest notion of what that means. I use terms s
such as "isolated", "scattered", "likely", "periods of," etc. The
percentage term actually means that the given percentage is the mathematical probability that any given point within the forecasting zone (about 4,000 square miles) will received 0.01 inch or more of precipitation. I think "likely" or "periods of" makes a lot more sense.
b) On accuracy: someone sent me a not very flattering enquiry about three
years ago on accuracy. He agreed to a set of parameters, and agreed to keep score for one month.

The parameters were: 1, the forecast temperatures were within three degrees, cloud cover and wind direction and velocity were correct, precipitation probabilities were scored on 40% or more we got some, 30% or less we did not. We ran the forecasts out for three days. In october 2003, we were about 92% correct. There were the 31 days times 3, and the multiple values for each day. The accuracy percentage was based on about 500 separate items.

Forecasting beyond 72 hours is about 85% accurate; beyond 168 hours, it
is about 65% accurate.

One more thing: Absolute candor requires this. In January 1963, when I had been doing this for about four months, I made two mistakes:

a) I missed the afternoon high temperature by 58 degrees, and

b) I believed my forecast.

I do not remember the exact date, but, on the evening before, the 8028
circuit had mal-functioned, and we did not get our up-to-date information.
Also, I was attending Stephen F. Austin State Teachers College (as it was
then called), working at the newspaper/radio station from 4 p.m. until 1
a.m., and going to Nacogdoches via Continental Trailways three days a week
to finish my masters degree.

On the day in question, I had forecast (based on an old analysis,) partly cloudy, high upper 70s. When I left Tyler that morning, it was mild. I wore a short-sleeved shirt. The Arctic air mass, which we thought would arrive overnight, must have followed the bus down. I was standing beside US-259, awaiting the bus at 2 p.m. on that afternoon, in my short-sleeved shirt, and the actual air temperature was 19 degrees.

Yes, I guess we're a lot better at forecasting--or I'm a lot older.

RKP

Why didn't the ground freeze during this last winter blast when the temperatures stayed below freezing for so long??

Why didn't the ground freeze during this last winter blast when
the temperatures stayed below freezing for so long?? (Posted by Administrator)

ANSWER

The ground failed to freeze because of something called latent heat--in
other words, the heat stored in the ground. At the onset of the freezing
temperatures, the soil temperature was about 52 deg. Soil has a high
specific heat--meaning it loses heat rather slowly. By now the soil
temperatures are down to around 40; so, if we get anything frozen next
week, we might see it sticking.
RKP

I looked for an extended winter forecast on the website but I could not find one. Can you tell me what the temps and precipitation will be for the upcoming winter?

I looked for an extended winter forecast on the website but I could not find one. Can you tell me what the temps and precipitation will be for the upcoming winter? (Posted by Administrator)

ANSWER

We carry it, but--unfortunately--only one day during the month--the day it is issued. I'll try to get that taken care of, as it is something which had not occurred to me. By the way, the long range forecasts are issued on the third Thursday of each month, and I usually carry them on the following Saturday or Sunday. Thus, the next one will come out on the 17th, and will probably appear the night of the 19th and morning of the 20th.

Based on our present analysis:

a) above normal precipitation; and

b) near to above normal temperatures.

Thus, the drought will be ending in three or four weeks, and it should not be unduly harsh. We base this on a neutral El Nino condition in the equatorial Pacific Ocean.

RKP

Could you tell me how to figure the wind chill while riding a motorcycle? If you are traveling at 50 mph would that equal to a 50 mph wind?

Could you tell me how to figure the wind chill while riding a motorcycle? If you are traveling at 50 mph would that equal to a 50 mph wind? (Posted by Administrator)

ANSWER

This is probably a lot more than you want to read. But, here goes:

a) If you are traveling due north (360 deg.), and the wind is calm, and your speed is 50 mph, then the wind chill effect would be as if the wind were blowing at 50 mph.

b) If you are traveling 360 deg., and the wind is blowing at 20 mph from 330 deg., then to compute the wind chill you would need to multiply the wind velocity by the cosine of a 30-deg. angle, which is .866. Thus, at 50 mph and a 20 mph wind, the effective velocity would be about 67 mph.

c) If you are traveling in a 360-deg. direction, and the wind velocity is 20 mph from 300 deg., then you would multiply the velocity by the cosine of 60 deg., which is .500, and add that to your speed. The effective wind velocity would be 60 mph.

d) If you are traveling in a direction of 360 deg., the wind velocity is 20 mph, and its direction is 180 deg., the cosine of 90 deg. (the difference between 270 deg. and 180 deg.) is 1.0. You would multiply the velocity of 20 mph by 1.0, and then subtract that from your speed. With a speed of 50 mph and a velocity of 20 mph, the effective speed would be 30 mph. Since the angle of incidence of the wind is greater than 90 deg., the velocity would have to be subtracted from your speed to obtain the effective velocity.

Note the use of 90 deg.; if the angle of incidence of the wind is less than 90 deg., than that wind adds to the effective wind velocity on you when you're riding the bike. If the angle of incidence is greater than 90 deg., than the effective velocity is decreased because you are traveling with a part or all of the wind. The same set of assumptions would apply for directions between 360 deg. and 90 deg.--you would add in the effect of the head wind; and for directions between 90 deg. and 180 deg., you would subtract the effect of the tail wind. I am submitting this to a mathematician who knows very, very much more than do I. If she tells me I am wrong, I will re-submit.

UPDATE: My wind chill calculation formula is correct.

RKP

What is a dry line? What is its relationship to storms, fronts, moisture, etc.? What does your sign off "that's 30" mean?

What is a dry line? What is its relationship to storms, fronts, moisture, etc.? What does your sign off "that's 30" mean? (Posted by Administrator)

ANSWER

a) A dry line--I prefer the older term dew point front--is a boundary between very moist air on one side and very dry air on the other. In our part of the country, the moist air is almost always to the east and south of the boundary, and the dry air to the west and north. The boundary is most common in West Texas during the Spring season, and oscillates back and forth, moving eastward to near the IH-35 Corridor during the day, and back to near the 103rd meridian (New Mexico border) at night. Since there is a sharp contrast in air masses across this boundary, thunderstorms often develop--particularly if there is available upper air lifting energy. These thunderstorms usually move into our area during the late-evenings or early-mornings. Not all dew point front-induced thunderstorm complexes make it this far east, though.

b) I got into the radio business from the newspaper business. In 1962 when I started, newspapers often owned radio stations. KTBB was owned by the Tyler papers--in fact, "TBB" stands for T. B. Butler--the name of the company which publishes the Tyler Morning Telegraph. We did reports from the newsroom on the radio station. "30" is a symbol used in newspaper editing to inform the typographer that this is the end of the story; it originated in the telegraphic symbol for end of story when wire stories were sent via Morse telegraph. The first time I was ever on the air, I couldn't figure out a way to quite--so I just said, "That's 30"; since I've been on the air forty-three years (in two months), I guess it has sort of stuck!

RKP

What are the typical affects that a Hurricane or Tropical Storm have had on the Tyler area in the past? I am supposing that the wind speeds would not be significant but that rainfall could be substantial?

What are the typical affects that a Hurricane or Tropical Storm have had on the Tyler area in the past? I am supposing that the wind speeds would not be significant but that rainfall could be substantial? (Posted by Administrator)

ANSWER

The effects are determined by where the tropical cyclone makes landfall, and its direction of movement afterwards. These observations assume a tropical cyclone with peak winds of 65 kts. (minimal hurricane) and central pressure of 975 mbs. at landfall, it has begun its northeastward re-curve, and that there are no other more potent features at the time it makes landfall.

a) From the mouth of the Mississippi River eastward: a northeasterly surface wind, considerable middle level and high level cloudiness, and insignificant rainfall;

b) from Galveston Bay to the mouth of the Mississippi River: northeasterly winds of 15-25 mph with gusts, rainfall of 0.5-1.0 inches;

c) Between Galveston Bay and Corpus Christi Bay: northeasterly winds backing to northwesterly of 15-30 mph with gusts, rainfall of 1.0 and higher inches;

d) From Corpus Christi Bay southward: northeasterly winds of 10 mph or less, some blow-off middle and high cloudiness, and little rainfall.

In 1961 when Carla came ashore southwest of Galveston, I was on a C-47 flying into Tyler--Pounds on the night of landfall; we had to circle for about 90 minutes because of a thunderstorm and heavy rain. There was a guy on the aircraft who had a bottle of hooch--which he largely consumed during the circling. To complicate matters, the tower did not think the landing gear had deployed, and the Fire Department met us. Fortunately, the gear were down, and all was well.

RKP

What is a cold front, warm front, and precipitation?

What is a cold front, warm front, and precipitation? (Posted by Administrator)

ANSWER

A cold front is the leading edge of a mass of cooler air which is moving into a mass of warmer air; a warm front is the exact opposite; precipitation is moisture vapor in the atmosphere which has condensed out with the droplets adhering together to form liquid or frozen "precipitation"--rain, snow, ice pellets, and the like.

RKP

Does evaporation affect temperature?

Does evaporation affect temperature? (Posted by Administrator)

ANSWER

Yes, evaporation does affect temperature. As air flows over a moist surface, the air is cooled by the conversion of that moisture from liquid water into moisture vapor.

The best evidence of this is that temperatures do not warm as much in humid air as they do in moist air.

A practical observation of this which you can make is to look at a glass containing an iced beverage. The glass will "fog up", which is caused by the temperature of the air immediately surrounding the glass lowers, and the moisture vapor in that air condenses as water on the side of the glass.

RKP

I was hoping that you could tell me why the sky turns a greenish color during some severe storms, and why that is usually associated with tornadoes?

I was hoping that you could tell me why the sky turns a greenish color during some severe storms, and why that is usually associated with tornadoes? (Posted by Administrator)

ANSWER

The "green" skies to which you refer are a trick of the refraction of light; the light rays are bent by the moisture vapor and particulate matter in the cloud mass of a strong thunderstorm; the part of the spectrum to which they are bent has a greenish or sometimes yellowish hue.

RKP

When given the probability of precipitation, is that percentage an indication of how likely any one spot is to receive rain? Is there a rough or more exact equivalent in gallons of an inch of measured rain?

When given the probability of precipitation, is that percentage an indication of how likely any one spot is to receive rain? Is there a rough or more exact equivalent in gallons of an inch of measured rain? (Posted by Administrator)

When given the probability of precipitation, is that percentage an indication of how likely any one spot is to receive rain or is that an indication of how much of the area is expected to have measurable precipitation? Is there a rough or more exact equivalent in gallons of an inch of measured rain?

ANSWER

First question: the probability refers to the likelihood of any given location within the forecast zone (usually about 5,000 square miles) receiving 0.01 inch of rainfall or greater; it says nothing about the proportion of the forecast area receiving rain, or the amount which that point can expect to receive.

Second: the amount of rain in gallons is determined by the area of the surface over which the inch falls. One inch of rain falling over an area 90 feet square would yield 5049.35 gallons.

RKP

Is is true the weather goes one direction on one side of the equator while going the opposite direction on the other? It seems logical the weather would tend to go the same direction since the planet is orbiting the same way.

Is is true the weather goes one direction on one side of the equator while going the opposite direction on the other? It seems logical the weather would tend to go the same direction since the planet is orbiting the same way. (Posted by Administrator)

ANSWER

Yes, winds circulate differently in the Northern and Southern Hemispheres. Though the orbital direction of the Earth is the same, the relation of that direction to the two poles is opposite. Thus, in the Northern Hemisphere, circulation around a high pressure ridge is clockwise; in the Southern Hemisphere, it is counter-clockwise.

To show this for yourself, fill your bathtub; sit down in it, and block across the tub with your knee; notice how the water flows into the drain--clockwise; if you were in Uruguay, the direction would be counterclockwise. This whole thing was figured out by a French astronomer in the 19th Century, and the effect is named for him: the Coreolus Effect. (I may have the spelling incorrect, as I can't find my biographical dictionary right now.)

RKP

Why does the Continental Polar--Dry Air Mass that flows from Canada into the northern United States produce snow for example in Illinois?

Why does the Continental Polar--Dry Air Mass that flows from Canada into the northern United States produce snow for example in Illinois? (Posted by Administrator)

ANSWER

Because it is overrun by moist air--usually from the Gulf of Mexico--at very low altitudes; the chilling of the moisture vapor in the bottom of the moist air layer combines with the lifting as it rides over the leading edge of this air to produce the snow. Another factor can be this: if an upper air disturbance is bringing some mid- and high-level moisture with it from the Eastern Pacific, quite light snow can occur.

RKP

I was wondering what is the difference between isolated thunderstorms and scattered thunderstorms. What makes it rain so much in the northeast and places like Arizona get so little rain?

I was wondering what is the difference between isolated thunderstorms and scattered thunderstorms. What makes it rain so much in the northeast and places like Arizona get so little rain? (Posted by Administrator)

ANSWER

Here are your answers:

a) Isolated thunderstorms implies rain coverage over about 10 percent of a given geographic area of about 5,000 square miles; scattered implies about 30 percent areal coverage.

b) the biggest difference between Arizona and New Hampshire: there is a very tall mountain range separating Arizona from the Pacific Ocean--its most likely source of available moisture for rain generation. In the case of New Hampshire, the terrain rises from southeast to northwest, and southeasterly winds off the Atlantic are common. Upslope conditions are favorable for producing lots of rain.

RKP

My question concerns the extreme deviation of the Earth's observed large-scale wind circulation from the predictions of a simple model - a solid ball spinning within a gas bound to the ball by gravity...

My question concerns the extreme deviation of the Earth's observed large-scale wind circulation from the predictions of a simple model - a solid ball spinning within a gas bound to the ball by gravity... (Posted by Administrator)

My question concerns the extreme deviation of the Earth's observed large-scale wind circulation from the predictions of a simple model - a solid ball spinning within a gas bound to the ball by gravity. The model has inertial boundary conditions at the center and the outer limit of the gas.

It seems as if every year in march or April, we have what is called, the "30 days of wind". I was wondering if you have heard of this or know why we get fresh to strong north east to east breezes during these months?

It seems as if every year in march or April, we have what is called, the "30 days of wind". I was wondering if you have heard of this or know why we get fresh to strong north east to east breezes during these months? (Posted by Administrator)

Hello, I have lived in Key West, Fl for about four years now and work on the water every day. It seems as if every year in march or April, we have what is called, the "30 days of wind". I was wondering if you have heard of this or know why we get fresh to strong north east to east breezes during these months for so long. After cold fronts move through the keys, strong high pressures follow's which give us very strong winds. We have had these winds now for over three weeks and it is expected to stay with us for another week or so. Can you help and thank you for your time.

ANSWER

Yes, I believe I can help you. The reason has to do with two synoptic scale map features; (synoptic means large--several score thousand square miles;)

a) In early Spring, low pressure begins to deepen along the Plains; the centers of the high pressure ridge which build into your area are to your north; the pressure gradient between the Southeastern states high and the Central states low brings the air around over you--from the east or northeast, and at a pretty fast clip.

b) The summer season Sub-Tropical upper air high is just beginning to build, and warm rather rapidly waters over the Gulf of Mexico; the land/sea differential in temperatures causes winds to rush from the warmer region (the land) to the still cooler region (the water.) There can be some transitory factors which also could result in gusty winds; the two I have listed above are responsible for the duration and period of occurrence.

RKP

I've heard the dry-bulb temperature of air decreases about 3 degf per thousand feet of vertical altitude. Is that a fair estimate? Is it worldwide? Seasonally stable?

I've heard the dry-bulb temperature of air decreases about 3 degf per thousand feet of vertical altitude. Is that a fair estimate? Is it worldwide? Seasonally stable? (Posted by Administrator)

ANSWER

In general, you are correct--though the number is actually closer to 3.6 deg. F.; there are, of course, exceptions; the rule applies up to about 10,000 feet. A classic exception--and one which can give us problems, is when a temperature inversion exists. This means that the temperature at about 5,000 feet or below is warmer than the surface temperature. This can cause persistent periods of fog or atmospheric pollution. This is rather common in valley locations.

RKP

Dr. Bob, I'm a mom whose trying to teach my children about the ocean's impact on weather. Could you shed some light on that for me?

Dr. Bob, I'm a mom whose trying to teach my children about the ocean's impact on weather. Could you shed some light on that for me? (Posted by Administrator)

ANSWER

There are several things I could use to show how profoundly the oceans affect the world's weather. I will select three. I am in Tyler, Texas--about 225 miles due north of the Gulf of Mexico.

a) About 70 percent of the world's surface is water. The oceans contain most of the world's supply of water. Thus, most of the rain which falls originated in the ocean--with the water vapor being lifted into the atmosphere through either evaporation or wind. Last night, Tyler received 1.31 inches of rain. This was almost all moisture which came from the Gulf of Mexico, with a small contribution from the Eastern Pacific.

b) Water gains and loses heat far more slowly than does dry land. Thus, cities near the ocean are warmer in the winter and cooler in the summer than are continental stations in the same latitude. Presently, the temperature in Tyler is 44 deg.; that at Galveston is 57 deg. (the water temperature at Galveston is 58 deg.); while that at Oklahoma City is 35 deg.

c) About every 45 days, a wave of warm water sweeps eastward through the Equatorial Pacific Ocean. We call this the Madden-Julian Oscillation. When this happens, cold air ruses southward through Central North America (during the Northern Hemisphere Winter). The last week or so has been cold, and the next week or two is likely to be cold. There is a wave of warm water presently moving eastward through the Central Equatorial Pacific.

I hope this helps.

RKP

The high is not the measure of temp for midday. Right? Or is it?

The high is not the measure of temp for midday. Right? Or is it? (Posted by Administrator)

Next Wednesday, here in Chicago, the High is expected to be 22 and the Low 7. A co-worker told be that " It will not be 7 then when I walk out my door in the Morning." I told her that is not a true statement. I'm I right? The High and Low readings are measured for a 24 hour period.

ANSWER

Sir, This is probably more than you really want to know.

To start with: you are correct. Chicago (KORD) reports their high and low temperature for the twenty-four hours ending at midnight. So, the high and low on January 7 will be the highest and lowest temperature observed between 12:01 a.m. and 11:59 p.m. on the 7th. At smaller manned stations (like mine here,) I report the highest and lowest temperatures for the twenty-four hours ending at midnight Greenwich Mean Time (6:00 p.m. Central Standard Time.) Thus, my report for January 7 will be the highest temperature between 6:01 p.m. on January 6 and 5:59 p.m. on January 7. In what we send to the news media, we usually report the highest during the twelve hours preceding midnight GMT and the lowest during the previous twenty-four hours. If you care to check the website, you will notice that I have a rather lengthy list of such temperatures.

Bottom line: you're right; your co-worker is not.

RKP

I see from maps that the Southern most portion of certain low pressure systems can have higher temps than the more Northern portions, despite having identical pressures. How does this happen?

I see from maps that the Southern most portion of certain low pressure systems can have higher temps than the more Northern portions, despite having identical pressures. How does this happen? (Posted by Administrator)

ANSWER

Sir, This is a very good question. Your basic assumption is correct. To go further: the southern end of low pressure troughs are closer to the Equator than the northern end; thus, one would expect the temperature to be warmer. Also, air pressure is but one factor for determining air temperature: others are a) moisture content of the air mass, b) proximity to bodies of water and water temperature, c) air temperature at the top of the boundary layer--about 5,000 feet, d) presence of precipitation, e) proportion of sky covered by cloud at the surface observing site, f) wind velocity at the surface, g) terrain factors at the observing site: e.g.: whether the site is higher or lower than the surrounding terrain. Though my statements may be something of an over-simplification, constant pressure does not necessarily mean constant temperatures. Sorry to be so long in responding, as I had to think this one out.

RKP

How are snow levels are reported? "When the weather man says the snow level is at 12,000 feet, and then on another day he says the snow level is at 15,000 feet, does that mean that there is more snow or less snow?

How are snow levels are reported? "When the weather man says the snow level is at 12,000 feet, and then on another day he says the snow level is at 15,000 feet, does that mean that there is more snow or less snow? (Posted by Administrator)

ANSWER

Snow levels are reported as the elevation above mean sea-level. An example: in the Seattle area, when snow levels are reported at 500 feet, this is 500 feet above sea-level. This is somewhat above the elevation of the city, which is under 100 feet. I hope this helps.

RKP

Why is it when it snows the temperature sometimes increases? And does this only happen near coastal areas due to the ocean?

Why is it when it snows the temperature sometimes increases? And does this only happen near coastal areas due to the ocean? (Posted by Administrator)

ANSWER

There are a couple of answers to your question:

a) Often, snow begins falling as more moist and warmer air overrides the cold air mass at the surface. This warmer air is mixed downward, and the temperature at the surface will rise slightly.

b) The process of precipitation formation releases some energy, which produces heat. Insofar, this is not a phenomenon peculiar to being located near an ocean; I would, however, think it more probable there.

RKPrface will rise slightly.

Why is it warmer during the winter in towns that border the ocean? Why is it warmer in San Francisco in the winter than Mobile, Al.?

Why is it warmer during the winter in towns that border the ocean? Why is it warmer in San Francisco in the winter than Mobile, Al.? (Posted by Administrator)

ANSWER

a) Because of proximity to the water.

b) San Francisco is warmer than Mobile because of the prevailing wind direction during the winter months; in both instances, that is northwesterly to northerly; the air reaching San Francisco has crossed a body of water; the air reaching Mobile has traveled over land.

I hope this helps.

RKP

What is the difference between Isolated and Scattered thunderstorms?

What is the difference between Isolated and Scattered thunderstorms? (Posted by Administrator)

ANSWER

There are two distinctions--which are inter-related.

The first relates to areal coverage. Generally speaking, "isolated" refers to less than 5 percent areal coverage, while scattered refers to 25 percent or more.

The second refers to probability for measurable precipitation. This concept, expressed usually as a percentage, means the probability that a given point will receive 0.01 inch or more of measurable rainfall. The probability for "isolated" is 10 percent or less; the probability figure for "scattered" is 30 percent. Since most folks don't really understand what the percentages really mean, I do not use them in verbal reports, and place them within parentheses in written reports.

RKP

The old saying "Red sky in the morning, sailor take warning. Red sky at night, sailors delight." Is there any basis to predict the weather on this saying?

The old saying "Red sky in the morning, sailor take warning. Red sky at night, sailors delight." Is there any basis to predict the weather on this saying? (Posted by Administrator)

ANSWER

Two "yes's" on your message.

First, you got the quotation correct.

Second, on its accuracy--a qualified "yes". For inland latitudes--at least ours--there is probably not much validity. For coastal locations in middle latitudes, there is. The reason is this: a "red" sky is caused by the sun's rays being bent by moisture droplets in the earth's atmosphere. Much rain at coastal locations in middle latitudes during the warm season is caused by something called the "sea-breeze front". As the land heats during the daylight hours, it warms more rapidly than does the adjacent ocean. If there is moisture vapor in the atmosphere at early-morning to cause a red sunrise, than this suggests that thunderstorms will develop along the sea-breeze front, and move inland from offshore during the day. In the evenings, the process reverses: the land cools more rapidly than does the ocean; air flows offshore, and thunderstorms are less likely.

So, a qualified "yes" to the old saying. Old sayings have validity sometimes because they are true.

RKP

Can you please explain how evaporation can cause a lack of rain reaching ground level?

Can you please explain how evaporation can cause a lack of rain reaching ground level? (Posted by Administrator)

ANSWER

Sir, Here is what can happen. Assume the atmosphere is moist above 5,000 feet, and dry below. If the air mass is saturated above 5,000 feet, and there is vertical air motion, then precipitation can form above that altitude. If the atmosphere is dry below that altitude, then the precipitation will evaporate when it goes below 5,000 feet. This is not uncommon, and such precipitation is called "virga", and cools temperatures at the surface.

RKP

I would like to know why there are not many lightning and thunder storms on the pacific coast. Is it because ocean storms are "different" than storms over land or what?

I would like to know why there are not many lightning and thunder storms on the pacific coast. Is it because ocean storms are "different" than storms over land or what? (Posted by Administrator)

ANSWER

Sir, Lightning occurs when there is a sharp difference in atmospheric properties (usually temperature and moisture content) within a very short distance. Storms along the Pacific Coast usually occur during the cool season, when the ocean temperature is cool, the adjacent land mass cool, and the atmosphere cool. Thus, the temperature difference is negligible; and the atmospheric properties are similar. So, it follows, that the electrical properties of the land, sea, and air are similar.

RKP

Does air pressure effect the temperature? Vice Versa? Does humidity effect the temperature? Vice Versa?

Does air pressure effect the temperature? Vice Versa? Does humidity effect the temperature? Vice Versa? (Posted by Administrator)

ANSWER

The relationship between air temperature and air pressure is indirect; that between air temperature and relative humidity is more direct.

As an example of the temperature/pressure relationship: take today. Until mid-afternoon, the pressure was falling because of a crossing low pressure center through the Red River Valley. This caused a strong southwest wind. Winds from that direction flow down slope before reaching here, and this causes warming. The pressure has been rising rapidly since about 3 p.m., and the temperature has been falling. Arctic high pressure is building into the area, with a cold air flow. However, during the warm season, an Atlantic/Gulf high pressure ridge controls our weather, and we are warm. So, the relationship is indirect.

The temperature/humidity relationship is stronger. High humidities retard nighttime cooling and daytime warming. Other things being equal, the temperature will not drop as far at night nor rise as far during the daytime with higher humidities as would be the case with lower humidities.

RKP

I no longer live in the Tyler area but I sure miss hearing your forecast. Who do you credit with having the most influence in your radio career?

I no longer live in the Tyler area but I sure miss hearing your forecast. Who do you credit with having the most influence in your radio career? (Posted by Administrator)

ANSWER

Sir, I appreciate your compliment. In answer to your question, I would say two individuals and one group.
a) News readers on the British Broadcasting Corporation: they were objective, absolutely trustworthy, and regardless of how bad things were--they were calm and unemotional. In reporting severe weather events, I tried to emulate them.
b) Kern Tipps: he was a Southwest Conference football broadcaster in the 1940s and 1950s; I took from him that you can be on the air, and did not have to mask your Texas accent. c) Edwin Smith: he was on the air in Tyler between 1942 and about 1976. I came very near to giving it up in 1973; he asked me to remain on the air two weeks longer; I still am. Your use of the word "career" brought me up short. Since I've been on for forty years--I guess it is a "career" instead of just something I do every day. I hope this helps.

RKP

When the forecast of the probability of precipitation is expressed in percentage terms, is that the percentage of the area that will be covered or is it the chance of precipitation in a given area?

When the forecast of the probability of precipitation is expressed in percentage terms, is that the percentage of the area that will be covered or is it the chance of precipitation in a given area? (Posted by Administrator)

ANSWER

Your confusion on this matter is why I do not use percentages in what I speak; I do use them in written form, but not in spoken form. Probabilities do not forecast either the extent or the amount of precipitation. Instead, they forecast the numerical chance that 0.01 inch of rain will fall at a given location.
I hope this helps.

RKP

Will our cooler temperatures be a factor in another slow hurricane season?

Will our cooler temperatures be a factor in another slow hurricane season? (Posted by Administrator)

We can all hope for the same slow hurricane season like last year
with that strong easterly flow we had that diverted most tropical waves
from entering the gulf.

With our cooler temps we've had so far will that be a determining factor
for the water temps in the gulf?

ANSWER

Yes, it should be; Gulf water temperatures are in the lower 80s now--3-5
degrees below where they usually are at this time of the year.

RKP

When the low is shown under Monday as 50, does that mean the low between Monday and Tuesday will be 50 since the low truly doesn't happen until after midnight?

When the low is shown under Monday as 50, does that mean the low between Monday and Tuesday will be 50 since the low truly doesn't happen until after midnight? (Posted by Administrator)

ANSWER

Low temperatures are those between midnight GMT and noon GMT, and high
temperatures are between noon GMT and midnight GMT. If you are in the
Eastern time zone--as I think you may be, the low temperature is that
between 8 p.m. EDT (7 p.m. EST) and 8 a.m. EDT (7 a.m. EST.) The high
temperatures are for the following twelve hours. This is a bit confusing,
as they are prepared from a product called the Coded Cities Forecast which
the National Weather Service releases twice daily. For a time zone other
than Eastern, add or subtract the appropriate numbers.
RKP

Can you, please, tell me what the relationships are between: Air pressure and cloud cover, Air pressure and wind direction, relative humidity and dew point?

Can you, please, tell me what the relationships are between: Air pressure and cloud cover, Air pressure and wind direction, relative humidity and dew point? (Posted by Administrator)

ANSWER

a) - Generally speaking, when air pressure is high, skies are clear to fair; when pressure is low, then there will be variable degrees of cloudiness. Today {March 16, 2003,} the pressure was low--10043 mbs. at 6 p.m.; we had multiple cloud layers.

What does the dew point have to do with the creation of fog?

What does the dew point have to do with the creation of fog? (Posted by Administrator)

ANSWER

The dew point actually has quite a lot--but not everything--to do with the formation of fog. The dew point is the temperature to which, if the air temperature were reduced to that point, the moisture vapor in the atmosphere would condense.

Why do you see your breath in cold weather and how do you explain what role water vapor plays in the weather?

Why do you see your breath in cold weather and how do you explain what role water vapor plays in the weather? (Posted by Administrator)

ANSWER

The air which emerges from your mouth when you breathe has an approximate temperature of 98.6 deg. F. It is also fairly moist.

Just several weeks ago, on a real humid day in the Tyler area - I observed (while wearing dark sun-glasses) a large gray circle around the sun, outlined by a rainbow. What did I see?

Just several weeks ago, on a real humid day in the Tyler area - I observed (while wearing dark sun-glasses) a large gray circle around the sun, outlined by a rainbow. What did I see? (Posted by Administrator)

ANSWER

What I think you saw was the combination of two tricks of optics:

a) moisture vapor in the air can refract light to create a rainbow effect, and

What is the difference between scattered showers and isolated showers? Probably a silly questions isn't it?

What is the difference between scattered showers and isolated showers? Probably a silly questions isn't it? (Posted by Administrator)

ANSWER

No, Sir, this is a very good question. I do not use NWS' percentage probability scheme in what I do by voice--radio or the telephone recordings; I do use it in what I do in print--this website or the newspaper. Most people don't know what the percentage probabilities mean.

What is "Heat Index" and how is it calculated?

What is "Heat Index" and how is it calculated? (Posted by Administrator)

ANSWER

The heat index is a value which takes into account the combined effects of temperature and relative humidity. The calculation is a complex mathematical formula which I do not know--I use a table.

Why does it often rain heavily just after loud thunder?

Why does it often rain heavily just after loud thunder? (Posted by Administrator)

ANSWER

You are quite observant. Some of the same things in the atmosphere which cause lightning and hence thunder also contribute to heavy rain. Lightning occurs when there is a sharp difference in potential energy in a fairly small segment of the atmosphere.

I need to find some weather for (any city) from about 30 years ago. How can I do this?

I need to find some weather for (*any city*) from about 30 years ago. How can I do this? (Posted by Administrator)

ANSWER

I would suggest you go to one of two places: a) the National Climatic Data Center; the website is a bit complex, but you should eventually get there; you can find it at www.noaa.gov and follow the links to the NCDC.

Where can I find average wind speeds for Tyler?

Where can I find average wind speeds for Tyler? (Posted by Administrator)

ANSWER

Average wind speeds are not calculated for Tyler. They are, however, calculated for Shreveport and Fort Worth, and an averaging between the two for Tyler would be valid.

Where can I find climate data and weather from Canada?

Where can I find climate data and weather from Canada? (Posted by Administrator)

ANSWER

Here is the website for Environment Canada.

What is the difference between "mostly" and "partly" in terms of cloudiness or sunniness? And what actually causes wind?

What is the difference between "mostly" and "partly" in terms of cloudiness or sunniness? And what actually causes wind? (Posted by Administrator)

ANSWER

a) the distinction in "mostly" vs. "partly" cloudy is the percentage of sky cover. "Mostly cloudy" is 50% or greater sky cover; "partly cloudy" is 12.5% to 50%; "sunny" is under 12.5%; "fair" is cloudiness above 12,000 feet, and under 12.5%.

I understand there are three forms (types) of lightning.

I understand there are three forms (types) of lightning. (Posted by Administrator)

Cloud-to-Cloud, Cloud-to-Ground and Ground-to-Cloud. Is this correct?

Has anyone else got temp data on the diff between lawns and sidewalks?

Has anyone else got temp data on the diff between lawns and sidewalks? (Posted by Administrator)

I have done an experiment. I placed a thermometer on the sidewalk and one about 7ft off the ground in a tree so it was shaded by the leaves. The temperature was about 25 degrees different for the whole time. Has anyone else got temp data on the diff between lawns and sidewalks? I would also like to know the different affect of concrete yards and grass yards on electric bills in summer.

On the Shreveport Weather Radar Page there is the option of choosing Base Reflectivity and Composite Reflectivity. What is the difference between the two?

On the Shreveport Weather Radar Page there is the option of choosing Base Reflectivity and Composite Reflectivity. What is the difference between the two? (Posted by Administrator)

ANSWER

In answer to your question, base reflectivity is the return in one-half degree slices in the vertical plane; composite reflectivity is an interpolation of the highest base returns in the entire 90-degree vertical plane.