ASK DR. BOB
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Questions and Answers
Have there been any predictions made yet for the winter of 2010?
ANSWER
Yes, Sir, there have. This will be a La Nina Winter–in other words, waters off North and Central America’s Pacific Coast will be cool. From Central Texas eastward, this usually translates to a mild and dry cool season. Last year was a textbook of an El Nino Winter, with warm waters off the west coast of the Americas. This translated to a cold and… Read more…
Why do high pressure ridges form so easily during the summer?
I believe high pressure systems provide sinking air, so I understand why clouds do not form but I do not understand why the air becomes so hot compared to the winter when high pressure provide cold weather. Thanks as always.
ANSWER:
Sir,
Would that it were so simple.
High pressure means subsiding air. These air masses have four possible origins: Tropical Continental (to our… Read more…
After reading most weather stations RAW/METAR there is a set of numbers at the end of their remarks. This set of numbers read like this. T02610244. Can you help me interpret these.
ANSWER
It is the Celsius temperature and dew point written in such a way as to accurately convert it to Fahrenheit; T02610233 is 79 temperature and 74 deg. dew point. If the first digit of either group of four numbers is a ’1′, then it indicates below zero Celsius. In other words, T10331050 would be a Fahrenheit temperature of 26 and dew point of 23.… Read more…
I don’t totally understand relative humidity, is it 100% when its raining?
ANSWER:
Sir,
I wish relative humidity was that simple. The actual definition is this: relative humidity is the percentage of moisture vapor in the air compared with the maximum amount of moisture vapor which the air could hold at that temperature. In other words, if the air temperature is 94 deg. (which is it as I am writing this), and the relative humidity was 50… Read more…
Dr. Bob, It seems to me over the past several years that our seasons seem to be “shifting” on the calendar.
Dr. Bob, It seems to me over the past several years that our seasons seem to be “shifting” on the calendar. By this I mean it seems that we are entering our seasons later in the year and exiting the season later. The length of the season seems the be the same. I have no research to support this. It just seems that the rainy/dry… Read more…
Some say tropical storms will be enhanced by the El Nino we’ve had this 09-10 season. Your take on this?
El Nino just doesn’t want to call it quits just yet. System in the gulf is just one of many we’ve had these past 6 months. Some say tropical storms will be enhanced by the El Nino we\’ve had this season. Your take on this?
ANSWER
I think there are factors more significant than El Nino which affect the Atlantic Basin tropical season: the… Read more…
Could you please tell me what is the heaviest one day rainfall total ever recorded for Tyler.
ANSWER: There are two days which nearly tied: 9.07 inches on September 13, 1913–during a major hurricane, and 9.06 inches on October 19, 1985. With that one, we had an upper air low to our northeast and a strong low-level jet which continually fed moisture into the low for about six hours. There was a drowning fatality in that one on East Erwin Street when… Read more…
When the % chance of precipitation is given, does it mean the % coverage of precipitation or the actual CHANCE of precipitation?
ANSWER
“Probability for measurable precipitation” means the mathematical likelihood that 0.01 inch of precipitation or greater will fall at any given location within the forecasting group–usually three or four counties and amounting to about 3,000 square miles. I do not like the term, but I’ve been persuaded to use it for pops of 50 percent or less. 60 and 70 percent are termed “likely,” 80… Read more…
Since we have received snow today on 3/21/10 is this the lastest snow fall that has been recorded for the East Texas area?
ANSWER
It is not; the latest trace snowfall was in April 2008; the latest measurable snowfall was March 29, 1937.
RKP
What effect will El Nino have on our usual spring storms. Should we look for more intense systems?
ANSWER: The determining factor is how long it persists; we’re expecting this one to persist into May or June. That would translate, in my judgement, to an active Spring severe weather period–beginning Next Monday. The January 20 event was an indirect result of ENSO.
RKP
Does a El Nino weather pattern in winter foretell what summer weather will be?
ANSWER: No, Sir, it does not very well. The best predictor is when the warm water in the East Central Equatorial Pacific and the high heat content of the top 300 meters of water gives way to a more normal or cooler value.
Though we were able to predict accurately last October that we’d have frozen precipitation at some time this Winter–we’ve had four… Read more…
How does the snow fall enter into the precipitation amount? Is it one inch of snow equals one inch of rain ?
ANSWER:
Sir,
The precipitation event of February 11/12 brought 1.00 inch exactly of liquid yield. About a third of that fell as a rain/sleet/snow mix through 6 p.m. of the 11th; the remainder fell as snow, and we reported a 6.0 inch snowfall. The usual snow-to-rain formula is 0.1 inch of snow equals 1.0 inch of liquid. However, this was a very wet snow–why… Read more…
What does the term dew point mean?
ANSWER
The dew point is the temperature, to which if you lowered the air temperature, the water vapor in the air would condense and form dew.
In other words, an air temperature of 45 and a dew point temperature of 36 means that, if you lowered the air temperature to 36, then the moisture in the air would condense and form dew.
RKP
I know you’ve probably had a hundred emails about the winter storm but please indulge me for a few questions.
I know you’ve probably had a hundred emails about the winter storm but please indulge me for a few questions.
Posted: Monday, 15th February 2010 3:27AM
I know you’ve probably had a hundred emails about the winter storm but please indulge me for a few questions.
1. What was the highest total snow amount observed in East Texas? Like most, we had right at 6… Read more…
When was the last time that we had a winter with an El Nino in control of the weather.
ANSWER
There was a weak El Nino in 2007-2008, and a strong one in 2003-2004.
RKP
What is the determination for how large a tropical cyclone is?
ANSWER
It is the wind speed, wave heights, and lowest central pressure.
RKP
Why do many in East Texas use the term bitter cold?
ANSWER
The best answer I can give you is that we don’t have all that much extreme cold down here; when it happens, folks tend to mob the grocery stores and prepare for an apocalyptic event. The term “bitterly cold” is one which NWS used in its forecasting language until a few years ago.
RKP
What is the difference between “mostly” and “partly” cloudy?
What is the difference between “mostly” and “partly” in terms of cloudiness or sunniness? And what actually causes wind?
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%.
b) Wind results from… Read more…
What is the difference between base/composite reflectivity?
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. Thus, composite reflectivity usually appears more impressive than does base reflectivity, because with base you are getting only one narrow slice of the return, while composite puts the entire echo… Read more…
I observed a large gray circle around the sun, outlined by a rainbow.
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
b) the lenses in your sunglasses acted as a prism to project this rainbow on the retinas of your eyes. There really was not a rainbow; but the moisture vapor in the air and the sunglass… Read more…
Why do you see your breath in cold weather?
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. When that air comes into contact with cold air outside the body, the moisture condenses on tiny particles which are always present in the air, and some of which emerge when you breathe. It is these particles, with a coating of… Read more…
What are the relationships are between: Air pressure and cloud cover…?
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.
b) – Air flows out of high pressure and into low pressure. Because of the friction exerted by the earth’s surface,… Read more…
Explain evaporation causing lack of rain reaching ground level?
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… Read more…
Expain how “lows” are calculated?
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… Read more…
Does air pressure effect the temperature?
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… Read more…
