Category: Ask Dr. Bob

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Noting your recent forecasts/comments seem to be a little more optimistic about rain, do you in fact see a change coming?

Dr. Peters, following up on our December email exchange below and noting that your recent forecasts and comments seem to be a little more optimistic about rain, do you in fact see a change coming? If so, do you see a return to “normal” spring rains in time to get some water before going into the summer? I appreciate your good work and all details are also appreciated.

ANSWER

Sir,
Unfortunately, our cool season forecast on precipitation was correct; on temperature, it was not; we did not go into a typical La Nina Winter until mid-February; we were there for much of December.

Now, for the Spring and Summer.

SST (sea-surface temperature) anomalies have weakened in the past few weeks, meaning that temperatures are back to near normal values in the far Eastern Pacific, and about 1.0C below normal in the Central Equatorial Pacific. In addition, ocean heat content is improving, with the below normal heat content now down to only about 150-200M. This suggests that the LaNina event is weakening, and will likely dissipate in a couple of months.

For us, this suggests continuing below normal monthly averages through mid-Summer, with improving averages at late-Summer. This said, there appers to be a short-term reprieve coming.

The storm track, which has been along about 45N for the past five or six weeks, is getting shoved back southward–at least for next week. In other words, I think we’ll see some rainfall Sunday/Monday, and perhaps again towards late-week.
RKP

P.S.: I wish I had been wrong about the cool season forecast.

Does lightning come up though the ground or down from the sky?

ANSWER

The answer is that it goes both ways. A narrow channel of negatively-charged particles drops from the cloud–which we cannot see; positively charged particles then travel back to the cloud through the negative channel. This is what we see.

I have pasted below the page from the National Severe Storms Laboratory which has much more information.
RKP

What is lightning?

Lightning, as best we understand, is a channel of negative charge, called a stepped leader that zigzags downward in roughly 50-yard segments in a forked pattern. This step leader is invisible to the human eye, and shoots to the ground in less time than it takes to blink. As it nears the ground, the negatively charged step leader is attracted to a channel of positive charge reaching up, a streamer, normally through something tall, such as a tree, house, or telephone pole. When the oppositely-charged leader and streamer connect, a powerful electrical current begins flowing. A return stroke of bright luminosity travels about 60,000 miles per second back towards the cloud. A flash consists of one or perhaps as many as 20 return strokes. We see flicker when the process rapidly repeats itself several times along the same path. The actual diameter of a lightning channel is one-to-two inches.

What causes lightning to be colored rather than the usual white or blue?

Lightning can appear to be many different colors depending on what the light travels through to get to your eyes. In snowstorms, where is somewhat rare, pink and green are often described as colors of lightning. Haze, dust, moisture, raindrops and any other particles in the atmosphere will affect the color by absorbing or diffracting a portion of the white light of lightning.

Why are positive lightning bolts deemed more dangerous than the more common negatively charged bolts?

Positive lightning is often considered more dangerous because its electrical field is stronger (forming at the top of the storm), the flash duration is typically longer, and its peak charge can be much greater than a negative strike. Plus, positively charged lightning can occur near the edge of a cloud or strike more than 10 miles away – when people aren’t aware of the danger.

What are cloud flashes?

A cloud flash is lightning that occurs inside the cloud, travels from one part of a cloud to another, or from the cloud to the air.

Does lightning strike from the sky down, or the ground up?

The answer is both. Cloud-to-ground lightning comes from the sky down, but the part you see comes from the ground up. A typical cloud-to-ground flash lowers a path of negative electricity (that we cannot see) towards the ground in a series of spurts. Objects on the ground generally have a positive charge. Since opposites attract, an upward streamer is sent out from the object about to be struck. When these two paths meet, a return stroke zips back up to the sky. It is the return stroke that produces the visible flash, but it all happens so fast – in about one-millionth of a second – so the human eye doesn’t see the actual formation of the stroke.

How does the Earth benefit from lightning?

The earth benefits from lightning in several ways. First, lightning helps the Earth maintain electrical balance. The Earth is recharged by thunderstorms. The Earth’s surface and the atmosphere conduct electricity easily-the Earth is charged negatively and the atmosphere, positively. There is always a steady current of electrons flowing upwards from the entire surface of the Earth. Thunderstorms help transfer the negative charges back to Earth (lightning is generally negatively charged). Without thunderstorms and lightning, the earth-atmosphere electrical balance would disappear in 5 minutes. Lightning also produces ozone, a gas that helps protect the Earth from the dangerous rays of the sun.

How many people are killed by lightning?

According to the National Weather Service, during the past 30 years (1979-2008) lightning killed an average of 58 people each year. Documented injuries average about 300 per year, although undocumented injuries are likely to be much higher.

What happens to the ground when lightning strikes it?

What tends to happen when lightning strikes ground is that it fuses dirt and clays in to silicas. The result is often a black, glassy rock (called a fulgarite) in the shape of a convoluted tube. The shape in the ground is the shape of the path the lightning current followed in the ground. There is often damage to grasses along this path too. Lightning traveling down a tree trunk turns water to steam. If it gets under the bark into the surface moisture of the wood, the rapidly expanding steam can blast pieces of bark from the tree, and the wood along the path is often killed.

Can lightning strike the same place twice?

Lightning does hit the same spot (or almost the same spot) more than once, contrary to folk wisdom. It could be simply a statistical fluke (i.e., with all the lightning that occurs, eventually lightning will strike somewhere near a previous lightning strike within a short period of time). It could also be that something about the site makes it somewhat more likely to be struck. Typically, when lightning strikes something on the ground, the object that is struck sends a faint channel upward that joins the downward developing flash and creates the connection to the ground. Taller objects are more likely than shorter objects to produce the upward channel. But it is also possible that something that locally affects the ability of the ground to conduct electricity (such as the salt or moisture content of the ground at the time, the presence or absence of rock, standing water, pipes or other metal objects in the ground), the terrain shape, the shape of leaves or twigs, or something else might make a particular location more likely than another nearby location to be struck.

What is a “stepped leader?”

A stepped leader is a stream of weakly charged particles that flows from the cloud – it moves towards the ground, starting and stopping, and sometimes branching, trying to find the path of least resistance.

Is it possible to have lightning without thunder?

No, it is not possible to have lightning without thunder. Thunder is a direct result of lightning. However, it IS possible that you could not hear the thunder because it was too far away. Sometimes it is called “heat lightning” because it occurs most often in the summer.

What is it called when lightning strikes sand and melts it, forming a tube?

Fulgarite. Fulgarite has been found all over the world, but is relatively rare. The color depends on the minerals in the sand that was struck.

Is lightning always produced by a thunderstorm?

Yes, lightning is always produced by a thunderstorm. Lightning causes thunder, and you can';t have a thunderstorm without thunder. Thunderstorms are the only weather condition strong enough to carry water droplets to the upper parts of the atmosphere where they will freeze and become charged – because thunderstorms have an updraft.

Does lightning always strike the tallest object?

Never say always! Lightning USUALLY strikes the tallest object. It makes sense that the tallest object is most attractive, because it is the easiest path for the lightning to take.

NOAA safety posters say lightning can strike 10 miles away from a thunderstorm. Is this true?

Yes, it is true. Lightning that strikes away from a thunderstorm are often called “bolts from the blue.” Lightning has its own agenda. It is random and unpredictable, and defies our attempts to fit it into a convenient box to describe its behavior. We don’t really know why it sometimes connects with the ground and not a tree, or a beach instead of the water. Check out these photos:

a.. www.srh.weather.gov/ffc/html/swaw05_lightning.shtml,
b.. www.crh.noaa.gov/gid/Web_Stories/2004/other/lightningsafety/intro/introduction.php,
c.. www.srh.noaa.gov/mlb/BBX.html shows a radar section with lightning data overlayed (white dots). See the white dots extending out from the core of the storm to the right – about 17km away from the back of the storm?
A helmeted bicyclist experienced a lightning strike to the head under fair weather conditions with a cloudless sky. It was determined that the bolt probably originated in a thunderstorm that was about 16km away and obscured by mountains.

Lightning strikes the ground approximately 25 million times each year in the U.S. According to the NWS, the chance of an individual in the U.S. being killed or injured during a given year is one in 240,000. Assuming an average life span of 80 years, a person’s odds over their lifetime becomes one in 3000. Assuming the average person has ten family members and others with whom they are close, then the chances are one in 300 that a lightning strike will closely affect a person during their lifetime.

What type of electricity is lightning?

Lightning is an electrostatic discharge accompanied by the emission of visible light and other forms of electromagnetic radiation.

How many volts and watts are in lightning?

Lightning can have 100 million to 1 billion volts, and contains billions of watts.

How hot can lightning make the air?

Energy from lightning heats the air anywhere from 18,000 degrees Fahrenheit to up to 60,000 degrees Fahrenheit.

How many lightning deaths are water-related?

In a study of 35 years of lightning incident statistics, 8% were water-related.

Can lightning kill fish?

Lightning striking the water can penetrate down and kill fish nearby.

Where can I get information on lightning strikes that occur in my area?

NSSL does not archive lightning data, but there are several other companies that do. We actually purchase lightning data ourselves (we do not have the funds to maintain our own network) and have strict rules about how we can use it.

What is dry lightning?

Dry lightning is lightning that occurs without rain nearby. The NOAA Storm Prediction Center routinely forecasts dry lightning because this kind is more likely to cause forest fires.

What causes thunder?

Thunder is caused by lightning. The bright light of the lightning flash caused by the return stroke mentioned above represents a great deal of energy. This energy heats the air in the channel to above 50,000 degrees F in only a few millionths of a second! The air that is now heated to such a high temperature had no time to expand, so it is now at a very high pressure. The high pressure air then expands outward into the surrounding air compressing it and causing a disturbance that propagates in all directions away from the stroke. The disturbance is a shock wave for the first 10 yards, after which it becomes an ordinary sound wave, or thunder. Thunder can seem like it goes on and on because each point along the channel produces a shock wave and sound wave.

How long can a lightning bolt be?

Recent research from Vaisala-GAI’s LDAR and LDAR II lightning detection networks show that lightning can travel 60 miles or more. The longest bolts start at the front of a squall line and travel horizontally back into clouds trailing behind the squall line. The longest bolt they have seen to date was 118 miles long in the Dallas-Ft. Worth, TX area. Since 3-D lightning measurements are relatively new, scientists are learning more every day and these numbers may change.

Where does lightning usually strike?

Lightning comes from a parent cumulonimbus cloud. These thunderstorm clouds are formed wherever there is enough upward motion, instability in the vertical, and moisture to produce a deep cloud that reaches up to levels somewhat colder than freezing.

These conditions are most often met in summer. In general, the US mainland has a decreasing amount of lightning toward the northwest. Over the entire year, the highest frequency of cloud-to-ground lightning is in Florida between Tampa and Orlando. This is due to the presence, on many days during the year, of a large moisture content in the atmosphere at low levels (below 5,000 feet), as well as high surface temperatures that produce strong sea breezes along the Florida coasts. The western mountains of the US also produce strong upward motions and contribute to frequent cloud-to-ground lightning. There are also high frequencies along the Gulf of Mexico coast westward to Texas, the Atlantic coast in the southeast US, and inland from the Gulf. Regions along the Pacific west coast have the least cloud-to-ground lightning.

Does lightning happen during the winter?

Lightning occurs less frequently in the winter because there is not as much instability and moisture in the atmosphere as there is in the summer. These two ingredients work together to make convective storms that can produce lightning. Without instability and moisture, strong thunderstorms are unlikely.

During the winter, the land surface is cooler because there is not as much heating by the sun to warm it up. Without warm surface temperatures, the near-surface air wouldn’t rise in the atmosphere very far. Thus, the kinds of deep (8-15 km deep) thunderstorms that develop in the summertime wouldn’t develop.

Warm air holds more water vapor. And, when water vapor condenses into liquid water cloud drops, latent heat is released which fuels the thunderstorm. So, warm, moist air near the surface (and the proper conditions aloft to give you lots of instability) can result in deep convection, which may produce lightning discharges.

Clouds become electrified when strong updrafts (fueled by the instability and moisture) bring supercooled liquid water drops and ice crystals at temperatures less than freezing (0 deg C) together. In this environment, interactions between the ice crystals and supercooled water droplets produce electric charges. The exact mechanisms by which this charging happens remain unknown. The electrical charges build up until they are strong enough to overcome the resistance of the surrounding air. The breakdown of the electric fields produced by these charges is the lightning bolt.

What is thundersnow?

Although thunderstorms are less common in the winter, sometimes lightning can occur within snowstorms. Called thundersnow, relatively strong instability and abundant moisture may be found above the surface, such as above a warm front, rather than at the surface where it may be below freezing. Thundersnow is sometimes observed downstream of the Great Salt Lake and the Great Lakes during lake-effect snowstorms, too.

What is a “bolt from the blue”?

A “Bolt from the Blue” is a cloud-to-ground flash which typically comes out of the back side of the thunderstorm cloud, travels a relatively large distance in clear air away from the storm cloud, and then angles down and strikes the ground. These lightning flashes have been documented to travel more than 25 miles away from the thunderstorm cloud. They can be especially dangerous because they appear to come from clear blue sky.

Can lightning be detected?

Since the 1980s, cloud-to-ground lightning flashes have been detected and mapped in real time across the entire US by several networks. In 1994, the networks were combined into one national network consisting of antennas that detect the angle from ground strike points to an antenna (direction-finder antenna), that detect the time it took for them to arrive at an antenna (time-of-arrival method), or a combination of both detection methods.

Flashes have also been detected from space during the past few years by an optical sensor . This experimental satellite covers the earth twice a day in tropical regions. The satellite also detects flashes that do not strike the ground, but cannot tell the difference between ground strikes and cloud flashes.

How many flashes a year are there?

Over the continental 48 states, an average of 20,000,000 cloud-to-ground flashes have been detected every year since the lightning detection network covered all of the continental US in 1989. In addition, about half of all flashes have more than one ground strike point, so at least 30 million points on the ground are struck on the average each year in the US. Besides cloud-to-ground flashes, there are roughly 5 to 10 times as many cloud flashes as there are ground flashes.

What types of damage can lightning cause?

Cloud-to-ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole, or other tall object. It is not known if all people are killed who are directly struck by the flash itself. In addition, flashes may conduct their current through the ground to a person after the flash strikes a nearby tree, antenna, or other tall object. The current also may travel through power or telephone lines, or plumbing pipes to a person who is in contact with an electric appliance, telephone, or plumbing fixture.

Similarly, objects can be directly struck and this impact may result in an explosion, burn, or total destruction. Or, the damage may be indirect when the current passes through or near it. Sometimes, current may enter a building and transfer through wires or plumbing and damage everything in its path. Similarly, in urban areas, it may strike a pole or tree and the current then travels to several nearby houses and other structures and enter them through wiring or plumbing.

How can I stay safe from lightning?

NOAA’s National Weather Service is an excellent source for information on indoor and outdoor lightning safety and lightning risks.

What are the odds of being struck by lightning?

The odds of being struck in your lifetime (estimated to be 80 years) are 1 in 3000.

Why do the clouds line up accross the sky like perfect rows in a plowed field?

ANSWER

In the case of high clouds (cirrus), they are bands of moisture pushed along by higher velocity winds. Low clouds (stratus) are less likely to do that, but occasionally do. In actuality, the cirrus clouds are ice crystals.
RKP

What has been the main reason for the winter storms this year during a La Nina?

What has been the main reason for the winter storms this year during a La Nina? My best guess is the jet stream has dipped further south than expected. I’d like to read about your thoughts.

ANSWER

Two things have come together. First, the Pacific-North American Tele-Connection (the flow of air from Siberia across the North Pacific and into North America) has been oriented from northwest to southeast; second, the Arctic Oscillation (the flow of air from the Arctic region) has been oriented northeast to southwest. Thus, very cold air has been funneled southward.

That is the simple part of the answer. The more complex part for which I have read no satisfactory answer, is why.
RKP

Why has it been so dry this winter (2010) and can we expect normal or below normal rain fall this wenter?

ANSWER: – The dryness this Winter is the result of La Nina–the opposite of El Nino; this means cool waters in the East Central Equatorial Pacific Ocean. The dry conditions look to continue well into 2011.
RKP

I understood that last year was a typical El Nino winter and someone said following that we would have a dry summer and fall.

Dr. Bob, I have followed your forecasts and comments for years and appreciate your good work. My question: I understood that last year was a typical El Nino winter and someone said following that we would have a dry summer and fall. That has been very correct and I am wondering if we follow the “normal” patterns, when would the rains return? Not an official forecast but just what is the normal coming off the El Nino? I live between W’house and Troup and we are probably 7 or 8 inches below Tyler which is not so good itself. Thank you for your time.

ANSWER:
This won’t be encouraging; the SST (sea-surface temperatures) and low ocean heat content (down to 300M) are quite certainly in a La Nina phase in the East Central Equatorial Pacific; those values are forecast to continue at present levels for several months, yet. I’d think it will probably be some time well into 2011 before we start getting significant rainfall again.
RKP

What’s the possibility of snow this year (2010), and how soon?

ANSWER

This year does not look promising for snow. Last Winter was a textbook example of an El Nino event, which usually results in cool and wet weather for us during the cool season. The current Winter is the exact opposite–La Nina–in other words cool waters off the North American Pacific Coast. This usually results in above normal cool season temperatures and below normal precipitation.

Dr. Bob you mentioned the other day you agreed with the Farmers Almanac that we are going to have above normal temperatures this winter.

Dr. Bob you mentioned the other day you agreed with the Farmers Almanac that we are going to have above normal temperatures this winter. What now is considered normal winter temperatures for us? Does that mean we are going to have spring weather from November to May?

ANSWER

No, ma’am, it does not mean Spring temperatures. What it means is
a) a small number of very cold outbreaks, and
b) little, if any, frozen precipitation.
The November average high is about 66 and average low about 46, December 58 and 38, January 57 and 37., February 60 and 40, and March 67 and 47.
RKP

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 wet cool season.
A cool season with above normal temperatures and below normal precipitation is what the long-range forecasts are predicting.
The next one comes out on August 19; if you’d care to write back after that time, I’ll check it.
However, sea-surface temperatures and sub-surface heat content out to the 170th merridian were still below normal last week, and I doubt there will be any change.
RKP

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 south or west over land areas; they are usually dry and hot); Tropical Maritime (they originate over ocean waters, are usually moist and warm); Polar Continental (they originate over land in extreme northern latitudes, and are cold and dry); and Polar Maritime (they originate over the North Pacific, are cool, and usually not moist–since the moisture was lost in crossing the Pacific coastal mountains).
Another factor in determining the ground temperature is the altitude at which the pressure falls to 500 millibars. If above about 18,000 feet, then we see above normal temperatures–our summertime heat machine. During the cool season, this altitude is quite a bit lower.
So, whether we are hot or not under high pressure depends on a) the air mass’s origin, and b) the altitude at which the air pressure drops to 500 mbs–about 15 inches of mercury. To make the latter value a bit more confusing, the 500-mb. level is reported in decameters; earlier last month, the 500-mb. level was 594 dm–about 19,600 feet.
Subsiding air warms as it moves downward through the atmosphere, explaining why the higher that level is–the warmer we are.
Another factor explaining how hot we get is the state of vegetation and soil moisture. A protracted dry period during the warm seasons dries soils and vegetation. This causes higher temperatures; some weeks in late-May and early-June were 5-7 degrees warmer than normal. Moist soils and green vegetation acts to lower temperatures, since moist air cannot hold as much heat as can dry air. One of the fringe benefits of our 11.55 inches of rainfall in June is that it is unlikely that we will see excessive heat this Summer.
The Spring and Summer of 1998 were extremely dry–there was very little rainfall after March 13. In 1998, we had over 40 days with the temperature at or above 100, including about 19 consecutive.
Temperatures did not begin to cool until late in September. The temperature exceeded 90 on 22 days in September 1998, and 100 on 2 days.
The Summer of 2000 was similar–though not quite as hot.
RKP

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.
RKP

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 percent, then the air contains one-half of the amount of moisture vapor which it could hold at the 94-degree temperature.
Relative humidity can be as low as 40 or 50 percent with rain. This happens because at the altitude where the raindrops form, the relative humidity is 100 percent–actually a little more than that because the moisture vapor condenses into droplets; they collide, form raindrops, which eventually get so heavy that they fall to Earth. If those drops fall through a dry layer of air, then much–but not all–of the water in the drop evaporates. The drops which reach the ground are small–and we call it light rain. But remember, the lower atmosphere is dry–otherwise the drops wouldn’t evaporate and shrink. So, the humidity on the ground can be under 50 percent.
This is most likely to occur during the cool season at the beginning of rain events when the ground temperature is cool.

By the way, thanks for the compliment. I still enjoy (after nearly 48 years) doing the weather.
RKP

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 or cold/wet times of the year are shifting slightly on our calendar. Is there any validity to this?

ANSWER
After thinking about this, I would agree to the point that, when our seasons have been extreme, then there has been something of a forward shift. In other words, extremely warm Summers tend to commence earlier–as occurred this year, in 2005, 2000, and 1998.

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 most important of which is the North Atlantic Oscillation–which rotates warm water around the basin in about 40-year intervals. The oscillation is currently warming along the North American east coast; about five years ago, the peak warmth and ocean heat content was in the Central North Atlantic, and we had an El Nino event the previous cool season–and we got Katrina and Rita.

Last year was an unusually mild tropical season; I’d expect something of an uptick this year–but I wouldn’t expect anything along the lines of 2005.
RKP

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 a woman was drowned in her car.

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 and 90 percent are “widespread”, and near 100 percent is “general”.
RKP

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 such events, I’m not ready yet to make a warm season prediction. El Nino looks to hang in through late-Spring. It showed a moderation in January, than a re-intensification this month.

The 90-day forecasting models are showing normal temperatures and normal precipitation; that actually means equal chances of above, normal, or below–in other words there are no clear signals yet, either way.

I think we can say this: I would be very surprised to see significantly above normal temperatures before mid-June.
RKP

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 so many power lines failed because of the weight of the snow. So, the 1/10 conversion was not accurate–it was more like 1/8 or 1/9.

In the precipitation event of February 23, it was all snow. We measured 0.17 inch of precipitation; though only a trace of snow accumulated in Tyler, we reported that as 1.7 inch snowfall.

To capture the precipitation, we dismantle the rain gauge–leaving a tube two feet high and 8 inches in diameter. The melting is pretty low-tech: I put it in the sink and fill the sink with hot water–that melts the snow. We then pour the water into the measuring tube–and voila.
RKP

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 inches.

2. How does this event compare record wise for the East Texas area?

3. It began as snow Wednesday morning, then changed to mix during the day Wednesday, then changed back to snow Wednesday at dark. If it would have been cold enough to snow continuously, how much total snow could we have gotten?

4. This was a rare event. How perfectly did the elements align for this to occur? Please be as technical as possible. If I\’m unsure of the vocabulary, I\’ll look it up.

5. Finally, have we been a warm winter pattern since the 1980s? I\’m 31 years old and most family and friends who can remember tell me this was much more common pre 1980s.

ANSWER
a) Total snowfall could have been about 9 or 10 inches had the entire precipitation been snow;
b) the highest snow totals I could find were in a band from northwestern Smith County into Titus and Bowie Counties–between 6.0 and 8.0 inches.
c) the reason that the entire precipitation event was snow was because of the temperatures between ground level and 10,000 feet, and the soil temperatures; both were above freezing at one time or another during the precipitation event;
d) This is our heaviest snow since January 13, 1982. And, yes, there were significant snow events between about 1951 and 1978–which with the exception of 1982 and 1985 have not been repeated. Climate is cyclical, and we were in a cooling trend between about 1961 and 1979; since that time, there has been significant warming through 2008.
I hope this answers your questions.
RKP

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

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