Reader Q&A 10/27/16

What is it about dry air that causes static electricity?

Question from Indy Fry

Air is better at conducting electrical charges when it’s moist (humid), so the static charges don’t build up as large when we shuffle our feet during moist conditions – instead they dissipate through the moist air.  When it’s dry the charges build up until they get large enough to give us a little shock when we start to touch an object with an opposite charge.

greg forbes, severe weather expert

What exactly is a rainbow, what makes it have the different colors?

Question from Yvonne Dewberry

Normal sunlight is white, composed of all the colors of the rainbow blended together.  When sunlight gets reflected off raindrops at the right angle from the sun, the different colors get bent/reflected slightly differently so we see them separately as a rainbow.

Greg Forbes, Severe Weather Expert

We know tides by the moon and the sun. Does the moon and the sun affect the atmosphere in some way?

Question from Jussi Kuortti

There is a pull on the atmosphere that creates a cycle of low and high pressures superimposed on the overall weather patterns.   On a fair weather day you may notice these falls and rises on your home barometer.  They don’t seem to have much impact on the weather.   The sun’s heating, of course, does have a huge effect on the weather in many ways.

Greg Forbes, Severe Weather Expert

In todays world of electronics at home what safety tips should we know while at home during a severe thunderstorm and lightning constantly flashing. Ex. Stay off our computers, TV, and game consoles? Thanks, Ron Noble

Question from Ron Noble

Don’t be in  contact with corded electronics like computers that plug in to electrical outlets, corded telephones, etc.   Cell phones and computers and iPads, etc., operating on battery power without lines attached to them are safe.  It’s lightning striking the house of utility lines outside that can come indoors through the wiring.   Also don’t take a bath or shower or do dishes, etc., because lightning can come in through the plumbing.

Greg Forbes, Severe Weather Expert

Why aren't shelf clouds considered dangerous? They can sure look it!

Question from Rich Sowden

Shelf clouds are found above the leading edge of rain-cooled thunderstorm outflow along what is called a gust front.  Some are tame, but some are associated with severe/damaging wind gusts.

Greg Forbes, Severe Weather Expert

What is a hit and miss storm?

Question from Trips Bryant

“Hit and miss” is  a phrase sometimes used in place of “isolated” or “scattered” showers and thunderstorms.  The horizontal size of the shower and thunderstorm rain is small enough, and the storms far enough between them, that some areas get hit with rain while others are missed.

Greg Forbes, Severe Weather Expert

Why do squall lines usually have the strongest storms as opposed to a single celled storm?

Question from Gwen Fieweger

squall lines cover a bigger area and can affect more locations with damaging wind gusts, but typically the largest hail and the strongest tornadoes come from individual supercell thunderstorms that have a large, long-lived, rotating updraft.  Short-lived single cell thunderstorms don’t last as long or affect a very big area, but can sometimes give localized heavy rain, hail, and localized intense downdrafts called microbursts.

greg forbes, severe weather expert

A couple of weeks ago I saw mammatus clouds for the first time. They were so cool. How do they form?

Question from Roger Myers

ice crystals fall down out of a thunderstorm anvil, and if there are enough of them they sublimate (turn from ice to vapor), cool and saturate the air below the original cloud base, and start to accelerate downward in bulges.  Some of the air below rises up in the clefts between the bulges.  The mammatus clouds develop downward until they run out of enough ice crystals to saturate the sub-cloud air.

Greg Forbes, Severe Weather Expert

As a aspiring sever weather expert (yes, like Dr. Forbes) in high school, is their anything that you can recommend that I do, read, or buy in order to further my studies. After high school I want to study severe weather at the University of Oklahoma!

Question from William Kortright

Take as advanced math classes in high school if you can and a course in physics if you can; computer science too.   Watch meteorologists on The Weather Channel and TV.   If you have watched me for several years you have probably gotten the equivalent of a college class in severe weather!    There is a lot of material on-line, and the Wikipedia material is pretty accurate.   There are on-line FAQs at the Storm Prediction Center web site.    There are books giving good overviews of meteorology that you can probably find at a bookstore.  Good luck!

Greg Forbes, Severe Weather Expert

When the barometric pressure numbers decrease, does that mean the air is "heavier" or "lighter" than before?

Question from Terry Martin

it means that the weight of air in the whole atmosphere above you is lowering.  That could be due to a warming (lighter/less dense), or some removal of air from the column (usually up near the jet stream level) or a combination of both.   It is usually a combination of the two.

Greg Forbes, Severe Weather Expert

If gravity goes down then how does rain go up to form clouds.

Question from Kaleb Krueger

there are upward-moving air currents (updrafts) that pull air upward, allow it to cool, which allows rain to form.   If there are thunderstorms the air can rise fast enough for raindrops to actually rise as well.   In more widespread rain storms the raindrops start to fall as soon as then form.

Greg Forbes, Severe Weather Expert

Noticed T.D. 8 formed near the Outer Banks. During the winter time, a lot of coastal lows form in that area. Is there something special about that area that causes low pressure systems to form in that area?

Question from Stephen Rozsa

There is a rather sharp edge to the Gulf Stream there, with very warm water about 50 miles or less from shore and cooler water near coast.  But this influence is larges in winter, playing a considerable role in the formation or intensification of East Coast storms and Nor’easters.

Greg Forbes, Severe Weather Expert

What makes Oklahoma City such a tornado target?

Question from Jon Dougherty

It’s right near where the dryline sets up – the west edge of where the Gulf of Mexico comes northward, and collides with a flow of drier air from the southwest.   That collision tends to set up thunderstorm formation just to there west and the south or southeast winds tend to give a favorable wind shear for tornado development.   Upper-air disturbances coming from the west give a “boost” to the storms there as they first encounter that dryline and Gulf of Mexico moisture.

Greg Forbes, Severe Weather Expert

Can a tornado and a hurricane occupy the same area

Question from michael johnson

Hurricanes are much larger weather systems so tornadoes can form within rainbands that develop within them.

Greg Forbes, Severe Weather Expert

What does it take to be a Storm Chaser?

Question from David Foryszewski

In principle, anybody CAN be a storm chaser just by heading out toward a storm.  To be a good, safe chaser, though, takes some additional knowledge and tools.  Best to start out as an “intern” riding with a veteran chaser, studying material about chasing and thunderstorm structure on-line.    You should have a cell or other type of mobile phone and a way to get warnings and high-resolution radar data.

Greg Forbes, Severe Weather Expert


Question from rebecca poole

We can’t make specific forecasts for severe weather outbreaks more than about 5 days in advance.  But historically there have often been severe weather outbreaks in these months, especially in November.   Storm systems that come into the South still can pull in warm, moist air off the Gulf of Mexico and at this time of year will tend to have strong low-level and upper-level winds that can turn thunderstorms severe or tornadic.

greg forbes, severe weather expert

if you had an area that was flooded, i.e. Louisiana, and a few days later there were tornados in the area, would they be called tornado's or water spouts since they are over a flooded area? Just wondering...

Question from Barbara Kirkland

If it’s a permanent water body we call them waterspouts (which are tornadoes over water) and they wouldn’t count in the tornado statistics for a state.   The ones you mention over a flooded area would technically be waterspouts, but they WOULD be counted in the state tornado statistics since that area would normally be a land area.  Interesting question.

Greg Forbes, Severe Weather Expert

What happens to a tropical storm/hurricane if the center/eye has half of it on land and the other over water? Could see this happen on the shores of the Carolinas.

Question from Raymond Rickley Jr.

the rainbands coming toward shore are still over water and can stay strong, so the tropical cyclone won’t weaken as rapidly as if it moved fully inland.   There can be tornadoes near the coast and heavy rain there and for some distance inland.

Greg Forbes, Severe Weather Expert

I would like to know, what does Doppler (radar) mean? I have little to no knowledge on such matters. thank you!

Question from dianne holle

Radar is a type of weather device used to detect precipitation (rain, snow, hail, etc.) by sending out pulses of energy which reflect off the precipitation particles and are then measured by the radar.  The time needed for that round-trip of the energy is used to determine the distance to the storm.  Doppler radar is a type of radar which can also detect winds in the storm.   It’s called Doppler because of the so-called Doppler shift in the frequency of the energy transmitted due to the motion of the particles.   The concept is like the change in the sound of the while of a truck as it moves toward or away from you.

greg forbes, severe weather expert

Greetings and happy almost Autumn. What causes sun dogs? Living in ND we have them quite often. Meteorologists have said it has nothing to do with a drop in tempurature coming but I can guarantee you, it does. The larger the dogs, the bigger the drop in temp. Assuming it has something to do with moisture in air. Thank you.

Question from Vicki Lenz

Sun dogs (parhelia) are optical phenomena caused by a refraction (bending) of light passing through horizontal ice crystals.  They don’t really tell you anything about future drops in temperature.

Greg Forbes, Severe Weather Expert

Is Hawaii prone to flash flooding because of their mountains? Thanks and keep up the good work!!!

Question from Anthony Dishon

yes they are.   Northeast winds can give flooding on the north side of the islands.   This is the most common wind direction.  Sometimes thunderstorms on the south slopes can bring localized flooding to the south side of the islands.

Greg Forbes, Severe Weather Expert

How many ef 5 tornadoes have on record in Wisconsin? The oakfield tornado was an ef 5 was i remember that in 1996.

Question from Edward Brath

Three since 1950 and unofficially 4 prior to 1950.

7/18/1996, 6/7/1984, 6/4/1958, 6/22/1944, 6/5/1906, 5/18/1898, 5/22/1893

Greg Forbes, Severe Weather Expert

Why does thunder sometimes crack very loudly and other times it rumbles on and on?

Question from Mary Scherer

Thunder from a lightning bolt very close by sounds like a clap.   More-distant lightning takes on a rolling sound due to arrival times differing from different altitudes in the storm and other factors (some of the bolt may have been horizontal in the cloud and travel a considerably longer distance, sound arriving later).

Greg Forbes, Severe Weather Expert

I love extreme weather. I would love to be a trained spotter for the NWS. How do I go about this?

Question from Bryan Bentley

Contact your local NWS office to see when they offer spotter training classes.

Greg Forbes, Severe Weather Expert

Aloha Dr. Forbes, Is the sky really purple? My studies show that it is actually purple but evolution has left us with too few purple cones in our eyes to see it but other animals and insects see purple- I would like to know what you think?-Thank you,Storm;

Question from Storm Steiger

From what I’ve been taught (and this isn’t a topic that I specialize in) the sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because during that long path through the air and its contaminants the blue light has been scattered out and away from the line of sight.  I’m not familiar with how other animals and insects may be more responsive to other colors.

Greg Forbes, Severe Weather Expert

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  2. What is “Ball Lightning ” I seen it once in te higher elevations in 1968?
    Is Sheet lightning for real?