Thread: Dry Thunderstorms?
08-19-2000, 12:10 AM #1DDFirehouse.com Guest
Someone please explain how a dry thunderstorm develops and functions. I just checked the humidity in my house. With central air units running, it is still 55%. It was very dry last summer around here, but I can't imagine a single digit humidity level.
08-22-2000, 01:39 PM #2KcAreaFFFirehouse.com Guest
I know it's hard to believe here in the midwest, but humidity levels get ridiculously low out west. I was in Washington State last month; humidity was in the teens to lower twenty percent - and that area had higher levels than others in the west at that time. To get back to your question, dry thunderstorms occur when the atmosphere is just right enough to produce storms, but the humidity levels are so low, the moisture evaporates right out of the air as it's falling. The rain never reaches the ground, however the two other dynamics of a thunderstorm - wind and lightning - are still present and very capable of creating havoc across tinder-box conditions. Have this occur for days, weeks, even months over an area already stricken by drought, and your looking at a one-of-a-kind fire season much like this year's.
08-23-2000, 08:37 AM #3akjFirehouse.com GuestOriginally posted by DD:
Someone please explain how a dry thunderstorm develops and functions.
"typically a thunderstorm with a high altitude base where thunder and lightning are observed, but little or no rain reaches the ground. For more information, see virga." http://www.weather.com/safeside/fire/facts.html
The following link is to a USA Today story on dry thunderstorms: http://www.usatoday.com/weather/wdryzap.htm
see also: http://www.mountwashington.org/noteb...997/04/14.html
08-23-2000, 11:01 AM #4bob1350Firehouse.com Guest
Don't know the answer to your question, but two weeks ago while helping to mix slurry for yet another Colorado wildfire, the humidity that day was 7%. Let me tell you it is getting scary. Temps ou here were in the 90's for weeks. We get lightning strikes every summer from dry thunderstorms.
08-23-2000, 11:55 PM #5DDFirehouse.com Guest
Thanks to everyone for the information. It has been an unusually wet summer in Southern Indiana. I wish that we could send some of our rain to help the crews in the West. It would take a napalm strike to start a woods fire here.
08-24-2000, 07:13 PM #6monteFirehouse.com Guest
Very quickly .... surface heating usually over the great basin area produces super heated air that rises. Sometimes called a thermal trough. Then subtropical moisture moves in from the south pacific, overlaying the thermal trough. This produces the high base cumulus that does produce moisture with the lightning. The super hot air under the base of the cumulus evaporates the moisture (virga) before it ever reaches the ground. What we get is the lightning and the winds from downdrafts of cold air off the clounds.
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