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Posted at 7:00 PM ET, 03/17/2008

Comment of the Week: Thunderstorm Winds

By Jason Samenow

Each week, the Capital Weather Gang will search for an outstanding reader comment to potentially highlight on the blog. We found a good one this week. In response to Dan Stillman's "Weather 101: The Madness to March Winds", 'Mike' provided this insightful commentary :

...[T]here is another big factor in thunderstorms that produces strong winds.....not just a dry layer at 10,000-15,000 feet.

Thunderstorms usually reach their most severe intensities with what are called "tilted-updraft" storms. A normal, summer, air-mass thunderstorm occurs in a weak upper-level flow, thus allowing the storm's downdraft to gradually choke off the updraft flow of incoming warm, moist air, and the storm's intensity abates and dies.

This does not happen when winds aloft are strong....such in the vicinity of a jet stream. That is why one of the key ingredients forecasters look for in predicting severe thunderstorms is the presence, aloft, of cold air and strong winds....what is known as "wind shear". In a tilted-updraft storm, the downdraft does not fall back down on the updraft and choke it off....it is tilted by the jet stream winds at an angle, and descends with considerable force out ahead of the updraft. This can allow for storms of incredible violence....triple-digit wind gusts, large hailstones, and, if the wind direction varies with height, spinning and tornadoes.

Storms known as super-cells, that also produce tornadoes and extremely strong winds/hail, can also form from these conditions, but they are different, structurally, from tilted-updraft storms. Supercells are huge, individual storms that sweep in warm, moist air from all sides in a spinning motion. The entire storm becomes one large, spinning dynamo.

By Jason Samenow  | March 17, 2008; 7:00 PM ET
Categories:  Thunderstorms  
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Comments

Good learning!!

Posted by: StormChaser | March 17, 2008 7:28 PM | Report abuse

Tonight, on the latest round of GFS hype:

Springtime? April Fool's!
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_pcp_348l.gif
(A look at an improbable April Nor'easter.)

Posted by: mcleaNed | March 17, 2008 9:06 PM | Report abuse

Yaay, my NOAA weather radio came today. I got one that has three power sources: wall plug, battery and hand crank. I've already programmed it for alerts.

I also have my emergency blankets and multipurpose lighter. Yes, matches would be better, the lighter involves less swearing.

I am good to go. Which with my luck means nothing bad will happen. So, either way we are covered.

Posted by: ep | March 17, 2008 10:23 PM | Report abuse

Thunderstorm winds...often a factor disrupting the smooth running of late afternoon errands during the warm season.

The major difference between supercells and garden-variety thunderstorms is that supercells tend to be self-sustaining and continually rejuvenate themselves over long periods of time. Generally the lifetime of a thunderstorm cell is 30-90 minutes and the storm goes through developmental, mature and dissipation stages over 45 minutes to an hour. Supercells are a differnt type of "beast". They tend to occur on a frontal or "dryline" boundary which permits continuous rejuvenation over 3-12 hours or more. Often a succession of cells goes through the standard life-cycle one after the other, a phenomenon known as "training" (entrainment). This can happen either over a fixed location or along the progression (usually west-east or SW-NE around here) of a boundary. Supercells are also generally responsible for our severe weather events. They tend to be full of wind, hail and rotation.

Posted by: El Bombo | March 18, 2008 11:18 AM | Report abuse

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