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Intense winds Tuesday night: no confirmed tornadoes

Tree blown down on a house in Jones Valley Tuesday night/Chad Kimel

Usually on the day after a big round of storms you see ‘confirmed’ straight-line wind damage or ‘confirmed’ tornado reports.  You won’t see that following Tuesday night’s storms.

Why not?

The National Weather Service did issue one Tornado Warning last night just before 10 PM for Colbert, Lawrence, and Lauderdale Counties, but the vast majority of the damage came from strong ‘outflow’ winds ahead of the rain in that long line of storms.

This is a cross-section of what that line would have looked like.  Note the ‘gust front’ on the leading (right) edge of the cloud base.

That was happening along the entire line over North Alabama, and that’s why we ended up with damage reports like this:  (see photos, reports here: WHNT.com)

39 damage reports in the NWS Huntsville County Warning Area (391 across the eastern US Tuesday night)

NWS Huntsville Meteorologist-in-Charge Chris Darden had this to say about why we don’t expect to find ‘tornado’ damage in all of this:

“Last night was one of those rather rare cases where an intense squall line of thunderstorms produced fairly widespread intense damaging winds. In fact, all 3 official NWS reporting sites (Muscle Shoals, Decatur, and Huntsville) recorded gusts of 60 to 70 mph. That is the first time I can recall that occurring in a long time.

I know there has been a lot of media coverage and post event inquiries today concerning the nature of the damage and whether the event was all straight line winds. When making such a determination we look at a variety of evidence including the environment, observations, radar data, reports, and ground truth including on site surveys. Based on the radar data from last night along with the environment I feel very comfortable saying the damage was of a linear nature.

For example, in Decatur while there was some concentration of damage near the marina the north/south extent of the intense winds was nearly 8 miles. In Madison county KHSV reported high winds and some damage while other areas also had significant pockets of damage. In these areas, the storms were extremely outflow dominant with the high winds occurring well ahead of the heavy rainfall. In fact, KHSV didn’t even record rain until 7 minutes after the wind gusted to 72 mph. That is very atypical for a tornado environment.

Winds on the order of 70 to 80 mph are more than capable of producing roof damage, damage to siding, and broken windows. In fact, that is in line with studies done by the Texas Tech Wind Engineering department. I realize residents may have some questions about this event, but severe thunderstorms can and do produce straight line damage that is equivalent to EF-0 or even EF-1 tornadoes. …not every significant severe weather event is caused by a tornado.”

So, whether it’s a Severe Thunderstorm Warning or a Tornado Warning, take it seriously. You don’t always have to go through the same safety plan when there’s a ‘severe’ storm as opposed to one with the ‘Tornado Warning’ on it, but you should use good judgment: stay inside, stay off the road, and if you’re in a mobile home, on a boat, or in a structure that isn’t sturdy (marinas, sheds, etc.), find more substantial shelter – especially when you have plenty of lead time like we did last night.

-Jason
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