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Severe Weather Risk for Wednesday 3/1


Jim Martin

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URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 57
   NWS Storm Prediction Center Norman OK
   1150 AM CST Wed Mar 1 2017

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Northern and Central Alabama
     Northern Georgia
     Central and Northeast Mississippi
     Extreme Western North Carolina
     Southeast Tennessee

   * Effective this Wednesday morning and evening from 1150 AM until
     600 PM CST.

   * Primary threats include...
     A few tornadoes likely
     Scattered large hail and isolated very large hail events to 2
       inches in diameter possible
     Scattered damaging wind gusts to 70 mph possible

   SUMMARY...Thunderstorms will slowly intensify this afternoon along a
   boundary extending from northern MS into southeast TN, and spread
   across the watch area.  Large hail and isolated tornadoes are the
   main threats with these storms.

   The tornado watch area is approximately along and 60 statute miles
   north and south of a line from 40 miles southwest of Greenwood MS to
   65 miles east of Chattanooga TN. For a complete depiction of the
   watch see the associated watch outline update (WOUS64 KWNS WOU7).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Tornado Watch means conditions are favorable for
   tornadoes and severe thunderstorms in and close to the watch
   area. Persons in these areas should be on the lookout for
   threatening weather conditions and listen for later statements
   and possible warnings.
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7 hours ago, BlunderStorm said:

same here... Russell county schools has refused to close early it seems.

Buchanan County let schools out right as the squall line hit, thus leading to downed trees delaying multiple school buses from making their rounds. Not sure why they made that call.

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This last 48 hrs has been one of the more extreme 2-day hail/wind events that I know of, simply judging on the number of reports. Here's part of the reason why: 82 kt measured 0-6km shear at KBNA Nashville Tennessee this morning!! 343 m2/s2 of 3km SRH and 1194 J/kg of MUCAPE!

0VnTunX.jpg

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Andover, Kansas 1991 was also a cool clammy drizzly morning all the way into early afternoon. Unfortunately the rapid destabilization can catch people off guard. 

On 2/28/2017 at 5:21 PM, Matthew70 said:

I remember the Murfreesboro tornado because I was in it.  It was cloudy & cool with rain showers. I remember saying to cloudy & cool for severe wx.  I was so wrong.   Then a couple hours later an EF4 came thru.  

Other times, the crud hangs in. A rainout on the boundary can keep it stable. Even previous night storms can leave the ATMO overturned and kill dewpoints. One needs a reason to forecast destabilization.

March 1 the intense LLJ and 850 winds scoured our the crud here. Back in 1991 a strong warm front lifted through southern Kansas. In both cases the boundary is a focus of severe wx. Even south of the lifting main boundary (WF or OFB) subtle differential heating zones can act as secondary and tertiary boundaries. Drizzle to intense tornado is not a rare scenario because of the boundaries. Still something must drive the destabilization; otherwise it'll stay cool and stable.

Regarding the Jasper gorilla size hail, that would be impressive in the Plains. Jasper hail is incredible in the South.

Nashville LEWP and comma head was impressive. Nashville survey shows multiple EF-1 tornadoes through the suburbs. That's what high shear and helicity gets you if the low levels are not quite backed enough for classic supercell tornadoes. For the time of day, really any time of day, the LEWP system was quite intense.

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  • Mr Bob unpinned this topic

Last minute on Wednesday March 1 decided on a local storm chase into northwest Georgia. Pictures are followed by a brief account of the afternoon.

Horse shoe cloud with attempted wall cloud right of the tower, east of Adairsville, GA

Adairsville_3-1-17.jpg

Scud cloud tease on 411 between Rydal and Fairmont, GA

Fairmont_3-1-17.jpg

Messy hail core was approaching Chattanooga, but with zero rotation so I started down I-75. Couple supercells were noted along I-59 but with fast motion figured I'd intercept over on I-75. Stopped in Dalton to check on sup #1 but a new cell developed overhead. HTX radar was not updating; FFC was worthless; and, I became unsure of my safety situation. Bailed out and retreated south. Dalton had high winds and large hail. Dalton cell eventually produced a tornado and very large hail in Chatsworth, GA but another cell was to its southeast which would have blocked safe viewing anyway. No regrets and safety first!

Approaching Calhoun, GA the next cell south (sup #2) actually had valid mid-level structure. No pix due to travel on I-75. While a nice surprise outside the Plains, it made perfect since given the mid-level winds and 3km helicity measures. Note the 1km helicity was lacking, relative to the 3km, due to veered off low-levels. Correctly sensing car crushing hail for Calhoun, I dropped down to Adairsville, yup the town that got hit a few years back. Started east on GA Hwy-140 and took the first picture of the horseshoe cloud. Wall cloud could/would have been right of the tower. Hanging fingers left of the tower are nothing interesting in that part of the storm. Well, they look cool. 

Second picture is after turning north from 140 onto US-411. Photo is head of the horseshoe becoming scraggly and less organized. Scud cloud hangs down but it was not rotating. Again, it is a neat picture little more. Radar rotation was noted from west of I-75 all the way to US-411 but mainly weak-moderate mid-level. However rotation crapped out which was fine anyway. Storm was crossing into unchasable southern Appalachian foothills. Again I never observed rotation in the field. Though no tornado is booked, it was still nice to get out for the first local chase in several years. No 12-hour return trip from the Plains is a pleasantly odd feeling. Chase is an appetizer for what I expect to be an active Plains and maybe Mid South season.

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