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March 27th-29th Severe Weather Thread


andyhb

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Morning Update from Jeff:

 

A threat for severe thunderstorms this afternoon.

 

Ingredients coming together for a potentially active afternoon/early evening as a strong short wave over New Mexico moves eastward forcing the west TX dryline well eastward today along with an incoming frontal boundary from the NW. Area is firmly warm sectored this morning with warm and muggy dewpoints well into the 60’s and pushing 70 at most locations. Satellite images are starting to show mid level cloud enhancements over the Pecos Valley and this is likely the incoming lift associated with the short wave trough over New Mexico. Forecast models show excessive instability by early to mid afternoon over SE/C TX ahead of the dryline with CAPE values of 2000-3000 J/kg and shear values of 30-50kts. While low level shear is modest the shear throughout the air column is more than enough to help with storm organization. Big question mark remains the capping inversion which held strong yesterday allowing virtually no thunderstorms at all over the area. A strong cap is noted at Corpus Christi and likely extends NE toward the Matagorda Bay region and then weakens across SE TX at some point. Given all the sea fog and low clouds again this morning it may be hard for the sun to break through and heat the surface today helping to erode that stubborn capping inversion. Will get some help with the cooling from the short wave in the mid levels and lift along both the dryline and approaching cold front…but if the cap breaks remains to be seen. Meso models are fairly evenly split strong to severe storms developing this afternoon.

 

If storms do develop the instability in place will likely result in rapid development with storms quickly going severe, currently thinking is about a 50/50 shot. Meso models showing development show initiate of activity late this morning at the intersection of the dryline and cool front over the Hill Country and then spread a cluster of storms/possible bow echo ESE into E TX this afternoon and evening. Think inflow is fairly weak to support any bow echo across the region (with widespread damaging winds), but instead favor clustering of storms or a possible squall line. Think the main threat will be along an north of a line from Columbus to Sugar Land to Galveston where the capping will be weakest. Main threats will be large hail (possible very large…golfball size or bigger) and wind damage. Any tornado threat will likely be more focused over C TX where initial storm mode will be more supercells before growing into more of a line or cluster.

 

Will have to watch trends closely this morning.

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00/06Z high res guidance both insist on right mover action out of Central Texas. That motion would solve any remaining doubts about low level winds, at least relative to the storm. Agree with the Jeff above that shear is adequate in other levels of the atmo. If confidence were better one could argue for a small 10% tornado area. SPC offers a subtle hint in their #2 point South Texas Arklatex paragraph. If I still lived in Houston I would plan on chasing.

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BULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE JACKSON MS  
618 PM CDT FRI MAR 28 2014  
 
THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A  
 
* TORNADO WARNING FOR...  
EAST CENTRAL ASHLEY COUNTY IN SOUTHEAST ARKANSAS...  
 
* UNTIL 645 PM CDT  
 
* AT 618 PM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A  
TORNADO WAS LOCATED 7 MILES SOUTH OF SNYDER...AND MOVING EAST AT 25  
MPH.  
 
HAZARD...TORNADO AND GOLF BALL SIZE HAIL.  
 
SOURCE...RADAR INDICATED ROTATION.  
 
IMPACT...FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT  
SHELTER. MOBILE HOMES WILL BE DAMAGED OR DESTROYED. DAMAGE  
TO ROOFS...WINDOWS AND VEHICLES WILL OCCUR. TREE DAMAGE IS  
LIKELY.  
 
* THIS DANGEROUS STORM WILL BE NEAR...  
PORTLAND AND MONTROSE AROUND 635 PM CDT.  
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...  
 
TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A  
STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR  
OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT  
YOURSELF FROM FLYING DEBRIS.

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