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kevinbente

Thursday, March 24th Severe Threat

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While it is the 4km NAM, that model along with the less, but still notable 12km NAM are both showing a decent chance of severe weather and potentially a tornado threat in Alabama and surrounding areas on Thursday, March 24th.

 

It seems right now, if this setup wants to be more significant, the surface low should want to slow down a bit so surface winds would be more backed in the area. Also, CAPE values generally range from around 1000 J/kg on the 12km NAM/GFS to 1500-2000 on the 4km NAM. Regardless of this, the 4km NAM shows discrete supercells in central Alabama Thursday afternoon.

 

03ehise.png

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There's beginning to look like a decent threat for severe weather across the deep south tomorrow. As of now (12z NAM) has a mixed mode of storms moving across AL from 21z to 03z tomorrow. The instability appears to be there, but the wind profile isn't screaming tornado to me as of now. Looking like a line of broken line of storms with embedded supercells -- Any discrete cells will have tornadic potential. Best place right now appears to be central C AL during the late afternoon into the evening.

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SPC update for Day 2:

...SUMMARY...
   SEVERE THUNDERSTORMS WITH A FEW TORNADOES...WIND DAMAGE AND ISOLATED
   LARGE HAIL WILL BE POSSIBLE ON THURSDAY ACROSS PARTS OF THE
   TENNESSEE VALLEY AND CENTRAL GULF COAST STATES.

   ...TN VALLEY/CNTRL GULF COAST STATES...
   AN UPPER-LEVEL TROUGH WILL BECOME LESS AMPLIFIED ON
   THURSDAY...MOVING EWD ACROSS THE OZARKS AND INTO THE MID MS VALLEY.
   AT THE SFC...A LOW WILL MOVE INTO THE SRN GREAT LAKES REGION AS A
   COLD FRONT ADVANCES QUICKLY EWD INTO THE LOWER AND MID MS VALLEY. A
   BROKEN LINE OF THUNDERSTORMS SHOULD BE ONGOING AHEAD OF THE FRONT AT
   THE START OF THE PERIOD. THE NRN PART OF THE LINE MAY REMAIN INTACT
   INTO THE AFTERNOON...BEING SUPPORTED BY A 50 TO 60 KT LOW-LEVEL JET
   AND LARGE-SCALE ASCENT ASSOCIATED WITH AN UPPER-LEVEL TROUGH IN THE
   MID MS VALLEY. AS INSTABILITY INCREASES DURING THE DAY...THE LINE IS
   EXPECTED TO REDEVELOP FROM WRN TN SWD INTO CNTRL MS AND MOVE EWD
   ACROSS THE SLIGHT RISK AREA.

   FORECAST SOUNDINGS AT 21Z/THU FROM TUPELO NEWD INTO MIDDLE TN SHOW
   MLCAPE OF 100O TO 1500 J/KG WITH MID-LEVEL LAPSE RATES NEAR 7.5 C/KM
   AND STRONG DEEP-LAYER SHEAR PROFILES. 0-6 KM SHEAR IS FORECAST TO BE
   FROM 55 TO 65 KT WITH 0-3 KM STORM RELATIVE HELICITIES IN THE 300 TO
   400 M2/S2 RANGE. THIS SHOULD SUPPORT ISOLATED SUPERCELL DEVELOPMENT
   AND POSSIBLY A FEW TORNADOES
WITH CELLS ALONG THE MORE ORGANIZED
   PARTS OF THE LINE AND WHERE GAPS DEVELOP WITHIN THE LINE. SUPERCELLS
   WITH ISOLATED LARGE HAIL WILL BE POSSIBLE IN AREAS THAT DESTABILIZE
   THE MOST. THE STRONG LOW-LEVEL FLOW WILL ALSO BE FAVORABLE FOR WIND
   DAMAGE WITH ORGANIZED MULTICELL LINE SEGMENTS THAT DEVELOP ALONG AND
   AHEAD OF THE FRONT.

 

Via the 4km NAM.. Not much on other models though we'll see if the threat holds.

 

Birmingham, AL valid 00z Fri

Uhc8SZC.png

 

 

SVRall_N1_110km_nam212F060.png

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BMX says models are trending toward more instability. They say strong tornadoes are possible.

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
406 PM CDT WED MAR 23 2016

.SHORT TERM...
TONIGHT THROUGH THURSDAY NIGHT.

MAIN FOCUS IN THE SHORT TERM IS THE SEVERE WEATHER THREAT FOR
TOMORROW AND TOMORROW NIGHT. LATEST MODELS HAVE BEEN TRENDING UPWARD
WITH INSTABILITY...BULK SHEAR...AND HELICITY VALUES. THEREFORE
CONFIDENCE IS INCREASING IN THE SEVERE WEATHER THREAT.
 CENTRAL
ALABAMA WILL BE IN THE RIGHT ENTRANCE REGION OF A 100 KT 300 MB JET
STREAK PROVIDING SYNOPTIC SCALE FORCING FOR ASCENT. AN UPPER-LEVEL
LOW/SHORTWAVE TROUGH WILL BE LIFTING FROM THE CENTRAL PLAINS TO THE
GREAT LAKES. ROUNDING THE BASE OF THE TROUGH WILL BE A 65-70 KT MID-
LEVEL JET STREAK THAT WILL MOVE ACROSS CENTRAL ALABAMA. THIS WILL
RESULT IN 0-6 KM BULK SHEAR VALUES OF 55-65+ KTS. THE STRONGEST 850
MB LOW LEVEL JET WINDS WILL BE LIFTING NORTH OF CENTRAL ALABAMA BUT
0-1KM SHEAR VALUES WILL STILL BE STRONG...AROUND 25-30 KTS. VEERING
WINDS WITH HEIGHT WILL RESULT IN 0-3 KM SRH VALUES OF 300 TO 400
M2/S2 WHICH IS AN INCREASE OVER PREVIOUS MODEL RUNS. DEW POINTS WILL
INCREASE INTO THE LOW 60S WITH SOME GUIDANCE INDICATING DEW
POINTS APPROACHING THE MID 60S. STEEP MID-LEVEL LAPSE RATES OF
6.5 TO 7 C/KM WILL ALSO OVERSPREAD THE WARM SECTOR. WITH THESE
STEEP MID- LEVEL LAPSE RATES NOT MUCH HEATING WILL BE REQUIRED FOR
DESTABILIZATION. CAPE VALUES HAVE INCREASED IN MODEL GUIDANCE FROM
PREVIOUS RUNS WITH MOST GUIDANCE INDICATING CAPE NOW IN THE 1000-
1500 J/KG RANGE...WITH THE HIGHEST VALUES IN SOUTHWEST AND WEST-
CENTRAL CENTRAL ALABAMA...AND SOME GUIDANCE INDICATES VALUES EVEN
HIGHER.
 CONVECTION WILL INITIATE ALONG THE FRONT AND POTENTIALLY
ALSO ALONG CONFLUENCE LINES AHEAD OF THE FRONT. THE STRONG 0-6 KM
SHEAR ORIENTED FROM THE WEST-SOUTHWEST FAVORS SUPERCELL
DEVELOPMENT INITIALLY...EVOLVING INTO A BROKEN LINE OF SUPERCELLS
AND POSSIBLY LINE SEGMENTS. THREATS WILL INCLUDE TORNADOES BASED
ON THE SRH VALUES AND INSTABILITY...DAMAGING WINDS IN ANY BOWING
SEGMENTS THAT DEVELOP...AND LARGE HAIL GIVEN THE MID-LEVEL LAPSE
RATES.
 THE FLOODING RISK REMAINS LOW GIVEN THE PROGRESSIVE NATURE
OF THE SYSTEM.

LIKE WITH MANY EVENTS THERE ARE SOME POTENTIAL LIMITING
FACTORS...MAINLY IF DESTABILIZATION CAN OCCUR BEHIND SHOWERS
DEVELOPING IN ISENTROPIC LIFT LATE TONIGHT AND TOMORROW MORNING AND
POSSIBLE REMNANTS OF CONVECTION DEVELOPING UPSTREAM TONIGHT. THE
DEGREE OF UPPER-LEVEL FORCING MAY ALSO BE A LIMITING FACTOR.
HOWEVER...THE GENERAL CONSENSUS OF MODEL GUIDANCE INDICATES ROBUST
CONVECTION DEVELOPING AND MOVING EASTWARD DURING THE AFTERNOON AND
EVENING. WITH THE INSTABILITY AND SHEAR PARAMETERS IN PLACE...THE
POTENTIAL IMPACTS WARRANT BUMPING UP THE CONFIDENCE LEVEL IN THE HWO
AND ADDING AN ELEVATED RISK IN OUR SEVERE WEATHER IMPACT GRAPHICS.
BASED ON THE PARAMETERS AND SUPERCELL STORM MODE...WILL ALSO HAVE TO
CLOSELY MONITOR THE POTENTIAL FOR STRONG TORNADOES.
 THE ELEVATED
RISK MAY BE EXPANDED EASTWARD IN FUTURE UPDATES AS THE EVOLUTION OF
THE CONVECTION INTO THE EVENING HOURS BECOMES CLEARER. THE THREAT IN
THE FAR NW COUNTIES IS A BIT CONDITIONAL DEPENDING ON WHEN STORMS
DEVELOP IN THE AFTERNOON BUT WILL KEEP AN ELEVATED RISK THERE AS
WELL.

 

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Any thoughts on how the widespread convection in the bmx area will effect the severe threat later?

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Any thoughts on how the widespread convection in the bmx area will effect the severe threat later?

Looks like any severe threat has shifted South closer to the Gulf...

 

...SUMMARY...   SEVERE STORMS REMAIN A THREAT ACROSS THE NORTHEAST GULF COAST INTO   THIS EVENING. A FEW STRONG TO SEVERE STORMS ALSO MAY OCCUR NORTHWARD   THROUGH THE OHIO VALLEY INTO LOWER MICHIGAN.   ...GULF COAST TO TN VALLEY REGION...   THE GREATEST SEVERE WEATHER THREAT THROUGH THE REST OF THE AFTERNOON   TO EARLY EVENING IS EXPECTED TO BE CONFINED TO THE NORTHEAST GULF   COAST REGION...ALONG AND AHEAD OF THE EASTWARD-MOVING BOW/QLCS   /CURRENTLY LOCATED IN SOUTH AL TO THE FAR WESTERN FL PANHANDLE/.    THE ENVIRONMENT DOWNSTREAM IS DESTABILIZING SOME WITH NORTHWARD   EXTENT ACROSS THE REST OF THE FL PANHANDLE INTO SOUTHWEST GA.  GIVEN   THIS LATTER FACTOR AND THE EASTWARD MOVEMENT OF THE BOW/QLCS...THE   SEVERE PROBABILITIES AND CATEGORICAL RISK AREAS HAVE BEEN SHIFTED   EAST ACCORDINGLY.     MEANWHILE...WEAK DESTABILIZATION IN THE WAKE OF THE QLCS AND AHEAD   OF THE COLD FRONT MAY PROVE FAVORABLE FOR ADDITIONAL STRONG TO   SEVERE STORMS...GIVEN THE PRESENCE OF STRONG EFFECTIVE BULK SHEAR   ACROSS THE CENTRAL GULF COAST/LOWER MS VALLEY.

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Looks like the potential for strong to severe thunderstorms is increasing here. Earlier runs of HRRR didn't get the squall line past the AL/GA border. Now they maintain it till it reaches coastal GA/FL. Line still looks good as well.

Still expect the line to weaken as it moves into a more stable environment and loss of daytime heating.

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