SWODY1
SPC AC 211256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0656 AM CST WED DEC 21 2011
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A SMALL PART OF SE TX AND
SRN LA...
...SYNOPSIS...
SPLIT FLOW PATTERN WILL PERSIST THIS PERIOD...WITH MEAN TROUGH OVER
THE RCKYS/HI PLNS AND BROAD RIDGE OFF THE S ATLANTIC CST. IN THE
CONFLUENT WSW FLOW E OF THE TROUGH...UPR LOW NOW OVER IL SHOULD
FURTHER WEAKEN AS IT CONTINUES ENE TO THE LWR GRT LKS. AT THE SAME
TIME...NW MEXICO UPR LOW ALSO SHOULD WEAKEN AS IT ACCELERATES ENE
INTO TX AHEAD OF NEXT IMPULSE DROPPING S INTO THE GRT BASIN.
TSTMS...A FEW OF WHICH COULD BECOME SVR...MAY OCCUR IN CONJUNCTION
WITH BOTH THE UPR SYSTEM CROSSING THE OH VLY...AND WITH THE
DISTURBANCE EMERGING FROM MEXICO.
...FL PANHANDLE INTO ERN AL AND WRN/SRN GA TODAY...
LOOSELY ORGANIZED CLUSTERS OF STORMS LIKELY WILL PERSIST OVER THE
WRN HALF OF THE FL PANHANDLE AND ADJACENT PARTS OF SE AL/SW GA
TODAY. THIS ACTIVITY WILL BE SUPPORTED BY WAA/MOISTURE TRANSPORT IN
CONFLUENT LOW LVL FLOW ON WRN FRINGE OF W ATLANTIC RIDGE.
INCREASINGLY LOW LCLS AND LOW LVL DIRECTIONAL SHEAR MAY YIELD A
WATERSPOUT OR TWO ALONG THE FL CST. A BRIEF TORNADO OR TWO ALSO MAY
OCCUR NEWD INTO PARTS OF AL AND PERHAPS SW GA. BUT GRADUALLY RISING
HEIGHTS AND ASSOCIATED WEAKENING OF MEAN FLOW SHOULD OFFSET SLIGHT
DIURNAL INCREASE IN LOW LVL BUOYANCY TO PRECLUDE ANY WIDESPREAD OR
SUSTAINED SVR THREAT.
...SRN AND CNTRL APPALACHIAN MTNS TODAY...
AS IL UPR LOW CONTINUES ENEWD TODAY...A BAND OF 70-80 KT WSWLY 500
MB WILL SPREAD FROM THE LWR TN AND OH VLYS TO THE CNTRL/SRN
APPALACHIANS THIS AFTN. AHEAD OF THE SYSTEM...A NARROW MOIST AXIS
WITH SFC DEWPOINTS IN THE MID 50S F WILL SPREAD NEWD ALONG THE WRN
SLOPES OF THE CNTRL/SRN APPALACHIANS.
LARGE SCALE ASCENT PROVIDED BY THE IL TROUGH...AND LOW LVL UPLIFT
ALONG/AHEAD OF ASSOCIATED COLD FRONT...SHOULD MAINTAIN EXISTING BAND
OF SCTD FRONTAL/PRE-FRONTAL STORMS NOW EXTENDING FROM WRN OH TO
CNTRL AL AS THE FRONT CONTINUES EWD. A NEW BAND OF LOW-TOPPED
CONVECTION/STORMS MAY FORM LATER THIS AFTN ALONG THE IMMEDIATE FRONT
IN ERN OH/WRN PA.
BUOYANCY WILL REMAIN LIMITED AS BOTH MID LVL LAPSE RATES AND SFC
HEATING REMAIN WEAK. BUT PRESENCE OF VERY STRONG WIND FIELD WITH
EVEN MODEST INSTABILITY WILL POSE A LOW PROBABILISTIC THREAT FOR
ISOLD DMGG WIND. THIS THREAT MAY BE GREATEST BENEATH CORE OF
STRONGEST 700 MB FLOW...I.E. OVER ERN KY...SRN/ERN OH...WV...WRN
MD...AND PERHAPS WRN PA THROUGH THE AFTN. ANY SVR THREAT SHOULD
DIMINISH BY EVE AS UPR SYSTEM FURTHER DEAMPLIFIES AND MOVES BEYOND
LOW LVL MOIST AXIS.
...SE TX/SW LA EARLY THU...
APPROACH OF NW MEXICAN UPR TROUGH WILL BACK AND STRENGTHEN LOW TO
MID LVL TROPOSPHERIC FLOW OVER E TX...THE LWR MS VLY...AND THE NWRN
GULF OF MEXICO LATER TODAY THROUGH EARLY THU. AS A RESULT...SWRN
PART OF AFOREMENTIONED COLD FRONT WILL STALL AND SUBSEQUENTLY REFORM
NWWD TO NEAR THE UPR GULF CST OF TX AND SW/S CNTRL LA BY 12Z THU.
INCREASING MOISTURE INFLOW ATOP FRONT AND STRENGTHENING LARGE SCALE
ASCENT/WAA AHEAD OF TROUGH SHOULD SUPPORT DEVELOPMENT OF A
WIDESPREAD AREA OF SHOWERS/STORMS TNGT AND ...ESPECIALLY...EARLY
THU...FROM S CNTRL THROUGH E TX. THIS ACTIVITY SHOULD MOVE/DEVELOP
E INTO PARTS OF LA BEFORE DAYBREAK.
BUOYANCY WILL REMAIN WEAK EXCEPT NEAR SFC FRONT NEAR THE UPR TX GULF
CST AND IN SRN LA...WHERE SBCAPE MAY EXCEED 500 J/KG. COUPLED WITH
60+ KT SWLY 0-6 KM SHEAR AND STRENGTHENING SSELY LOW LVL
WINDS...SETUP MAY YIELD AN EXTENSIVE SSW-NNE SQLN ON THE ERN EDGE OF
THE AREA OF CONVECTION/STORMS. THE SQLN COULD CONTAIN EMBEDDED
SUPERCELLS/LEWPS WITH A CONDITIONAL THREAT FOR ISOLD
TORNADOES/STRONG WINDS FROM NEAR HOUSTON ENE INTO S CNTRL LA. THIS
THREAT SHOULD BE GREATEST AFTER 09Z THU AND LIKELY WILL CONTINUE
..CORFIDI/HURLBUT.. 12/21/2011
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