DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0655 AM CST WED DEC 23 2015
VALID 231300Z - 241200Z
...THERE IS A MDT RISK OF SVR TSTMS PORTIONS ERN AR...NRN MS...WRN
TN...EXTREME WRN KY...EXTREME SERN MO...EXTREME SRN IL...
...THERE IS AN ENH RISK OF SVR TSTMS SURROUNDING MDT RISK FROM NRN
LA TO MIDDLE TN AND SRN PORTIONS INDIANA/IL...
...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM CENTRAL GULF
COAST AND ARKLATEX REGIONS TO SRN APPALACHIANS...SRN WI AND SRN
LOWER MI...
...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING SLGT RISK AND
EXTENDING EWD TO MUCH OF CAROLINAS...
...SUMMARY...
THE GREATEST THREAT FOR TORNADOES...ALONG WITH DAMAGING WIND AND
OCCASIONAL HAIL...WILL BE FROM EASTERN ARKANSAS AND NORTHERN
MISSISSIPPI TO EXTREME SOUTHERN ILLINOIS. SOME RISK FOR ALL THOSE
SEVERE-WEATHER THREATS EXISTS TODAY ELSEWHERE OVER A VAST SWATH FROM
THE CENTRAL GULF COAST REGION AND LOWER MISSISSIPPI VALLEY TO THE
SOUTHERN UPPER GREAT LAKES REGION AND PARTS OF THE OHIO VALLEY.
SEVERE WEATHER MAY SHIFT EASTWARD INTO THE SOUTHERN APPALACHIANS
REGION TONIGHT. A MARGINAL SEVERE-STORM THREAT EXISTS FARTHER
EASTWARD TO PARTS OF THE CAROLINAS.
...SYNOPSIS...
MIDDLE/UPPER-LEVEL PATTERN TODAY WILL BE DOMINATED BY LONGWAVE
TROUGH OVER WRN CONUS AND ASSOCIATED BROADLY CYCLONIC FLOW FROM PAC
COAST TO SRN PLAINS...MS VALLEY AND GREAT LAKES. EMBEDDED SHORTWAVE
TROUGH -- NOW EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER SRN KS...WRN
OK AND NW TX -- IS FCST TO EJECT NEWD TO IL...SERN MO AND NRN AR BY
00Z.
AT SFC...COMPLEX PATTERN WAS EVIDENT IN 11Z ANALYSIS WITH LOW OVER
E-CENTRAL KS...COLD FRONT SWWD ACROSS SRN TX PANHANDLE...AND
STATIONARY FRONT EXTENDING NEWD TO OCCLUSION TRIPLE POINT OVER NWRN
MO. DIFFUSE WARM FRONT EXTENDED FROM THERE ESEWD ACROSS LOWER OH
VALLEY AND NRN KY. LOW SHOULD MOVE NEWD TO WI BY 00Z...WITH COLD
FRONT SWWD ACROSS SERN MO...SERN OK...AND W-CENTRAL TX. BY
THEN...DIFFUSE SYNOPTIC WARM FRONTAL ZONE WILL MOVE NWD ACROSS
WI/LOWER MI TO LOWER GREAT LAKES...AHEAD OF RETURN-FLOW MOISTURE
PLUME THAT SHOULD REACH MUCH OF IL/INDIANA AND PERHAPS OH.
LOW-LEVEL WARM-FRONTAL ZONE ALSO IS LIFTING NWD ACROSS PORTIONS
GA/CAROLINAS...REINFORCED BY EXTENSIVE CONVECTIVE PLUME THAT EXTENDS
FROM AL TO ERN NC. SURFACE MANIFESTATION OF THAT BOUNDARY -- NOW
NEAR SC/NC COAST -- SHOULD MOVE INLAND TODAY.
...MS VALLEY AND OH VALLEY STATES TO TN VALLEY...
SCATTERED TSTMS IN BKN BANDS AND DISCRETE MODES SHOULD MOVE NEWD
ACROSS THIS REGION TODAY...OFFERING RISKS FOR TORNADOES...DAMAGING
GUSTS AND OCNL LARGE HAIL. GREATEST POTENTIAL CONCENTRATION OF
DISCRETE SUPERCELLS...JUXTAPOSED WITH FAVORABLE CAPE/SHEAR PARAMETER
SPACE...CURRENTLY APPEARS TO BE IN CORRIDOR FROM SERN AR/WRN MS
NNEWD TOWARD SRN IL...FROM MIDDAY THROUGH AFTN. MULTIPLE TORNADIC
SUPERCELLS ARE POSSIBLE IN THAT AREA...WHOSE TORNADO PROBABILITIES
ACCORDINGLY HAVE BEEN UPGRADED...MEETING THRESHOLD FOR CATEGORICAL
MDT RISK. THIS THREAT WILL BE MANIFEST ONCE EXISTING PRECIP ACROSS
SRN PARTS OF THIS AREA -- OVER ERN AR -- HAS SHIFTED NEWD AND
DIABATIC HEATING BEGINS TO BOOST BUOYANCY...AMIDST ROUGHLY 60 KT
EFFECTIVE-SHEAR MAGNITUDES AND EFFECTIVE SRH GENERALLY 250-400 J/KG.
MLCAPE VALUES MAY REACH 1000-2000 J/KG OVER ERN AR...NRN MS AND MEM
AREA THIS AFTN...DECREASING TO AROUND 500 J/KG OVER SRN IL.
BUOYANCY WILL INCREASE WITH SWD EXTENT...BUT COUNTERACTED TO SOME
EXTENT BY GREATER CINH AND LESS WELL-FOCUSED LOW-LEVEL FORCING.
WITH NRN EXTENT...STG LOW-LEVEL AND DEEP SHEAR WILL EXIST BUT
BUOYANCY WILL BECOME PROGRESSIVELY MORE LIMITED. AS
SUCH..PROBABILITIES TAPER NWD AND SWD FROM MDT-RISK AREA.
...LA TO AL AND SRN APPALACHIANS...
POCKETS OF FAVORABLE DEEP-SHEAR/INSTABILITY JUXTAPOSITION WILL EXIST
ACROSS GULF COAST STATES FROM LA TO AL TODAY AND TONIGHT...AND
EPISODES OF TSTMS ARE POSSIBLE WITH FULL RANGE OF ASSOCIATED SVR
HAZARDS. UNCERTAINTY INCREASES WITH SEWD EXTENT FROM CURRENT
MDT-RISK AREA...HOWEVER...GIVEN PRESENCE OF SEVERAL FACTORS
INCLUDING...
1. COVERAGE OF SFC-BASED CONVECTION AMIDST NEBULOUS BOUNDARY-LAYER
FORCING FOR ASCENT...
2. NET HEIGHT RISES ALOFT...WITH NO SUBSTANTIAL UPPER PERTURBATIONS
EVIDENT UPSTREAM ONCE AFOREMENTIONED SHORTWAVE TROUGH PASSES NW-N OF
AREA..
3. FRAGMENTED CAPE SPACE DUE TO BOTH ANTECEDENT TSTMS AND ONGOING
CONVECTION WITHIN ABOUT 100 NM INLAND FROM GULF.
NONETHELESS...WIDESPREAD SWATH OF AT LEAST SLGT SVR RISK IS
APPARENT. ONCE MESOSCALE FACTORS THAT WILL STRONGLY REGULATE SVR
THREAT OVER LOWER DELTA TO AL CAN BE DIAGNOSED WITH MORE
CLARITY...SOME OF THIS AREA MAY REQUIRE PROBABILISTIC UPGRADE.
...GA/CAROLINAS...
ISOLATED SUPERCELL OVER SERN NC...NEAR INTERSECTION OF MOSTLY
OFFSHORE CONFLUENCE BAND WITH NWD-RETREATING/CONVECTIVELY ENHANCED
BAROCLINIC ZONE...MAY POSE RISK OF DAMAGING GUSTS OR TORNADO. REF
SPC MESOSCALE DISCUSSION 2031 FOR NEAR-TERM DETAILS.
OTHERWISE...MODIFIED MHX/CHS RAOBS AND MODEL FCST SOUNDINGS SUGGEST
FAVORABLE ENVIRONMENT FOR AT LEAST MRGL TORNADO RISK AND ISOLATED
SVR GUSTS FOR CONVECTION DEVELOPING THROUGH LATE AFTN ACROSS THIS
REGION ALONG LOW-LEVEL CONFLUENCE/DIFFERENTIAL-HEATING BOUNDARIES.
RICH LOW-LEVEL MOISTURE ASSOCIATED WITH MARITIME RETURN FLOW SHOULD
OFFSET WEAK LAPSE RATES ALOFT ENOUGH TO CONTRIBUTE TO 500-1500 J/KG
MLCAPE...WITH AROUND 150 J/KG EFFECTIVE SRH AND 35-45 KT
EFFECTIVE-SHEAR MAGNITUDES POSSIBLE. ANY RELATIVE CONCENTRATIONS OF
MESOSCALE FOCI THAT MAY DEVELOP COULD LEAD TO UPGRADE OF
PROBABILITIES FOR PARTS OF THIS AREA AS WELL.
..EDWARDS/COOK.. 12/23/2015
