Dec 23, 2015 1300 UTC Day 1 Convective Outlook
Updated: Wed Dec 23 12:55:43 UTC 2015 (20151223 1300Z Day 1 shapefile | 20151223 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20151223 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MODERATE 45,600 3,188,955 Memphis, TN...Jackson, TN...Jonesboro, AR...Bartlett, TN...Southaven, MS...
ENHANCED 129,883 15,039,889 Indianapolis, IN...Nashville, TN...Cincinnati, OH...Lexington-Fayette, KY...Louisville, KY...
SLIGHT 287,347 45,386,869 Chicago, IL...Columbus, OH...Atlanta, GA...St. Louis, MO...Toledo, OH...
MARGINAL 299,716 38,260,421 Detroit, MI...Charlotte, NC...Milwaukee, WI...New Orleans, LA...Cleveland, OH...
Probabilistic Tornado Graphic
20151223 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
SIG SEVERE 53,792 3,691,784 Memphis, TN...Jackson, TN...Jonesboro, AR...Pine Bluff, AR...Bartlett, TN...
15 % 45,582 3,193,895 Memphis, TN...Jackson, TN...Jonesboro, AR...Bartlett, TN...Southaven, MS...
10 % 79,059 6,981,443 Nashville, TN...Little Rock, AR...Huntsville, AL...Evansville, IN...Clarksville, TN...
5 % 196,491 22,896,817 St. Louis, MO...Cincinnati, OH...Lexington-Fayette, KY...Louisville, KY...Birmingham, AL...
2 % 317,753 52,442,260 Chicago, IL...Indianapolis, IN...Columbus, OH...Charlotte, NC...Milwaukee, WI...
Probabilistic Damaging Wind Graphic
20151223 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 175,609 18,210,174 Indianapolis, IN...Memphis, TN...Nashville, TN...Cincinnati, OH...Lexington-Fayette, KY...
15 % 287,264 45,485,641 Chicago, IL...Columbus, OH...Atlanta, GA...St. Louis, MO...Toledo, OH...
5 % 299,395 38,169,776 Detroit, MI...Charlotte, NC...Milwaukee, WI...New Orleans, LA...Cleveland, OH...
Probabilistic Large Hail Graphic
20151223 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 211,455 15,230,616 Memphis, TN...Nashville, TN...Birmingham, AL...Shreveport, LA...Little Rock, AR...
5 % 139,480 15,848,425 New Orleans, LA...St. Louis, MO...Louisville, KY...Baton Rouge, LA...Montgomery, AL...
   SPC AC 231255

   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

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