Dec 20, 2015 1300 UTC Day 1 Convective Outlook
Updated: Sun Dec 20 12:44:20 UTC 2015 (20151220 1300Z Day 1 shapefile | 20151220 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20151220 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Tornado Graphic
20151220 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
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
20151220 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
No Risk Areas Forecast
Probabilistic Large Hail Graphic
20151220 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
No Risk Areas Forecast
   SPC AC 201244

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0644 AM CST SUN DEC 20 2015

   VALID 201300Z - 211200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...SUMMARY...
   A FEW SMALL AREAS OF EVENING AND OVERNIGHT THUNDERSTORMS ARE
   POSSIBLE WITHIN A BROAD SWATH FROM SOUTH AND EAST TEXAS TO EASTERN
   KANSAS...MISSOURI AND IOWA.  A FEW THUNDERSTORMS ALSO MAY OCCUR OVER
   PARTS OF THE COASTAL PACIFIC NORTHWEST TODAY.  IN EITHER
   AREA...SEVERE-THUNDERSTORM POTENTIAL IS TOO MINIMAL FOR AN OUTLOOK.

   ...SYNOPSIS...
   IN MID/UPPER LEVELS...SYNOPTIC-SCALE RIDGING NOW OVER MS VALLEY
   REGION IS EXPECTED TO SHIFT EWD ACROSS E COAST THROUGH PERIOD...AS
   BROAD REGION OF CYCLONIC FLOW BOTH TRANSLATES AND EXPANDS EWD FROM
   WRN THROUGH CENTRAL CONUS.  IN LATER REGIME...EMBEDDED SHORTWAVE
   TROUGH IS EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER WRN AZ.  THIS
   PERTURBATION IS FCST TO MOVE RAPIDLY EWD ACROSS SRN ROCKIES BY 00Z. 
   THIS PERTURBATION THEN SHOULD TURN ENEWD WITHIN THAT EXPANSIVE
   CYCLONIC-FLOW ZONE...WHILE LOSING SOME AMPLITUDE...EJECTING NEWD TO
   SRN IA AND MO BY 12Z.  UPSTREAM...MINOR PERTURBATION NOW ABOUT 500
   NM OFFSHORE CAPE MENDOCINO IS FCST TO UNDERGO GRADUAL AMPLIFICATION
   AS IT TRACKS SEWD TO SRN CA BY 00Z...THEN EWD TO NM AROUND END OF
   PERIOD.

   AT SFC...WEAK LOW ANALYZED AT 11Z OVER ERN SD IS FCST TO MIGRATE
   NEWD TO ERN MN/WRN WI AREA BY 00Z...WITH TRAILING COLD FRONT ACROSS
   SRN MN...WRN IA...SERN NEB...CENTRAL KS...THROUGH SECONDARY LOW
   DEVELOPING OVER WRN KS...TO ERN CO.  LEE TROUGH WILL EXTEND FROM LOW
   SSWWD ACROSS TX SOUGH PLAINS AND PERMIAN BASIN REGION...WITH
   DEVELOPING DRYLINE TO ITS E OVER WRN OK AND W-CENTRAL TX.  BY END OF
   PERIOD...SWRN LOW SHOULD MOVE NEWD TO ERN IA AND BECOME PRIMARY
   CYCLONE...ASSOCIATED WITH PROXIMAL MID/UPPER-LEVEL SHORTWAVE TROUGH.
    COLD FRONT SHOULD EXTEND FROM THAT LOW SWWD ACROSS NRN/WRN MO AND
   SWRN OK.

   ...CENTRAL/E TX TO IA...
   ISOLATED TO WIDELY SCATTERED TSTMS IN CLUSTERS OR SMALL BANDS ARE
   POSSIBLE WITHIN THIS SWATH OVERNIGHT.  COVERAGE IS EXPECTED TO BE
   VERY UNEVENLY DISTRIBUTED WITHIN THIS SWATH...AND THERE MAY BE SOME
   FAIRLY LARGE GAPS WITHOUT THUNDER.  HOWEVER...LATEST OPERATIONAL AND
   HIGH-RES/CONVECTION-ALLOWING GUIDANCE...WHILE CONSISTENTLY
   GENERATING DEEP CONVECTION SOMEWHERE WITHIN EACH OF TWO REGIMES
   DISCUSSED BELOW....IS NOT CONSISTENT ENOUGH IN LOCATING MINIMA TO
   JUSTIFY ANY CATEGORICAL GAPS ATTM.  THE MAIN PROCESSES SUPPORTING
   THIS EPISODIC/STREAKY CONVECTION WILL BE...

   1. WAA PLUME COVERING ALMOST THE ENTIRE SWATH OF THIS OUTLOOK. 
   THOUGH LARGE-SCALE SUPPORT IN MID/UPPER LEVELS WILL BE STRONGEST
   OVER KS/MO/IA...GREATEST MOISTURE AND DEEPEST BUOYANCY WILL BE FROM
   ARKLATEX REGION AND ERN OK SWD...IN ASSOCIATION WITH LARGEST AMOUNT
   OF LOW-LEVEL MOISTURE.  THOUGH LAPSE RATES WILL BE ONLY SLIGHTLY
   ABOVE MOIST-ADIABATIC FROM ERN OK/WRN AR SWD...200-500 J/KG MUCAPE
   SHOULD EXTEND INTO FAVORABLE ICING LAYERS FOR LTG RISK WITH ANY
   CONVECTION THAT OCCURS.  MAIN LOW-LEVEL LIFT MECHANISM SUPPORTING
   CONVECTION WILL BE ISENTROPIC ASCENT TO LFC...INDICATING TSTM
   POTENTIAL WILL BE GRADUAL IN NATURE.

   2. STG LARGE-SCALE LIFT/DESTABILIZATION ALOFT...ACCOMPANYING ZONE OF
   DCVA THAT IMMEDIATELY PRECEDES COMPACT SHORTWAVE TROUGH.  THIS
   REGIME WILL STREAK ENEWD FROM CENTRAL HIGH PLAINS ACROSS KS AND
   PORTIONS MO/IA...CURRENTLY EXPECTED TO ENCOUNTER AT LEAST MRGL
   MOISTURE IN WRN FRINGE OF WAA PLUME SOMEWHERE OVER CENTRAL/ERN KS. 
   THOUGH THAT MOISTURE WILL BE LESS THAN FARTHER S...AND ELEVATED
   BUOYANCY SHALLOWER...STEEPER MIDLEVEL LAPSE RATES STILL MAY SUPPORT
   DEVELOPMENT OF 200-500 J/KG MUCAPE.  MOST INTENSE CELLS MAY OFFER
   SMALL HAIL...BUT INFLOW-LAYER MOISTURE SUPPLY SHOULD BE TOO LIMITED
   TO SUPPORT LARGE-HAIL GROWTH.

   ...COASTAL PAC NW...
   WELL-DEFINED SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE-CHANNEL
   IMAGERY OFFSHORE SWRN BC AND WA -- IS FCST TO MOVE EWD TO ESEWD
   TODAY AND ONSHORE WA/NERN ORE.  AS THIS OCCURS...ASSOCIATED
   LARGE-SCALE DCVA/COOLING ALOFT WILL OVER SPREAD MARINE LAYER AND
   YIELD SUFFICIENTLY STEEP LAPSE RATES TO SUPPORT SHALLOW BUT STILL
   GLACIATED CONVECTIVE TURRETS.  ISOLATED LTG IS POSSIBLE FROM THAT
   CONVECTION.

   ..EDWARDS/COOK.. 12/20/2015

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