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Day 2 Convective Outlook Valid 12Z July 24, 2013
Updated: Tue Jul 23 17:33:50 UTC 2013 (Print Version | 20130723 1730Z Day 2 shapefile | 20130723 1730Z Day 2 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Probabilistic
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 Forecast Discussion

   SPC AC 231730

   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT TUE JUL 23 2013

   VALID 241200Z - 251200Z

   ...NO SVR TSTM AREAS FORECAST...

   ...SYNOPSIS...
   BASIC UPPER-AIR PATTERN OF ERN CONUS TROUGHING AND WRN RIDGING WILL
   PERSIST THROUGH DAY-2...AS SERIES OF SHORTWAVES AND A COUPLE OF
   CLOSED LOWS REVOLVE AROUND COMMON CENTER OVER ERN HUDSON BAY/NRN QUE
   REGION.  ASSOCIATED/ENHANCED BELT OF NWLY FLOW ALOFT WILL EXTEND
   FROM NRN ROCKIES TO MID MS RIVER AND LOWER OH RIVER
   VALLEYS...TURNING EWD THROUGH SYNOPTIC TROUGH OVER CENTRAL
   APPALACHIANS AND NEWD ACROSS NEW ENGLAND.  STG MID-UPPER LEVEL
   DIFLUENCE WILL EXIST OVER MUCH OF CENTRAL/SRN APPALACHIANS REGION
   AND OH VALLEY SWD ACROSS GA/AL TO FL PANHANDLE.  UPSTREAM PHASING OF
   INITIALLY SEPARATE VORTICITY MAXIMA -- NOW OVER NW TERRITORIES AND
   SRN NUNAVUT -- WILL RESULT IN STG SHORTWAVE TROUGH DIGGING SSEWD
   OVER MB/SK BY END OF PERIOD...AND HEIGHT FALLS ACROSS NRN BORDER
   REGION OF ND/MN.

   LOWER-AMPLITUDE PERTURBATIONS -- SOME CONVECTIVELY
   GENERATED/ENHANCED UPSTREAM -- WILL TRAVERSE NW-FLOW BELT BETWEEN
   THERE AND APPALACHIANS SYNOPTIC TROUGH...BUT SPECIFIC PREDICTABILITY
   OF THESE FEATURES IS LOW GIVEN THEIR SMALL SIZE AND INCONSISTENT
   DEPICTION IN NUMERICAL GUIDANCE.  HOWEVER...ONE FAIRLY WELL-DEFINED
   SHORTWAVE TROUGH -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY OVER
   4-CORNERS/GREAT BASIN REGION AMIDST LARGER-SCALE RIDGING -- IS FCST
   TO PIVOT ANTICYCLONICALLY ACROSS CENTRAL ROCKIES TO ERN CO/WRN KS BY
   25/12Z.

   AT SFC...COLD FRONT NOW CROSSING UPPER GREAT LAKES...IL...MO AND KS
   IS EXPECTED TO MOVE EWD TO PORTIONS NEW ENGLAND AND COASTAL MID-ATLC
   AROUND START OF PERIOD THEN SWWD THROUGH TN VALLEY AND AR TO
   FRONTAL-WAVE LOW OVER OK.  BY 25/00Z...FRONT SHOULD EXTEND GENERALLY
   FROM CENTRAL/ERN NC ACROSS CENTRAL/NRN PORTIONS GA/AL/MS...THROUGH
   WEAK FRONTAL WAVE OVER RED RIVER REGION OF SWRN O/NW TX..TO NERN NM.
   THROUGH OVERNIGHT HOURS...FRONT SHOULD BE QUASISTATIONARY OVER SRN
   PLAINS WHILE MOVING SLOWLY SEWD ACROSS CAROLINAS..GA...AL AND MS. 
   IMPORTANT CAVEAT--SPECIFIC/EFFECTIVE FRONTAL POSITION THROUGHOUT
   DAY-2...OVER SERN CONUS INTO SRN PLAINS...WILL BE MODULATED BY
   PREFRONTAL CONVECTIVE BOUNDARIES.  WEAK...EWD-DRIFTING TO
   QUASISTATIONARY  SFC FRONTAL ZONE AND WIND-SHIFT/CONFLUENCE LINE
   SHOULD EXTEND FROM SERN MB ACROSS ERN/SRN ND TO SWRN SD AT 25/00Z. 
   LATE IN PERIOD...THIS BOUNDARY WILL BE OVERTAKEN FROM NW BY COLD
   FRONT PRECEDING CANADIAN SHORTWAVE TROUGH.

   ...CAROLINAS/EXTREME SERN VA...
   SCATTERED TO LOCALLY NUMEROUS TSTMS ARE EXPECTED TO DEVELOP
   ALONG/AHEAD OF FRONT...MAINLY NEAR PREFRONTAL SFC TROUGH THAT SHOULD
   LIE OVER ERN CAROLINAS...AND ALONG SEA BREEZE/OUTFLOW BOUNDARIES. 
   MAIN STORM MODE SHOULD BE MULTICELLULAR...SOME BEING ORGANIZED
   ENOUGH FOR MRGL SVR HAIL AND DAMAGING GUSTS NEAR SVR LEVELS. THREAT
   APPEARS LARGELY DIURNAL...BUT MAY EXTEND INTO EVENING OVER SRN
   PORTIONS OF THIS AREA IF COLD POOL CAN BECOME LARGE/ORGANIZED ENOUGH
   FOR FORCED ASCENT OF OTHERWISE GRADUALLY STABILIZING EVENING
   BOUNDARY LAYER.

   ...NM/CO TO LOWER MS VALLEY...
   SVR THREAT OVER THIS SWATH IS ASSOCIATED WITH FRONTAL ZONE AND
   NEARBY OUTFLOW BOUNDARIES...AND TEMPORALLY BIMODAL WITH TWO MAIN
   EPISODES.  IN BOTH CASES...RISK APPEARS TOO CONDITIONAL TO ASSIGN
   SPECIFIC CATEGORICAL/15% SVR AREA ATTM...HOWEVER RELATIVE
   CONCENTRATION OF SVR MAY BECOME BETTER APPARENT AS REQUIRED
   MESOSCALE FOCI TAKE SHAPE.

   1. ONE OR MORE CLUSTERS OF CONVECTION ASSOCIATED WITH DAY-1 SVR TSTM
   DEVELOPMENT...OVER OZARKS/NERN OK/SERN KS REGION...MAY BE ONGOING AT
   START OF PERIOD.  SOME OF THIS ACTIVITY STILL MAY POSE SVR RISK FOR
   WIND OR HAIL FROM THOSE AREAS SEWD OVER LOWER MS VALLEY AS IT MOVES
   INTO RICHLY MOIST AIR MASS...ESPECIALLY IF IT HAS MAINTAINED ROBUST
   COLD POOL OVERNIGHT TO COUNTERACT NOCTURNAL/MORNING MIN IN SFC-BASED
   INSTABILITY.

   2. DIURNAL CONVECTION FORMING ALONG OUTFLOW...DIFFERENTIAL-HEATING
   AND FRONTAL BOUNDARIES AS STG DIABATIC SFC HEATING ERODES MLCINH. 
   MAIN SUSPECT HERE APPEARS TO BE OUTFLOW BOUNDARY PRODUCED BY PRIOR
   OVERNIGHT AND MORNING CONVECTION...WHICH SHOULD OFFER MESOSCALE
   CONCENTRATION OF LIFT...VORTICITY AND PERHAPS LOW-LEVEL SHEAR FOR
   ORGANIZED MULTICELLS AND BRIEF SUPERCELLS.  FAVORABLE BUOYANCY WILL
   BE SUPPORTED BY SFC DEW POINTS 70S F FROM ERN OK/N TX EWD AND
   SOMEWHAT STEEPER LAPSE RATES ALOFT FARTHER W.

   ...S-CENTRAL HIGH PLAINS...
   WIDELY SCATTERED TO SCATTERED TSTMS ARE EXPECTED INVOF SFC FRONT AND
   OUTFLOW BOUNDARIES...NWD ALONG HIGHER TERRAIN OF NERN NM AND SERN
   CO.  ISOLATED STG-SVR GUSTS AND LARGE HAIL ARE POSSIBLE.
   STRONGEST DIRECTIONAL SHEAR MAY EXIST OVER HIGH-PLAINS PORTION OF
   THIS CORRIDOR...WHERE 50S TO MID 60S F SFC DEW POINTS CONTRIBUTE TO
   MLCAPE 1500-2000 J/KG.  POSTFRONTAL ELY COMPONENT WILL SERVE TO
   1. ADVECT RELATIVELY MOIST AIR MASS INTO THIS AREA N OF FRONT...
   2. AUGMENT LIFT ALREADY PROVIDED BY HEATING ALONG HIGHER
   TERRAIN...AND
   3. ENHANCE DEEP-LAYER SHEAR...OFFSETTING MODEST MIDLEVEL WINDS TO
   YIELD EFFECTIVE SHEAR MAGNITUDES 35-40 KT IN SUPPORT OF ORGANIZED
   MULTICELLS AND AT LEAST TRANSIENT/SLOW-MOVING SUPERCELL POTENTIAL.

   ...CENTRAL/NRN HIGH PLAINS TO UPPER MIDWEST...
   WIDELY SCATTERED TO SCATTERED TSTMS SHOULD DEVELOP ALONG
   AFOREMENTIONED SFC BOUNDARY OVER DAKOTAS/WRN MN...AND OVER HIGHER
   TERRAIN OF ERN WY/SWRN SD AND NEB PANHANDLE.  ISOLATED SVR GUSTS AND
   HAIL ARE EXPECTED.  DEEP-WELL-MIXED SUBCLOUD LAYERS SHOULD DEVELOP
   BY MID-LATE AFTERNOON...ESPECIALLY OVER HIGH-PLAINS PORTION-OF THIS
   CORRIDOR...WITH SFC DEW POINTS GENERALLY 50S F SUPPORTING MLCAPE IN
   1500-2000 J/KG RANGE.  THOUGH LOW-LEVEL HODOGRAPHS ARE PROGGED TO BE
   SMALL...STG DIRECTIONAL SHEAR AMIDST NW FLOW ALOFT WILL CONTRIBUTE
   TO EFFECTIVE SHEAR MAGNITUDES POTENTIALLY RANGING FROM AROUND 35 KT
   OVER NEB PANHANDLE TO 45-50 KT FROM NERN WY AND ERN DAKOTAS...IN
   SUPPORT OF LOCALIZED TSTM ORGANIZATION.  BAND OF TSTMS MAY GET
   BETTER ORGANIZED DURING EVENING/OVERNIGHT HOURS ACROSS MN...IN
   REGIME OF ELEVATED LOW-LEVEL WAA/MOISTURE TRANSPORT...BUT ALSO
   INCREASING SFC STABILITY WITH TIME.  ATTM SVR POTENTIAL APPEARS TO
   CONDITIONAL AND/OR ISOLATED AREA-WIDE FOR CATEGORICAL OUTLOOK.

   ..EDWARDS.. 07/23/2013

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Page last modified: July 23, 2013
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