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    Day 2 Outlook >
Dec 3, 2016 1300 UTC Day 1 Convective Outlook
Updated: Sat Dec 3 12:57:59 UTC 2016 (Print Version | 20161203 1300Z Day 1 shapefile | 20161203 1300Z Day 1 KML)
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 Forecast Discussion
   SPC AC 031257

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0657 AM CST SAT DEC 03 2016

   VALID 031300Z - 041200Z

   ...THERE IS A MRGL RISK OF SVR TSTMS FROM THE LOWER RIO GRANDE
   VALLEY TO SOUTHWESTERN LOUISIANA...

   ...SUMMARY...
   THUNDERSTORMS MAY PRODUCE MARGINALLY SEVERE HAIL AND STRONG TO
   LOCALLY DAMAGING WINDS ACROSS PARTS OF SOUTH TEXAS...THE UPPER TEXAS
   COASTAL PLAIN AND SOUTHWESTERN LOUISIANA.  A TORNADO CANNOT BE RULED
   OUT...BUT THIS THREAT IS MARGINAL AND ISOLATED.

   ...SYNOPSIS...
   A HIGHLY AMPLIFIED UPPER-AIR PATTERN FEATURES A STRONG
   NORTHERN-STREAM SHORTWAVE TROUGH FROM THE DAKOTAS SOUTHWARD ACROSS
   THE CENTRAL PLAINS...AND A CLOSED...NEARLY CUT-OFF SOUTHERN-STREAM
   CYCLONE OVER NORTHWESTERN MEXICO...THE GULF OF CALIFORNIA AND BAJA. 
   THAT CYCLONE IS FORECAST TO PIVOT SOUTHEASTWARD THROUGH MUCH OF THE
   PERIOD...THEN EASTWARD TOWARD NORTH-CENTRAL MEXICO.  

   AT THE SURFACE...AN 11Z ANALYSIS SHOWED A WAVY FRONTAL ZONE FROM
   ABOUT 100 NM SOUTH OF THE CENTRAL LOUISIANA COAST TO JUST OFFSHORE
   FROM BRAZORIA AND GALVESTON COUNTIES...TX...TO NEAR BAFFIN BAY...TO A
   WEAK LOW OVER ZAPATA COUNTY...THEN SOUTHWARD OVER NORTHEASTERN
   MEXICO.  THE GULF SEGMENT IS A WARM FRONT DRIFTING ERRATICALLY
   NORTHWARD...THE REST QUASISTATIONARY.  THE LOW SHOULD REMAIN NEAR ITS
   PRESENT LOCATION...ON EITHER SIDE OF THE RIO GRANDE...UNTIL IT BEGINS
   TO SHIFT SOUTHEAST OR EAST LATE TONIGHT.  THE FRONT WILL LIKEWISE
   START TO MOVE SOUTHEAST TONIGHT OVER SOUTH TEXAS AND ADJACENT GULF...
   PERHAPS ASSISTED BY CONVECTIVE OUTFLOW...WHILE BEING NEARLY
   STATIONARY OR DRIFTING VERY SLOWLY NORTHWARD ELSEWHERE.

   ...SOUTH TEXAS TO SOUTHWESTERN LOUISIANA...
   ALTHOUGH ISOLATED STRONG STORMS CANNOT BE RULED OUT IN THE TIME AND
   SPACE BETWEEN THEM...TWO REGIMES WILL BE RESPONSIBLE FOR THE BULK OF
   THE MARGINAL SEVERE RISK THROUGH THE PERIOD:

   1. NOW THROUGH MOST OF THE PERIOD...SOUTHEAST TEXAS AND SOUTHWESTERN
   LOUISIANA:
   SCATTERED THUNDERSTORMS SHOULD CONTINUE MAINLY ALONG AND NORTH OF
   THE FRONT...WITH WIDELY SCATTERED CONVECTION ALONG AN INTERSECTING
   WARM-SECTOR CONVERGENCE BOUNDARY NOW EVIDENT FROM WESTERN GALVESTON
   ISLAND SOUTH-SOUTHWESTWARD ACROSS THE OPEN GULF.  THE BULK OF
   CONVECTION OVER THIS REGION SHOULD ORIGINATE IN THE WARM-SECTOR
   CONVERGENCE ZONE AND ITS ELEVATED EXTENSION NORTH OF THE SURFACE
   FRONT.  THE SURFACE WARM SECTOR MAY EXTEND SLIGHTLY INLAND OVER THE
   UPPER TEXAS COAST AND SOUTHWESTERN LOUISIANA...BUT ONLY IN NARROW
   CORRIDOR...GIVEN: 
   * PERSISTENT CONVECTIVE PRECIP EXPECTED NORTH OF THE FRONT...WHOSE
   OUTFLOW AND RELATED REINFORCEMENT OF STATIC STABILITY WILL IMPEDE
   THE POLEWARD PROGRESS OF THE BAROCLINIC ZONE;
   * THE PRESENCE OF MID/UPPER RIDGING AND ASSOCIATED ANTICYCLONIC FLOW
   ALOFT...NEARLY PARALLEL TO THE FRONT; AND 
   * RELATED LACK OF MEANINGFUL LARGE-SCALE SUPPORT ASIDE FROM WARM
   ADVECTION...WHICH WILL CONTRIBUTE OFFSETTING FACTORS IN THE FORM OF
   DESTABILIZATION NEAR THE FRONT BUT PARCELS LIFTED TO AN LFC FOR
   MAINTENANCE OF STORMS TO ITS NORTH.

   STILL...ANY SUPERCELLS THAT CROSS THE WARM FRONT WHILE MATURE MAY
   POSE A TORNADO RISK...ALONG WITH DAMAGING GUSTS AND MARGINALLY SEVERE
   HAIL.  THAT ENVIRONMENT SHOULD REMAIN CHARACTERIZED BY RELATIVELY
   MAXIMIZED LOW-LEVEL VORTICITY/SRH...SURFACE DEW POINTS UPPER 60S TO
   LOW 70S F AND WEAK LAPSE RATES ALOFT...WITH 500-800 J/KG MLCAPE.

   2.  OVERNIGHT...SOUTH TEXAS:
   HEIGHT FALLS ASSOCIATED WITH THE APPROACHING MEXICAN MID/UPPER-LEVEL
   LOW WILL BEGIN TO SPREAD ACROSS DEEP SOUTH TEXAS AND THE LOWER RIO
   GRANDE VALLEY REGION OVERNIGHT...CONTERMINOUS WITH THE SOUTHEASTWARD
   ADVANCE OF THE FRONT.  AS LOW-LEVEL MASS RESPONSE OCCURS BOTH AT AND
   ABOVE THE SURFACE...THUNDERSTORM COVERAGE SHOULD INCREASE OVER DEEP
   SOUTH TEXAS AND ADJOINING MEXICO AFTER 00Z...SPREADING NORTHEASTWARD
   AND BACKBUILDING AS WELL.  STORMS SHOULD UNDERGO A NET EASTWARD
   SHIFT ACROSS THE LOWER VALLEY LATE TONIGHT.  ACTIVITY SHOULD BE
   CLUSTERED TO QUASI-LINEAR IN MODE...GIVEN THE GEOMETRY OF THE
   DEEP-LAYER FLOW...AND WILL POSE A RISK OF ISOLATED DAMAGING GUSTS AND
   SEVERE HAIL...AND A TORNADO CANNOT BE RULED OUT WITH ANY QLCS
   CIRCULATIONS OR EMBEDDED SUPERCELLS ACCESSING SURFACE-BASED INFLOW
   IN THE WARM SECTOR BEFORE MOVING OFFSHORE.

   ..EDWARDS/LEITMAN.. 12/03/2016

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z

        
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