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    Day 2 Outlook >
Sep 20, 2014 2000 UTC Day 1 Convective Outlook
Click to see valid 1Z - 12Z Day 1 Convective Outlook
Updated: Sat Sep 20 19:55:26 UTC 2014 (Print Version | 20140920 2000Z Day 1 shapefile | 20140920 2000Z Day 1 KML)
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 Forecast Discussion
   SPC AC 201955

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0255 PM CDT SAT SEP 20 2014

   VALID 202000Z - 211200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM FAR NORTHEAST SD INTO THE
   UPPER MS VALLEY...

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM NORTHEAST MO INTO SOUTHERN
   LOWER MI...

   ...SUMMARY...
   SEVERE THUNDERSTORM WIND GUSTS AND HAIL ARE MOST PROBABLE INTO THE
   EVENING OVER PORTIONS OF MINNESOTA AND FAR NORTHEAST SOUTH
   DAKOTA...AS WELL AS FROM NORTHERN MISSOURI ACROSS CENTRAL AND
   NORTHERN ILLINOIS TO SOUTHERN LOWER MICHIGAN.  A MARGINAL THREAT OF
   SEVERE WEATHER EXISTS ACROSS NEVADA...NORTHWESTERN ARIZONA AND
   WESTERN UTAH...AS WELL AS ACROSS PARTS OF NORTHEAST KANSAS.

   ...FAR NORTHEAST SD AND MN THROUGH THIS EVENING...

   A LINE OF STRONG TO SEVERE THUNDERSTORMS AHEAD OF THE COLD FRONT
   WILL CONTINUE TO TRACK E/SE ACROSS CENTRAL/SRN MN AND FAR NORTHEAST
   SD. STRONG WINDS AND SOME HAIL WILL BE THE MAIN THREATS. THE 30
   PERCENT WIND AREA WAS SHRUNK AND SHIFTED SOUTHWARD A BIT WHERE
   BETTER SFC HEATING IS OCCURRING AND STORMS ALONG THE SOUTHERN END OF
   THE LINE APPEAR TO BE MORE ROBUST...POSING A THREAT FOR MORE
   WIDESPREAD STRONG/DAMAGING WINDS THAN FURTHER NORTH. SEVERE
   THUNDERSTORM WATCH 503 REMAINS IN EFFECT UNTIL 01Z.

   ...NORTHEAST MO INTO NORTHERN IL/LOWER MI...

   STRONG TO SEVERE THUNDERSTORMS WILL CONTINUE TO INCREASE IN COVERAGE
   LATE THIS AFTERNOON INTO THE EVENING AS DEEP LAYER SHEAR INCREASES
   WITH THE APPROACH OF THE UPPER TROUGH. SEVERE THUNDERSTORM WATCH 504
   COVERS PARTS OF NORTHERN AND CENTRAL IL INTO NORTHERN IND AND
   SOUTHWESTERN LOWER MI UNTIL 01Z. REF MCD 1738 FOR MORE DETAILS. 

   ...NE KS...

   A THUNDERSTORM CLUSTER CONTINUES TO FESTER OVER THE AREA IN THE WAKE
   OF EARLIER SEVERE THUNDERSTORM NORTH OF TOPEKA. WHILE THE AIRMASS IS
   STRONGLY UNSTABLE WITH ADEQUATE SHEAR AND SFC MOISTURE TO SUPPORT
   CONTINUED THUNDERSTORM DEVELOPMENT...LACKLUSTER MIDLEVEL LAPSE RATES
   AND WEAKER FORCING FOR ASCENT COMPARED TO FURTHER NORTH OVER MN MAY
   BE LIMITING SEVERE POTENTIAL. THESE STORMS MAY PRODUCE SOME GUSTY
   WINDS AND HAIL. ANY GREATER ORGANIZED SEVERE THREAT APPEARS
   CONDITIONAL AND DEPENDENT ON UPSCALE GROWTH/COLD POOL GENERATION.
   LOW CONFIDENCE IN THIS SCENARIO WILL PRECLUDE AN UPGRADE TO SLIGHT
   RISK AT THIS TIME.

   ...GREAT BASIN...

   NO CHANGES MADE AND PREVIOUS FORECAST REMAINS ON TRACK WITH SOME
   MARGINAL WIND GUSTS AND HAIL POSSIBLE THROUGH THE EVENING HOURS.

   ..LEITMAN.. 09/20/2014

   .PREV DISCUSSION... /ISSUED 1130 AM CDT SAT SEP 20 2014/

   ...EASTERN DAKOTAS ACROSS MN THIS AFTERNOON AND EVENING...
   A POTENT AND COMPACT SHORTWAVE TROUGH EVIDENT IN SATELLITE IMAGERY
   AND SHORT-TERM MODEL DATA WILL TRACK QUICKLY SOUTHEAST FROM ND AND
   ACROSS THE UPPER MS VALLEY THROUGH TONIGHT. LATEST INDICATIONS
   SUPPORT AT LEAST AN 80KT 500MB JET AIDING IN THE RAPID SOUTHEASTWARD
   TRANSLATION OF THIS IMPULSE ACROSS MN THIS AFTERNOON AND EVENING.
   STRONGLY FORCED DEEP-LAYER ASCENT WITHIN/BENEATH LEFT EXIT REGION OF
   THE MID/UPPER JET WILL BE REALIZED ALONG A SECONDARY COLD
   FRONT/WIND-SHIFT THAT IS FORECAST TO TRACK EAST-SOUTHEAST FROM ND/MN
   BORDER TO EXTREME SOUTHEAST MN AND WESTERN WI THROUGH EVENING.
   DESPITE LIMITED BOUNDARY LAYER MOISTURE AHEAD OF THE FRONTAL SURGE
   WITH SURFACE DEWPOINTS GENERALLY IN THE LOW-MID 50S F...THE
   MAGNITUDE OF FORCING/LIFT WILL COINCIDE PREFERENTIALLY WITH THE
   DIURNAL HEATING CYCLE TO SUPPORT DEVELOPMENT OF STRONG LOW-TOPPED
   LINEAR CONVECTION...AND POSSIBLY EMBEDDED SUPERCELL STRUCTURES
   ACROSS WESTERN MN BY EARLY AFTERNOON. GIVEN INTENSITY OF MESO-BETA
   SCALE FORCING...HIGH RES MODELS ARE QUITE CONSISTENT IN THE
   EVOLUTION OF A LINEAR MCS MOVING RAPIDLY SOUTHEAST ACROSS CENTRAL
   AND SOUTHEAST MN THROUGH THE DAYLIGHT HOURS. WITH LATEST VISIBLE
   SATELLITE IMAGERY INDICATING NEARLY CLOUDLESS CONDITIONS FROM
   EASTERN DAKOTAS ACROSS THE SOUTHERN HALF OF MN...CONFIDENCE IS
   INCREASING THAT SUFFICIENT HEATING/INSTABILITY WILL DEVELOP TO
   CONTRIBUTE TO A CORRIDOR OF STRONG TO DAMAGING THUNDERSTORM WIND
   GUSTS AS STORMS MOVE OVER THESE AREAS THROUGH THE AFTERNOON. HAIL UP
   TO AN INCH ALSO APPEARS LIKELY TO OCCUR WITH A FEW OF THE MORE
   ROBUST UPDRAFTS OR EMBEDDED SUPERCELLS WITH THIS CONVECTIVE SYSTEM.

   ...NORTHEAST MO/EASTERN IA TO SOUTHERN WI/NRN IL/IND AND LOWER MI...

   SOMEWHAT LOWER CONFIDENCE EXISTS REGARDING THUNDERSTORM
   DEVELOPMENT/EVOLUTION ACROSS THESE AREAS COMPARED TO FARTHER NORTH.
   ISOLATED...MOSTLY WEAK...CONVECTION HAS PERSISTED NEAR THE LEADING
   FRONTAL WIND-SHIFT ACROSS PARTS OF IA AND EXTREME SOUTHEAST NEB THIS
   MORNING. CI/DEBRIS CLOUDS AHEAD OF THIS ACTIVITY WERE THINNING AND
   THIS SHOULD CONTRIBUTE TO SURFACE HEATING/DESTABILIZATION THROUGH
   THE AFTERNOON. AS WEAK INHIBITION IS OVERCOME EXPECT MORE ROBUST
   STORM DEVELOPMENT TO OCCUR ALONG SOUTHWEST-NORTHEAST ORIENTED WEAK
   CONFLUENCE ZONES ASSOCIATED WITH 1) LEADING FRONT...AND 2)
   PRE-FRONTAL TROUGH/RESIDUAL OUTFLOW BOUNDARY...FROM NORTHERN MO TO
   SOUTHERN WI/NORTHERN IL. MODEST TO LOCALLY STRONG INSTABILITY
   /SBCAPE 2000-2500 J PER KG/ IS FORECAST TO EXIST NEAR/AHEAD OF THE
   INCREASE CONVECTION OVER MO/IL...WITH A GENERAL DECREASE IN CAPE TO
   UNDER 1000 J PER KG WITH EAST-NORTHEASTWARD EXTENT INTO LOWER MI.
   GREATEST SUPPORTIVE JUXTAPOSITION OF INSTABILITY AND STRENGTHENING
   DEEP-LAYER VERTICAL SHEAR FOR SEVERE STORMS THROUGH EARLY EVENING IS
   LIKELY TO EVOLVE FROM NEAR THE SOUTHERN TIP OF LAKE MICHIGAN
   SOUTHWESTWARD TO NEAR THE KS/MO BORDER. THIS ACTIVITY WILL HAVE A 
   CHANCE TO PRODUCE DAMAGING GUSTS AND SPORADIC LARGE HAIL. A COUPLE
   OF SUPERCELLS MAY DEVELOP A BRIEF OPPORTUNITY FOR A TORNADO IF
   STORMS CAN RETAIN DISCRETE CHARACTER AND ENCOUNTER LOCALLY ENHANCED
   LOW LEVEL SHEAR NEAR ANY LAKE BREEZES...OR RESIDUAL BOUNDARIES.
   SEVERE THREAT SHOULD DIMINISH FROM LATE EVENING INTO OVERNIGHT HOURS
   AS AIRMASS BECOMES MORE STABLE.

   ...GREAT BASIN...
   WIDELY SCATTERED AFTERNOON AND EVENING STORMS ARE EXPECTED TO TRACK
   NORTHWARD/NORTHEASTWARD OVER NV THROUGH TONIGHT. ACTIVITY WILL BE
   SPURRED/SUSTAINED BY A SLOW INCREASE IN BOTH MID-UPPER LEVEL WINDS
   AND LARGE-SCALE ASCENT AS DEEP-LAYER CLOSED LOW DEVELOPS EASTWARD
   FROM CA. MOISTURE WILL REMAIN MARGINAL FOR MORE ROBUST STORMS BUT
   DEEPENING/WELL-MIXED SUBCLOUD LAYER WILL DEVELOP WITH NEARLY
   DRY-ADIABATIC LAPSE RATES EVOLVING COINCIDENT WITH GENERALLY WEAK
   MLCAPE AOB 500 J PER KG. ALTHOUGH DEEP-LAYER SHEAR VALUES ARE MODEST
   FOR MORE ORGANIZED STORMS...SUFFICIENT AND STRENGTHENING FLOW
   THROUGH THE CLOUD-BEARING LAYER...IN COMBINATION WITH THE INCREASE
   IN LARGE SCALE FORCING FOR ASCENT....SHOULD CONTRIBUTE TO MODEST
   STORM ORGANIZATION INTO THIS EVENING WITH LOCALIZED SEVERE WIND AND
   HAIL POSSIBLE.

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z

        
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Page last modified: September 20, 2014
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