The SPC is forecasting ...Severe thunderstorms expected over parts of the middle and lower Missouri Valley into the middle Mississippi Valley this afternoon and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

   SPC AC 031629

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1129 AM CDT TUE JUN 03 2014

   VALID 031630Z - 041200Z

   ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NORTHERN AND
   EASTERN NEBRASKA...WESTERN/SOUTHERN IOWA...NORTHERN MISSOURI AND
   WESTERN ILLINOIS...

   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA
   FROM THE NRN HIGH PLAINS TO MID MS VALLEY/MIDWEST...

   ...SUMMARY...
   AN OUTBREAK OF SEVERE STORMS IS FORECAST THIS AFTERNOON THROUGH 
   TONIGHT FROM PARTS OF NEBRASKA THROUGH IOWA...NORTHERN
   MISSOURI...AND INTO ILLINOIS. DESTRUCTIVE WINDS...VERY LARGE
   HAIL...AND A COUPLE OF STRONG TORNADOES ARE EXPECTED.

   ...SYNOPSIS...
   FAST-MOVING SHORTWAVE TROUGH AND ASSOCIATED 70KT MID-LEVEL SPEED MAX
   CURRENTLY CROSSING THE GREAT BASIN/INTERMOUNTAIN WEST WILL CREST A
   STRONG SUB-TROPICAL RIDGE AND PRODUCE MODEST MID-LEVEL HEIGHT FALLS
   ACROSS THE CENTRAL PLAINS THROUGH THIS EVENING. IN ADDITION TO
   SPURRING LEE-SIDE CYCLOGENESIS ACROSS THE CENTRAL HIGH
   PLAINS...LARGE SCALE ASCENT ASSOCIATED WITH THE MID/UPPER
   DISTURBANCE WILL BE FOCUSED ALONG AND NORTH OF A WARM FRONT SITUATED
   FROM NEB PANHANDLE ESEWD TO NEAR THE IA/MO BORDER.

   A BROAD ZONE OF SFC LOW PRESSURE OVER ERN WY/CO WILL CONSOLIDATE
   INTO LEE-CYCLONE AND TRACK TO WRN NEB BY THIS EVENING. ADDITIONAL
   MESO-LOWS/FRONTAL WAVES MAY FORM AND TRACK EAST ALONG THE WARM
   FRONT...AIDED BY LATENT HEATING/DEEP CONVECTION...INTO LATE EVENING.
   SOUTH OF THE LOW/WARM FRONT...A DRYLINE/THERMAL TROUGH WILL
   STRENGTHEN THROUGH THE AFTERNOON AND EXTEND FROM WRN NEB SSWWD
   THROUGH WRN KS TO FAR ERN NM.

   IN THE EAST...COLD FRONT ASSOCIATED WITH DEEP LOW PRESSURE NEAR
   JAMES BAY WILL CONTINUE EAST FROM ERN GREAT LAKES TO NEW ENGLAND.

   ...SD/NEB TO IA/MO THROUGH LATE EVENING...
   INTENSE STORMS POSING PRIMARILY A THREAT FOR LARGE HAIL ARE ALREADY
   UNDERWAY NORTH OF SFC WARM FRONT AND NEAR THE SD/NE BORDER THIS
   MORNING /REF WW 206/. THIS CONVECTION WAS LIKELY ROOTED ABOVE THE
   850MB LEVEL IN AN ENVIRONMENT CHARACTERIZED BY STEEPENING MID-LEVEL
   LAPSE RATES AND STRONG VERTICAL SHEAR. EXPECT THESE ELEVATED STORMS
   TO PERSIST GIVEN MASS AND MOISTURE FLUXES NOW UNDERWAY IN RESPONSE
   TO LARGE SCALE ASCENT AND DIABATIC PROCESSES.

   BY MID-AFTERNOON...ELEVATED STORMS WILL CONTRIBUTE TO... 1) A
   REINFORCEMENT OF THE EXISTING LOW LEVEL BAROCLINIC ZONE/WARM
   FRONT...AND 2) A DEEPENING COLD POOL ALONG AND NORTH OF THE FRONT.
   MODEST TO LOCALLY STRONG WARM SECTOR SFC HEATING WILL CONTRIBUTE TO
   WEAKENING INHIBITION AND AN INCREASING POTENTIAL FOR CONVECTION TO
   BECOME ROOTED IN A VERY UNSTABLE BOUNDARY LAYER NEAR THE FRONT BY
   LATE AFTERNOON. ADDITIONAL STORMS ARE EXPECTED TO INCREASE WITHIN
   THE LOW-LEVEL UPSLOPE FLOW REGIME OVER PARTS OF SD/NEB.

   A FEW MODELS SUPPORT AT LEAST ISOLATED WARM SECTOR DISCRETE STORMS
   BY LATE AFTERNOON/EARLY EVENING ACROSS CNTRL/ERN NEB. ANY DISCRETE
   STORMS INITIATING NEAR THE WARM FRONT WILL EXIST IN AN IDEAL
   ENVIRONMENT FOR TORNADIC SUPERCELLS WITH EFFECTIVE SRH IN EXCESS OF
   200 M2/S2 AND RELATIVELY LOW LFC. AWAY FROM THE FRONT AND NEAR THE
   DRYLINE...HEATING AND DEEPER MIXING MAY OFFSET THE TORNADO POTENTIAL
   SOMEWHAT AND RESULT IN MORE OUTFLOW-DOMINANT STORMS WITH HIGH WIND
   AND VERY LARGE HAIL POTENTIAL.

   WHILE ABOVE SCENARIO HAS LOW TO MODEST CONFIDENCE...GREATER
   CONFIDENCE EXISTS IN THE CONTINUATION AND GRADUAL UPSCALE GROWTH OF
   ONGOING CONVECTION INTO AN COMPLEX OF EVEN MORE INTENSE
   STORMS...INCLUDING EMBEDDED SUPERCELLS...MOVING ESEWD TO ERN NEB AND
   THEN TO SRN IA/NRN MO THROUGH THE LATE EVENING. THIS CONVECTION WILL
   DEVELOP INTO AN AXIS OF STRONG INSTABILITY /SBCAPE TO 3000-4000 J
   PER KG/ COINCIDENT WITH INTENSIFICATION OF A WLY 60-70KT MID-LEVEL
   JET. BOTH PARALLEL ARW/NMMB HIRES WINDOWS DEPICT THIS SCENARIO QUITE
   WELL BUT STILL OFFER DIFFERING OUTCOMES IN TIME/INTENSITY AND
   PLACEMENT OF GREATEST HIGH WIND POTENTIAL.

   THUS...WILL MAINTAIN A RELATIVELY HIGH CONFIDENCE FORECAST IN
   DERECHO EVOLUTION ACROSS NEB/IA/MO AREA THROUGH THE LATE EVENING.
   EXPECT AN INCREASING CHANCE FOR WIDESPREAD DAMAGING WINDS...LARGE
   HAIL...AND A COUPLE OF POTENTIALLY STRONG TORNADOES IN THESE AREAS.
   IF CONFIDENCE CONTINUES TO INCREASE IN THIS WIDESPREAD SEVERE WIND
   SCENARIO...A HIGH RISK AREA MAY BE ADDED IN THE AFTERNOON SWODY1
   UPDATE.

   ...ACROSS THE MS RIVER TO IL/IND BEFORE DAYBREAK WED...
   MCS/DERECHO SHOULD MAINTAIN DAMAGING WIND AND SOME HAIL POTENTIAL
   EAST ACROSS THE MS RIVER AND INTO IL/IND...ESPECIALLY AFTER MIDNIGHT
   CDT. WHILE BOUNDARY LAYER STABILIZATION MAY ACT TO OFFSET MORE
   SUBSTANTIAL WIND THREAT WITH TIME...UPSCALE STORM ORGANIZATION AND
   CONTINUING LARGE SCALE SUPPORT FOR ASCENT SUGGESTS AT LEAST MODEST
   SEVERE WIND PROBABILITIES/SLGT RISK AREA IS WARRANTED AS FAR EAST AS
   CENTRAL IND THROUGH DAYBREAK WED.

   ...LOWER GREAT LAKES/OH VALLEY NEWD TO CHAMPLAIN VALLEY...
   DIURNAL HEATING OF MIDDLE 60S-LOWER 70S PRE-FRONTAL SFC
   DEWPOINTS WILL SUPPORT POCKETS OF MLCAPE FROM 1000 TO 2000 J/KG THIS
   AFTERNOON. THE STRONGEST INSTABILITY IS FORECAST TO OCCUR ACROSS THE
   OHIO VALLEY -- I.E. IN THE WAKE OF A BAND OF WEAK H85-H7 WARM
   ADVECTION AND ASSOCIATED CLOUDS/PRECIPITATION CROSSING THE CNTRL
   APPALACHIANS. LOW-LEVEL ASCENT ALONG AND AHEAD OF A COLD FRONT
   CROSSING THE GREAT LAKES WILL BE WEAK...BUT SHOULD BE SUFFICIENT FOR
   ISOLATED TO WIDELY SCATTERED THUNDERSTORMS. THIS ASCENT WILL BE
   LOCALLY AUGMENTED BY DIFFERENTIAL-HEATING-INDUCED BAROCLINICITY
   AHEAD OF THE ZONE OF WARM ADVECTION -- I.E. ACROSS NRN NY TO THE
   CHAMPLAIN VALLEY. HOWEVER...GIVEN THE MAGNITUDE OF THE
   AFOREMENTIONED BUOYANCY AND 30-40 KT OF MID-LEVEL FLOW...SPORADIC
   INSTANCES OF DMGG WINDS AND MARGINALLY SVR HAIL WILL BE POSSIBLE
   WITH CONVECTION PRIMARILY ORGANIZED IN MULTICELL CLUSTERS.

   ..CARBIN/COHEN/KERR.. 06/03/2014

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z