Jul 18, 2007 1300 UTC Day 1 Convective Outlook
Updated: Wed Jul 18 12:42:11 UTC 2007
Probabilistic to Categorical Outlook Conversion Table (Effective Feb 14, 2006).
Public Severe Weather Outlook

The SPC is forecasting ...severe thunderstorms expected over parts of the midwest this afternoon and tonight....   Please read the latest public statement about this event.

Categorical Graphic
20070718 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20070718 1300 UTC Day 1 Tornado Probabilities Graphic
Probabilistic Damaging Wind Graphic
20070718 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probabilistic Large Hail Graphic
20070718 1300 UTC Day 1 Large Hail Probabilities Graphic
   SPC AC 181237
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0737 AM CDT WED JUL 18 2007
   
   VALID 181300Z - 191200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT
   ACROSS PARTS OF EASTERN SD...NORTHEAST NEB...MUCH OF IA...AND
   NORTHERN IL...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE
   NORTHERN/CENTRAL PLAINS AND INTO THE UPPER MS AND OH VALLEYS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE MID
   ATLANTIC REGION...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF WA/ID/MT...
   
   MORNING WATER VAPOR IMAGERY SHOWS MID LEVEL SHORTWAVE TROUGH TOPPING
   THE RIDGE OVER THE ROCKIES ACROSS WY.  THIS FEATURE WILL TRACK
   EASTWARD TODAY AND BECOME EMBEDDED IN FASTER WEST-NORTHWESTERLY
   FLOW.  IMPULSE IS FORECAST TO TRACK DOWN SURFACE BOUNDARY THAT
   CURRENTLY EXTENDS FROM WESTERN SD INTO IL...AND RESULT IN A
   POTENTIALLY ACTIVE SEVERE WEATHER EVENT THIS AFTERNOON AND EVENING.
   
   ...ERN SD INTO IL/IND...
   12Z SURFACE ANALYSIS SHOWS WEAK LOW OVER SOUTH CENTRAL SD...WITH
   BOUNDARY EXTENDING EASTWARD ACROSS NORTHERN IA AND INTO IL.  THIS
   BOUNDARY IS EXPECTED TO REMAIN NEARLY STATIONARY TODAY AS UPPER
   TROUGH APPROACHES FROM THE WEST.  STRONG DAYTIME HEATING...STEEP LOW
   AND MID LEVEL LAPSE RATES...AND SURFACE DEWPOINTS IN THE 60S TO NEAR
   70F WILL RESULT IN A LARGE AREA OF EXTREME INSTABILITY THIS
   AFTERNOON FROM SERN SD/NERN NEB ACROSS MUCH OF IA INTO NRN IL.  WEAK
   CAPPING SHOULD LIMIT CONVECTIVE DEVELOPMENT ALONG THIS AXIS UNTIL AT
   LEAST MID AFTERNOON...WHEN INCREASING LARGE SCALE FORCING FOR ASCENT
   WILL SPREAD INTO EASTERN SD/NEB.  ISOLATED SUPERCELL THUNDERSTORMS
   MAY DEVELOP IN THIS AREA WITH A RISK OF VERY LARGE HAIL AND DAMAGING
   WINDS.  STORMS ARE LIKELY TO INCREASE IN COVERAGE THROUGH THE
   EVENING AND ORGANIZE INTO A FAST-MOVING MCS ACROSS IA AND INTO IL. 
   POTENTIAL EXISTS FOR A DERECHO EVENT ALONG THIS AXIS WITH WIDESPREAD
   DAMAGING WINDS.  EASTWARD EXTENT OF SEVERE THREAT DEPENDS ON
   ORGANIZATION OF MCS...BUT MAY BE AS FAR EAST AS PARTS OF OH BEFORE
   19/12Z.
   
   ...WY/WRN SD/WRN NEB...
   NORTHWEST FLOW ALOFT AND EASTERLY COMPONENT OF LOW LEVEL WINDS WILL
   RESULT IN A FAVORABLE VERTICAL SHEAR PROFILE FOR SUPERCELL
   THUNDERSTORMS THIS AFTERNOON FROM THE BIGHORN MTNS AND BLACK HILLS
   INTO PARTS OF CENTRAL SD AND THE NEB PANHANDLE.  UPPER TROUGH NOW
   MOVING ACROSS WY MAY HELP TO INITIATE SEVERE STORMS IN THIS AREA
   RELATIVELY EARLY /18-21Z/ WITH A RISK OF LARGE HAIL AND DAMAGING
   WINDS IN STRONGER CELLS.
   
   ...WA/ID/MT...
   SEVERAL SHORTWAVE TROUGHS ARE EVIDENT IN WATER VAPOR IMAGERY
   ROTATING NORTHWARD ACROSS CA AND INTO ORE/WA.  A DRY LOW LEVEL AIR
   MASS WILL LIMIT CONVECTIVE POTENTIAL OVER MUCH OF NV AND SOUTHERN ID
   TODAY.  HOWEVER...CONSIDERABLE MOISTURE REMAINS IN THE MOUNTAINS OF
   NORTHERN ID AND EASTERN WA.  THIS AREA WILL LIKELY SEE SCATTERED
   AFTERNOON THUNDERSTORM DEVELOPMENT.  FORECAST SOUNDINGS SHOW
   FAVORABLE VERTICAL SHEAR PROFILES TO SUPPORT A RISK OF A FEW SEVERE
   THUNDERSTORMS CAPABLE OF LARGE HAIL AND DAMAGING WINDS.
   
   ...MID ATLANTIC REGION...
   A WEAK SHORTWAVE TROUGH IS CURRENTLY MOVING ACROSS PARTS OF NY/PA
   AND NORTHERN WV.  THIS FEATURE WILL AFFECT THE MID ATLANTIC REGION
   AND SOUTHERN NEW ENGLAND LATER TODAY.  MORNING VISIBLE SATELLITE
   IMAGERY SUGGESTS POCKETS OF DAYTIME HEATING WILL OCCUR FROM NJ
   SOUTHWARD...WITH DEWPOINTS NEAR 70F AND MLCAPE VALUES EXPECTED TO BE
   AROUND 1000 J/KG.  SCATTERED THUNDERSTORMS ARE POSSIBLE BY MID
   AFTERNOON...SPREADING OFFSHORE AFTER DARK.  SUFFICIENT WESTERLY FLOW
   ALOFT AND LARGE SCALE FORCING SUGGEST A RISK OF ISOLATED SEVERE
   STORMS.  DAMAGING WINDS ARE EXPECTED TO BE THE MAIN THREAT.
   
   ..HART/JEWELL.. 07/18/2007
   
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