Watch coming up
Posted by JAC on 4/10/2011, 2:57 pm



MESOSCALE DISCUSSION 0396
  NWS STORM PREDICTION CENTER NORMAN OK
  0130 PM CDT SUN APR 10 2011
 
  AREAS AFFECTED...EXTREME SERN MN...NERN IA...NWRN IL AND MUCH OF WI
 
  CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
 
  VALID 101830Z - 102030Z
 
  OUTBREAK OF SEVERE STORMS IS EXPECTED THIS AFTERNOON...INITIALLY
  FROM ERN MN THROUGH NERN IA...THEN SPREADING RAPIDLY EWD THROUGH WI
  AND EXTREME NWRN IL. SUPERCELLS WITH STRONG TORNADOES...VERY LARGE
  HAIL AND DAMAGING WIND WILL BE THE MAIN THREATS. A TORNADO WATCH
  WILL LIKELY BE ISSUED BY 20Z.
 
  THIS AFTERNOON A COLD FRONT EXTENDS FROM A DEEP LOW PRESSURE AREA IN
  E-CNTRL MN SSWWD THROUGH SRN MN...NWRN IA INTO SERN NEB WITH A WARM
  FRONT FROM THE SURFACE LOW IN E-CNTRL MN THROUGH NRN WI. THE LOW
  WILL DEVELOP EWD TO NEAR THE WI BORDER BY 21Z. NEWD ADVECTION OF
  HIGHER THETA-E AIR ALONG A STRONG SSWLY LLJ BENEATH EML PLUME /8.5
  C/KM LAPSE RATES/ AND DIABATIC WARMING IS RESULTING IN NEWD
  DESTABILIZATION WITH TIME. HOWEVER...THE BOUNDARY LAYER REMAINS
  CAPPED BY THE WARM EML AS EVIDENCED BY 18Z MINNEAPOLIS SOUNDING.
 
  UPPER JET IS SHIFTING NEWD INTO THE UPPER MS VALLEY. RAPID ACCAS
  DEVELOPMENT RECENTLY OBSERVED FROM NERN IA THROUGH SWRN WI IS LIKELY
  INDICATIVE OF NEWD EXPANDING ZONE OF AGEOSTROPHIC FORCING WITHIN THE
  UPPER JET EXIT REGION. THIS FORCING IN CONJUNCTION WITH FRONTAL
  CONVERGENCE WILL LIKELY MAINTAIN A DEEPER ZONE OF ASCENT THAT SHOULD
  EVENTUALLY ERODE THE CAP ENOUGH FOR STORMS TO DEVELOP ALONG THE COLD
  FRONT FROM ERN MN INTO NERN IA. STORMS WILL LIKELY MAINTAIN DISCRETE
  MODES FOR SEVERAL HOURS AND WILL BE EMBEDDED WITHIN STRONG DEEP
  LAYER WIND AND VERTICAL SHEAR SUPPORTIVE OF SUPERCELLS. LARGEST
  HODOGRAPHS ARE EXPECTED ACROSS CNTRL THROUGH NRN WI WHERE NEAR
  SURFACE WINDS SHOULD REMAIN BACKED TO SLY EAST OF THE SURFACE LOW
  WITH 0-1 KM STORM RELATIVE HELICITY EXCEEDING 250 M2/S2. STORMS
  DEVELOPING WITHIN THIS ENVIRONMENT WILL LIKELY BECOME CAPABLE OF
  PRODUCING STRONG TORNADOES...VERY LARGE HAIL AND DAMAGING WIND.
 
  ..DIAL.. 04/10/2011
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Significant Severe Outbreak Today Upper MS Valley - JAC, 4/10/2011, 6:34 am
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