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August 21-26 ROF Type Severe


IWXwx

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see text added for NE IL...possible upgrade to slight later....

 

 

 DAY 1 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   1124 AM CDT MON AUG 25 2014

   VALID 251630Z - 261200Z


   ...CNTRL PLAINS INTO UPPER MS VALLEY THIS AFTERNOON INTO TONIGHT...

   A NE-SW-ORIENTED BROKEN BAND OF TSTMS IS ONGOING AS OF MID MORNING
   FROM NRN LOWER MI TO SRN WI WITH THIS ACTIVITY LIKELY BEING FORCED
   BY A COMBINATION OF WAA ALONG A WEAKENING NOCTURNAL LLJ AND THE
   INFLUENCE OF THE MID-LEVEL TROUGH TO THE NORTH. TO THE SOUTH OF
   THESE STORMS...THE 12Z DVN AND ILX SOUNDINGS REVEALED THE PRESENCE
   OF A STRONGLY UNSTABLE ENVIRONMENT WITH MUCAPE UPWARDS OF 3500-4500
   J/KG. HOWEVER...IT REMAINS UNCERTAIN AS TO WHETHER THE CURRENT
   STORMS WILL BE ABLE TO TAP INTO THE HIGH THETA-E RESERVOIR...DUE IN
   PART TO THE TENDENCY OF RISING MID-LEVEL HEIGHTS THROUGH THE PEAK OF
   THE DIURNAL HEATING CYCLE. LATEST CONVECTION-ALLOWING MODEL GUIDANCE
   IS SUGGESTIVE IN THE DEVELOPMENT OF A SWD-MOVING MCS ACROSS NRN INTO
   CNTRL PARTS OF IL/IND. SHOULD THIS SCENARIO UNFOLD AS INDICATED...A
   MORE CONCENTRATED AREA OF DAMAGING WIND POTENTIAL COULD
   EVOLVE...REQUIRING A POSSIBLE UPGRADE TO SLIGHT RISK WITH THE 20Z
   ISSUANCE.

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PRELIMINARY LOCAL STORM REPORT

NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL

1153 AM CDT MON AUG 25 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...

..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....

            ..REMARKS..

1120 AM     HEAVY RAIN       HIGHWOOD                42.21N 87.81W

08/25/2014  M0.42 INCH       LAKE               IL   TRAINED SPOTTER

            RAIN FELL IN 10 MINUTES UP TO REPORT TIME.

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MESOSCALE DISCUSSION 1614
NWS STORM PREDICTION CENTER NORMAN OK
0110 PM CDT MON AUG 25 2014

AREAS AFFECTED...NORTHERN IL/NORTHERN INDIANA AND SOUTHWEST LOWER MI

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 251810Z - 252015Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...ISOLATED INSTANCES OF DAMAGING WINDS/SOME HAIL WILL BE
POSSIBLE THIS AFTERNOON ACROSS NORTHERN IL/NORTHERN INDIANA AND
POSSIBLY PORTIONS OF LOWER MI. WHILE A WATCH IS NOT CURRENTLY
ANTICIPATED...CONVECTIVE TRENDS WILL MONITORED THIS AFTERNOON FOR A
POSSIBLE SLIGHT RISK UPGRADE/SEVERE THUNDERSTORM WATCH.

DISCUSSION...THUNDERSTORMS HAVE SHOWN SOME RECENT SIGNS OF
INTENSIFICATION IN A NORTHEAST-SOUTHWEST ORIENTED CORRIDOR ACROSS
FAR SOUTHERN LOWER MI AND THE CHICAGOLAND VICINITY. THESE STORMS ARE
FOCUSED ALONG SOUTHEASTWARD-SPREADING OUTFLOW...AS IT INTERCEPTS A
VERY MOIST/UNSTABLE BOUNDARY LAYER ACROSS NORTHERN IL/INDIANA INTO
SOUTHWEST LOWER MI. IN THIS CORRIDOR...70S F SURFACE DEWPOINTS AND
AMPLE INSOLATION ARE ALREADY CONTRIBUTING TO AS MUCH AS 3500-4000
J/KG OF MLCAPE. LARGE-SCALE INFLUENCES ARE WEAK ASIDE FROM THE
AFOREMENTIONED BOUNDARY...WHILE VERTICAL SHEAR IS ALSO LIMITED
/20-25 KT 0-6 KM CHICAGO WSR-88D VWP/. HOWEVER...ADDITIONAL
DESTABILIZATION AND STORM DEVELOPMENT/MERGERS MAY LEAD TO GRADUAL
UPSCALE GROWTH/ORGANIZATION...WITH SOME DEGREE OF FORWARD
ACCELERATION/PROPAGATION AS A SOUTHEASTWARD-MOVING CONVECTIVE LINE.
THIS IS A SCENARIO WELL-SUPPORTED BY LATEST HRRR RUNS AND THE 12Z
WRF-NSSL. STEEPENING LOW-LEVEL LAPSE RATES AND AMPLE
MOISTURE/BUOYANCY WILL BE SUPPORTIVE OF MICROBURST POTENTIAL WITH AT
LEAST LOCALLY DAMAGING WINDS POSSIBLE THROUGH EARLY EVENING.

 

mcd1614.gif

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