SWODY1
SPC AC 251937
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0237 PM CDT FRI APR 25 2008
VALID 252000Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTN/EVE FROM PARTS OF THE
UPPER GREAT LAKES REGION SOUTHWARD THRU THE SRN PLAINS....
...MID MS/LWR OH VALLEY INTO THE GREAT LAKES REGION...
VIGOROUS SHORT WAVE IMPULSE IS JUST NOW IN THE PROCESS OF TAKING ON
A MORE NEUTRAL TO NEGATIVE TILT AS IT BEGINS TO LIFT NORTHEAST OF
THE CENTRAL PLAINS. AND...WITH THE MID LEVEL COLD CORE LAGGING TO
THE WEST OF THE MOIST WARM SECTOR OF SURFACE CYCLONE NOW MIGRATING
NORTHEASTWARD INTO WESTERN WISCONSIN...MID-LEVEL LAPSE RATES ARE NOT
AS STEEP AS THEY COULD BE. COUPLED WITH CONSIDERABLE LINGERING
LOW-LEVEL CLOUD COVER BENEATH A SUBSIDENT/ CAPPING MID-LEVEL DRY
SLOT...PRE-FRONTAL MIXED LAYER CAPE IS STILL WEAK AND GENERALLY ONLY
MAXIMIZED IN A NARROW BAND ALONG THE FRONTAL ZONE EXTENDING
NORTHEAST OF THE OZARK PLATEAU INTO THE SURFACE LOW CENTER.
THIS HAS SLOWED THE INTENSIFICATION OF ONGOING DEVELOPING FRONTAL
CONVECTIVE BAND...BUT RUC GUIDANCE IS SUGGESTIVE THAT MIXED LAYER
CAPE WILL PROBABLY APPROACH/EXCEED 1000 J/KG IN THE PEAK AFTERNOON
HEATING. IN THE PRESENCE OF STRONG DEEP LAYER SHEAR NEAR A 70+ KT
500 MB JET CORE...WHICH IS PROGGED TO STRENGTH EAST OF THE UPPER
TROUGH LATER TODAY/TONIGHT...EVOLUTION OF SEVERE SQUALL LINE WITH
POSSIBLE EMBEDDED SUPERCELLS...IS EXPECTED TO PROCEED ACROSS EASTERN
MISSOURI/EXTREME EASTERN IOWA INTO ILLINOIS AND SOUTHERN/ EASTERN
WISCONSIN INTO EARLY EVENING.
IN THE WAKE OF AN INITIAL MID-LEVEL IMPULSE ALREADY LIFTING THROUGH
MICHIGAN...AND PROGGED INTO ONTARIO BY EARLY EVENING...VEERING
SURFACE FLOW IS REDUCING THE SIZE OF LOW-LEVEL HODOGRAPHS BENEATH
35-40 KT SOUTHERLY 850 MB FLOW. AND...A STRENGTHENING MID-LEVEL CAP
MAY CONTINUE TO INHIBIT ISOLATED CONVECTIVE DEVELOPMENT IN ADVANCE
OF FRONTAL SQUALL. THIS IS CONTRIBUTING TO UNCERTAINTY CONCERNING
THE EXTENT OF TORNADO POTENTIAL IN PROXIMITY TO THE SURFACE CYCLONE.
BUT...LOW-LEVEL HODOGRAPHS WILL STILL BE LARGE ENOUGH TO SUPPORT A
RISK FOR TORNADOES IN SUPERCELLS WITHIN THE SQUALL LINE AND PERHAPS
JUST AHEAD IT...PARTICULARLY ACROSS PARTS OF CENTRAL/EASTERN
WISCONSIN. ISOLATED TORNADOES ARE ALSO POSSIBLE WITH STORM
DEVELOPMENT NOW OCCURRING IN ADVANCE OF INITIAL IMPULSE ACROSS LOWER
MICHIGAN LATE THIS AFTERNOON. OTHERWISE...THE RISK FOR LARGE HAIL
WILL EXIST WITH MOST STORMS...AND FAST SQUALL LINE MOTION WITHIN A
40+ KT SOUTHWESTERLY MEAN ENVIRONMENTAL FLOW WILL CONTRIBUTE TO
POTENTIAL FOR DAMAGING WIND GUSTS.
THE SEVERE THREAT IS EXPECTED TO WANE LATE THIS EVENING WITH LOSS OF
DAYTIME HEATING...BUT SPORADIC WIND DAMAGE/HAIL MAY CONTINUE IN
CONVECTION SPREADING ACROSS THE GREAT LAKES REGION AND OHIO VALLEY
OVERNIGHT.
...TEXAS...
DEEP LAYER SHEAR IS WEAK...BUT DIVERGENT UPPER FLOW FIELD BETWEEN
THE POLAR TROUGH TO THE NORTH...AND THE SUBTROPICAL STREAM TO THE
SOUTH...PROBABLY WILL ENHANCE CONVECTIVE DEVELOPMENT NOW UNDERWAY
ALONG THE FRONT ACROSS PARTS OF CENTRAL INTO NORTHEAST TEXAS. WITH
MIXED LAYER CAPE ON THE ORDER OF 2000-3000 J/KG AHEAD OF THE
FRONT...PARTICULARLY IN THE VICINITY OF THE FRONT/DRY LINE
INTERSECTION SOUTHWEST OF THE AUSTIN/TEMPLE AREA...SEVERE STORMS ARE
POSSIBLE AS INHIBITION WEAKENS LATE THIS AFTERNOON. LARGE HAIL IS
LIKELY IN MOST ACTIVITY. AND...THERMODYNAMIC PROFILES WITH A FAIRLY
DEEP MIXED BOUNDARY LAYER AND LOW MID-LEVEL HUMIDITY LEVELS...COULD
PROVE SUPPORTIVE OF ISOLATED STRONG DOWNBURSTS AND SURFACE COLD POOL
DEVELOPMENT.
..KERR.. 04/25/2008
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