[LeArc] SPC Outlook for Sunday (W. IL is at Risk)

[Duane Whittingham]

This is the SPC Outlook for Sunday, we are in a Mod risk.  Duane


    DAY 2 CONVECTIVE OUTLOOK
    NWS STORM PREDICTION CENTER NORMAN OK
    1111 AM CST SAT APR 01 2006

    VALID 021200Z - 031200Z

    ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF IA...MO AND MUCH
    OF IL...

    ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES SWD INTO
    THE MID SOUTH AND ARKLATEX...

    --POTENTIALLY SIGNIFICANT SEVERE WEATHER EPISODE IS BEING FORECAST
    ACROSS THE MIDWEST AND MID MS VALLEY SUNDAY AND SUNDAY NIGHT--

    ...SYNOPSIS...

    MID AND UPPER-LEVEL TROUGH NOW OVER THE PACIFIC NW AND GREAT BASIN
    WILL TRANSLATE EWD INTO THE GREAT PLAINS LATE SATURDAY NIGHT INTO
    SUNDAY MORNING...PRIOR TO INTENSIFYING INTO A CLOSED CIRCULATION
    OVER THE UPPER MIDWEST SUNDAY NIGHT.  AS THIS OCCURS...ACCOMPANYING
    MID AND HIGH-LEVEL JET STREAKS WILL PROPAGATE THROUGH THE TROUGH
    BASE INTO MO AND IL/IND SUNDAY AFTERNOON AND EVENING.

    IN THE LOW-LEVELS...PRIMARY SURFACE LOW INITIALLY OVER ERN NEB WILL
    DEVELOP ENEWD INTO LOWER MI BY MONDAY MORNING. ASSOCIATED WARM
    FRONT WILL CONCURRENTLY LIFT NEWD THROUGH THE OH VALLEY AND GREAT
    LAKES WHILE TRAILING COLD FRONT SURGES EWD THROUGH THE MID/LOWER MO
    AND MS VALLEYS AND INTO THE OH AND TN VALLEYS THROUGH THE FORECAST
    PERIOD.

    ...MID/LOWER MO VALLEY INTO THE GREAT LAKES...MID MS AND OH
    VALLEYS...

    A NW-SE ORIENTED BAND OF MAINLY ELEVATED TSTMS IS EXPECTED TO BE
    ONGOING 02/12Z FROM VICINITY OF THE SURFACE LOW OVER ERN NEB/WRN IA
    INTO WRN KY AND MIDDLE TN...LARGELY DRIVEN BY WAA ALONG BROAD SWLY
    LLJ.  THIS ACTIVITY WILL LIKELY CONTINUE THROUGH THE PERIOD AHEAD OF
    RETREATING WARM FRONT INTO THE GREAT LAKES WITH THE STRONGEST STORMS
    CAPABLE OF MAINLY LARGE HAIL.

    IN THE WAKE OF THIS INITIAL ACTIVITY...THE PRESENCE OF STEEP
    MID-LEVEL LAPSE RATES / 7-8 C/KM / COUPLED WITH BOUNDARY-LAYER
    DEWPOINTS IN THE LOW TO MID 60S WILL CONTRIBUTE TO A MODERATELY
    UNSTABLE AIR MASS ACROSS SYSTEM WARM SECTOR WITH MLCAPES INCREASING
    TO 1500-2500 J/KG FROM SERN SE/CNTRL MO SWWD INTO THE ARKLATEX AND
    LOWER MS VALLEY.

    INCREASED FORCING FOR ASCENT AHEAD OF MID-LEVEL TROUGH AND EXIT
    REGIONS OF ACCOMPANYING JET STREAKS WILL CONTRIBUTE TO RAPID
    SURFACE-BASED TSTM DEVELOPMENT BY EARLY TO MID AFTERNOON FROM NEAR
    SURFACE LOW OVER WRN OR CNTRL IA SWD ALONG COLD FRONT INTO MO.
    ADDITIONAL SURFACE-BASED STORMS WILL ALSO BE POSSIBLE AT THIS TIME
    ALONG WARM FRONT.

    FORECAST SOUNDINGS INDICATE A POTENT COMBINATION OF INSTABILITY AND
    VERTICAL SHEAR ACROSS MODERATE RISK AREA...WHICH SHOULD SUPPORT
    INTENSE SUPERCELL DEVELOPMENT WITH THE POTENTIAL FOR A FEW STRONG
    TORNADOES IN ADDITION TO VERY LARGE...DESTRUCTIVE HAIL AND DAMAGING
    WINDS. WITH TIME...STORMS MAY EVOLVE INTO BOWING LINE SEGMENTS OR A
    MESOSCALE LEWP STRUCTURE WITH CORRIDORS OF DAMAGING WINDS POSSIBLE
    EWD ACROSS THE OH VALLEY SUNDAY NIGHT.

    ...MID SOUTH INTO ARKLATEX...

    AS MENTIONED ABOVE...PRE-FRONTAL AIR MASS IS FORECAST TO BECOME
    MODERATELY UNSTABLE BY AFTERNOON OWING TO STEEPENING LAPSE RATES AND
    A MOIST BOUNDARY-LAYER.  GIVEN A STRONGER CAP AND THAT LARGE-SCALE
    FORCING FOR ASCENT AND LOW-LEVEL FRONTAL CONVERGENCE WILL TEND TO
    WEAKEN WITH SWD EXTENT...SOME UNCERTAINTY EXISTS WITH REGARD TO
    EVENTUAL CONVECTIVE COVERAGE AND INTENSITY ACROSS REGION.  LATEST
    SHORT TERM MODEL GUIDANCE SUGGESTS THAT TSTMS SHOULD BEGIN TO BUILD
    SWWD ALONG FRONT BY MID TO LATE AFTERNOON FROM NEAR THE CONFLUENCE
    OF THE OH AND MS RIVERS INTO PORTIONS OF ERN AR...WRN TN AND PERHAPS
    SWD INTO NRN LA AND NRN MS.

    THE COMBINATION OF MODERATE INSTABILITY AND 45-55 KT WLY MID-LEVEL
    FLOW SUGGEST THE THREAT FOR A FEW SUPERCELLS AND BOWING LINE
    SEGMENTS CAPABLE OF DAMAGING WINDS...LARGE HAIL AND A FEW TORNADOES.
     THIS SEVERE THREAT WILL LIKELY CONTINUE SUNDAY NIGHT ACROSS THE TN
    VALLEY AND NRN PORTIONS OF MS AND AL.

    ..MEAD.. 04/01/2006


-------------------------------------------------------
Amateur Radio Operator
Duane Whittingham - N9SSN
Skywarn, ARES/RACES, EMA/ESDA
Red Cross and SATERN