SWODY1
SPC AC 250554
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT WED APR 25 2007
VALID 251200Z - 261200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM ERN PARTS OF THE SRN
PLAINS THROUGH LOWER AND MID MS VALLEY TO TN/LOWER OH VALLEYS...
..SYNOPSIS...
MODEL CONSENSUS CONTINUES TO SHOW LARGE CLOSED MID/UPPER LEVEL LOW
SHIFTING ENEWD FROM THE CENTRAL/SRN PLAINS AT 12Z TODAY TO THE LOWER
MO AND LOWER MS VALLEYS BY 12Z THURSDAY. SHORT WAVE TROUGH...
CURRENTLY TRANSLATING THROUGH THE BASE OF THE CLOSED LOW OVER WRN
TX...IS EXPECTED TO TRACK ACROSS ERN TX TO THE LOWER MS/TN VALLEYS
BY LATE THIS AFTERNOON. A SECOND SHORT WAVE TROUGH IS PROGGED TO
MOVE THROUGH NRN TX TO AR DURING SECOND HALF OF PERIOD AIDING IN
CLOSED UPPER LOW/TROUGH TO BECOME MORE NEGATIVELY TILTED INTO LOWER
MS/TN VALLEYS LATER TONIGHT.
IN THE LOW LEVELS...SURFACE LOW IS EXPECTED TO TRACK FROM NRN OK
INTO CENTRAL MO THIS FORECAST PERIOD WITH ATTENDANT WARM FRONT
LIFTING SLOWLY NWD ACROSS NRN HALF OF OH VALLEY AND MID ATLANTIC
REGION. MEANWHILE...PROGRESSIVE COLD FRONT TRAILING SWD FROM
SURFACE LOW IS EXPECTED TO EXTEND FROM ERN OK THROUGH ERN TX BY LATE
THIS AFTERNOON...AND THEN REACH THE LOWER TN VALLEY INTO MS AND SERN
LA BY 12Z THURSDAY.
..ERN TX THROUGH LOWER MS AND TN VALLEYS...
AT 12Z TODAY...ONE TO TWO POTENTIALLY STRONG TO SEVERE MCS/S ARE
EXPECTED TO BE ONGOING FROM SOUTH CENTRAL THROUGH ERN TX. AS CLOSED
LOW PROGRESSES EWD...THIS ACTIVITY IS ALSO EXPECTED TO MOVE EWD INTO
THE LOWER MS VALLEY AND LIKELY INCREASE IN INTENSITY AS DOWNSTREAM
AIR MASS DESTABILIZES. SURFACE HEATING SHOULD BE STRONGEST EWD FROM
SRN LA AND MS ALONG ERN PERIPHERY OF CLOUD SHIELD ASSOCIATED WITH
UPSTREAM MCS/S. THIS COMBINED WITH MOISTURE RETURN /SURFACE
DEWPOINTS INTO THE MID 60S REACHING NRN LA/CENTRAL MS TO SWRN AL/ BY
MID-LATE AFTERNOON WILL CONTRIBUTE TO MLCAPE VALUES AROUND 1000
J/KG. 60-70 KT SWLY MID LEVEL JET AND A SWLY LLJ BOTH TRANSLATING
EWD INTO THE LOWER MS VALLEY WILL RESULT IN STRONG DEEP LAYER SHEAR
FOR ORGANIZED TSTMS WITH STRONG WIND GUSTS AND A FEW TORNADOES BEING
THE PRIMARY THREATS INTO THE AFTERNOON.
A SECOND ROUND OF TSTMS IS EXPECTED TO SPREAD EWD FROM SERN OK/ERN
TX THROUGH THE LOWER MS/TN VALLEYS THIS EVENING INTO THURSDAY
MORNING AS COLD FRONT MOVES EWD INTO THIS REGION. ASCENT AHEAD OF
SECOND SHORT WAVE TROUGH WILL AID IN MAINTAINING CONVECTIVE THREAT
DURING THIS PART OF THE FORECAST PERIOD. ALTHOUGH INSTABILITY WILL
TEND TO DECREASE WITH LOSS OF DAYTIME HEATING...STRONG DEEP LAYER
SHEAR AND STRENGTHENING SWLY LLJ TO 40-50 KT WOULD SUGGEST A THREAT
FOR DAMAGING WINDS AS THE COLD FRONT PROGRESSES EWD TOWARD THE
CENTRAL GULF COAST STATES TONIGHT.
..ERN KS/ERN OK THROUGH MO/AR TO LOWER OH VALLEY...
DRY SLOT WITH UPPER LOW IS EXPECTED TO TRANSLATE NEWD FROM NERN TX
THROUGH ERN OK/ SERN KS INTO PARTS OF MO/WRN AR THIS MORNING INTO
THE AFTERNOON ALLOWING FOR SURFACE HEATING AND STEEPENING LAPSE
RATES. MODERATE INSTABILITY SHOULD DEVELOP BY LATE MORNING/EARLY
AFTERNOON...GIVEN WEAKLY CAPPED AIR MASS...THOUGH INSTABILITY SHOULD
BE WEAKER EWD INTO LOWER OH VALLEY. TSTMS SHOULD DEVELOP THIS
MORNING IN THE VICINITY OF SURFACE LOW AND ALONG WARM FRONT...WITH
EVENTUAL DEVELOPMENT SWD ALONG COLD FRONT BY THIS AFTERNOON.
SUFFICIENT DEEP LAYER SHEAR AND INSTABILITY WILL FAVOR ORGANIZED
STORMS WITH HAIL AND STRONG WINDS BEING PRIMARY THREATS.
ISOLATED TORNADO THREAT IS EXPECTED TO DEVELOP BENEATH COLD POOL
WITH CLOSED MID/UPPER LEVEL LOW WHERE AMBIENT VORTICITY WITH NEARLY
STACKED LOWS WILL FAVOR STORM ROTATION. POINT FORECAST SOUNDINGS
ALSO INDICATE STEEP LOW AND MID LEVEL LAPSE RATES WITH STRONG
SURFACE VORTICITY IN THE VICINITY OF SURFACE LOW AND ATTENDANT
SURFACE BOUNDARIES AIDING IN TORNADO POTENTIAL.
..SRN OH/WV EWD TO MID ATLANTIC STATES...
FARTHER E...WEAK MID LEVEL IMPULSE AND ACCOMPANYING 50-60 WLY MID
LEVEL JET SHOULD AID IN TSTM DEVELOPMENT ALONG SURFACE BOUNDARY
EXTENDING W-E FROM WV THROUGH VA TO DELMARVA. ALTHOUGH DEEP LAYER
SHEAR WILL BE SUFFICIENT FOR ORGANIZED STORMS...WEAK INSTABILITY IS
EXPECTED TO LIMIT COVERAGE OF SEVERE STORMS. THUS...LOW SEVERE
PROBABILITIES FOR HAIL AND WIND GUSTS ARE FORECAST EWD FROM SRN
OH/WV TO DELMARVA.
.PETERS/GUYER.. 04/25/2007
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