SWODY1
SPC AC 210552
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT MON APR 21 2008
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF NRN OK/SERN-ERN
KS/WRN-NRN MO TO FAR SRN IA...
...SYNOPSIS...
MODELS REMAIN CONSISTENT SHOWING LARGE UPPER LOW/TROUGH IN THE NWRN
U.S./SWRN CANADA WILL EVOLVE INTO AN ELONGATED POSITIVE TILTED
TROUGH WITH TWO SEPARATE CLOSED LOW CENTERS...1) ONE DEVELOPING NEWD
INTO CENTRAL CANADA...AND 2) SECOND LOW SHIFTING SLOWLY SWWD OFF THE
PAC NW COAST. A LEAD WEAK IMPULSE IS EXPECTED TO TRACK ENEWD INTO
THE WRN GREAT LAKES REGION TODAY...WHILE A STRONGER AND FAST MOVING
SHORT WAVE TROUGH MOVES FROM THE GREAT BASIN TO THE CENTRAL HIGH
PLAINS BY 22/00Z...AND THEN NEWD INTO THE UPPER MS VALLEY TONIGHT.
IN THE LOW LEVELS...COLD FRONT ATTENDANT TO LEAD IMPULSE AND CENTRAL
CANADA CLOSED LOW WILL SPREAD EWD ACROSS UPPER MS VALLEY THIS
FORECAST PERIOD...WITH SRN EXTENT SPREADING SSEWD INTO NWRN MO TO
NWRN OK BY LATE THIS AFTERNOON.
...SRN PLAINS TO LOWER MO VALLEY REGION...
00Z GFS/NAM HAVE COME INTO BETTER AGREEMENT WITH THE MOVEMENT OF THE
COLD FRONT SSEWD THROUGH THE SRN PLAINS THIS AFTERNOON. THIS
BOUNDARY IS EXPECTED TO EXTEND FROM THE TX PANHANDLE NEWD THROUGH
NWRN OK TO ERN KS/NWRN MO TO CENTRAL IA BY LATE AFTERNOON.
MEANWHILE...A DRY LINE WILL MIX EWD INTO WRN OK AND CENTRAL TX THIS
AFTERNOON BEFORE RETREATING WWD SOME TONIGHT. SWLY LOW LEVEL FLOW
LOCATED OVER THE WARM SECTOR THIS MORNING IS FORECAST TO BACK TO SLY
DURING THE AFTERNOON IN RESPONSE TO APPROACH OF GREAT BASIN SHORT
WAVE TROUGH. THIS WILL RESULT IN NWD MOISTURE RETURN WITH SURFACE
DEWPOINTS IN THE MID 60S SPREADING ACROSS MUCH OF OK AND WRN AR EAST
OF THE DRY LINE...WHILE UPPER 50S DEWPOINTS REACH INTO CENTRAL PARTS
OF IA ALONG COLD FRONT.
SWLY FLOW LOCATED ABOVE THE BOUNDARY LAYER WILL MAINTAIN A STRONG
EML ATOP THE MOISTURE RETURN...WITH STEEP MID LEVEL LAPSE RATES
CONTRIBUTING TO MODERATE INSTABILITY WITHIN THE WARM SECTOR FROM THE
SRN PLAINS NEWD INTO SRN/ERN KS TO WRN MO. THIS EML IS EXPECTED TO
CAP THE WARM SECTOR FOR MUCH OF THE AFTERNOON AND LIKELY PRECLUDE
SURFACE BASED TSTM DEVELOPMENT UNTIL THE ARRIVAL OF FORCING FOR
ASCENT WITH SHORT WAVE TROUGH MOVING NEWD THROUGH THE CENTRAL PLAINS
THIS EVENING. HOWEVER...GIVEN DEGREE OF INSTABILITY /MUCAPES
APPROACHING 2500 J/KG/...DEEP LAYER SHEAR AROUND 40 KT AND
CONVERGENCE AT THE TRIPLE POINT...THE POTENTIAL FOR AT LEAST
ISOLATED TSTM DEVELOPMENT MAY OCCUR LATE THIS AFTERNOON /AFTER 21Z/.
IF STORMS DEVELOP DURING THAT TIME FRAME...ISOLATED SUPERCELLS WOULD
BE LIKELY WITH ATTENDANT THREATS FOR A FEW TORNADOES AND LARGE
HAIL...SOME VERY LARGE...GIVEN THE FAVORABLE THERMODYNAMICS AND
KINEMATICS.
OTHERWISE...AS THE SHORT WAVE TROUGH TRACKS NEWD THROUGH THE CENTRAL
PLAINS TO UPPER MS VALLEY THIS EVENING/OVERNIGHT...TSTMS SHOULD
DEVELOP NEWD ALONG THE COLD FRONT INTO ERN KS/WRN MO AND IA.
ALTHOUGH STRONGEST DEEP LAYER SHEAR SHOULD REMAIN OVER THE POST
FRONTAL ENVIRONMENT TONIGHT...MORE SUBSTANTIAL MOISTURE RETURN INTO
SERN KS/WRN MO COMBINED WITH MODEST DEEP LAYER SHEAR SHOULD SUPPORT
THE POTENTIAL FOR STRONG TO SEVERE TSTMS.
...ERN OK/AR/SRN MO MAINLY TONIGHT...
LOW LEVEL WINDS ARE EXPECTED TO VEER TO SWLY TONIGHT AS GREAT BASIN
SHORT WAVE TROUGH TRACKS N OF THIS REGION TOWARD THE UPPER MS
VALLEY. TSTMS SHOULD DEVELOP WITHIN WAA REGIME...WITH ELEVATED
INSTABILITY UP TO 1000 J/KG AND EFFECTIVE BULK SHEAR AROUND 30 KT
SUPPORTING A FEW STRONGER STORMS PRODUCING HAIL.
...UPPER MS VALLEY...
MODELS SUGGEST FORCING FOR ASCENT ATTENDANT TO A LEAD MID LEVEL
IMPULSE SPREADING ENEWD ACROSS THIS REGION TODAY COMBINED WITH
FRONTAL CIRCULATION ALONG COLD FRONT SHOULD SUPPORT TSTMS SPREADING
EWD THROUGH ERN DAKOTAS/MN TO WRN WI/WRN U.P. OF MI. EFFECTIVE BULK
SHEAR OF 25-30 KT MAY SUPPORT A FEW ORGANIZED STORMS...BUT WEAK
INSTABILITY IS EXPECTED TO LIMIT THE SEVERE WEATHER THREAT. STORMS
SHOULD BECOME UNDERCUT AS THE COLD FRONT SPREADS EWD...WITH ISOLATED
HAIL BEING THE PRIMARY THREAT.
...ERN NC...
CLOSED UPPER LOW LOCATED OVER CENTRAL NC AT 12Z TODAY IS EXPECTED TO
WEAKEN AS IT TRACKS SEWD TO OFF THE NC/SC COAST BY MID-LATE THIS
EVENING. RESIDUAL SURFACE MOISTURE /DEWPOINTS IN THE MID 50S/
COMBINED WITH SURFACE HEATING BENEATH COLD MID LEVEL TEMPERATURES
/-22 C AT 500 MB/ ARE EXPECTED TO RESULT IN MARGINAL INSTABILITY
/MUCAPE 500-1000 J/KG/ INTO THE AFTERNOON. ALTHOUGH DEEP LAYER
SHEAR WILL BE WEAK ALONG TRACK OF UPPER LOW...STEEP LAPSE RATES/COLD
MID LEVEL TEMPERATURES MAY PROVE SUFFICIENT FOR ISOLATED HAIL/WIND
THREATS WITH STRONGEST STORMS.
..PETERS/GRAMS.. 04/21/2008
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