SWODY1
SPC AC 211624
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1124 AM CDT MON APR 21 2008
VALID 211630Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF OK...KS AND MO...
...SYNOPTIC DISCUSSION...
LARGE SCALE ADJUSTMENTS UNDERWAY WITH COLD WRN TROUGH AS ONE STRONG
CIRCULATION CENTER SHIFTS NWD THRU SRN PRAIRIE PROVINCES WHILE
ANOTHER LOW CENTER DROPS SWD OFFSHORE PAC NW. COLD FRONT HAS PUSHED
EWD ACROSS HIGH PLAINS AND SWWD INTO NWRN OK/TX PANHANDLE.
WHILE A SHALLOW BUT VERY MOIST AIR MASS HAS SPREAD NWD THRU TX/OK
AHEAD OF THE COLD FRONT...UPPER SUPPORT FOR STORM DEVELOPMENT WILL
BE LIMITED AS FLAT RIDGING DEVELOPS EWD FROM CENTRAL ROCKIES IN
RESPONSE TO THE LARGE SCALE WRN TROUGH READJUSTMENT.
UPPER LOW NOW OVER NC WILL MOVE SEWD OFFSHORE BY THIS EVENING WITH
CONVECTIVE POTENTIAL GRADUALLY ENDING OVER LAND LATER TODAY.
...OK/KS/MO...
BY MID AFTERNOON THE COLD FRONT WILL EXTEND FROM ERN KS SSWWD THRU
WRN OK TO THE W OF OKC. TRIPLE POINT OF COLD FRONT AND A DRY LINE
WILL BE ACROSS WCENTRAL OK AS N-S DRY LINE MIXES EWD ACROSS SWRN
OK/NWRN TX. STRONG HEATING WITH TEMPS RISING INTO THE 80S SHOULD BE
SUFFICIENT TO WEAKEN INHIBITION SUFFICIENTLY TO SUPPORT THUNDERSTORM
DEVELOPMENT FROM THE TRIPLE POINT NEWD ALONG THE FRONT INTO ERN KS
BY LATER THIS AFTERNOON. AIR MASS EXPECTED TO BECOME VERY UNSTABLE
WITH MLCAPES AOA 3000 J/KG ACROSS CENTRAL OK DURING AFTERNOON. THE
LACK OF UPPER LEVEL SUPPORT AND FORECASTED WEAKENING OF LOW LEVEL
FLOW LEADS TO THE CONDITIONAL SEVERE THREAT OF THE OUTLOOK. ANY
STORM THAT IS ABLE TO FORM WILL QUICKLY BECOME SEVERE. GREATEST
SEVERE POTENTIAL WOULD BE A STORM THAT DEVELOPS NEAR THE TRIPLE
POINT WHERE INSTABILITY IS MAXIMIZED. FURTHER N ALONG THE FRONT
INSTABILITY WILL BE LESS BUT STRONGER FRONTAL CONVERGENCE WOULD BE
MORE LIKELY TO INITIATE STORMS BY THIS EVENING.
30-40 KT OF DEEP LAYER SHEAR GIVEN THE INSTABILITY SUPPORT SUPERCELL
POTENTIAL. PRIMARY THREAT WILL BE VERY LARGE HAIL GIVEN THE VERY
UNSTABLE AIR AND RATHER WEAK LOW LEVEL SHEAR. SEVERE POTENTIAL WILL
CONTINUE EWD AFTER DARK INTO ERN OK NEWD INTO WRN MO AS LOW LEVEL
JET INCREASES TO 30PLUS KTS ENHANCING SHEAR AND NWD MOISTURE
TRANSPORT.
...UPPER MS VALLEY...
WHILE FORCING BOTH FRONTAL AND WITH MID LEVEL JET ROTATING NEWD
ACROSS THE NRN PLAINS WILL SUPPORT THUNDERSTORMS FROM MN INTO
IA...SEVERE POTENTIAL WILL BE MARGINAL GIVEN THE LIMITED
INSTABILITY. MLCAPES GENERALLY LESS THAN 1000 J/KG COUPLED WITH
FAVORABLY LOW WET BULB ZERO LEVELS WILL SUPPORT POTENTIAL FOR HAIL
AND GUSTY SURFACE WINDS. STORMS SHOULD BE FOCUSED VICINITY THE COLD
FRONT.
...ERN NC...
THE MAIN SURFACE LOW IS NOW OFFSHORE...BUT GENERALLY LIGHT EAST/
NORTHEASTERLY LOW-LEVEL FLOW IS MAINTAINING MODEST BOUNDARY LAYER
MOISTURE BENEATH A LINGERING MID-LEVEL COLD POCKET OVER EAST CENTRAL
NORTH CAROLINA. THIS FEATURE IS EXPECTED TO MOVE LITTLE UNTIL
ACCELERATING SOUTHEASTWARD LATER THIS AFTERNOON...AS A WEAK IMPULSE
PIVOTS AROUND ITS SOUTHERN/EASTERN PERIPHERY.
DESPITE CONSIDERABLE CLOUD COVER...LATEST RUC GUIDANCE SUGGESTS THAT
INHIBITION FOR MOIST BOUNDARY LAYER PARCELS IS ALREADY BECOMING
NEGLIGIBLE. AND...WITH FURTHER HEATING...THUNDERSTORMS ARE EXPECTED
TO BECOME INCREASINGLY NUMEROUS THRU THE AFTERNOON.
ALTHOUGH MIXED LAYER CAPE IS EXPECTED MOSTLY ON THE ORDER OF 500
J/KG...LOCALIZED HIGHER VALUES ARE POSSIBLE...WITH COOL SOUNDINGS
BENEATH -22C 500 MB COLD CORE SUPPORTIVE OF HAIL IN STRONGER STORMS.
WEAK SHEAR IS EXPECTED TO LIMIT HAIL SIZE...BUT SOME OF THIS COULD
APPROACH OR BRIEFLY EXCEED SEVERE LIMITS. GIVEN AT LEAST LIGHT
VEERING WIND PROFILES WITH HEIGHT...AND THE PRESENCE OF FAVORABLE
AMBIENT VERTICAL VORTICITY NEAR THE LOWER/MID TROPOSPHERIC
CIRCULATION...TORNADO POTENTIAL MAY NOT BE COMPLETELY NEGLIGIBLE.
BUT...THIS THREAT APPEARS LOW.
..HALES/HURLBUT.. 04/21/2008
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