SWODY1
SPC AC 182211
DAY 1 CONVECTIVE OUTLOOK AMEND 1
NWS STORM PREDICTION CENTER NORMAN OK
0511 PM CDT SAT APR 18 2009
VALID 182205Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL/SRN
PLAINS...WRN/SWRN MO AND NWRN AR TO ERN HALF OF TX AND LOWER MS
VALLEY...
AMENDED TO EXTEND SLIGHT RISK FARTHER EAST INTO SWRN MO AND WRN/NWRN
AR
TSTMS WILL CONTINUE TO DEVELOP AND INCREASE IN COVERAGE/INTENSITY
INTO THIS EVENING ACROSS CENTRAL/ERN OK...SERN KS/SWRN MO...AND
EVENTUALLY SPREAD INTO AR AS THE UPPER LOW MOVES EWD. INCREASING
EFFECTIVE BULK SHEAR WILL SUPPORT ADDITIONAL ORGANIZED SEVERE
STORMS...WITH AN ATTENDANT THREAT FOR HAIL/DAMAGING WINDS AND AN
ISOLATED TORNADO.
.PREV DISCUSSION... /ISSUED 0309 PM CDT SAT APR 18 2009/
...SE/E TX TO LOWER MS VALLEY...
REGIONAL RADARS/SATELLITE IMAGERY INDICATE AN ONGOING MCS TRACKING
EWD ACROSS SERN TX/FAR WRN LA...WITH AIRMASS DOWNSTREAM OVER MUCH OF
LA/SWRN MS UNDERGOING DESTABILIZATION. DESPITE A LARGE VEIL OF
CIRRUS SPREADING E/NEWD IN ADVANCE OF THE MCS...SOME SURFACE HEATING
COUPLED WITH MOISTURE RETURN PER SLY LOW LEVEL FLOW HAS RESULTED IN
MLCAPE 500-1000 J/KG. PRIND SUGGEST THIS MCS WILL PROGRESS EWD INTO
LA THIS AFTERNOON INTO THE EVENING...WITH EFFECTIVE BULK SHEAR
AROUND 50 KT MAINTAINING LIKELIHOOD FOR STORM ORGANIZATION. THIS
OUTLOOK HAS EXTENDED THE SLIGHT RISK EWD INTO PARTS OF SERN LA/SWRN
MS WHERE MODELS INDICATE A STRENGTHENING LOW LEVEL JET/INCREASING
HODOGRAPH CURVATURE DEVELOPING THIS EVENING/OVERNIGHT FOR AN
ATTENDANT TORNADO THREAT.
FOR SHORT TERM DETAILS...REFER TO WW/S AND MESOSCALE DISCUSSIONS FOR
THIS REGION.
...KS/OK/N TX...
SEVERE STORMS DEVELOPED A LITTLE EARLIER THAN PREVIOUSLY FORECAST
ACROSS SWRN KS. HOWEVER...OVERALL EVOLUTION APPEARS TO BE ON TRACK
AS SHORT WAVE TROUGH SPREADS ENEWD INTO SWRN/SRN KS AND WRN OK.
DISCRETE STORMS WILL REMAIN LIKELY WITH ONGOING ACTIVITY IN SWRN KS
TO NWRN OK.
FOR SHORT TERM DETAILS...REFER TO WW/S AND MESOSCALE DISCUSSIONS FOR
THIS REGION.
FARTHER E...ACROSS NERN OK/NWRN AR...TSTMS HAVE INCREASED WITHIN
EXIT REGION OF UPPER JET. STEEP MID LEVEL LAPSE RATES/COLD MID
LEVEL TEMPERATURES SUGGEST A POTENTIAL FOR HAIL WITH THIS ACTIVITY.
..PETERS.. 04/18/2009
.PREV DISCUSSION... /ISSUED 1203 PM CDT SAT APR 18 2009/
CORRECTED FOR REFERENCE TO SOUTHEAST KS
A LARGE UPPER LOW CURRENTLY OVER SOUTHEAST CO WILL TRACK SLOWLY
EASTWARD TODAY INTO THE CENTRAL PLAINS...WHILE FAST CYCLONIC FLOW
ALOFT PERSISTS ACROSS THE SOUTHERN PLAINS. TWO AREAS APPEAR AT RISK
OF ORGANIZED SEVERE STORMS...SOUTHEAST TX/WESTERN LA...AND OK/KS.
...SOUTHEAST TX/WESTERN LA...
A LARGE CLUSTER OF THUNDERSTORMS IS ONGOING THIS MORNING OVER PARTS
OF EAST-CENTRAL TX. SEVERAL MODERATE LOW LEVEL CIRCULATIONS HAVE
BEEN NOTED ON LOCAL RADARS WITHIN THIS MCS. KHGX/LCH VADS SUGGEST
40KT+ SOUTHERLY LOW LEVEL WINDS AND SUBSTANTIAL EFFECTIVE HELICITY
VALUES /250-400 M2/S2/. DESPITE WIDESPREAD CLOUDS AND LIMITED
DESTABILIZATION...A COMBINATION OF A VERY MOIST AIRMASS...WEAK
CAP...SUBTLE FORCING...AND STRONG LOW LEVEL SHEAR WILL LIKELY
MAINTAIN A RISK OF EMBEDDED SUPERCELLS AND BRIEF TORNADOES THROUGH
MUCH OF THE AFTERNOON. STORMS WILL SPREAD INTO SOUTHWEST LA THIS
EVENING AS LOW LEVEL JET SHIFTS EASTWARD. PLEASE REFER TO MOST
RECENT SWOMCDS FOR FURTHER DETAILS.
...OK/KS/NORTH TX...
LATEST SURFACE ANALYSIS SHOWS A STACKED LOW OVER SOUTHEAST KS WITH
THE DRYLINE EXTENDING SOUTHWARD FROM LOW INTO WESTERN OK. VISIBLE
SATELLITE IMAGERY SHOWS WIDESPREAD LOW CLOUDS OVER THE WARM SECTOR
OF SOUTHEAST KS AND MUCH OF OK. HOWEVER...THESE CLOUDS ARE EXPECTED
TO ERODE BY MID AFTERNOON AND ALLOW AIRMASS TO DESTABILIZE RAPIDLY.
COLD TEMPERATURES ALOFT...VERY STEEP LAPSE RATES...AND SURFACE
DEWPOINTS IN THE 50S WILL YIELD AFTERNOON MLCAPE VALUES OF 1000-1500
J/KG. PRESENT INDICATIONS ARE THAT SHORTWAVE TROUGH NOW APPROACHING
THE TX PANHANDLE WILL ROTATE EASTWARD BY LATER THIS AFTERNOON AND
HELP INITIATE SCATTERED THUNDERSTORMS ALONG THE DRYLINE OF WESTERN
OK/SOUTH-CENTRAL KS. THESE STORMS WILL EXPAND AND INTENSIFY AS THEY
SPREAD ACROSS KS/OK DURING THE EVENING. FORECAST GENERALLY
STRAIGHT-LINE HODOGRAPHS AND STRONG EFFECTIVE SHEAR APPEAR FAVORABLE
FOR SPLITTING SUPERCELLS. LOW LEVEL VERTICAL SHEAR WILL BE
MARGINAL...BUT SOME RISK OF TORNADOES WILL BE PRESENT IN SUPERCELLS
OVER SOUTH-CENTRAL KS AND NORTHWEST OK WHERE BACKED LOW LEVEL
WINDS...SUBTLE SURFACE BOUNDARIES...AND AMBIENT VORTICITY ARE MOST
LIKELY TO COEXIST. VERY LARGE HAIL WILL BE POSSIBLE IN STRONGEST
CELLS THROUGHOUT THE AREA. STORMS MAY BUILD SOUTHWARD ALONG DRYLINE
INTO NORTH TX TOWARD DARK.
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