SPC AC 041948
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0248 PM CDT SUN APR 04 2010
VALID 042000Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SRN LK MI SSWWD INTO PARTS
OF AR/OK/KS...
...IL/MO/SERN KS/NERN OK...
ONGOING FORECAST APPEARS TO REMAIN ON TRACK...THOUGH MORE WIDESPREAD
DEVELOPMENT ALONG THE FRONT MAY OCCUR A BIT LATER THAN INITIALLY
EXPECTED. NONETHELESS...STORM DEVELOPMENT SHOULD BEGIN IN THE NEXT
1-2 HOURS...AS VORT MAX EVIDENT IN WV IMAGERY NOW CROSSING THE MID
MO VALLEY REGION CONTINUES ENEWD. AIRMASS CONTINUES TO DESTABILIZE
WHICH -- COMBINED WITH WIND SHEAR PROFILES FAVORABLE FOR SUPERCELLS
-- SUGGESTS THAT STORMS WILL BECOME SEVERE SHORTLY AFTER
INITIATION...WITH VERY LARGE HAIL...DAMAGING WINDS...AND PERHAPS A
COUPLE OF TORNADOES POSSIBLE. STORMS WILL SHIFT EWD/SEWD
OVERNIGHT...ACROSS THE MS VALLEY AND POSSIBLY SHIFTING TOWARD THE OH
VALLEY REGION LATE.
...AR EWD INTO THE MID MS VALLEY REGION...
MODELS -- INCLUDING MORNING HI-RES WRF RUNS -- PERSIST IN BREAKING
OUT SEVERE CONVECTION ACROSS AR THIS EVENING...DESPITE CONTINUED
LACK OF AN APPARENT FORCING MECHANISM. WRF RUNS SUGGEST THAT A BAND
OF STORMS/SUPERCELLS WILL BEGIN INITIATING AHEAD OF THE EXPECTED
FRONTAL BAND OF STORMS FARTHER TO THE NW...AND THEN INCREASE AND
EVENTUALLY MERGE WITH THE FRONTAL CONVECTION AS THE BOUNDARY PUSHES
SEWD OVERNIGHT. GIVEN THAT ANY DEVELOPMENT WOULD LIKELY BE ISOLATED
INITIALLY...AND WITH SUFFICIENT THERMODYNAMIC ENVIRONMENT ALONG WITH
SHEAR FAVORABLE FOR SUPERCELLS...A CONDITIONAL SEVERE THREAT IS
EVIDENT -- INCLUDING THE POTENTIAL FOR VERY LARGE HAIL AND A TORNADO
OR TWO.
..GOSS.. 04/04/2010
.PREV DISCUSSION... /ISSUED 1117 AM CDT SUN APR 04 2010/
...MO/IL...
MORNING WATER VAPOR LOOPS SHOW A SUBTLE SHORTWAVE TROUGH TRACKING
ACROSS PARTS OF WY/CO/KS. THIS FEATURE IS FORECAST TO MOVE RAPIDLY
EASTWARD INTO IA/MO BY THIS EVENING...THEN INTO THE SOUTHERN GREAT
LAKES REGION OVERNIGHT. MEANWHILE...SOUTHERLY LOW LEVEL WINDS ARE
QUICKLY TRANSPORTING GULF MOISTURE NORTHWARD ACROSS THE PLAINS AND
MS VALLEY. THIS WILL LEAD TO 50S/60S DEWPOINTS THROUGH MOST OF
MO/IL BY THIS EVENING...AND MODERATE CAPE VALUES /1000-2000 J/KG/
OVER THE REGION.
PRESENT INDICATIONS ARE THAT CLUSTER OF SHOWERS AND THUNDERSTORMS
OVER NORTHEAST MO WILL DEVELOP SLOWLY NORTHEASTWARD INTO IL THIS
AFTERNOON...AND MAY INTENSIFY AFTER 21Z AS GREATER LOW LEVEL
MOISTURE ARRIVES IN AREA. OTHER AND MORE INTENSE STORMS ARE LIKELY
TO FORM ALONG THE FRONT FROM NORTHERN IL/SOUTHEAST IA INTO NORTHERN
MO AROUND THE SAME TIME AS SHORTWAVE TROUGH APPROACHES FROM THE
WEST. FORECAST SOUNDINGS SHOW THERMODYNAMIC AND VERTICAL SHEAR
PROFILES FAVORABLE FOR ORGANIZED SEVERE STORMS AND POSSIBLE
SUPERCELLS. LARGE HAIL WILL BE THE MAIN INITIAL THREAT...WITH A
GREATER RISK OF DAMAGING WINDS DEVELOPING THROUGH THE EVENING AS THE
LINE OF STORMS MOVES ACROSS IL AND INTO WESTERN IND. ISOLATED
TORNADOES WILL ALSO BE POSSIBLE IN EMBEDDED SUPERCELLS ALONG THE
LINE...AND ESPECIALLY IF ANY CELLS CAN BECOME SUSTAINED AHEAD OF THE
SQUALL LINE.
...KS/OK...
THUNDERSTORMS ARE EXPECTED TO DEVELOP SOUTHWESTWARD ALONG THE FRONT
THIS EVENING INTO PARTS OF SOUTHEAST KS AND NORTHERN OK. THE
SHORTWAVE TROUGH WILL HAVE PASSED THIS REGION...WITH ONLY WEAK LARGE
SCALE FORCING OCCURRING AFTER DARK. THIS LEADS TO CONSIDERABLE
UNCERTAINTY REGARDING HOW FAR SOUTHWEST SEVERE STORMS CAN
DEVELOP...WITH SOME 12Z GUIDANCE SHOWING INITIATION AS FAR SOUTHWEST
AS WESTERN NORTH TX.
...AR...
FOR SEVERAL DAYS...MODELS HAVE BEEN CONSISTENT IN DEVELOPING
SCATTERED THUNDERSTORMS ACROSS AR TODAY...ALTHOUGH FORCING
MECHANISMS FOR ACTIVITY ARE HARD TO FIND. MOISTURE IS RAPIDLY
INCREASING OVER THIS REGION WITH AFTERNOON MLCAPE VALUES LIKELY TO
EXCEED 1500 J/KG OVER CENTRAL/EASTERN AR WHERE STRONGEST HEATING IS
EXPECTED. IT CURRENTLY APPEARS MOST LIKELY THAT STORM INITIATION
WILL OCCUR LATER THIS AFTERNOON OR EARLY EVENING. VERTICAL SHEAR
PROFILES ARE QUITE FAVORABLE SUGGESTING A CONDITIONAL RISK OF
DISCRETE SUPERCELLS CAPABLE OF LARGE HAIL AND TORNADOES.
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