SWODY1
SPC AC 241629
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT WED JUN 24 2009
VALID 241630Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE
NRN/CENTRAL PLAINS INTO THE WRN GREAT LAKES/MID MS RIVER VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS ALONG THE CENTRAL GULF COAST...
...NRN PLAINS ACROSS THE MID MO/MID MS RIVER VALLEYS INTO THE NRN
GREAT LAKES...
SURFACE PATTERN WILL REMAIN QUITE DIFFUSE TODAY WITH RELATIVELY WEAK
LOW LEVEL FLOW PREVAILING AND RESIDUAL EFFECTS OF PRIOR MOIST
CONVECTION MUDDLING THE WARM SECTOR. HOWEVER...WLY WINDS ALOFT WILL
STRENGTHEN SOME AS FAST MOVING SHORTWAVE TROUGH FLATTENS TOP OF
RIDGE OVER THE NRN PLAINS. IN ADDITION...SURFACE FRONT/TROUGH
SHOULD BECOME BETTER DEFINED ROUGHLY N-S ACROSS THE WRN DAKOTAS THIS
AFTERNOON...WITH SURFACE THETA-E/INSTABILITY GRADIENT BECOMING
ESTABLISHED FROM NRN WI SWWD INTO SRN MN/CENTRAL SD BY LATE TODAY.
ONGOING...ELEVATED THUNDERSTORM CLUSTER OVER SRN ND/NRN SD THIS
MORNING APPEARS TO BE TIED TO FAST MOVING AREA OF ASCENT SPREADING
ENEWD TOWARDS THE RED RIVER VALLEY TODAY. TAIL END OF THIS ACTIVITY
MAY BECOME NEAR SURFACE-BASED LATER TODAY...WITH ADDITIONAL
DEVELOPMENT POSSIBLE NEAR RESIDUAL SURFACE BOUNDARIES WITHIN WARM
SECTOR AS CAP BREAKS FROM PORTIONS OF THE UP OF MI/NRN WI WSWWD INTO
THE MID MO RIVER VALLEY. DESPITE THE RELATIVELY WEAK H85
FLOW...UPSCALE EVOLUTION INTO ONE OR MORE SEVERE MCS/S CAN BE
EXPECTED THROUGH THE LATE AFTERNOON/EVENING GIVEN FEED OF EXTREME
INSTABILITY AND MODERATE WLY FLOW ALOFT. LARGE HAIL AND DAMAGING
WINDS WILL BE PRIMARY THREATS...ALTHOUGH AN ISOLATED TORNADO CANT BE
RULED OUT. MORNING MODELS SUGGEST EVOLUTION INTO ONE OR TWO SEVERE
MCS/S POSSIBLE MOVING SEWD ACROSS THE MID MS RIVER VALLEY THIS
EVENING/OVERNIGHT...WITH ANOTHER EVOLVING/PERSISTING AHEAD OF NRN
STREAM IMPULSE AND ASSOCIATED FRONT INTO THE WRN/NRN GREAT LAKES BY
25/12Z.
ROBUST DEVELOPMENT IS ALSO EXPECTED DURING THE LATE AFTERNOON ALONG
SURFACE FRONT/TROUGH OVER WRN ND/NWRN SD WITHIN AXIS OF MODERATE
INSTABILITY AHEAD OF STRONGER NRN STREAM IMPULSE
MOVING OUT OF THE NRN ROCKIES. THIS REGIME APPEARS FAVORABLE FOR
SUPERCELLS AND POSSIBLY A FEW TORNADOES THIS AFTERNOON...WITH
ADDITIONAL THREAT OF ISOLATED VERY LARGE HAIL. THESE STORMS MAY
WEAKEN DURING THE EVENING WITH EWD EXTENT AS THEY SHIFT EAST OF
FAIRLY NARROW INSTABILITY AXIS INTO CENTRAL/ERN ND.
...CENTRAL GULF COAST...
SEASONABLY STRONG NNELY FLOW ALOFT WILL REMAIN IN PLACE OVER THIS
REGION BETWEEN VERY STRONG UPPER HIGH OVER THE SRN PLAINS AND TROUGH
OFF THE EAST COAST. SURFACE FRONT NOW FROM THE SRN APPALACHIANS
INTO THE MID SOUTH SHOULD SHIFT SWD THROUGH THE DAY AND...ALONG WITH
GULF BREEZE...MAY FOCUS LATE DAY THUNDERSTORMS WITHIN VERY UNSTABLE
AIR MASS. OVERALL SETUP APPEARS FAVORABLE FOR STRONG/SEVERE
DOWNBURSTS GIVEN VERY DRY MID LEVEL AIR ATOP LARGE LOW LEVEL THETA-E
VALUES...WITH ADDITIONAL POTENTIAL FOR CLUSTERING OR LINEAR
ORGANIZATION AS ACTIVITY MOVES SSWWD THROUGH THE EVENING GIVEN
MODEST DEEP LAYER SHEAR.
..EVANS/JEWELL.. 06/24/2009
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