SWODY1
SPC AC 261536
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1036 AM CDT FRI JUN 26 2009
VALID 261630Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NORTHERN AND
CENTRAL PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NORTHEAST STATES INTO
THE LOWER OH AND MID MS VALLEYS...
WATER VAPOR LOOPS SHOW A LARGE UPPER RIDGE CENTERED OVER THE
SOUTHERN PLAINS...WITH AN UPPER TROUGH OVER THE GREAT LAKES AND OVER
THE PACIFIC NORTHWEST STATES. SCATTERED THUNDERSTORMS ARE EXPECTED
OVER MUCH OF THE GREAT BASIN AND ROCKIES EASTWARD INTO THE
CENTRAL/NORTHERN PLAINS...AND OVER MUCH OF THE EASTERN UNITED
STATES. CONCENTRATIONS OF STRONG/SEVERE STORMS ARE EXPECTED THIS
AFTERNOON AND EVENING OVER THE CENTRAL/NORTHERN PLAINS...AND ALONG A
COLD FRONT FROM NEW ENGLAND INTO THE LOWER OH VALLEY.
...NORTHEAST...
CYCLONIC FLOW ALOFT AND RELATIVELY COOL MID LEVEL TEMPERATURES ARE
IN PLACE THIS MORNING OVER MUCH OF THE NORTHEAST UNITED STATES.
SCATTERED MORNING SHOWERS AND THUNDERSTORMS ARE ONGOING OVER
NY/VT/CT...AND OVER PARTS OF ONTARIO/QUEBEC AND WESTERN ME. POCKETS
OF CLOUD COVER AND PRECIPITATION THROUGHOUT THE REGION WILL
COMPLICATE THE FORECAST OF WHERE/WHEN STRONG CONVECTION MAY DEVELOP
THIS AFTERNOON. HOWEVER...A COMBINATION OF SUFFICIENT DEEP LAYER
VERTICAL SHEAR AND MODERATE CAPE VALUES WILL POSE A RISK OF
ORGANIZED MULTICELL THUNDERSTORMS CAPABLE OF LOCALLY DAMAGING WINDS
AND HAIL FROM ME INTO PA/NJ.
...OH VALLEY AND MID ATLANTIC...
STRONG DAYTIME HEATING HAS BEGUN ACROSS MUCH OF THE OH VALLEY AND
CENTRAL APPALACHIANS...INTO VA/MD. TEMPERATURES WILL CLIMB INTO THE
80S/90S OVER THIS REGION WITH DEWPOINTS IN THE UPPER 60S TO LOWER
70S. THIS WILL YIELD A CORRIDOR OF STRONG INSTABILITY FROM MO/AR
EASTWARD. SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP
ALONG/AHEAD OF THE WEAK COLD FRONT MOVING SOUTHWARD ACROSS THE OH
VALLEY THIS AFTERNOON. THE BEST COMBINATION OF CAPE/SHEAR WILL BE
OVER PARTS OF WV/EASTERN KY...BUT SUFFICIENT PARAMETERS SUGGEST A
RISK OF SEVERE STORMS THROUGHOUT THE AREA. WARM TEMPERATURES ALOFT
MAY MITIGATE THE RISK OF LARGE HAIL...BUT LOCALLY DAMAGING WINDS
WILL BE POSSIBLE IN STRONGER CELLS.
...NORTHERN/CENTRAL PLAINS...
SATELLITE LOOPS SHOW A SHORTWAVE TROUGH LIFTING NORTHEASTWARD ACROSS
UT/CO. THIS FEATURE IS EXPECTED TO SPREAD INTO THE NORTHERN PLAINS
BY THIS EVENING. STRONG HEATING IS OCCURRING OVER MOST OF THE
DAKOTAS AND NORTHERN NEB...WHERE AFTERNOON MLCAPE VALUES ARE
EXPECTED TO REACH 3000-4000 J/KG. MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT THUNDERSTORMS WILL INTENSIFY BY MID/LATE AFTERNOON
FROM THE BLACK HILLS SOUTHWARD INTO WESTERN NEB...AND EVENTUALLY
NORTHWARD INTO THE CENTRAL DAKOTAS. THESE STORMS MAY INITIALLY BE
SUPERCELLULAR WITH A RISK OF A FEW TORNADOES. STORMS ARE LIKELY TO
ORGANIZE INTO A LINEAR MCS AND TRACK EASTWARD ACROSS THE DAKOTAS AND
NEB THROUGH THE EVENING WITH A CONTINUED RISK OF LARGE HAIL AND
DAMAGING WINDS. MESOSCALE MODELS SUGGEST SOME RISK OF BOW ECHO
FORMATION OVER THIS REGION...SUGGESTING A MORE CONCENTRATED RISK OF
DAMAGING WINDS IF THIS OCCURS.
...GREAT BASIN...
A RATHER COOL UPPER TROUGH CONTINUES TO DIG SOUTHWARD ACROSS CA/NV
THIS MORNING. STEEP MID LEVEL LAPSE RATES AND POCKETS OF HEATING
WILL RESULT IN SUFFICIENT INSTABILITY FOR SCATTERED AFTERNOON
THUNDERSTORMS AHEAD OF THE TROUGH ACROSS MUCH OF THE GREAT BASIN.
FORECAST SOUNDINGS SHOW MLCAPE VALUES OF 500-1000 J/KG AND EFFECTIVE
SHEAR OF 25-35 KNOTS. THIS SHOULD BE SUFFICIENT FOR A FEW ORGANIZED
MULTICELL OR ISOLATED HIGH-BASED SUPERCELL STORMS CAPABLE OF HAIL
AND GUSTY/DAMAGING WINDS. AREAL COVERAGE OF SEVERE ACTIVITY REMAINS
IN QUESTION...SO WILL MAINTAIN ONLY LOW PROBABILITIES OF SEVERE
WEATHER AT THIS TIME.
...CENTRAL GULF COAST...
MORNING RAOBS FROM LA/MS/AL SHOW AMPLE MOISTURE/INSTABILITY FOR
SCATTERED AFTERNOON AND EVENING THUNDERSTORMS...ALONG WITH
SUBSTANTIAL DRY AIR ALOFT/DCAPE. THIS MAY HELP TO ENHANCE
CONVECTIVE DOWNDRAFTS AND CONTRIBUTE TO A RISK OF ISOLATED WET
MICROBURSTS IN STRONGER CORES.
..HART/HURLBUT.. 06/26/2009
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