SPC AC 271936
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0236 PM CDT FRI APR 27 2007
VALID 272000Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN/EVE ACROSS PARTS
OF THE MID ATLANTIC COAST STATES....
...ATLANTIC SEABOARD...
INCREASING DOWNSLOPE FLOW TO THE LEE OF THE CENTRAL APPALACHIANS IS
ONGOING...AS STRONGER FORCING ASSOCIATED WITH INITIAL UPPER IMPULSE
LIFTS NORTHEAST OF THE LOWER GREAT LAKES/NORTHERN AND CENTRAL
APPALACHIANS REGION. HOWEVER...AS NEXT IMPULSE SHIFTS TOWARD MID
ATLANTIC COASTAL AREAS...ASSOCIATED LARGE-SCALE ASCENT COULD STILL
AID CONVECTIVE DEVELOPMENT ACROSS PARTS OF EASTERN NORTH
CAROLINA/SOUTHEAST VIRGINIA. BOUNDARY LAYER ACROSS THIS REGION IS
EXPECTED TO REMAIN MOIST AND POTENTIALLY UNSTABLE INTO EARLY
EVENING...AND DEEP LAYER SHEAR BENEATH 40-50 KT CYCLONIC 500 MB FLOW
IS SUPPORTIVE OF SUPERCELLS. THE STRONGER LOW-LEVEL JET IS IN THE
PROCESS OF SHIFTING NORTHEAST OF MID ATLANTIC COASTAL AREAS...BUT
LOW-LEVEL HODOGRAPHS MAY REMAIN FAIRLY LARGE THROUGH THE PEAK
HEATING HOURS ACROSS PARTS OF NORTHEAST NORTH CAROLINA/EXTREME
SOUTHEAST VIRGINIA...WHERE AN ISOLATED TORNADO APPEARS POSSIBLE.
...CENTRAL/SOUTHERN PLAINS...
A VIGOROUS SHORT WAVE TROUGH CONTINUES TO DIG ACROSS THE CENTRAL
PLAINS INTO THE OZARK PLATEAU. COLD CORE AND STRONGER MID-LEVEL
FORCING ASSOCIATED WITH THIS SYSTEM STILL APPEARS LIKELY TO REMAIN
DISPLACED WELL TO THE NORTH OF BETTER RETURN FLOW. AND...THIS IS
EXPECTED TO BE A LIMITING FACTOR WITH RESPECT TO CONVECTIVE
POTENTIAL.
MOISTENING ABOVE THE BOUNDARY LAYER...ASSOCIATED WITH LOW-LEVEL
ISENTROPIC ASCENT TO THE SOUTH/SOUTHWEST OF UPPER IMPULSE...IS
EXPECTED TO CONTINUE TO PROVIDE THE FORCING FOR THE PRIMARY
CONVECTIVE DEVELOPMENT. THIS IS IN THE PROCESS OF BECOMING FOCUSED
NEAR THE RED RIVER...WHERE STRONGEST STORMS ARE ANTICIPATED LATE
THIS AFTERNOON AND EVENING. SHEAR IN THE CLOUD BEARING LAYER SEEMS
MARGINALLY SUPPORTIVE OF UPDRAFT ROTATION...WHICH MAY PROMOTE THE
RISK FOR HAIL IN AN ENVIRONMENT WITH MOST UNSTABLE CAPE AT OR ABOVE
500 J/KG. IT SEEMS POSSIBLE THAT CONVECTION COULD AT LEAST BRIEFLY
BECOME ROOTED IN THE BOUNDARY LAYER BEFORE NIGHTFALL...SOUTH OF THE
CHILDRESS/ WICHITA FALLS AREA...WHERE...LOCALLY...MIXED LAYER CAPE
COULD APPROACH 1000 J/KG. IF THIS OCCURS...BETTER VERTICAL SHEAR
FOR BOUNDARY LAYER BASED STORMS MAY SUPPORT AN ISOLATED SUPERCELL
BEFORE ACTIVITY WEAKENS WITH LOSS OF DAYTIME HEATING.
...SOUTHERN PLATEAU/ROCKIES...
TO THE NORTHEAST OF A CLOSED LOW BECOMING CUT-OFF NEAR THE BAJA
SPUR...DEEPENING CONVECTION IS ALREADY EVIDENT ALONG PARTS OF THE
MOGOLLON RIM AND MOUNTAINS OF SOUTHWEST NEW MEXICO. THIS APPEARS
ROUGHLY BETWEEN STRONGER MID-LEVEL SUBSIDENCE ASSOCIATED WITH UPPER
RIDGE...AND STRONGER MID-LEVEL UPWARD VERTICAL MOTION ASSOCIATED
WITH CUT-OFF LOW. BUT...EVEN IF MORE FAVORABLE FORCING IS SOUTH OF
REGION...FURTHER HEATING MAY SUPPORT A FEW THUNDERSTORMS ALONG THE
HIGHER TERRAIN LATE THIS AFTERNOON.
...PACIFIC COAST STATES...
STRONG HEATING IS ALSO CONTRIBUTING TO DESTABILIZATION ALONG THE
NORTHERN SIERRA NEVADA INTO THE SOUTHERN CASCADES. AS UPPER RIDGE
AXIS SHIFTS TO THE EAST...LOW/MID-LEVEL MOISTENING MAY SUPPORT
ISOLATED TO WIDELY SCATTERED THUNDERSTORMS LATE THIS AFTERNOON AND
EVENING. MID-LEVEL HEIGHT FALLS COULD ALSO ALLOW CONVECTIVE
DEVELOPMENT INTO PARTS OF CENTRAL/EASTERN OREGON BY THIS EVENING.
..KERR.. 04/27/2007
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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