SWODY1
SPC AC 262000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT THU APR 26 2007
VALID 262000Z - 271200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER OHIO
VALLEY...THRU MUCH OF THE APPALACHIANS INTO PARTS OF THE MID
ATLANTIC COAST STATES....
..EAST OF MISSISSIPPI VALLEY...
CONSIDERABLE EARLY DAY CLOUD COVER AND MODEST LAPSE RATES HAVE
SLOWED DESTABILIZATION. BUT...CONVECTIVE DEVELOPMENT NOW APPEARS TO
BE INCREASING IN COVERAGE/INTENSITY IN PEAK AFTERNOON HEATING ACROSS
MUCH OF THE LOWER OHIO VALLEY...SOUTHWARD INTO THE UPPER TENNESSEE
VALLEY/WESTERN SLOPES OF THE SOUTHERN APPALACHIANS. THIS IS WELL
AHEAD OF PRIMARY SURFACE COLD FRONT WHICH IS JUST NOW ADVANCING
THROUGH THE MIDDLE MISSISSIPPI VALLEY. THIS FRONT TRAILS SOUTH
SOUTHWEST OF SURFACE LOW LIFTING ACROSS NORTHERN ILLINOIS INTO THE
GREAT LAKES REGION...BUT IS PRECEDED BY AN INITIAL SURGE OF
COOLER/DRIER AIR...WHICH PROVIDES WESTERN EDGE OF CONTINUING SEVERE
THREAT THIS AFTERNOON.
EAST OF SOUTHERN BRANCH CLOSED LOW/TROUGH...WHICH IS LIFTING
NORTHEAST OF THE MID/LOWER MISSISSIPPI VALLEY...50+ KT CYCLONIC 500
MB FLOW IS CONTRIBUTING TO FAVORABLE DEEP LAYER SHEAR FOR
SUPERCELLS...FROM LEAD SURFACE BOUNDARY INTO THE APPALACHIANS.
STRONGEST UPPER FORCING IS SPREADING NORTHEAST OF THE LOWER OHIO
VALLEY TOWARD THE LOWER GREAT LAKES REGION...BUT LARGE-SCALE ASCENT
WILL REMAIN FAVORABLE FOR CONVECTION SOUTHWARD TO THE WEST OF THE
CENTRAL/SOUTHERN APPALACHIANS...WHERE A 40+ KT SOUTHERLY LOW-LEVEL
JET IS ENHANCING LOW-LEVEL HODOGRAPHS. LOW-LEVEL JET STREAK IS
LIFTING NORTHWARD ALONG THE WESTERN SLOPES OF THE APPALACHIANS...AND
MAY CONTRIBUTE TO A RISK FOR TORNADOES IN ADDITION TO LARGE
HAIL/DAMAGING WIND GUSTS ACROSS PARTS OF NORTHEAST TENNESSEE INTO
WESTERN KENTUCKY LATE THIS AFTERNOON.
LATER THIS AFTERNOON THROUGH THE EVENING HOURS...MODELS SUGGEST THAT
A 30-40 KT SOUTHERLY LOW-LEVEL JET WILL DEVELOP/LIFT NORTHWARD TO
THE LEE OF THE CENTRAL/SOUTHERN APPALACHIANS. THIS SEEMS LIKELY TO
ENHANCE FORCING FOR CONVECTIVE DEVELOPMENT...AND CONTRIBUTE TO
INCREASING RISK FOR SUPERCELLS FROM PARTS OF THE WESTERN CAROLINAS
INTO SOUTHWESTERN VIRGINIA. SURFACE FRONTAL ZONE NOW OVER SOUTHERN
VIRGINIA WILL LIKELY RETREAT NORTHWARD AHEAD OF ACTIVITY...BUT A
LINGERING SOUTHEASTERLY COMPONENT TO SURFACE WINDS MAY ENHANCE
LOW-LEVEL HODOGRAPHS FURTHER... SUPPORTING A RISK OF TORNADOES
ACROSS THIS AREA...EVEN WELL AFTER DARK.
..NORTH CENTRAL HIGH PLAINS...
SHORT WAVE TROUGH NOW DIGGING TO THE LEE OF THE NORTH CENTRAL
ROCKIES IS CONTRIBUTING TO CONVECTIVE DEVELOPMENT EAST OF THE
COLORADO/WYOMING FRONT RANGE. LAPSE RATES ARE BECOMING VERY STEEP
ACROSS THIS REGION WITH STRONG SURFACE HEATING/DIFFERENTIAL THERMAL
ADVECTION...AND...DESPITE SPARSE MOISTURE...MODELS SUGGEST MIXED
LAYER CAPE MAY INCREASE IN EXCESS OF 500 J/KG. EVEN WITH PRONOUNCED
VEERING OF WINDS WITH HEIGHT IN LOWER/MID-LEVELS...DEEP LAYER SHEAR
PROBABLY WILL REMAIN WEAK. BUT...POTENTIAL FOR ISOLATED DAMAGING
DOWNBURSTS WILL EXIST LATE THIS AFTERNOON/EVENING IN A DEEP MIXED
BOUNDARY LAYER WITH SIZABLE TEMPERATURE/DEW POINTS SPREADS. SOME
HAIL IS ALSO POSSIBLE.
**FOR MORE SPECIFIC INFORMATION CONCERNING ONGOING OR MORE IMMINENT
SEVERE THREATS...PLEASE REFER TO LATEST SPC MESOSCALE DISCUSSIONS.
.KERR.. 04/26/2007
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