Moderate risk issued, but it looks to me like things will be complicated (as usual) by outflow boundaries, residual cloudcover and the resulting destabilization (or lack thereof), and the other usual suspects, so it will probably be early afternoon before we know where the greatest risks shall be.
WIDESPREAD SEVERE THUNDERSTORMS WITH THE POTENTIAL FOR VERY LARGE
AND DESTRUCTIVE HAIL...TORNADOES...AS WELL AS DAMAGING STRAIGHT-
LINE WINDS...ARE LIKELY OVER PARTS OF NEBRASKA...KANSAS...
MISSOURI...OKLAHOMA...AND ARKANSAS LATER TODAY THROUGH TONIGHT.
...SYNOPSIS...
A COMPLEX SPLIT FLOW REGIME WILL CONTINUE TO EXIST ACROSS SRN CANADA
AND THE NCNTRL U.S. EARLY IN THE PERIOD DOWNSTREAM FROM A LARGE
MID/UPPER LEVEL BLOCK FROM THE GREAT BASIN INTO NWRN CANADA. A LARGE
MID LEVEL LOW MAKING UP THE SRN COMPONENT OF THE BLOCK IS FCST TO
SPLIT INTO TWO DISTINCT MID LEVEL CENTERS TODAY. ONE CENTER...AND
ITS ASSOCIATED MID LEVEL COLD POOL...WILL REMAIN NEARLY STATIONARY
OVER THE ID/ORE BORDER. THE OTHER LOW CENTER... NOW BEGINNING TO
TAKE SHAPE IN THE FORM OF A STRONG IMPULSE/SPEED MAX CROSSING THE
FOUR CORNERS REGION...WILL SPREAD EAST ACROSS NEB THROUGH TONIGHT IN
THE FORM OF A STRONG AND PROGRESSIVE DEEP LAYER CYCLONE. EVENTUALLY
THIS EWD MOVING IMPULSE WILL PHASE WITH ANOTHER SHORT WAVE TROUGH
CURRENTLY DROPPING SOUTH ACROSS NCNTRL CANADA.
ELSEWHERE...COOL AND PRIMARILY NORTHWEST FLOW WILL ENCOMPASS THE
GREAT LAKES AND NORTHEAST WHILE HEIGHTS ARE FCST TO RISE ACROSS THE
SOUTHWEST U.S.
...NEB/NRN KS TO NRN MO...
SEVERAL DAYS OF MODEST SLY LOW LEVEL FLOW FROM THE GULF COAST TO THE
CNTRL PLAINS...AS WELL AS A PERSISTENT WSWLY MID LEVEL FETCH OFF THE
DRIER AND WARMER ELEVATED TERRAIN OF THE WRN/SWRN U.S. AND NRN
MEXICO...HAS RESULTED IN A BROAD SWATH OF POTENTIALLY STRONG
INSTABILITY FROM TX TO NEB. THIS INSTABILITY WILL COMBINE WITH
FAVORABLE DYNAMICS ASSOCIATED WITH THE PROGRESSIVE SHORT WAVE TROUGH
AND DEEPENING SURFACE LOW OVER KS/NEB TODAY TO PRODUCE WIDESPREAD
ORGANIZED TSTMS. GREATEST CONCENTRATION OF SEVERE STORMS...AND
ENHANCED LARGE HAIL AND TORNADO POTENTIAL...WILL PROBABLY BE
ASSOCIATED WITH THE SURFACE LOW AS IT TRACKS EAST FROM SRN NEB/NRN
KS INTO NWRN MO THROUGH THIS EVENING. THE LOW WILL THEN CONTINUE
EAST ALONG A WARM FRONT INTO WRN IL THROUGH EARLY FRIDAY.
...ERN KS/WRN MO SOUTH ACROSS ERN OK/NERN TX AND WRN AR...
THE COLD FRONT CURRENTLY DEVELOPING SOUTH ACROSS WRN KS SHOULD
CONTINUE SWD/SEWD ACROSS THE TX PNHDL AND WRN OK THROUGH THIS
MORNING WHILE GRADUALLY WEAKENING. BOUNDARY LAYER WARMING AND
MOISTENING AHEAD OF THE WIND SHIFT...FROM CNTRL/ERN OK INTO ERN KS
AND SWRN MO...WILL CONTRIBUTE TO THE DEVELOPMENT OF VERY UNSTABLE
CONDITIONS /MLCAPE 2000-3000 J/KG/ ACROSS THESE AREAS BY AFTERNOON.
STRONG CAP ACROSS THE REGION IS EXPECTED TO INHIBIT DEEP CONVECTION
FROM FORMING UNTIL LATE AFTERNOON WHEN MID LEVEL HEIGHT FALLS BEGIN
TO SPREAD EAST WITH THE TROUGH ACROSS NEB AND WRN KS. GIVEN
MAGNITUDE OF INSTABILITY...INCREASINGLY DIFFLUENT AND STRENGTHENING
MID LEVEL FLOW NORMAL TO THE LOW LEVEL WIND SHIFT/DRYLINE...THE
POTENTIAL WILL EXIST FOR LOCALLY EXPLOSIVE STORM DEVELOPMENT BY
EVENING. DEEP LAYER SHEAR WILL BE FAVORABLE FOR SUPERCELLS WITH
LARGE HAIL AND HIGH WINDS POSSIBLE. TORNADO POTENTIAL...WHILE NOT AS
GREAT AS FARTHER NORTH NEAR THE SFC LOW...MAY EVOLVE IN A NARROW
CORRIDOR IN SPACE AND TIME...FROM SERN KS INTO ERN OK DURING THE
EVENING. STORMS MAY THEN MERGE BEFORE SPREADING INTO NWRN AR WITH A
WIND AND HAIL THREAT BY LATE EVENING.
OTHER STORMS/SUPERCELLS MAY BACKBUILD INTO THE INSTABILITY AXIS AS
FAR SOUTH AS NERN TX THROUGH EVENING AS FORCING AND HEATING ACT TO
OVERCOME CAPPING OVER THESE AREAS. MORE ISOLATED SUPERCELLS WITH
HAIL ARE POSSIBLE FARTHER SW INTO SCNTRL AND ERN TX AS CAP IS
LOCALLY OVERCOME BY DIURNAL HEATING.
...SRN IA...CNTRL/ERN MO TO WRN IL...
ADDITIONAL ORGANIZED STORMS ARE LIKELY TO EXIST AND/OR DEVELOP ALONG
THE WARM FRONT...FROM SRN IA INTO ERN MO AND WRN IL THROUGH THE DAY
AND NIGHT. WHILE DEEP LAYER SHEAR IS FCST TO BE SOMEWHAT LIMITED
OVER THESE AREAS...INSTABILITY AND LOW LEVEL SHEAR ALONG THE FRONT
SHOULD BECOME SUPPORTIVE OF ROTATING STORMS. IN ADDITION TO HAIL...A
TORNADO OR TWO COULD DEVELOP FROM CELLS TRACKING SEWD ALONG THE
FRONTAL ZONE.
...VA/NC AREA...
SCATTERED AFTERNOON CONVECTION NEAR COLD FRONT/LEE TROUGH
INTERSECTION ACROSS CNTRL VA MAY POSE A LIMITED SEVERE HAIL/WIND
THREAT THROUGH EARLY EVENING. RELATIVELY WEAK SHEAR ACROSS THE
REGION SUGGESTS THIS ACTIVITY WOULD BE POORLY ORGANIZED AND
SHORT-LIVED.
..CARBIN.. 04/21/2005
