SWODY2
SPC AC 220600
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT THU APR 22 2010
VALID 231200Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
CENTRAL AND S CENTRAL CONUS...
...SYNOPSIS...
VERY LARGE UPPER LOW/TROUGH WILL CONTINUE MOVING OUT OF THE ROCKIES
AND INTO THE CENTRAL U.S. THIS PERIOD...ACCOMPANIED BY A BROAD ZONE
OF STRONG SWLY FLOW ON ITS SRN AND ERN FRINGES -- I.E. ACROSS THE
SRN PLAINS AND INTO THE MO VALLEY REGION.
A COMPLEX EVOLUTION OF THE SURFACE PATTERN IS PROGGED OVER THE
PLAINS...BUT AN OCCLUDING LOW IS FORECAST INVOF WRN KS DURING THE
LATE AFTERNOON AND EARLY EVENING. W OF A TRIPLE POINT PROGGED INVOF
SERN NEB/NERN KS AT 24/00Z...AN OCCLUDED FRONT SHOULD ARC WWD ACROSS
NEB...WHILE A WARM FRONT EXTENDS ESEWD ACROSS MO AND INTO THE MID
MS/LOWER OH VALLEYS. MEANWHILE...THE TRAILING COLD FRONT IS PROGGED
TO CROSS KS/OK/TX THROUGH THE DAY...APPROACHING MO/WRN AR/WRN LA
LATE IN THE PERIOD.
...MID MO/MID MS VALLEYS SWD INTO SRN AND ERN TX/LA/MS...
A COMPLEX BUT ACTIVE -- AND POTENTIALLY SIGNIFICANT -- SEVERE
WEATHER EVENT IS FORECAST ACROSS A LARGE PORTION OF THE CENTRAL AND
S CENTRAL U.S. AS THE LARGE/POWERFUL STORM SYSTEM AFFECTS THE
CENTRAL THIRD OF THE COUNTRY THIS PERIOD. WITH A LARGE WARM SECTOR
BECOMING INCREASINGLY MOIST/UNSTABLE THROUGH THE AFTERNOON...AND AN
EXPANSIVE AREA OF STRONG FLOW ALOFT/FAVORABLE DEEP-LAYER SHEAR...A
VERY BROAD AREA OF SEVERE POTENTIAL IS EVIDENT.
HAVING SAID THAT...SORTING OUT DETAILS IN TERMS OF TIMING AND
LOCATION OF GREATER SEVERE THREAT REMAINS DIFFICULT ATTM. THIS IS
DUE IN PART TO SHOWERS AND THUNDERSTORMS -- AND ASSOCIATED CLOUD
COVER -- WHICH SHOULD BE RELATIVELY WIDESPREAD ACROSS WRN PORTIONS
OF THE RISK AREA AT THE START OF THE PERIOD -- FOCUSED BOTH ALONG
THE WARM FRONT FROM NEB ESEWD INTO THE LOWER OH VALLEY...AND ALONG
THE COLD FRONT...EXTENDING FROM KS SWD INTO W CENTRAL TX. WITH
POTENTIAL FOR AFTERNOON DESTABILIZATION LIKELY AFFECTED BY THE
CLOUDS/PRECIPITATION ONGOING...AND WITH SOME QUESTIONS EVIDENT IN
MODEL TIMING/LOCATION OF THE LARGE-SCALE FEATURES...WILL REFRAIN
FROM AN UPGRADE TO MODERATE RISK THIS FORECAST.
HAVING SAID THAT...SUBSTANTIAL SEVERE POTENTIAL IS EVIDENT --
POSSIBLY CONCENTRATED WITHIN TWO SEPARATE AREAS.
THE FIRST AREA -- NEAR THE OCCLUDED FRONT/TRIPLE POINT/WARM FRONT
ZONE FROM NEB EWD ACROSS THE MID MO VALLEY INTO NRN MO/SRN IA --
APPEARS TO CONTAIN THE GREATEST TORNADO POTENTIAL THIS PERIOD.
HERE...VERY FAVORABLE SHEAR -- BOTH LOW-LEVEL AND DEEP-LAYER -- IS
EXPECTED. WHILE QUESTIONS REGARDING DESTABILIZATION
EXIST...INSTABILITY SHOULD BE SUFFICIENT TO FUEL A CONVECTIVE
INCREASE DURING THE AFTERNOON. GIVEN THE KINEMATIC
ENVIRONMENT...EXPECT SUPERCELLS -- INCLUDING THE THREAT FOR
TORNADOES...ONE OR TWO OF WHICH COULD BE SIGNIFICANT.
A SECOND AREA REMAINS MORE UNCERTAIN -- BUT POTENTIALLY
SIGNIFICANT...MAINLY WITH RESPECT TO VERY LARGE HAIL. THIS AREA --
ACROSS PARTS OF CENTRAL AND ERN TX AND INTO THE ARKLATEX -- SHOULD
DESTABILIZE MORE SUBSTANTIALLY THAN AREAS FARTHER N...GIVEN STEEP
MID-LEVEL LAPSE RATES AND THE LIKELIHOOD OF BEING FARTHER REMOVED
FROM ONGOING CLOUDS/PRECIPITATION. VERY FAVORABLE DEEP-LAYER SHEAR
IS PROGGED ACROSS THIS REGION...BUT CAPPING WILL REMAIN A LIMITING
FACTOR -- AT LEAST WELL INTO THE AFTERNOON. MODELS DO SUGGEST THAT
A SECONDARY UPPER FEATURE WILL SHIFT NEWD ACROSS THIS REGION
OVERNIGHT...WITH MODELS FORECASTING EVENING STORM DEVELOPMENT INVOF
THE FRONT ACROSS THIS REGION. ALONG WITH WIND AND POSSIBLY ISOLATED
TORNADO POTENTIAL...VERY LARGE HAIL WOULD BE LIKELY WITH STORMS
DEVELOPING OVER THIS AREA.
ONE OTHER AREA OF NOTE EXISTS FARTHER E -- INTO SRN MO/AR/LA AND
POSSIBLY ACROSS THE MS VALLEY INTO WRN TN/MS. IN THIS
AREA...IMPETUS FOR STORM INITIATION REMAINS UNCERTAIN/UNCLEAR.
HOWEVER...MODELS ALL FORECAST CONVECTIVE INITIATION DURING THE
AFTERNOON. GIVEN AMPLE MOISTURE/INSTABILITY EXPECTED OVER THIS
REGION AND FAVORABLE DEEP-LAYER SHEAR...ANY STORM COULD
ORGANIZE/BECOME SEVERE -- WITH THREATS FOR HAIL/WIND AND ISOLATED
TORNADOES THUS EVIDENT. HOWEVER...WILL MAINTAIN ONLY A CONDITIONAL
15% PROBABILITY IN THIS AREA GIVEN UNCERTAINTY REGARDING DEVELOPMENT
OF STORMS.
..GOSS.. 04/22/2010
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