SWODY2
SPC AC 120600
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SAT SEP 12 2009
VALID 131200Z - 141200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A PAIR OF UPPER LOWS -- ONE MOVING NNWWD ACROSS WY/MT AND A
SECOND/WEAKER ONE DRIFTING NNEWD ACROSS THE S CENTRAL U.S. -- WILL
BE THE PREDOMINANT FEATURES ACROSS THE CENTRAL 2/3 OF THE U.S. THIS
FORECAST. ELSEWHERE...A SHARP TROUGH SHOULD REACH THE W COAST LATE
IN THE PERIOD...WHILE A SECOND TROUGH MOVES SLOWLY NEWD/AWAY FROM
NEW ENGLAND THROUGH THE PERIOD.
AT THE SURFACE...A LOW IS FORECAST ACROSS E TX IN CONJUNCTION WITH
THE SRN-MOST UPPER LOW...WITH A WARM FRONT PROGGED TO LINGER FROM
THE LOW EWD/ESEWD ACROSS THE CENTRAL GULF COAST REGION.
ELSEWHERE...HIGH PRESSURE WILL PREVAIL ACROSS MUCH OF THE REST OF
THE U.S. E OF THE ROCKIES...WITH A BROAD AREA OF LOW PRESSURE FROM
THE PAC NW EWD INTO THE NRN INTERMOUNTAIN REGION AHEAD OF THE
APPROACHING WRN TROUGH...AND INVOF THE UPPER LOW SHIFTING NWD ACROSS
WY/MT.
...NRN HIGH PLAINS...
DESPITE THE FORECAST FOR A RELATIVELY COOL/DRY BOUNDARY
LAYER...MODEST AFTERNOON DESTABILIZATION IS FORECAST ACROSS THE NRN
HIGH PLAINS REGION -- AIDED BY THE NNWWD PASSAGE OF THE MID-LEVEL
LOW AND ASSOCIATED COLD POOL ALOFT. THIS SHOULD SUPPORT AFTERNOON
DEVELOPMENT OF SCATTERED SHOWERS AND STORMS...MAINLY OVER THE HIGHER
TERRAIN GIVEN A FORECAST LACK OF STRONG LOW-LEVEL CONVERGENCE ACROSS
THE HIGH PLAINS.
WITH A CURVED 40-PLUS KT MID-LEVEL JET AROUND THE SOUTH AND EAST
FRINGE OF THE UPPER LOW SHIFTING NWD ACROSS THE AREA ATOP LOW-LEVEL
SELYS...SHEAR SUPPORTIVE OF SUPERCELLS IS EXPECTED TO PERSIST
THROUGH THE AFTERNOON AND EVENING. WHILE THE OVERALL LACK OF
FAVORABLE INSTABILITY SHOULD LIMIT SEVERE POTENTIAL...A FEW
STRONGER/ROTATING STORMS CAPABLE OF PRODUCING HAIL/WIND WARRANT A
CONTINUATION OF LOW SEVERE PROBABILITIES ATTM.
...SERN TX INTO THE CENTRAL GULF COAST STATES/LOWER MS VALLEY...
RELATIVELY WIDESPREAD/PERSISTENT CONVECTION IS FORECAST ACROSS THE
CENTRAL GULF COAST REGION THIS PERIOD...AS THE LARGE UPPER LOW
DRIFTS SLOWLY NNEWD ACROSS THE S CENTRAL CONUS. WITH THIS LIKELY TO
LIMIT DESTABILIZATION ACROSS THE GULF COAST REGION...WIDESPREAD 500
J/KG MIXED-LAYER CAPE WILL BE POSSIBLE WITHIN THE WARM SECTOR --
AIDED BY A VERY MOIST BOUNDARY LAYER.
ATTM...MODELS SUGGEST THAT 25 TO 35 KT MID-LEVEL SWLYS WILL RESIDE
ACROSS THIS REGION...ON THE SERN PERIPHERY OF THE LOW. THIS SHOULD
RESULT IN FAVORABLE SHEAR FOR ORGANIZED/ROTATING STORMS --
PARTICULARLY NEAR AND N OF THE ROUGHLY W-E WARM FRONT...WHERE
LOW-LEVEL FLOW WILL REMAIN MORE BACKED/ESELY. WHILE LIMITED BY THE
OVERALL LACK OF INSTABILITY...SOME SEVERE POTENTIAL APPEARS EVIDENT
GIVEN THE FAVORABLY MOIST/SHEARED ENVIRONMENT. THUS...WILL
INTRODUCE 5% SEVERE PROBABILITY ACROSS THIS REGION...WHERE LOCALLY
GUSTY WINDS OR EVEN AN ISOLATED TORNADO WILL BE POSSIBLE WITH A
COUPLE OF THE LONGER-LIVED STORMS.
..GOSS.. 09/12/2009
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