SWODY1
SPC AC 181951
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT FRI MAR 18 2011
VALID 182000Z - 191200Z
...NO SVR TSTM AREAS FORECAST...
--- UPDATES ---
...MO/IL...
ADJUSTMENTS MADE TO BACK EDGE OF GEN TSTM AREA OVER PORTIONS MO/IL
GIVEN CONVECTIVE TRENDS...WITH PRIMARY/ELEVATED BAND MOVING E/SE OF
AREA...AND ADDITIONAL POSTFRONTAL CONVECTION NOT ANTICIPATED BEFORE
END OF PERIOD. ERN PORTIONS OF THIS REGIME AND/OR MORE ISOLATED
CONVECTION TO ITS E MAY SHIFT EWD AND YIELD MRGL THUNDER POTENTIAL
ACROSS PORTIONS WV AND SRN OH BEFORE WEAKENING.
...CENTRAL/NRN CA COAST...
GUSTS APCHG SVR LIMITS AND CAPABLE OF MINOR DMG MAY AFFECT PORTIONS
MRY BAY REGION OF CA FOR ANOTHER 1-2 HOURS...AS BAND OF MOSTLY
LOW-TOPPED CONVECTION MOVES ASHORE. ACTIVITY SHOULD WEAKEN RAPIDLY
AS IT MOVES INLAND...AWAY FROM SUPPORTIVE MARINE AIR AND INTO REGIME
OF LOWER THETAE/BUOYANCY. UNCONDITIONAL SVR POTENTIAL APPEARS TO BE
TOO SMALL/ISOLATED FOR AOA 5% PROBABILITIES.
...SW TX...
INTENSE CAPPING OVER MOST OF SRN PLAINS SHOULD SUPPRESS DIURNAL DEEP
CONVECTION S OF FRONTAL ZONE...HOWEVER VERY BRIEF/ISOLATED THUNDER
CANNOT BE RULED OUT WITH CONVECTION OVER DAVIS MOUNTAINS/BIG BEND
REGION...WHERE SEVERAL TCU AND STRUGGLING/IMMATURE CB NOW ARE
EVIDENT IN VIS IMAGERY. VERY DRY AIR MASS IN LOW LEVELS WILL KEEP
BUOYANCY MINIMAL...THOUGH MOISTURE MAY INCREASE BEFORE SUNSET WITH
ADVECTION FROM AREA OF HIGHER DEW POINTS NOW OBSERVED AROUND 6R6.
OROGRAPHIC LIFT AND HEATING OF HIGHER TERRAIN WILL REMAIN PRIMARY
ASCENT FOCI.
..EDWARDS.. 03/18/2011
.PREV DISCUSSION... /ISSUED 1121 AM CDT FRI MAR 18 2011/
THE LARGE UPPER LOW OFF THE PACIFIC NORTHWEST COAST WILL CONTINUE TO
DIG SLOWLY SOUTHWARD DURING THIS FORECAST PERIOD...WHILE A WEAK
UPPER RIDGE BUILDS ACROSS THE CENTRAL STATES. THE RESULT WILL BE A
RELATIVELY BENIGN PATTERN FOR THUNDERSTORMS. A FEW AREAS WILL HAVE
A LOW-END RISK OF STRONG STORMS LATER TODAY AND TONIGHT...BUT
ORGANIZED SEVERE STORMS ARE NOT ANTICIPATED.
...MID MS AND LOWER OH VALLEYS...
A CLUSTER OF ELEVATED THUNDERSTORMS OVER MO/IL WILL CONTINUE TO MOVE
EASTWARD TODAY AND SLOWLY WEAKEN. SMALL HAIL HAS BEEN REPORTED IN
THE STRONGEST CORES...BUT VERY LIMITED INSTABILITY SHOULD GREATLY
LIMIT THE SEVERE THREAT. LATER THIS AFTERNOON...SUFFICIENT HEATING
IN THE VICINITY OF THE SURFACE WARM FRONT MAY RESULT IN ISOLATED
THUNDERSTORMS OVER SOUTHERN MO/NORTHERN AR. MOST OF THE ACTIVITY IS
LIKELY TO BE ELEVATED JUST NORTH OF THE SURFACE FRONT.
HOWEVER...STEEP MID LEVEL LAPSE RATES AND SUFFICIENT VERTICAL SHEAR
MAY POSE A RISK OF A FEW STRONG STORMS CAPABLE OF HAIL THROUGH THE
EVENING. CONVECTION MAY SPREAD EASTWARD OVERNIGHT INTO THE LOWER OH
VALLEY WITH A MINIMAL RISK OF GUSTY WINDS IN THE STRONGER STORMS.
...WEST-CENTRAL TX...
A SURFACE COLD FRONT IS SAGGING SOUTHWARD TODAY INTO WESTERN NORTH
TX...AND SHOULD LIE FROM NEAR MAF TO WEST OF FTW BY LATE AFTERNOON.
SOUTHERLY LOW LEVEL WINDS SOUTH OF THE FRONT WILL HELP TO MAINTAIN
50S TO LOWER 60S SURFACE DEWPOINTS AND A MARGINALLY UNSTABLE AIR
MASS. FORECAST SOUNDINGS SHOW A STOUT CAP OVER THE WARM
SECTOR...WHICH SHOULD SUPPRESS THUNDERSTORMS SOUTH OF THE FRONT.
HOWEVER...LIFT ALONG AND JUST NORTH OF THE FRONT MAY BE SUFFICIENT
FOR A FEW STRONG THUNDERSTORMS CAPABLE OF HAIL. MOST MESOSCALE AND
12Z OPERATIONAL MODELS HAVE NOW CONVERGED ON THIS SOLUTION. WILL
MAINTAIN ONLY LOW SEVERE PROBABILITIES DUE TO RATHER WEAK VERTICAL
SHEAR AND LACK OF CERTAINTY ON COVERAGE OF SEVERE STORMS.
...TX PANHANDLE AND NORTHWEST OK...
HAVE OPTED TO MAINTAIN LOW SEVERE PROBABILITIES OVER THIS REGION FOR
LATE TONIGHT AS LOW LEVEL WARM ADVECTION AND LIFT HELP IN THE
DEVELOPMENT OF SCATTERED SHOWERS AND THUNDERSTORMS. FORECAST
SOUNDINGS APPEAR TO SUPPORT SOME RISK OF HAIL IN THE STRONGER
CORES...BUT CONSIDERABLE UNCERTAINTY EXISTS WHETHER HAIL COULD REACH
SEVERE LIMITS.
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