Thursday, September 10, 2009

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 101248
SWODY1
SPC AC 101244

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0744 AM CDT THU SEP 10 2009

VALID 101300Z - 111200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS EVENING INTO TONIGHT FOR
THE NRN PLAINS...

...NRN PLAINS THIS EVENING INTO TONIGHT...
A PRONOUNCED NRN STREAM MID LEVEL TROUGH OVER ALBERTA THIS MORNING
WILL DIG SEWD OVER NRN MT TODAY AND REACH THE DAKOTAS
OVERNIGHT...ACCOMPANIED BY A SURFACE COLD FRONT. MEANWHILE...THE
BAROCLINIC ZONE IN THE WAKE OF THE PREVIOUS MID LEVEL TROUGH IS NOW
LIFTING NWD FROM SD TOWARD CENTRAL/ERN ND. CONTINUED NWD ADVECTION
OF BOUNDARY LAYER DEWPOINTS IN THE LOW 60S BENEATH STEEP MID LEVEL
LAPSE RATES...IN CONJUNCTION WITH DAYTIME HEATING...WILL SUPPORT
LATE AFTERNOON MLCAPE VALUES OF 1500-2500 J/KG.

THUNDERSTORM DEVELOPMENT IS EXPECTED THIS EVENING AND WILL CONTINUE
OVERNIGHT ALONG THE COLD FRONT MOVING SEWD FROM ERN MT INTO THE WRN
DAKOTAS...IN PHASE WITH THE BELT OF LOW-MID LEVEL ASCENT DOWNSTREAM
FROM THE MID LEVEL TROUGH. THE MODERATE WARM SECTOR INSTABILITY AND
MODEST VERTICAL SHEAR ALONG THE FRONT WILL SUPPORT ORGANIZED
MULTICELL CLUSTERS...ALONG WITH SOME POTENTIAL FOR EMBEDDED BOW
AND/OR MARGINAL SUPERCELL STRUCTURES IN A BROKEN BAND ALONG THE
FRONT. LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY SEVERE
THREATS THIS EVENING INTO TONIGHT.

...MID ATLANTIC COAST THIS EVENING INTO TONIGHT...
SEVERAL MID LEVEL VORTICITY CENTERS CONTINUE TO ROTATE AROUND THE
WEAK OH VALLEY-MID ATLANTIC LOW. SHORT TERM MODEL FORECASTS ARE
REASONABLY CONSISTENT IN SUGGESTING THAT THE OFFSHORE FRONTAL WAVE
WILL MOVE NWWD TO NEAR THE MID ATLANTIC COAST LATE TODAY AND
TONIGHT. THIS WILL RESULT IN A TENDENCY FOR LOW-LEVEL
MOISTENING/DESTABILIZATION NEAR THE COAST...AND AT LEAST SOME
POTENTIAL FOR ROTATING STORMS WITH WEAK SURFACE-BASED INSTABILITY
AND STRONG LOW-LEVEL SHEAR NEAR AND JUST N OF THE SURFACE LOW.
STILL...THE INLAND PROGRESSION OF THE UNSTABLE WARM SECTOR IS NOT
CERTAIN...THUS WILL MAINTAIN ONLY LOW TORNADO PROBABILITIES.

...NW GULF COAST THROUGH TONIGHT...
THUNDERSTORM COVERAGE IS EXPECTED TO INCREASE TODAY THE TX COASTAL
PLAINS AND NW GULF OF MEXICO...NEAR A SURFACE TROUGH AND DOWNSTREAM
FROM A WEAK UPPER TROUGH MOVING EWD FROM NRN MEXICO. WEAK MEAN FLOW
AND PW VALUES OF 2.25-2.50 INCHES WILL SUPPORT LOCALLY HEAVY
RAINFALL RATES WITH THESE STORMS...BUT THE SEVERE STORM THREAT WILL
REMAIN NEGLIGIBLE.

...AZ/NM THIS AFTERNOON/EVENING...
SCATTERED DIURNAL STORMS WILL OCCUR AGAIN...MAINLY OVER THE HIGHER
TERRAIN OF WRN NM INTO NE AZ. THUNDERSTORMS WILL BE SUPPORTED BY
DAYTIME HEATING...A ROUGHLY 0.25 INCH INCREASE IN PW VALUES DURING
THE PAST 24 HOURS...AND WEAK ASCENT WITH A SUBTLE MID LEVEL TROUGH
OVER AZ.

..THOMPSON/GARNER.. 09/10/2009

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.

No comments: