SWODY1
SPC AC 312016
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0316 PM CDT SUN MAY 31 2009
VALID 312000Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
PLAINS...NRN PLAINS AND UPPER MIDWEST...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF NE MAINE...
CORRECTED FOR WORDING
THE FIRST CHANGE TO THE OUTLOOK IS TO ADJUST THE SLIGHT RISK IN THE
NCNTRL STATES. PULLED THE SLIGHT RISK BACK WEST TO NEAR RAPID CITY
FOR THE ISOLATED SEVERE STORMS DEVELOPING IN THE BLACK HILLS. THIS
ACTIVITY SHOULD CONTINUE SEWD INTO INCREASING INSTABILITY NEAR THE
SD-NEB STATE-LINE. SECOND...MOVED THE SLIGHT RISK AREA NWD INTO FAR
SERN ND AND ACROSS PARTS OF WCNTRL MN WHERE CONVECTION IS DEVELOPING
IN A MODERATELY UNSTABLE AND ADEQUATELY SHEARED ENVIRONMENT.
ALSO...TRIMMED THE SLIGHT RISK AREA IN FAR ERN IA AND NW IL WHERE
INSTABILITY WILL BE QUITE WEAK AFTER MIDNIGHT WHEN AN MCS OR
CONVECTIVE CLUSTER IS FORECAST TO MOVE INTO THAT AREA. THE THIRD
CHANGE TO THE OUTLOOK IS TO CONFINE THE SLIGHT RISK AREA TO
NORTHEAST MAINE AHEAD OF A STRONG CONVECTIVE LINE. THE LAST CHANGE
TO THE OUTLOOK WAS TO ADJUST THE 5 PERCENT WIND AND HAIL
PROBABILITIES IN WEST TX TO BETTER CONFORM TO THE AREA OF MODERATE
INSTABILITY ANALYZED BY THE RUC.
..BROYLES.. 05/31/2009
.PREV DISCUSSION... /ISSUED 1109 AM CDT SUN MAY 31 2009/
...NEW ENGLAND...
VIGOROUS POLAR VORTEX CROSSING SRN QUEBEC THIS AFTERNOON AND MAINE
EARLY TONIGHT WILL PUSH A COLD FRONT ACROSS NEW ENGLAND PRIOR TO
SUNSET. FRONT CURRENTLY EXTENDS SSWWD FROM NEAR BTV THRU ERN PA.
MOISTURE/INSTABILITY IN ADVANCE OF THE FRONT IS QUITE MEAGER AS
DEWPOINTS ARE GENERALLY LESS THAN 50F. HOWEVER WITH SOME HEATING
AND COOL STEEP LAPSE RATES...SBCAPES FROM 300-500 J/KG HAVE
DEVELOPED ACROSS MUCH OF ME. AT 16Z CINH WAS ABOUT GONE WITH
DEVELOPMENT OF LOW TOPPED CONVECTION ACROSS NRN ME. WILL CONTINUE A
LOW END SLIGHT RISK ACROSS MUCH OF ME THIS AFTERNOON AS STRONG/BRIEF
DAMAGING WINDS WILL BE POSSIBLE WITH STRONGER UPDRAFTS ALONG AND
AHEAD OF COLD FRONT AS DEEP LAYER SHEAR RAMPS UP AS 90-100KT 500MB
JET TRAVERSES SRN ENGLAND. ALSO GIVEN THE COOL LAPSE RATES...HAIL
WILL BE ASSOCIATED WITH MOST STRONGER UPDRAFTS.
...NRN-CNTRL PLNS/UPR MS VLY...
LATEST SFC AND SATELLITE/PW DATA SUGGEST THAT MOISTURE WILL REMAIN
QUITE SPARSE BY LATE MAY STANDARDS IN WARM SECTOR OVER THE NRN
PLNS/UPR MS VLY. BUT WITH STRONG HEATING...MID-LVL LAPSE RATES AOA
7 DEG C/KM...LOW/MID 50S SFC DEW POINTS SHOULD YIELD SBCAPE OF
1000-2000 J/KG OVER PARTS OF SD/WRN MN/NEB AND WRN IA BY LATE IN THE
DAY.
PERSISTENT CONVERGENCE NEAR SFC TRIPLE POINT/WRMFNT AND GLANCING
INFLUENCE OF LEAD IMPULSE CROSSING SRN MB/NRN MN...SHOULD SUPPORT
WDLY SCTD HIGH-BASED TSTM DEVELOPMENT OVER CNTRL/ERN SD AND PERHAPS
WRN MN/SE ND. OTHER STORMS MAY FORM SW ALONG PRE-FRONTAL TROUGH
ACROSS CNTRL NEB INTO NE CO.
SUFFICIENT DEEP SPEED AND DIRECTIONAL SHEAR /20-25 KT SWLY LOW LVL
FLOW VEERING TO 30-40 KT WNW FLOW AT 500 MB/ WILL BE PRESENT FOR
SUPERCELLS WITH LARGE HAIL AND...GIVEN SIZABLE TEMP-DEW POINT
SPREADS...HIGH WIND.
WARM ADVECTION ON THE STRENGTHENING LOW LEVEL JET THIS EVENING WILL
SUPPORT THE DEVELOPMENT OF AN MCS MOVING EWD ACROSS IA. PRIMARILY A
WIND DAMAGE THREAT WILL ACCOMPANY ANY MCS.
...W TX AND EXTREME SE NM...
WEAK HEIGHT FALLS OVER THE SRN RCKYS ASSOCIATED WITH LWR CO VLY UPR
LOW WILL INDUCE A MODEST SELY LOW LVL FLOW ACROSS SW TX. SFC DEW
POINTS WILL LIKELY MIX INTO THE 50S DURING THE AFTN...DESPITE
PRESENCE OF FAIRLY SUBSTANTIAL MOISTURE /PW TO 1.25 INCHES/ OVER THE
LWR RIO GRANDE. BUT PERSISTENT UPSLOPE FLOW...DIFFERENTIAL
HEATING...AND WEAK FORCING ALOFT LIKELY WILL YIELD HIGH-BASED STORMS
OVER THE TRANSPECOS REGION INTO SE NM BY MID/LATE AFTN. 30 KT DEEP
WNWLY SHEAR MAY PROVE SUFFICIENT FOR A FEW ORGANIZED/ SUSTAINED
STORMS WITH LARGE HAIL/LOCALLY STRONG WINDS.
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