SWODY1
SPC AC 311257
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 AM CDT SUN MAY 31 2009
VALID 311300Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN-CNTRL PLNS AND UPR
MS VLY...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF NEW ENGLAND...
...SYNOPSIS...
THE WLYS WILL REMAIN CONFINED TO THE FAR NRN TIER OF STATES AND NEW
ENGLAND THIS PERIOD AS A REX BLOCK EVOLVES OFF THE PACIFIC CST AND
LWR CO VLY UPR LOW DRIFTS E TO NEAR THE FOUR CORNERS. POLAR VORT
NOW N OF GEORGIAN BAY SHOULD CONTINUE ESE TO NEAR MONTREAL THIS EVE
...BEFORE TURNING MORE E ACROSS NRN ME/NB EARLY MON. IN THE
WLYS...AN IMPULSE NOW OVER SRN MB WILL MOVE ESE INTO NRN MN/WRN ONT
BY THIS EVE...WHILE UPSTREAM DISTURBANCE OVER NRN AB SHEARS SE
ACROSS CNTRL/SRN PORTIONS OF AB AND SK.
AT THE SFC...A CDFNT WILL CONTINUE SE ACROSS THE NERN AND MID
ATLANTIC STATES TODAY/EARLY TONIGHT. THE SAME BOUNDARY WILL BECOME
DIFFUSE/QSTNRY OVER THE TN VLY...WHILE WRN PART /NOW OVER KS/
REDEVELOPS N TO MERGE WITH WRMFNT/SFC LOW ALREADY PRESENT OVER THE
ERN DAKOTAS. THE DAKOTAS LOW AND ITS ASSOCIATED CDFNT SHOULD MOVE
GENERALLY ESE THROUGH THE PERIOD...WITH A PREFRONTAL TROUGH/WIND
SHIFT EXTENDING SW INTO THE CNTRL HI PLNS.
...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.
TONIGHT...AS UPR IMPULSE CONTINUES ESEWD AND ASSOCIATED LLJ VEERS
AND SOMEWHAT STRENGTHENS...EXPECT WAA WILL FOCUS MODEST
WARMTH/MOISTURE ADVECTION FARTHER ENE INTO SE MN/NRN IA AND SRN
WI/NRN IL. THUS...THE PLNS STORMS COULD EVOLVE INTO ONE OR TWO
SMALL MCSS THAT MOVE/DEVELOP GENERALLY ESE TOWARD/INTO THE MID/UPR
MS VLY. THE STORMS LIKELY WILL BE INCREASINGLY ELEVATED WITH EWD
EXTENT...AND SPARSE MOISTURE WILL KEEP BUOYANCY LIMITED.
NEVERTHELESS...STRENGTH AND UNIDIRECTIONAL NATURE OF WIND FIELD WILL
BE FAVORABLE FOR FORWARD-PROPAGATING SEGMENTS. THESE MAY YIELD
STRONG WINDS IN ADDITION TO MARGINALLY SVR HAIL.
...NRN/CNTRL NEW ENGLAND...
UNUSUALLY STRONG LARGE SCALE FORCING FOR ASCENT /150 M HEIGHT FALLS/
WILL OVERSPREAD UPSTATE NY AND NRN/CNTRL NEW ENGLAND TODAY AHEAD OF
AFOREMENTIONED POLAR VORT. 500 MB TEMPERATURES AOB MINUS 20 DEG C
ATOP UPR 40S/LWR 50S SFC DEW POINTS AND DEEP/STRONG CYCLONIC FLOW
SHOULD SUPPORT TSTM DEVELOPMENT BY EARLY AFTN. GIVEN STRONG
FRONTOGENETIC FORCING...STEEPENING LOW LVL LAPSE RATES WITH GOOD SFC
HEATING...AND STRENGTH OF MEAN WIND FIELD... SETUP COULD YIELD A
BAND OF LOW-TOPPED...FORWARD-PROPAGATING STORMS. EMBEDDED BOWING
SEGMENTS IN THE BAND WILL BE CAPABLE OF DMGG SFC WINDS AND POSSIBLY
MARGINALLY SVR HAIL.
...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 TSTMS
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.
..CORFIDI/GARNER.. 05/31/2009
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