SWODY1
SPC AC 291259
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 AM CDT FRI MAY 29 2009
VALID 291300Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MID AND S
ATLANTIC COAST...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE MID/LWR MO
AND MID MS VLYS...
...SYNOPSIS...
A COMPLEX WRN RIDGE/ERN TROUGH PATTERN WILL PREVAIL THIS PERIOD...
WITH SLIGHT AMPLIFICATION. LEAD PORTION OF ERN TROUGH NOW EXTENDS
FROM THE LWR GRT LKS SW INTO A VORT MAX ERN AR. THE NRN PART OF
THIS LEAD DISTURBANCE SHOULD REACH THE LWR HUDSON VLY BY EVE...WHILE
THE AR VORT PROGRESSES MORE SLOWLY INTO AL. AT THE SAME
TIME...UPSTREAM IMPULSE NOW OVER UPR MI EXPECTED TO AMPLIFY SE
TOWARD WRN NY/PA AS DISTURBANCE NOW IN CNTRL SK CONTINUES SE INTO
MN. ON THE SW FRINGE OF RCKYS/NRN GRT BASIN RIDGE...A WEAK UPR LOW
WILL PERSIST OVER THE LWR CO VLY.
AT LWR LVLS...FRACTURED CDFNT SHOULD REACH THE MID ATLANTIC CST BY
EVE...WHILE SRN PART OF BOUNDARY MOVES MORE SLOWLY ACROSS THE S
ATLANTIC PIEDMONT/CSTL PLN. FARTHER NW...SECONDARY CDFNT NOW OVER
MI AND THE UPR MS VLY SHOULD CONTINUE SE INTO THE LWR GRT LKS/OH VLY
THIS EVE AS A STRONGER FRONT NOW EVOLVING OVER SK/MB ACCELERATES SE
INTO NRN ND THIS EVE...AND ACROSS THE UPR MS VLY TONIGHT/EARLY SAT.
...MID-ATLANTIC/SERN STATES...
PLUME OF 1.5+ INCH PW WILL CONTINUE TO SPREAD NE ALONG THE ERN
SEABOARD FROM FL INTO ERN PA/NJ AHEAD OF LEAD DISTURBANCE ASSOCIATED
BROAD ERN TROUGH. COUPLED WITH SFC HEATING AND RELATIVELY COOL MID
LVL TEMPERATURES...EXPECT MODERATE INSTABILITY WILL DEVELOP. AFTN
SBCAPE SHOULD RANGE FROM 1000 J/KG IN NRN NJ TO AROUND 2500 J/KG S
OF WEAK WARM FRONT NOW OVER THE NRN DELMARVA
PENINSULA.
TSTMS SHOULD FORM ALONG CDFNT AND THE HIGHER TERRAIN FROM SRN PA SWD
INTO MD/VA NC. OTHER STORMS SHOULD FORM ALONG ERN-MOST FRACTURED
FRONT FROM TIDEWATER VA SW INTO ERN GA/N FL. WITH MODEST DEEP
UNIDIRECTIONAL WSW FLOW OVER THE ENTIRE REGION...SETUP SHOULD YIELD
SCTD STG TO SVR MULTICELL CLUSTERS/LINES CAPABLE OF LOCALLY DMGG
WIND/SVR HAIL. MOST STRONGER ACTIVITY WILL WEAKEN DURING THE
EVE...BUT ISOLD SVR STORMS MAY PERSIST OVER THE CSTL SECTIONS OF THE
CAROLINAS INTO THE NIGHT AS CONTINUED EWD ADVANCE OF AR-AL VORT
ENHANCES UVV ACROSS REGION.
...NRN PLNS/UPR MS VLY SE INTO LWR MO/MID MS VLYS...
AFOREMENTIONED SECONDARY CDFNT MAY BE THE FOCUS OF SCTD AFTN/EVE
STORMS FROM SRN MI/NR OH W INTO PARTS OF IND/IL AND MO LATER TODAY.
LOW LVL MOISTURE WILL BE LIMITED. BUT LOW-MID 50S F SFC DEW POINTS
BENEATH MID LVL TEMPERATURE GRADIENT ASSOCIATED WITH UPR MI UPR
IMPULSE WILL YIELD 1500-2000 J/KG SBCAPE NEAR FRONT FROM CNTRL IL
INTO NRN MO/SRN IA. ALTHOUGH WEAK LOW LVL CONVERGENCE WILL LIMIT
COVERAGE...ISOLD/WDLY SCTD STORMS THAT DO FORM MAY EVOLVE INTO
SHORT...FAST-MOVING LINES. EMBEDDED ROTATING STRUCTURES BENEATH
INCREASING WNW UPR FLOW COULD YIELD DMGG WIND/SVR HAIL. MORE ISOLD
STG-BRIEFLY SVR TSTMS MAY OCCUR FARTHER E FROM CNTRL INTO SE MI/NW
OH WHERE BUOYANCY WILL BE LESS...BUT UVV WILL INCREASE WITH SE
MOTION OF UPR MI IMPULSE.
MEANWHILE...FARTHER NW...STRONG HEATING WILL OCCUR OVER THE NRN
PLNS/UPR MS VLY IN AREA OF WAA/DPVA AHEAD OF UPSTREAM IMPULSE
ACCELERATING SE FROM CANADA. SPARSE MOISTURE WILL LIMIT
INSTABILITY...BUT A CORRIDOR OF 1500 J/KG SBCAPE MAY DEVELOP FROM
CNTRL NEB INTO SCNTRL SD....WITH LESSER VALUES NWD INTO ERN ND/NRN
MN. ACROSS THE REGION WEAK S/SELY LOW LVL WINDS WILL EXIST BENEATH
WNW FLOW ALOFT...BOOSTING DEEP SHEAR TO AOA 50 KTS. COUPLED WITH
STEEP LOW TO MID LVL LAPSE RATES...SETUP COULD YIELD A FEW
RELATIVELY HI-BASED SUPERCELLS WITH LARGE HAIL IN NEB/SRN SD BY LATE
AFTN. OTHER ISOLD SVR STORMS /LARGE HAIL/ COULD OCCUR FARTHER N
ACROSS PARTS OF ND AND NRN MN ALONG CDFNT. THERE... MID-LVL
TEMPERATURES AROUND MINUS 20 C WILL COMPENSATE FOR LOWER SFC
MOISTURE AVAILABILITY.
TONIGHT...A SMALL CLUSTER OR TWO MAY EVOLVE ALONG STRENGTHENING
WSWLY LLJ INVOF STALLING FRONT FROM ERN NEB ESE INTO NRN MO/WRN IL.
HAIL/HIGH WIND MAY ACCOMPANY A FEW OF THE STORMS...ESPECIALLY IN NRN
MO.
...SW/S CNTRL TX...
CONVECTION OVER REGION YESTERDAY...AND GENERAL PATTERN OF LOW LVL
RIDGING...WILL FURTHER WEAKEN OLD FRONTAL ZONE OVER S TX TODAY.
NEVERTHELESS...COMBINATION OF WEAKLY CONFLUENT AND PERSISTENT LOW
LVL ELY /UPSLOPE/ FLOW BENEATH ENHANCED HI-LVL WLY FLOW ON NRN
FRINGE OF SUBTROPICAL JET LIKELY WILL SUPPORT DEVELOPMENT OF SCTD
STG AFTN/EVE STORMS OVER SW TX AND THE MOUNTAINS OF N CNTRL MEX W OF
THE RIO GRANDE. WITH SBCAPE OF 1500-2000 J/KG...A FEW MULTICELL
CLUSTERS/BRIEF SUPERCELLS COULD OCCUR POSING A RISK FOR ISOLD LARGE
HAIL/GUSTY WINDS. STORM COVERAGE SHOULD...HOWEVER... BE REDUCED
OVER S TX RELATIVE TO PREVIOUS DAYS.
...CNTRL/NRN CA INTO ORE/ID...
SLIGHTLY STRONGER MID/UPR LVL FLOW IS EXPECTED OVER THIS REGION
TODAY AS GRADIENT STRENGTHENS ON N SIDE OF LWR CO VLY UPR LOW.
SATELLITE AND GPS DATA SHOW PW OVER CA/ORE NOW AVERAGING AROUND .75
INCH...SUPPORTING SOMEWHAT GREATER INSTABILITY THAN IN RECENT DAYS.
COMBINATION OF INCREASED INSTABILITY WITH MODEST...
UNIDIRECTIONAL...DEEP SSE TO SSW FLOW MAY SUPPORT A FEW
FORWARD-PROPAGATING STORM CLUSTERS. THIS ACTIVITY APPEARS TO BE
MOST LIKELY FROM THE NRN CA SIERRA TO THE ERN SLOPES OF THE ORE
CASCADES. A SMALL CLUSTER OR TWO MAY ALSO PROPAGATE WNW ACROSS
CNTRL/NRN PARTS OF THE SACRAMENTO VLY. THE STORMS WILL POSE AN
ISOLD RISK FOR SVR HAIL/DMGG WIND THROUGH EARLY TONIGHT.
..CORFIDI/GARNER.. 05/29/2009
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