SWODY1
SPC AC 301256
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT SAT MAY 30 2009
VALID 301300Z - 311200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE LWR OH VLY...
...SYNOPSIS...
POLAR VORT NOW OVER NW ONTARIO EXPECTED TO CONTINUE SE TO NEAR
GEORGIAN BAY THIS PERIOD AS BROADER TROUGH PERSISTS SWD ACROSS THE
ERN THIRD OF THE U.S. ELSEWHERE...WEAK UPR LOW WILL LINGER OVER THE
LWR CO VLY...AS WILL RIDGE OVER THE RCKYS.
AT LWR LVLS...COLD FRONT NOW OVER THE UPR MS VLY SHOULD ACCELERATE
SE ACROSS THE UPR GRT LKS/MID MS VLY BY THIS EVE. AHEAD OF THE
FRONT...PORTION OF WEAKENING BOUNDARY NOW OVER THE MID MS/LWR OH VLY
REGION SHOULD ADVANCE ENEWD AS A WEAK WARM FRONT.
...MID-MS AND OH VLYS...
ELEVATED STORMS NOW OVER MO/IA SHOULD CONTINUE ESE INTO THE LWR OH
VLY LATER TODAY. ADDITIONAL STORMS...MORE-NEARLY SFC-BASED...SHOULD
FORM AHEAD OF THIS ACTIVITY OVER SRN IL AND WRN KY THIS AFTN AS LOW
LVL WAA STRENGTHENS AHEAD OF WEAK IMPULSE MOVING SE FROM WI/IA.
AIR MASS INVOF WEAKENING FRONT OVER THE REGION WILL BECOME MODESTLY
UNSTABLE GIVEN UPR 50S F SFC DEW POINTS...STRONG HEATING AND
SEASONABLY COOL AIR ALOFT. COUPLED WITH 40+ KT DEEP NWLY
SHEAR...STORMS COULD BECOME ORGANIZED INTO SMALL...FORWARD-
PROPAGATING MULTICELLULAR CLUSTERS/BANDS...PERHAPS WITH
SPORADIC/EMBEDDED SUPERCELL STRUCTURES. THIS WILL ESPECIALLY BE
TRUE NEAR THE OH RVR IN SRN IND/NRN-CNTRL KY...WHERE LOW TO MID LVL
DIRECTIONAL SHEAR SHOULD BE GREATEST. STORMS COULD YIELD SVR
HAIL/WIND AND POSSIBLY A BRIEF TORNADO OR TWO. THE CONVECTION
SHOULD MOVE RAPIDLY ESE AND WEAKEN OVER THE WRN SLOPES OF THE
APPALACHIANS BY EVE.
...NRN/ERN LWR MI TO LKS ERIE/ONTARIO...
SRN EDGE OF FAST FLOW SKIRTING THE ONTARIO POLAR VORT WILL
OVERSPREAD THE CNTRL GRT LKS THIS AFTN. COMBINATION OF 70-80 KT
NWLY MID LVL WINDS AND COLD 500 MB TEMPERATURES ATOP MODEST LOW LVL
LAPSE RATES MAY YIELD A BKN BAND OF LOW-TOPPED TSTMS FROM E CNTRL
ONTARIO SWWD INTO NRN/ERN LWR MI BY MID AFTN. ALTHOUGH MOISTURE
WILL REMAIN LIMITED...SUFFICIENT BUOYANCY LIKELY WILL EXIST FOR
ISOLD MARGINALLY SVR HAIL AND GUSTY WINDS. SOME OF THIS ACTIVITY
MAY SURVIVE IN A DIMINISHED STATE E/ESE TOWARD LKS ERIE AND ONTARIO
THIS EVE/TONIGHT.
...S FL...
STRONG HEATING WILL OCCUR AHEAD OF REMNANT COLD FRONTAL SEGMENT
CROSSING N CNTRL FL ATTM. VERY MOIST PRE-FRONTAL AIR AND MODEST
...LARGELY UNIDIRECTIONAL WLY FLOW SHOULD SUPPORT DEVELOPMENT OF
STRONG TSTM CLUSTERS/LINES ALONG AND AHEAD OF FRONT. THESE WILL
HAVE THE POTENTIAL TO PRODUCE ISOLD DMGG WIND GUSTS...ESPECIALLY S
OF A FMY-VRB LINE.
...ORE/NRN ID...
ANOTHER ROUND OF SCTD STRONG DIURNAL STORM CLUSTERS EXPECTED OVER
THE ORE CASCADES...SISKIYOUS...BLUES AND WALLOWAS MOUNTAINS TODAY.
REGION WILL REMAIN IN AREA OF ENHANCED FLOW BETWEEN LWR CO VLY UPR
LOW AND AN IMPULSE CROSSING SRN BC. SETUP MAY RESULT IN
MULTICELL/BRIEF SUPERCELL STRUCTURES WITH ISOLD LARGE HAIL AND DMGG
WINDS.
..CORFIDI/GARNER.. 05/30/2009
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