SWODY3
SPC AC 300730
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 AM CDT WED JUL 30 2008
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FRI ACROSS PARTS OF THE UPR MS
VLY....
...THERE IS A SLGT RISK OF SVR TSTMS LATE FRI AFTN/FRI NIGHT ACROSS
PARTS OF THE NRN PLAINS....
...SYNOPSIS...
BOUNDARY LAYER MOISTURE CONTENT IS EXPECTED TO REMAIN HIGH ACROSS
THE MID MISSOURI AND UPPER MISSISSIPPI VALLEY REGION INTO FRIDAY/
FRIDAY NIGHT...NEAR THE NORTHEASTERN PERIPHERY OF A SUBTROPICAL
RIDGE...WHICH IS PROGGED TO EXPAND NORTHWARD/EASTWARD OUT OF THE
FOUR CORNERS REGION. IN ASSOCIATION WITH THE EVOLVING UPPER
PATTERN...A VERY WARM ELEVATED MIXED LAYER APPEARS LIKELY TO ADVECT
OUT OF THE GREAT BASIN...CONTRIBUTING TO INCREASING INHIBITION
THROUGH MUCH OF THE CENTRAL/NORTHERN PLAINS AND UPPER HALF OF THE
MISSISSIPPI VALLEY. BY 12Z FRIDAY...THE EDGE OF THE STRONGER CAP
MAY EXTEND FROM SOUTHWESTERN NORTH DAKOTA THROUGH NORTHEAST SOUTH
DAKOTA AND SOUTHERN MINNESOTA INTO EASTERN IOWA. THIS SHOULD
PROVIDE THE FOCUS FOR THE COUPLING OF STRONGEST INSTABILITY AND
WEAKEST INHIBITION IN THE PRESENCE OF STRONG DEEP LAYER SHEAR ON THE
SOUTHERN FRINGE OF THE WESTERLIES. BUT...THE LIKELY TENDENCY FOR
THIS STRONGER CAPPING TO CONTINUE TO SPREAD NORTHEASTWARD THROUGH
THE PERIOD CONTRIBUTES TO UNCERTAIN CONVECTIVE POTENTIAL.
...UPPER MISSISSIPPI VALLEY...
VARIABILITY AMONG THE MODELS WITH REGARD TO THE PROGRESSION OF
IMPULSES AROUND THE UPPER RIDGE IS EXACERBATING THIS UNCERTAINTY.
BUT...GUIDANCE IS SUGGESTIVE THAT ONE WEAK IMPULSE PROGRESSING
AROUND THE CREST OF THE UPPER RIDGE...TOWARD THE BASE OF A LINGERING
LOW AMPLITUDE UPPER TROUGH OVER THE GREAT LAKES AND
NORTHEAST...COULD SUPPORT AN EARLY PERIOD STORM CLUSTER ACROSS PARTS
OF THE UPPER MISSISSIPPI VALLEY. THE BEST CHANCE FOR THIS APPEARS
TO BE ACROSS PARTS OF SOUTHEAST MINNESOTA...EASTERN IOWA AND
SOUTHERN WISCONSIN INTO NORTHERN ILLINOIS. IF THIS
MATERIALIZES...THE ENVIRONMENT WILL BE SUPPORTIVE OF LARGE HAIL/
DOWNBURSTS AND SURFACE COLD POOLS ACCOMPANIED BY POTENTIALLY
DAMAGING WIND GUSTS.
...NORTHERN PLAINS...
THEREAFTER...LATEST ECMWF AND GFS/MREF ARE IN AGREEMENT IN AT LEAST
INDICATING AN EASTWARD ACCELERATION OF A SIGNIFICANT SHORT WAVE
IMPULSE OUT OF THE WESTERN CANADIAN/PACIFIC NORTHWEST UPPER TROUGH.
AS THIS OCCURS...A DOWNSTREAM WARM ADVECTION REGIME MAY SUPPORT
CONVECTIVE DEVELOPMENT IN A STEEP LAPSE RATE ENVIRONMENT NEAR A LEE
TROUGH ACROSS WESTERN NORTH DAKOTA LATE FRIDAY AFTERNOON. THIS
FORCING IS EXPECTED TO STRENGTHEN AND SHIFT TOWARD THE NORTH
DAKOTA/MANITOBA BORDER FRIDAY/FRIDAY NIGHT. COUPLED WITH AN
INCREASE IN MOISTURE ON STRENGTHENING SOUTHERLY LOW-LEVEL
FLOW...UPSCALE EVOLUTION INTO AN ORGANIZED MESOSCALE CONVECTIVE
SYSTEM CAPABLE OF PRODUCING DAMAGING WINDS/HAIL APPEARS POSSIBLE.
..KERR.. 07/30/2008
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