DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 041952
SWODY1
SPC AC 041951

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT WED JUL 04 2012

VALID 042000Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE UPPER GREAT LAKES SOUTHEASTWARD THROUGH THE
UPPER OH VALLEY AND MID ATLANTIC COAST REGION...

...20Z OUTLOOK UPDATE...
CHANGES TO PRIOR OUTLOOK ARE GENERALLY CONFINED TO PORTIONS OF THE
UPPER GREAT LAKES REGION...MOSTLY TO ACCOUNT FOR ONGOING CONVECTIVE
ACTIVITY. POTENTIAL EVOLUTION INTO THE EVENING HOURS IS STILL NOT
PARTICULARLY CLEAR...BUT A SIGNIFICANT...SIZABLE CONVECTIVE CLUSTER
HAS ALREADY EVOLVED ACROSS NORTHERN MINNESOTA ...AND THIS SEEMS TO
SUPPORT INCREASING PROBABILITIES FOR SEVERE HAIL AND WIND ACROSS AT
LEAST PARTS OF MINNESOTA TO THE WEST AND SOUTHWEST OF
DULUTH...THROUGH NORTHERN WISCONSIN.

STRONGER FORCING FOR UPWARD VERTICAL MOTION ASSOCIATED WITH CANADIAN
CYCLONE WILL REMAIN NORTH OF THE INTERNATIONAL BORDER. THE
MID-LEVEL LOW CENTER IS NOW OVER NORTHERN SASKATCHEWAN...AND STILL
LIFTING NORTHEASTWARD...WITH A TENDENCY FOR LARGER SCALE MID-LEVEL
HEIGHT RISES OVER THE UPPER MISSISSIPPI VALLEY/GREAT LAKES REGION.
HOWEVER...A REMNANT IMPULSE WITHIN THE MONSOONAL REGIME ON THE
NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGING COULD STILL CONTRIBUTE
TO CONVECTIVE DEVELOPMENT ACROSS MINNESOTA AND WISCONSIN LATE THIS
AFTERNOON AND EVENING.

ONGOING ACTIVITY MAY CONTINUE EASTWARD WITH A SEVERE HAIL AND WIND
THREAT THROUGH THE MINNESOTA ARROWHEAD. 20-30 KT WESTERLY DEEP
LAYER MEAN FLOW PROBABLY WILL MAINTAIN EASTWARD MOTION INTO THE LAKE
SUPERIOR VICINITY...WHERE IT IS STILL NOT CLEAR WHETHER NEAR SURFACE
INFLOW OF COOL AIR FROM THE LAKE WILL STRONGLY WEAKEN IT...OR
LOWER/MID TROPOSPHERIC WARM ADVECTION WILL BE ABLE TO MAINTAIN
SIGNIFICANT ELEVATED CONVECTION INTO THE UPPER PENINSULA OF
MICHIGAN.

IT MAY BE THAT THE SUBTROPICAL PERTURBATION CONTRIBUTES TO A
DISTINCT NEW CLUSTER OF STORMS TO THE SOUTHWEST OF THE ONGOING
ACTIVITY...WHERE UNINTERRUPTED INFLOW OF VERY MOIST AIR IN THE
PRESENCE OF SIZABLE CAPE AND MODEST SHEAR COULD PROVE FAVORABLE TO A
FORWARD/EASTWARD PROPAGATING MESOSCALE CONVECTIVE SYSTEM ACROSS
NORTHERN WISCONSIN THIS EVENING...PERHAPS LOWER MICHIGAN OVERNIGHT.

OTHERWISE...LOW-LEVEL WARM ADVECTION BENEATH LIGHT TO MODERATE
NORTHWEST MID-LEVEL FLOW COULD STILL SUPPORT ADDITIONAL EVOLVING
CLUSTERS OF STORMS WITH RISK FOR DAMAGING WINDS AND HAIL ACROSS
LOWER MICHIGAN INTO PARTS OF THE UPPER OHIO VALLEY AND MID ATLANTIC
COAST STATES LATE THIS AFTERNOON AND EVENING.

..KERR.. 07/04/2012

.PREV DISCUSSION... /ISSUED 1134 AM CDT WED JUL 04 2012/

...NRN MN/WI THROUGH THIS EVENING...
THE PRIMARY NRN STREAM SHORTWAVE TROUGH NOW OVER SK WILL CREST THE
RIDGE AND BEGIN TO MOVE MORE EWD OVER MB/WRN ONTARIO LATER TODAY
INTO TONIGHT. AT THE SURFACE...A LOW IN ERN ND THIS MORNING WILL
SLOWLY WEAKEN BY LATE EVENING...AS A SURFACE WARM FRONT LIFTS NWD
ACROSS NRN MN/WI...AND A COLD FRONT PROGRESSES SEWD ACROSS NEB AND
THE ERN DAKOTAS. A RESERVOIR OF LOW 70S BOUNDARY LAYER DEWPOINTS
BENEATH STEEP MIDLEVEL LAPSE RATES...IN COMBINATION WITH DAYTIME
HEATING...WILL SUPPORT A CORRIDOR OF STRONG INSTABILITY ALONG AND S
OF THE WARM FRONT IN MN/WI...WHERE MLCAPE WILL RANGE FROM 3000-4000
J/KG.

ONGOING STORMS ACROSS NW MN SHOULD PERSIST THROUGH THE DAY AND
SPREAD EWD ACROSS NRN MN...NEAR AND JUST N OF THE WARM FRONT.
DEEP-LAYER AND LOW-LEVEL VERTICAL SHEAR WILL BE SOMEWHAT STRONGER ON
THE IMMEDIATE COOL SIDE OF THE BOUNDARY...WHERE BOTH ORGANIZED
MULTICELL CLUSTER AND SOME SUPERCELL STRUCTURES WILL BE POSSIBLE.
LARGE HAIL AND DAMAGING WINDS WILL BE THE MAIN SEVERE THREATS WITH
THIS ACTIVITY.

...NRN WI TO LOWER MI THIS AFTERNOON/EVENING...
FARTHER SE ALONG THE WARM FRONT ACROSS WI/LOWER MI...STRONG SURFACE
HEATING AND STRONG INSTABILITY WILL BE PRESENT. THE ONLY CLEAR
FOCUS FOR STORM INITIATION WILL BE LOW-LEVEL CONVERGENCE ALONG THE
BOUNDARY...WHILE A DIFFUSE SPEED MAX ALOFT MOVES ESEWD FROM WRN
UPPER MI TOWARD LOWER MI. STORM COVERAGE REMAINS QUESTIONABLE ALONG
THIS CORRIDOR...BUT THE STEEP LAPSE RATES/LARGE BUOYANCY WILL
SUPPORT A CONDITIONAL RISK FOR LARGE HAIL/DAMAGING WINDS...PRIMARILY
WITH MULTICELL STORMS.

...ERN OH/WRN PA/WV/NRN VA THIS AFTERNOON/EVENING...
THE FOCUS FOR STORM DEVELOPMENT IS STILL A BIT UNCERTAIN...BUT
STRONG SURFACE HEATING IS WELL UNDERWAY ACROSS THE AREA...WHERE
MODERATE-STRONG INSTABILITY IS EXPECTED THIS AFTERNOON. THE REMNANT
COLD POOL WITH THE ONGOING NW PA STORMS COULD BE ASSOCIATED WITH NEW
STORM DEVELOPMENT THIS AFTERNOON...AS WELL AS SURFACE HEATING OVER
THE HIGHER TERRAIN. ANY STORMS/CLUSTERS THAT DO FORM WILL BE
CAPABLE OF PRODUCING DAMAGING DOWNBURST WINDS...AND SOME HAIL.

...UPSTATE NY AREA THIS AFTERNOON...
A SHORTWAVE TROUGH OVER QUEBEC WILL ROTATE SEWD OVER NRN NY/NRN NEW
ENGLAND THIS AFTERNOON/EVENING...ALONG WITH AN ASSOCIATED SURFACE
COLD FRONT. VERTICAL SHEAR WILL BE SUFFICIENT FOR ORGANIZED DEEP
CONVECTION...BUT POOR LAPSE RATES WILL TEND TO LIMIT BUOYANCY.
THUS...WILL MAINTAIN LOW WIND/HAIL PROBABILITIES IN THIS UPDATE.
PREVIOUS FORECAST REMAINS ON TRACK.

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