DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201247
SWODY1
SPC AC 201246

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0746 AM CDT SUN MAY 20 2012

VALID 201300Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR THE CNTRL UPPER PENINSULA
OF MI/ERN WI/NERN IL/FAR NWRN IND/WRN LAKE MI...

...SYNOPSIS...
A COMPOSITE SHORTWAVE TROUGH IN THE MID/UPPER LEVELS...EXTENDING SWD
FROM SASKATCHEWAN/MANITOBA INTO THE NRN/CNTRL PLAINS...WILL TRACK
EWD THROUGH THE PERIOD. EMBEDDED WITHIN THIS TROUGH...AN IMPULSE
WILL LIFT NEWD FROM THE MID MO VALLEY TOWARD LAKE SUPERIOR. AN
ATTENDANT SFC FRONT PRESENTLY STRETCHES FROM WRN LAKE SUPERIOR SSWWD
INTO THE SRN PLAINS...WHERE IT ARCS WSWWD INTO ERN NM. THE NRN/ERN
EXTENT OF THE FRONT WILL SHIFT EWD AND REACH FROM THE LOWER
PENINSULA OF MI TO WRN PARTS OF THE TN VALLEY INTO THE LOWER MS
VALLEY BY LATE TONIGHT...WHILE THE SRN PLAINS EXTENT OF THE FRONT
REMAINS QUASI-STATIONARY ROUGHLY INVOF THE RED RIVER/TX SOUTH PLAINS
REGION. A WAVE WILL MOVE NEWD ALONG THE FRONT FROM NWRN WI TO THE
UPPER PENINSULA OF MI WHILE BECOMING INCREASINGLY ILL DEFINED.

ELSEWHERE IN THE MID/UPPER LEVELS...A RIDGE WILL BUILD ACROSS MUCH
OF THE INTERMOUNTAIN WEST...AS A TROUGH APPROACHES THE PACIFIC NW.
AN ELONGATED TROUGH COMPLEX WILL PERSIST OVER PARTS OF THE WRN
ATLANTIC AND SERN STATES TO THE SOUTH OF AN ANTICYCLONE MOVING EWD
ACROSS PORTIONS OF THE NORTHEAST STATES. MEANWHILE...THE CENTER OF
TROPICAL STORM ALBERTO AND ASSOCIATED BUOYANCY FOR DEEP CONVECTION
ARE FORECAST TO REMAIN OFF THE COAST OF SC THROUGH THE PERIOD. FOR
ADDITIONAL DETAILS ON ALBERTO...PLEASE REFERENCE ADVISORIES ISSUED
BY THE NATIONAL HURRICANE CENTER.

...CNTRL UPPER PENINSULA OF MI/ERN WI/NERN IL/FAR NWRN IND/WRN LAKE
MI TODAY INTO THIS EVENING...
LARGE-SCALE ASCENT IN ASSOCIATION WITH THE AFOREMENTIONED SHORTWAVE
TROUGH/IMPULSE WILL AID IN DESTABILIZATION WITHIN THE
NNE-SSW-ORIENTED WARM SECTOR LEADING THE FRONT. WITHIN THIS
SECTOR...BUOYANCY WILL BE LIMITED TO SOME DEGREE BY THE MODEST
DEGREE OF BOUNDARY-LAYER MOISTURE...AS PERSISTENT SFC RIDGING INTO
THE NRN GULF OF MEXICO CONTINUES TO LARGELY PREVENT RICHER LOW-LEVEL
MOISTURE FROM ADVANCING NWD. REGARDLESS...MODEST MOISTURE RETURN
WILL BE SUFFICIENT TO SUPPORT AN AXIS OF UPPER 50S TO LOWER 60S
DEWPOINTS EAST OF THE FRONT. FORECAST SOUNDINGS SUGGEST THAT THIS
WILL SUPPORT THE DEVELOPMENT OF MODERATE INSTABILITY AS LOW-LEVEL
LAPSE RATES STEEPEN OWING TO POCKETS OF INSOLATION/DIABATIC HEATING
AMIDST THE WARM SECTOR BENEATH FAIRLY STEEP MID-LEVEL LAPSE RATES
PER 12Z RAOBS /AROUND 7.5 C PER KM WITHIN THE 700-500-MB LAYER/.

ONGOING ELEVATED CONVECTION ACROSS NWRN WI...IN ASSOCIATION WITH THE
EXIT REGION OF A LOW-LEVEL JET LEADING THE IMPULSE...WILL LIKELY
PERSIST THIS MORNING WHILE MOVING NNEWD TOWARD LAKE SUPERIOR. A
LOW-END HAIL THREAT MAY EVOLVE WITH THIS ACTIVITY BY LATE MORNING AS
BUOYANCY OF INFLOW INCREASES OWING TO WARM-SECTOR DESTABILIZATION.
ADDITIONAL CONVECTION IS EXPECTED TO FORM ALONG THE FRONT AND INVOF
A PREFRONTAL CONFLUENCE AXIS BY EARLY/MID AFTERNOON FROM THE UPPER
PENINSULA OF MI INTO NERN IL...AND THEN TRACK EWD IN CORRESPONDENCE
WITH THE MOTION OF THE FRONT. MAINLY UNIDIRECTIONAL WIND FIELDS
ORIENTED PARALLEL TO THE FRONT...FEATURING 30-40 KT OF DEEP
SHEAR...WILL AID IN THE DEVELOPMENT OF MULTICELL CLUSTERS AND LINE
SEGMENTS CAPABLE OF PRODUCING SVR WIND/HAIL. A COMPARATIVELY GREATER
RISK FOR MORE ORGANIZED CONVECTION...AND PERHAPS A TRANSIENT
SUPERCELL STRUCTURE OR TWO...MAY EVOLVE INVOF THE FRONTAL WAVE
ACROSS ERN WI AND THE UPPER PENINSULA OF MI...WHERE SFC WINDS SHOULD
BE SOMEWHAT MORE BACKED. A WEAK TORNADO CANNOT BE ENTIRELY RULED OUT
IN THIS REGION.

...SOUTH OF THE SLIGHT RISK AREA INTO THE TN VALLEY AND LOWER MS
VALLEY REGION THIS AFTERNOON INTO EARLY EVENING...
ASCENT IN ASSOCIATION WITH THE FRONT AND A PREFRONTAL CONFLUENCE
AXIS WILL FOSTER THE DEVELOPMENT OF ISOLATED TO WIDELY SCATTERED
CONVECTION THIS AFTERNOON. HOWEVER...THIS REGION WILL BE REMOVED TO
THE SOUTH OF THE STRONGER DEEP SHEAR AND DEEP FORCING FOR
ASCENT...YIELDING COMPARATIVELY MORE WEAKLY ORGANIZED STORM
STRUCTURES. AMPLE SFC HEATING SHOULD CONTRIBUTE TO MODERATE TO
PERHAPS STRONG INSTABILITY DEVELOPING THIS AFTERNOON...WITH ISOLATED
INSTANCES OF SVR WIND/HAIL POSSIBLE WITH PULSE/MULTICELLULAR
CONVECTION.

...PARTS OF THE SRN PLAINS THIS AFTERNOON INTO TONIGHT...
ASCENT IN ASSOCIATION WITH THE SRN PLAINS EXTENT OF THE
FRONT...OUTFLOW BOUNDARIES RESULTING FROM OVERNIGHT CONVECTION...AND
MOIST UPSLOPE FLOW ACROSS PARTS OF SWRN TX AND SERN NM WILL SUPPORT
ISOLATED TO WIDELY SCATTERED CONVECTION THIS AFTERNOON INTO THIS
EVENING. THERE IS SOME POTENTIAL THAT STORMS COULD ALSO DEVELOP
TONIGHT FROM PARTS OF OK TO THE TX SOUTH PLAINS AS WEAK WARM
ADVECTION OCCURS ATOP A W-E-ORIENTED EFFECTIVE BOUNDARY. WITH
RELATIVELY STEEP MID-LEVEL LAPSE RATES OVERLAYING MODEST LOW-LEVEL
MOISTURE...ISOLATED INSTANCES OF SVR HAIL/WIND WILL BE POSSIBLE.
HOWEVER...THE LACK OF DEEP FORCING FOR ASCENT SHOULD LARGELY
MITIGATE THE OVERALL THREAT.

...FRONT RANGE OF THE ROCKIES THIS AFTERNOON...
MODESTLY MOIST SELY UPSLOPE LOW-LEVEL FLOW BENEATH WEAK TO MODERATE
NWLY FLOW IN THE MID/UPPER LEVELS MAY SUPPORT A THREAT FOR WEAK
SUPERCELL STRUCTURES WITH ISOLATED TO WIDELY SCATTERED
THUNDERSTORMS. HOWEVER...BUOYANCY IS EXPECTED TO REMAIN MARGINAL
OWING TO THE LIMITED QUANTITY OF BOUNDARY-LAYER MOISTURE -- SFC
DEWPOINTS MAINLY IN THE UPPER 30S TO AROUND 40. MARGINALLY SVR
HAIL/WIND CANNOT BE RULED OUT WITH THIS ACTIVITY...ESPECIALLY FOR
LOCATIONS IN CLOSER PROXIMITY TO HIGHER TERRAIN.

...SOUTH FL THIS AFTERNOON...
ISOLATED TO SCATTERED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
ALONG SEA BREEZE CONVERGENCE ZONES BENEATH MODESTLY STRONG
HIGH-LEVEL FLOW YIELDING EFFECTIVE BULK SHEAR MAGNITUDES AROUND
20-25 KT. AND...WITH THE DEVELOPMENT OF MODERATE INSTABILITY AMIDST
PW VALUES OF 1.3 TO 1.6 INCH PER GPS DATA...MULTICELL CLUSTERS WITH
ISOLATED SVR WIND/HAIL MAY ENSUE.

..COHEN/CORFIDI.. 05/20/2012

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