DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 250534
SWODY1
SPC AC 250533

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1233 AM CDT WED APR 25 2012

VALID 251200Z - 261200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MIDWEST/OH VALLEY
REGION...

...SYNOPSIS...
AS ONE PIECE OF THE ERN U.S. UPPER TROUGH SHIFTS NEWD ACROSS NEW
ENGLAND TODAY...THE OVERALL TROUGHING WILL BE SOMEWHAT MAINTAINED AS
A COMBINATION OF WEAK DISTURBANCES MOVING THROUGH CYCLONIC NWLY FLOW
BEHIND THIS TROUGH AND A STRONGER PIECE OF ENERGY DIGS SEWD ACROSS
WRN ONTARIO AND EVENTUALLY INTO THE UPPER GREAT LAKES.

MEANWHILE FARTHER W...THE TWO CLOSED LOWS -- ONE OFF THE BRITISH
COLUMBIA COAST AND THE OTHER OFF THE CA/BAJA COAST -- APPEAR LIKELY
TO BECOME PARTIALLY PHASED THIS PERIOD...AFFECTING THE W COAST AND
EVENTUALLY THE DESERT SW LATE.

AT THE SURFACE...THE MAIN FEATURE WITH RESPECT TO THE SEVERE WEATHER
FORECAST WILL BE A SURFACE LOW -- INITIALLY PROGGED TO LIE INVOF ERN
SD/SWRN MN. THIS LOW IS FORECAST TO SHIFT SEWD ACROSS THE UPPER
MIDWEST THROUGH THE DAY...ALONG A NW-SE WARM FRONT. LATER...THE LOW
SHOULD TURN EWD AND MOVE ACROSS THE OH VALLEY REGION THROUGH THE END
OF THE PERIOD.

...MIDWEST/OH VALLEY REGION...
AS THE AFOREMENTIONED SURFACE LOW SHIFTS SEWD ACROSS IA DURING THE
DAY AND REACHES THE MS RIVER...A SWLY LOW-LEVEL JET IS FORECAST TO
DEVELOP -- NOSING NEWD TOWARD/ACROSS THE SURFACE WARM FRONT. AS THE
MOISTENING BOUNDARY LAYER DESTABILIZES THROUGH THE
AFTERNOON...EXPECT STORM INITIATION TO OCCUR -- LIKELY NEAR AND TO
THE COOL SIDE OF THE FRONT AS WARM SECTOR CAPPING IS LIKELY TO
LARGELY INHIBIT CONVECTIVE DEVELOPMENT. INITIAL DEVELOPMENT SHOULD
OCCUR INVOF ERN IA/NWRN IL...AND WITH STEEP LAPSE RATES/MODERATE
CAPE FUELING THE CONVECTION...INCREASING STORM COVERAGE -- AND
EVENTUALLY UPSCALE GROWTH INTO A BOWING LINE OF STORMS -- APPEARS
POSSIBLE.

INITIAL STORM MODE IS LIKELY TO BE SUPERCELLULAR...WITH LOW-LEVEL
FLOW VEERING RAPIDLY AND INCREASING TO 40 KT FROM THE NW. THESE
STORMS WILL LIKELY BE ACCOMPANIED BY LARGE HAIL...WITH LOCALLY
DAMAGING WINDS AND EVEN AN ISOLATED TORNADO POSSIBLE. PRESUMING
UPSCALE LINEAR GROWTH DOES OCCUR...THREAT FOR WIND WOULD INCREASE --
AIDED BY MID-LEVEL NWLYS ALOFT INCREASING A BIT TO 40 TO 50 KT
DRIVING A FAST-MOVING MCS ACROSS THE OH VALLEY ROUGHLY ALONG THE
WARM FRONTAL ZONE. SOME SEVERE THREAT MAY LINGER WELL INTO THE
OVERNIGHT HOURS -- PARTICULARLY IF THE LINEAR/BOWING MCS CAN
DEVELOP.

...PARTS OF THE PAC NW...
MODEST DESTABILIZATION ACROSS PARTS OF NERN OREGON/SERN WA AND INTO
ID/WRN MT COMBINED WITH HEIGHT FALLS ALOFT ASSOCIATED WITH THE
EVOLVING/COMPLEX/EWD-MOVING UPPER TROUGH SHOULD RESULT IN SCATTERED
CONVECTIVE DEVELOPMENT DURING THE AFTERNOON. WHILE DEGREE OF
INSTABILITY APPEARS TO BE A LIMITING FACTOR FOR APPRECIABLE SEVERE
WEATHER THREAT...ISOLATED POTENTIAL FOR WIND/LOW-END HAIL IS
EXPECTED...WITH THREAT POSSIBLY ENHANCED BY SHEAR PROFILES
SUFFICIENT FOR A FEW LONGER-LIVED UPDRAFTS. THREAT WILL DIMINISH
LATER IN THE EVENING AS THE AIRMASS DIURNALLY STABILIZES.

..GOSS/SMITH.. 04/25/2012

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