DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 210729
SWODY3
SPC AC 210728

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0228 AM CDT SUN OCT 21 2012

VALID 231200Z - 241200Z

...SYNOPSIS...
THE LARGE SCALE PATTERN WILL CONTINUE TO UNDERGO AMPLIFICATION ON
TUESDAY...HIGHLIGHTED BY AN INCREASINGLY PROMINENT WESTERN STATES
LONGWAVE TROUGH. ONE OR MORE WEAK MID-LEVEL TROUGHS MAY CONTRIBUTE
TO TSTM POTENTIAL ACROSS THE MIDDLE/UPPER MS VALLEY AND GREAT LAKES
REGION...BUT GRADUALLY RISING UPPER HEIGHTS ARE OTHERWISE
ANTICIPATED EAST OF THE MS RIVER.

...MIDDLE/UPPER MS VALLEY AND GREAT LAKES...
GIVEN THE LARGE SCALE SCENARIO AS PREVIOUSLY DESCRIBED...A SHORTWAVE
TROUGH SHOULD CONTINUE TO WEAKEN AND OUTRUN THE PRIMARY LOW-LEVEL
MOIST AXIS AS IT SPREADS EAST-NORTHEASTWARD TOWARD THE MIDDLE MS
VALLEY/OH VALLEY ON TUESDAY. WARM ADVECTION WILL OTHERWISE ACCOUNT
FOR SOME TSTMS ACROSS THE LOWER GREAT LAKES REGION DURING THE
PERIOD.

FARTHER WEST...THE POTENTIAL FOR SURFACE BASED CONVECTION WITHIN A
RELATIVELY MOIST/POTENTIALLY UNSTABLE AIRMASS ACROSS PARTS OF
NORTHERN MO AND IA INTO SOUTHERN MN/SOUTHERN WI/NORTHERN IL APPEARS
LOW...OR AT LEAST UNCERTAIN AT THE DAY 3 TIME FRAME GIVEN THE
POTENTIAL FOR CAPPING AND LITTLE OR NO READILY DISCERNIBLE BROAD
SCALE ASCENT. OF GREATER LIKELIHOOD WOULD BE FOR ELEVATED CONVECTION
TO INCREASE TUESDAY NIGHT TO THE NORTH OF A NORTHWARD-SHIFTING WARM
FRONT ACROSS THE UPPER MIDWEST/UPPER MS VALLEY. SOME HAIL CANNOT BE
RULED OUT IN THIS SCENARIO. BUT GIVEN THE OVERALL UNCERTAINTY AND
SEEMINGLY MODEST POTENTIAL...NO SEVERE PROBABILITIES CURRENT APPEAR
WARRANTED.

...COASTAL ORE/NORTHERN CA...
STEEPENING LAPSE RATES ALOFT WILL ACCOUNT FOR ISOLATED TSTMS FOR
COASTAL AREAS AND PERHAPS PORTIONS OF INTERIOR NORTHERN CA ON
TUESDAY. THIS WILL BE WITHIN THE POST-FRONTAL ENVIRONMENT IN THE
WAKE OF AN INITIAL FRONT...AND/OR NEAR AN APPROACHING SECONDARY
FRONT/TROUGH LATER IN THE PERIOD. SMALL HAIL MAY BE POSSIBLE FOR
AREAS SUCH AS COASTAL NORTHERN CA...BUT ORGANIZED/SUSTAINED SEVERE
TSTMS ARE NOT CURRENTLY EXPECTED.

..GUYER.. 10/21/2012

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