SPC AC 041729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT THU JUN 04 2009
VALID 051200Z - 061200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF EASTERN
ORE/WESTERN ID/SOUTHEAST WA...
...SYNOPSIS...
CLOSED UPPER LOW CURRENTLY OFF THE NORTHERN CA COAST IS EXPECTED TO
MOVE ONSHORE EARLY FRIDAY...AND GRADUALLY OPEN AS IT CROSSES THE
GREAT BASIN FRIDAY NIGHT INTO EARLY SATURDAY. FARTHER EAST...BRUNT
OF CANADIAN UPPER TROUGH SHOULD GRADUALLY TAKE ON A NEGATIVE TILT
OVER ONTARIO...WHILE THE RESIDUAL UPPER TROUGH OVER THE SOUTHEAST
STATES SLOWLY MIGRATES EASTWARD. WITHIN THIS LARGE SCALE
REGIME...PRIMARY SURFACE COLD FRONT WILL PROGRESS EASTWARD ACROSS
THE GREAT LAKES REGION...WHILE THE WESTERN PORTION OF THE FRONT
DEVELOPS SOUTHWARD ACROSS THE CENTRAL PLAINS AND NORTHERN HIGH
PLAINS/NORTHERN GREAT DIVIDE VICINITY.
...CENTRAL PLAINS...
AFOREMENTIONED COLD FRONT SHOULD MOVE SOUTHWARD ACROSS THE CENTRAL
PLAINS EARLY FRIDAY...AND BEGIN TO STALL IN A WEST-EAST FASHION
ACROSS NEB BY AFTERNOON. POTENTIAL FOR EARLY DAY CLOUD
COVER/PRECIPITATION ACROSS NEB SHOULD CONTRIBUTE TO A RELATIVELY
STABLE NORTH-SIDE OF THE SURFACE BOUNDARY AWAY FROM THE HIGHER
TERRAIN. AS LARGE SCALE HEIGHT FALLS BEGIN TO OCCUR ACROSS THE
CENTRAL ROCKIES AHEAD OF CA/GREAT BASIN UPPER TROUGH...LEE
CYCLOGENESIS ALONG THE CO/KS BORDER DURING THE DAY WILL ENHANCE
UPSLOPE POST-FRONTAL TRAJECTORIES INTO THE HIGHER TERRAIN/FRONT
RANGE OF EASTERN WY/NORTHEAST CO AND THE IMMEDIATELY ADJACENT
CENTRAL HIGH PLAINS. IT SEEMS PROBABLE THAT DIFFERENTIAL
HEATING/UPSLOPE TRAJECTORIES SHOULD RESULT IN INCIPIENT TSTM
DEVELOPMENT BY EARLY/MID AFTERNOON ACROSS SOUTHEAST WY/NORTHEAST
CO...INCLUDING THE CHEYENNE RIDGE AND ALONG/NORTH OF THE PALMER
DIVIDE. OTHER INITIAL TSTM DEVELOPMENT WILL BE POSSIBLE A BIT
FARTHER EAST NEAR THE CO/NEB/KS BORDER AREA AMIDST A DEEP MIXED
BOUNDARY LAYER IN VICINITY OF THE DEEPENING SURFACE LOW AND PERHAPS
RESIDUAL OUTFLOW PENDING LINGERING OVERNIGHT/EARLY MORNING
DEVELOPMENT ACROSS NEB.
THE BOUNDARY LAYER IN VICINITY OF THE WEST-EAST FRONTAL ZONE WILL
NOT BE PARTICULARLY MOIST /SURFACE DEWPOINTS MAINLY UPPER 40S TO
MIDDLE 50S F/...BUT SUFFICIENT MOISTURE/HEATING BENEATH A STRONG
ELEVATED MIXED LAYER/VERY STEEP MID LEVEL LAPSE RATES WILL
CONTRIBUTE TO A MODERATELY UNSTABLE BOUNDARY LAYER ACROSS SOUTHEAST
WY/NORTHEAST CO TO SOUTHWEST NEB/WESTERN KS. WITH MID LEVEL WINDS
EXPECTED TO STEADILY INCREASE THROUGH THE AFTERNOON ATOP EASTERLY
FLOW IN THE BOUNDARY LAYER...EFFECTIVE BULK SHEAR OF 40-50 KT WILL
BE MORE THAN ADEQUATE FOR SUPERCELLULAR DEVELOPMENT. SEVERE HAIL
WILL LIKELY BE PRIMARY HAZARD...BUT ISOLATED TORNADOES AND DAMAGING
WINDS WILL BE POSSIBLE AS WELL.
...SOUTHERN HIGH PLAINS...
BENEATH RESIDUAL INFLUENCE OF AN UPPER RIDGE...THE SEVERE THREAT
WILL BE MUCH MORE CONDITIONAL/ISOLATED IN NATURE WITH SOUTHWARD
EXTENT ACROSS THE SOUTHERN HIGH PLAINS. NONETHELESS...A FEW TSTMS
WILL BE CAPABLE OF SEVERE HAIL/STRONG WINDS...MAINLY IN VICINITY OF
DRYLINE FROM FAR SOUTHWEST KS INTO THE TX/OK PANHANDLES AND
WEST/SOUTHWEST TX FRIDAY LATE AFTERNOON/EARLY EVENING. MAINLY
PORTIONS OF THE OK/TX PANHANDLES MAY ULTIMATELY WARRANT A
CATEGORICAL SLIGHT RISK SHOULD CONFIDENCE IN TSTM
DEVELOPMENT/COVERAGE INCREASE.
...NORTHERN INTERMOUNTAIN WEST...
IN VICINITY OF A SURFACE LOW...THE PRESENCE OF STEEP LAPSE RATES AND
PW VALUES OF 0.75-1.0 INCH WILL CONTRIBUTE TO A MODERATELY UNSTABLE
AIRMASS FRIDAY WITH MLCAPE LOCALLY APPROACHING 1000 J/KG ACROSS
PORTIONS OF THE NORTHERN INTERMOUNTAIN REGION...WITH AN UPSWING IN
SCATTERED TSTM DEVELOPMENT EXPECTED DURING THE AFTERNOON. VERTICAL
SHEAR WILL BE WEAK...BUT THE PRESENCE OF A RESIDUALLY MOIST
AIRMASS/STEEP LAPSE RATES WILL SUPPORT HAIL/STRONG WIND GUSTS WITH
THE STRONGEST TSTMS.
...SOUTHEAST STATES/CAROLINAS...
SCATTERED TO NUMEROUS TSTMS ARE EXPECTED TO DIURNALLY INCREASE ALONG
A SURFACE FRONT AND SEA BREEZE BOUNDARIES ON FRIDAY...AS DEEP ASCENT
ASSOCIATED WITH THE SOUTHEAST STATES SLOW MOVING UPPER TROUGH
INTERACTS WITH A RESIDUALLY MOIST/POTENTIALLY UNSTABLE AIRMASS. A
FEW OF THE STRONGER STORMS WILL BE CAPABLE OF LOCALLY STRONG WIND
GUSTS/PERHAPS SMALL HAIL THROUGH THE AFTERNOON/EARLY EVENING HOURS.
..GUYER.. 06/04/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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