SWODY2
SPC AC 271657
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1157 AM CDT TUE APR 27 2010
VALID 281200Z - 291200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A STRONG BELT OF WESTERLIES ASSOCIATED WITH THE POLAR JET OVER THE
PACIFIC IS UNDERGOING AMPLIFICATION...AND MODELS INDICATE THAT THIS
PROCESS WILL CONTINUE THROUGH THIS FORECAST PERIOD. AN EVOLVING
UPPER TROUGH ON THE LEADING EDGE OF THIS REGIME IS PROGGED TO
TRANSLATE EASTWARD THROUGH THE INTERMOUNTAIN WEST AND ROCKIES...WITH
AN EMBEDDED CLOSED LOW DEVELOPING NEAR THE MONTANA/CANADIAN BORDER
AREA...WHILE A SIGNIFICANT SHORT WAVE IMPULSE DIGS ACROSS
NORTHERN/CENTRAL CALIFORNIA TOWARD THE SOUTHERN GREAT BASIN. AS
THIS OCCURS...A LARGE DOWNSTREAM UPPER TROUGH SHOULD FINALLY BEGIN
TO PROGRESS EAST OF THE ATLANTIC SEABOARD.
GUIDANCE INDICATES THAT THE EVOLVING UPPER PATTERN WILL BE
ACCOMPANIED BY DEEPENING SURFACE TROUGHING TO THE LEE OF THE
ROCKIES. THIS IS LIKELY TO ENCOMPASS MUCH OF THE PLAINS BY 12Z
THURSDAY...WITH EMBEDDED LOW CENTERS OVER THE CENTRAL PLAINS AND
SOUTHERN SASKATCHEWAN...ALONG WITH A STRONG AND INTENSIFYING
SOUTHERLY LOW-LEVEL JET. HOWEVER...IN THE WAKE OF THE EASTERN
SYSTEM...AND A WEAK SUBTROPICAL IMPULSE MIGRATING EAST OF THE LOWER
RIO GRANDE VALLEY INTO THE GULF OF MEXICO...A SUBSTANTIVE RETURN
FLOW OF MOISTURE OFF THE GULF OF MEXICO INTO THE PLAINS IS EXPECTED
TO BE SLOW TO DEVELOP. COUPLED WITH VERY WARM ELEVATED MIXED LAYER
AIR ADVECTING EAST OF THE ROCKIES/PLATEAU REGION... THIS WILL LIMIT
THE CONVECTIVE POTENTIAL WEDNESDAY/WEDNESDAY NIGHT. BUT INSTABILITY
ASSOCIATED WITH COLD MID-LEVEL AIR SETTLING INTO THE INTERMOUNTAIN
WEST...AND WEAKER MID-LEVEL COOLING/STRENGTHENING LIFT BENEATH
INCREASINGLY DIVERGENT UPPER FLOW SPREADING EAST OF THE NORTHERN
ROCKIES INTO THE NORTHERN PLAINS...PROBABLY WILL BE SUFFICIENT AT
LEAST FOR SCATTERED THUNDERSTORM ACTIVITY.
...WRN NEBRASKA THRU PARTS OF THE WRN AND CNTRL DAKOTAS...
SURFACE HEATING AND DIFFERENTIAL THERMAL ADVECTION ARE EXPECTED TO
CONTRIBUTE TO STEEP LOW AND MID-LEVEL LAPSE RATES ACROSS THE
NORTHERN HIGH PLAINS BY WEDNESDAY AFTERNOON. DESPITE LIMITED
MOISTURE...MODELS ARE SUGGESTIVE THAT A DEEPLY MIXED BOUNDARY LAYER
WILL BECOME CHARACTERIZED BY CAPE UP TO AROUND 500 J/KG OR SO...IN
THE PRESENCE OF STRONG DEEP LAYER SHEAR NEAR A 50-70+ KT
SOUTHWESTERLY 500 MB JET STREAK. THIS ENVIRONMENT APPEARS AT LEAST
MARGINALLY SUPPORTIVE OF ORGANIZED VIGOROUS STORM DEVELOPMENT...WITH
LARGE SUB-CLOUD TEMPERATURE/DEW POINT SPREADS ENHANCING THE RISK FOR
LOCALIZED POTENTIALLY DAMAGING SURFACE GUSTS. THIS THREAT MAY
CONTINUE INTO THE EVENING HOURS...AS CONVECTION SPREADS WITH DEEP
LAYER MEAN FLOW AND FORCING INTO THE CENTRAL DAKOTAS...WHERE
INTERACTION WITH THE STRENGTHENING LOW-LEVEL JET COULD CONTRIBUTE TO
AT LEAST SOMEWHAT BETTER POTENTIAL FOR LARGE HAIL THROUGH DAYBREAK
THURSDAY.
..KERR.. 04/27/2010
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