SWODY1
SPC AC 210556
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT TUE OCT 21 2008
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE CNTRL AND
SRN PLAINS...
...SYNOPSIS...
PRIMARY FEATURE OF INTEREST DURING THE DAY ONE PERIOD IS MID AND
UPPER LEVEL TROUGH WHICH WILL UNDERGO SIGNIFICANT INTENSIFICATION
OVER THE CNTRL PART OF THE NATION. INCREASING AGEOSTROPHY IN LEFT
EXIT REGION OF DIGGING UPPER LEVEL JET STREAK WILL CONTRIBUTE TO A
ZONE OF STRONG HEIGHT FALLS FROM THE NRN ROCKIES SEWD INTO THE NRN
AND CNTRL PLAINS.
IN THE LOW LEVELS...SURFACE CYCLONE INITIALLY OVER ERN WY WILL
DEEPEN TODAY WHILE DEVELOPING SEWD THROUGH THE CNTRL INTO SRN HIGH
PLAINS. AN ATTENDANT COLD FRONT WILL STRENGTHEN WHILE SURGING SEWD
THROUGH THE PLAINS AND WILL LIKELY EXTEND FROM THE CNTRL DAKOTAS
SWWD THROUGH SWRN NEB TO LOW PRESSURE OVER E-CNTRL CO BY EARLY
EVENING. AS THIS OCCURS...FRONTAL BOUNDARY CURRENTLY STALLED ACROSS
SRN OK INTO WRN TX WILL LIFT NWD THROUGH OK INTO KS TODAY INTO
TONIGHT.
...CNTRL/SRN PLAINS...
CURRENT GOES/GPS PW DATA AND SURFACE OBSERVATIONS INDICATE THAT A
RELATIVELY MOIST AIR MASS /I.E. PW VALUES OF .8-.9 INCH AND
DEWPOINTS IN THE MID TO UPPER 50S/ IS PRESENT INVOF STALLED FRONTAL
BOUNDARY FROM THE OZARK PLATEAU INTO SRN OK. STRENGTHENING SLY/SELY
FLOW WILL SUPPORT THE NWD ADVECTION OF THIS MOISTURE THROUGH OK INTO
KS ALONG AND S OF RETREATING SURFACE FRONT. THIS PROCESS WILL OCCUR
BENEATH AN EML/STEEP LAPSE RATE PLUME SPREADING EWD ACROSS THE
CNTRL/SRN PLAINS IN ADVANCE OF AMPLIFYING UPPER TROUGH. THESE
DIFFERENTIAL ADVECTIONS WILL RESULT IN AIR MASS DESTABILIZATION
TODAY AHEAD OF SURFACE COLD FRONT WITH MLCAPE INCREASING TO 500-1000
J/KG FROM SWRN NEB SWD INTO THE TX PNHDL.
LOW-LEVEL FRONTOGENETIC FORCING COUPLED WITH DIVERGENT UPPER JET
EXIT REGION WILL CONTRIBUTE TO VIGOROUS TSTM DEVELOPMENT BY LATE
AFTERNOON OR EARLY EVENING ALONG THE COLD FRONT OVER THE CNTRL HIGH
PLAINS. ANAFRONTAL AIRFLOW REGIME SHOULD SUPPORT UPSCALE GROWTH
INTO A CONVECTIVE BAND ALONG OR PERHAPS IN IMMEDIATE WAKE OF COLD
FRONT. IN ADDITIONAL TO THE POTENTIAL FOR SOME MARGINALLY SEVERE
HAIL...THE ADDITIVE EFFECTS OF GROWING STORM-SCALE COLD POOLS AND
ISALLOBARIC FORCING ALONG STRONG COLD SUGGEST THE POTENTIAL FOR
DAMAGING WIND GUSTS. THIS SEVERE THREAT WILL CONTINUE SEWD THROUGH
WRN/CNTRL KS INTO THE TX/OK PNHDLS AND THE WRN HALF OF OK
TONIGHT.
AN ADDITIONAL CLUSTER OF TSTMS MAY INCREASE TODAY FARTHER TO THE E
OVER KS/OK IN ASSOCIATION WITH A WEAKER LEAD SHORT WAVE TROUGH
MOVING ACROSS THE CNTRL/SRN PLAINS. THIS ACTIVITY WILL LIKELY BE
FOCUSED ALONG AND TO THE N OF SURFACE FRONT LIFTING NWD WHERE WAA
AND DCVA IN ADVANCE OF SHORT WAVE TROUGH CONTRIBUTE TO DEEP LAYER
ASCENT. STORMS SHOULD TEND TO INCREASE IN AREAL COVERAGE TONIGHT
FROM ERN KS INTO THE LOWER MO VALLEY AS A BROADER AND MORE INTENSE
LLJ DEVELOPS IN RESPONSE TO INTENSIFYING...PRIMARY TROUGH. WHILE
BOUNDARY LAYER WILL BE MORE MOIST THAN THAT IN ADVANCE OF COLD FRONT
OVER THE HIGH PLAINS...LAPSE RATES WILL BE WEAKER WHICH WILL LIMIT
THE DEGREE OF INSTABILITY.
OF INTEREST IS THE NOTABLE INCREASE IN LOW-LEVEL SHEAR ALONG
RETREATING BOUNDARY ACROSS NRN OK/SRN KS LATER THIS AFTERNOON INTO
EVENING. DESPITE THE MARGINAL INSTABILITY...THERE APPEARS TO BE
SOME POTENTIAL FOR EMBEDDED...ROTATING STORMS. SOME SMALL HAIL
APPEARS TO BE THE PRIMARY THREAT WITH THE MORE INTENSE
STORMS...HOWEVER A BRIEF TORNADO CANNOT BE RULED OUT WITH ANY MORE
INTENSE STORMS ROOTED IN THE BOUNDARY LAYER.
..MEAD/HURLBUT.. 10/21/2008
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