SWODY2
SPC AC 211718
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CST MON DEC 21 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
BUILDING UPPER RIDGE ACROSS THE ERN PACIFIC/ALASKA WILL AID IN A
PRONOUNCED SHORTWAVE TROUGH...CURRENTLY LOCATED OFF THE PACIFIC NW
COAST...DIGGING SEWD AND AMPLIFYING THE LONGWAVE TROUGH OVER THE WRN
CONUS TUESDAY. A CLOSED LOW IS FORECAST TO BE LOCATED WITHIN THE SRN
BASE OF THE TROUGH OVER AZ TUESDAY NIGHT. WEAK AREA OF SURFACE LOW
PRESSURE WILL BE SITUATED AHEAD OF THIS UPPER SYSTEM ACROSS THE SRN
ROCKIES/PLAINS. THE COMBINATION OF THE SURFACE LOW PRESSURE AND
RETREATING HIGH PRESSURE WILL INCREASE THE SLY WINDS AND BEGIN
RETURNING MODIFIED GULF MOISTURE NWD INTO THE ERN PORTIONS OF THE
SRN PLAINS AND WRN LOWER MS VALLEY.
..ARKLATEX REGION...
DESPITE GRADUAL MOISTENING OF THE BOUNDARY LAYER AND DEWPOINTS
INCREASING INTO THE 50S...AN INVERSION AROUND 850 MB SHOULD LIMIT
SURFACE BASED CONVECTION THROUGHOUT THIS FORECAST PERIOD. HOWEVER
...COMBINATION OF LOW LEVEL THETA-E ADVECTION AND INCREASING
DIFFLUENCE ALOFT...LOCATED BETWEEN POLAR JET NOSING INTO THE TX
PANHANDLE AND SUBTROPICAL JET IN SRN TX...IS EXPECTED TO PROVIDE
SUFFICIENT FORCING FOR ELEVATED CONVECTION TUESDAY NIGHT. IN
RESPONSE TO THE INCREASED LIFT...FORECAST SOUNDINGS SHOW LAPSE RATES
STEEPENING BETWEEN 750-500 MB AFTER 23/00Z...RESULTING IN MUCAPE
VALUES BETWEEN 500-1000 J/KG. ALTHOUGH DEEP LAYER SHEAR AT 40 TO 50
KT IS FORECAST...WEAK DIRECTIONAL SHEAR BETWEEN 850 AND 300 MB
SUGGEST THE EFFECTIVE SHEAR WILL BE CLOSER TO 30 KT. THIS AMOUNT OF
SHEAR AND INSTABILITY...ALONG WITH THE STEEPER MID LEVEL LAPSE
RATES...MAY SUPPORT A FEW STORMS WITH MARGINALLY SEVERE HAIL.
..IMY.. 12/21/2009
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