SWODY1
SPC AC 281246
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0746 AM CDT WED SEP 28 2011
VALID 281300Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS TODAY INTO THIS EVENING FROM
SERN TX EWD INTO FAR SRN MS...
...MID-ATLANTIC STATES...
DEEP-LAYER CYCLONE OVER THE GREAT LAKES/OH VALLEY WILL EDGE EWD THIS
PERIOD IN RESPONSE TO THE APPROACH OF AN UPSTREAM IMPULSE AMPLIFYING
OVER THE N-CNTRL STATES. WITHIN THIS BROADER-SCALE
PATTERN...VORTICITY MAXIMUM AND ATTENDANT 50 KT MIDLEVEL JET STREAK
OVER IL/IND/NRN KY WILL ROTATE NNEWD INTO THE UPPER OH VALLEY TODAY
WITH WEAK HEIGHT FALLS/DYNAMIC FORCING FOR ASCENT GLANCING THE
REGION DURING PEAK HEATING. IN THE LOW LEVELS...WEAK LOW PRESSURE
ANALYZED ALONG N-S-ORIENTED QUASI-STATIONARY BOUNDARY OVER S-CNTRL
VA WILL SLOWLY DEVELOP NWD TODAY IN CONJUNCTION WITH ABOVE-MENTIONED
VORTICITY MAXIMUM. AS THIS OCCURS...TRAILING SEGMENT OF FRONT WILL
ADVANCE EWD THROUGH THE PIEDMONT.
12Z SOUNDINGS AT RNK AND GSO INDICATE THAT MIDLEVEL LAPSE RATES HAVE
WEAKENED SINCE 00Z...AND DESPITE THE MOIST BOUNDARY LAYER...MODEL
FORECAST SOUNDINGS INDICATE THAT AFTERNOON MLCAPE VALUES WILL REMAIN
AOB 1000-1300 J/KG. THOUGH NOT NECESSARILY WEAK...THIS INSTABILITY
AXIS WILL RESIDE TO THE EAST OF THE STRONGER DEEP-LAYER WIND FIELD
ATTENDANT TO OH VALLEY UPPER LOW. AND WHILE ISALLOBARIC RESPONSE TO
WEAK SURFACE WAVE WILL YIELD CYLCONICALLY CURVED HODOGRAPHS...THE
OVERALL MAGNITUDE OF THE WIND FIELD IS FORECAST TO REMAIN MARGINALLY
SUPPORTIVE FOR SUSTAINED/ROTATING UPDRAFTS. THOUGH LOCALLY STRONG
WIND GUSTS AND PERHAPS A BRIEF TORNADO WILL BE POSSIBLE LATER
TODAY...THE POTENTIAL FOR A MORE ROBUST SEVERE WEATHER THREAT WILL
LIKELY BE TEMPERED BY THE WEAK MIDLEVEL LAPSE RATES AND MARGINAL
VERTICAL SHEAR. AS SUCH...ONLY LOW SEVERE WEATHER PROBABILITIES
WILL BE INCLUDED IN THIS FORECAST.
...CNTRL GULF COAST...
VORTICITY MAXIMUM OVER OK WILL TRANSLATE SEWD TOWARD THE REGION
TODAY...COMBINING WITH STRONG DAYTIME HEATING AND CONVERGENCE ALONG
SURFACE FRONT TO FOSTER SCATTERED TSTMS THIS AFTERNOON AND EVENING.
12Z REGIONAL SOUNDINGS SHOW THAT CO-LOCATION OF A VERY MOIST
BOUNDARY LAYER AND STEEP MIDLEVEL LAPSE RATES ARE ALREADY YIELDING A
VERY TO EXTREMELY UNSTABLE AIR MASS FOR MOST-UNSTABLE PARCELS WITH
CAPE VALUES UPWARDS OF 4000-5000 J/KG. THOUGH DEEP-LAYER WIND FIELD
WILL REMAIN RELATIVELY WEAK...THE DEGREE OF INSTABILITY AND
LARGE-SCALE FORCING FOR ASCENT ASSOCIATED WITH VORTICITY MAXIMUM
WILL SUPPORT INTENSE UPDRAFTS CAPABLE OF LARGE HAIL. MOREOVER...THE
HIGH MOISTURE CONTENT /I.E. PW VALUES AOA TWO INCHES/ WILL BE
SUPPORTIVE OF DAMAGING WET MICROBURSTS OWING TO WATER-LOADING
EFFECTS.
..MEAD/ROGERS.. 09/28/2011
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