SPC AC 211625
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1125 AM CDT FRI MAY 21 2010
VALID 211630Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER
PARTS OF THE CNTRL AND SRN HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE OH VALLEY SWD
INTO THE GULF COAST STATES...
...SYNOPSIS...
LARGE-SCALE PATTERN WILL AMPLIFY THROUGH THE PERIOD AS STRONG ERN
PACIFIC JET STREAK DIGS SEWD ALONG THE WEST COAST...EFFECTIVELY
SUPPORTING THE INTENSIFICATION OF A BROAD TROUGH OVER THE WRN
STATES. WITHIN THIS BROADER-SCALE PATTERN...A SHORT WAVE TROUGH NOW
OVER CNTRL ORE/NRN CA WILL TRANSLATE NEWD INTO THE NRN HIGH PLAINS
LATER TONIGHT. ELSEWHERE...A NEGATIVELY-TILTED MIDLEVEL TROUGH WILL
CONTINUE TO LIFT NEWD THROUGH THE OH VALLEY AND GREAT LAKES
REGION...WHILE AN ASSOCIATED VORTICITY MAXIMUM PROGRESSES FROM THE
SRN APPALACHIANS INTO THE PIEDMONT AND COASTAL PLAINS.
...HIGH PLAINS...
MORNING SURFACE ANALYSIS SHOWS A BAROCLINIC ZONE EXTENDING FROM
CNTRL ND SWWD THROUGH SWRN SD...SRN WY TO CNTRL UT. THIS FRONT IS
EXPECTED TO MOVE LITTLE THROUGH THE DAY WHILE A LEE TROUGH
STRENGTHENS SWD ALONG THE CO FRONT RANGE TO ALONG THE TX/NM BORDER.
INTENSIFYING SLY LOW-LEVEL FLOW E OF THIS LEE TROUGH WILL SERVE TO
ENHANCE THE NWD FLUX OF AN INCREASINGLY MOIST BOUNDARY LAYER WITH
DEW POINTS RISING THROUGH THE 50S OVER THE CNTRL HIGH PLAINS...TO
60S FARTHER S. AT THE SAME TIME...STRENGTHENING SWLY MIDLEVEL FLOW
REGIME ACROSS THE ROCKIES WILL RESULT IN THE EWD PROGRESSION OF AN
EML ACROSS THE MOISTURE AXIS WITH MLCAPE INCREASING TO 1000-1500
J/KG AS FAR N AS THE PALMER DIVIDE AND CHEYENNE RIDGE...TO 1500-2000
J/KG OVER THE OK/TX PNHDLS AND W TX.
12Z MODEL GUIDANCE SUGGESTS THAT THE MOST SIGNIFICANT HEIGHT
FALLS/DYNAMIC FORCING FOR ASCENT WILL REMAIN TO THE W OF THE
DEVELOPING INSTABILITY AXIS THROUGH THE DIURNAL HEATING CYCLE.
HOWEVER...THESE DATA DO SUGGEST THAT AFTERNOON/EVENING TSTM
DEVELOPMENT WILL BE MOST LIKELY NEAR THE ABOVE-MENTIONED STATIONARY
FRONT AND NRN EXTENSION OF LEE TROUGH OVER WY/NERN CO/NEB PNHDL.
HERE...THE COMBINATION OF 45-55 KT OF DEEP-LAYER SHEAR AND A
STRENGTHENING LOW-LEVEL WIND FIELD WILL RESULT IN A KINEMATIC
ENVIRONMENT QUITE SUPPORTIVE OF SUPERCELLS CAPABLE OF LARGE HAIL AND
A FEW TORNADOES.
FARTHER S ALONG THE LEE TROUGH/DRY LINE...CONVECTIVE INITIATION
BECOMES MUCH MORE UNCERTAIN DUE TO THE ABSENCE OF ANY APPRECIABLE
LARGE-SCALE FORCING MECHANISMS. GIVEN THE DEGREE OF INSTABILITY AND
MODERATELY STRONG LOW/DEEP-LAYER SHEAR...A CONDITIONAL THREAT FOR
SUPERCELLS CAPABLE OF LARGE HAIL AND PERHAPS A COUPLE OF TORNADOES
WILL EXIST SHOULD ISOLATED STORMS DEVELOP AND BECOME SUSTAINED LATER
TODAY.
...SERN STATES...
A COUPLE OF MCS/S ARE ONGOING THIS MORNING OVER NRN GA AND NRN PARTS
OF AL/MS. 12Z OBSERVED SOUNDING DATA INDICATE THAT A MOIST AND
POTENTIALLY MODERATELY UNSTABLE AIR MASS RESIDES TO THE S OF A
COMPOSITE OUTFLOW BOUNDARY/SYNOPTIC FRONT EXTENDING FROM N OF GWO TO
AUO TO AYS. VISIBLE SATELLITE IMAGERY SUGGESTS STRONG DIABATIC
HEATING SHOULD OCCUR TODAY ALONG AND TO THE S OF THIS
BOUNDARY...SUPPORTING MLCAPE OF 2000-2500 J/KG. WHILE REGION WILL
RESIDE ALONG THE SRN FRINGE OF STRONGER MIDLEVEL WIND FIELD
ATTENDING OH VALLEY TROUGH...THE PRESENCE OF AROUND 30 KT OF DEEP
NWLY SHEAR SHOULD ALLOW FOR THE ONGOING MCS/S TO DEVELOP
FORWARD-PROPAGATING CHARACTERISTICS. CURRENTLY...IT APPEARS THAT
THE HIGHEST LIKELIHOOD FOR A CORRIDOR OF WIND DAMAGE MAY DEVELOP
TODAY FROM PARTS OF CNTRL AL INTO CNTRL/SRN GA AS THE WRN MCS
PROPAGATES SEWD ALONG THE SURFACE BAROCLINIC ZONE.
...OH/TN VALLEYS...
TSTMS ARE GRADUALLY INTENSIFYING THIS MORNING OVER WRN IND ALONG
DEEPER WIND SHIFT ASSOCIATED WITH THE MIGRATORY UPPER TROUGH.
FAIRLY WIDESPREAD LOW CLOUDS WILL SLOW THE DESTABILIZATION
PROCESS...THOUGH THE CONTINUED NWD FLUX OF 60+ F BOUNDARY LAYER DEW
POINTS AND MIDLEVEL COOLING ASSOCIATED WITH THE TROUGH WILL SUPPORT
MODEST INSTABILITY BY AFTERNOON WITH MLCAPE RANGING FROM 500-1000
J/KG OVER PARTS OF IND/OH TO 1000-1500 J/KG ACROSS KY/TN.
FORCING FOR ASCENT ASSOCIATED WITH THE MIDLEVEL TROUGH COUPLED WITH
THE DESTABILIZING ENVIRONMENT ARE EXPECTED TO FOSTER A BROKEN BAND
OF TSTMS BY AFTERNOON FROM IND SWD INTO KY AND PERHAPS TN. VERTICAL
SHEAR WILL NOT BE PARTICULARLY STRONG...BUT SUFFICIENT FOR SOME
STORM ORGANIZATION. HAIL AND STRONG WIND GUSTS WILL BE THE PRIMARY
SEVERE WEATHER HAZARDS...THOUGH A TORNADO OR TWO WILL BE POSSIBLE.
..MEAD/HURLBUT.. 05/21/2010
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