SWODY1
SPC AC 210528
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 AM CDT WED APR 21 2010
VALID 211200Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PORTIONS OF THE CNTRL AND SRN HIGH PLAINS...
...SYNOPSIS...
AN INTENSE MID AND UPPER-LEVEL LOW CURRENTLY DIGGING SSEWD ALONG THE
CA COAST WILL UNDERGO FURTHER STRENGTHENING WHILE PROGRESSING SEWD
INTO THE GREAT BASIN AND LOWER CO VALLEY. THIS SYSTEM WILL BE
ACCOMPANIED BY A 100+ KT UPPER-LEVEL JET STREAK AND SIGNIFICANT
HEIGHT FALLS WHICH WILL SPREAD EWD THROUGH THE GREAT BASIN AND LOWER
CO VALLEY INTO THE CNTRL AND SRN ROCKIES THROUGH THE DAY ONE
PERIOD.
AT THE SURFACE...BROAD LEE CYCLOGENESIS IS FORECAST OVER THE CNTRL
AND SRN HIGH PLAINS TODAY...PRIOR TO CONSOLIDATION INTO A MORE
CONCENTRATED LOW CENTER OVER ERN CO TONIGHT. AS THIS PROCESS
OCCURS...A NW-SE ORIENTED BAROCLINIC ZONE IS EXPECTED TO STRENGTHEN
FROM SERN CO THROUGH THE OK/TX PNHDLS INTO THE RED RIVER VALLEY. A
WEAK DRYLINE OR LEE TROUGH WILL THEN EXTEND FROM THE INTERSECTION
WITH THIS FRONT SWD THROUGH WRN TX.
FARTHER W...A SURFACE LOW INITIALLY OVER WRN UT WILL DEEPEN WHILE
DEVELOPING NWD AND THEN NWWD INTO THE SNAKE RIVER VALLEY IN
CONJUNCTION WITH A STRONG VORTICITY MAXIMUM ROTATING AROUND THE
PARENT UPPER SYSTEM. MEANWHILE...TRAILING PACIFIC FRONT WILL SURGE
EWD THROUGH THE GREAT BASIN AND LOWER CO VALLEY INTO THE CNTRL AND
SRN ROCKIES.
...CNTRL AND SRN HIGH PLAINS...
THE DEEPENING LEE CYCLONE WILL ALLOW FOR THE NWD/NWWD FLUX OF AN
INCREASINGLY MOIST BOUNDARY LAYER WITH DEW POINTS INCREASING THROUGH
THE 50S FROM THE LOWER RIO GRANDE VALLEY INTO OK AND THE ERN OK/TX
PNHDLS. WHEN COUPLED WITH THE PRESENCE OF STEEP LAPSE RATES...THE
AFTERNOON AIR MASS OVER THE SLIGHT RISK AREA WILL BECOME MODERATELY
UNSTABLE WITH MLCAPE RANGING FROM AROUND 1000 J/KG OVER SERN CO TO
1500-2000 J/KG ACROSS THE ERN TX PNHDL AND NWRN TX INTO WRN OK.
00Z MESOSCALE MODEL GUIDANCE SUGGESTS THAT THE REGION WILL INITIALLY
RESIDE UNDER GRADUALLY BUILDING MIDLEVEL HEIGHTS DOWNSTREAM FROM
AMPLIFYING UPPER-LEVEL SYSTEM. HOWEVER...BY LATE AFTERNOON AND MORE
SO THIS EVENING...THE LEADING EDGE OF MORE MEANINGFUL HEIGHT FALLS
WILL BEGIN TO OVERSPREAD THE AREA FROM THE W. THIS PROCESS IN
CONJUNCTION WITH OROGRAPHIC UPSLOPE FLOW OVER SERN CO AND
CONVERGENCE ALONG THE ABOVE-MENTIONED SURFACE BOUNDARIES SHOULD
ALLOW FOR THE DEVELOPMENT OF ISOLATED TO SCATTERED DIURNAL STORMS
ACROSS THE SLIGHT RISK AREA.
SELY SURFACE WINDS VEERING TO WLY AT 25-35 KT IN THE MIDLEVELS WILL
RESULT IN 35-45 KT OF DEEP-LAYER SHEAR...SUFFICIENT FOR SUPERCELLS
GIVEN THE DEGREE OF INSTABILITY. SEVERE HAIL WILL BE THE PRIMARY
HAZARD WITH THESE STORMS AS THEY MATURE AND SLOWLY MOVE EWD/SEWD. A
TORNADO OR TWO IS POSSIBLE...ESPECIALLY WITH ANY SUPERCELLS THAT CAN
FAVORABLY INTERACT WITH PRE-EXISTING SURFACE BOUNDARIES -- MESOSCALE
OR SYNOPTIC. A MORE ROBUST TORNADO THREAT WILL LIKELY BE LIMITED BY
THE MARGINAL MOISTURE QUALITY WHICH WILL LEAD TO A STRENGTHENING CAP
LATER THIS EVENING WHEN THE LLJ AND NEAR-GROUND SHEAR ARE RAPIDLY
INTENSIFYING.
CLUSTERS OF MAINLY ELEVATED STORMS WILL LIKELY CONTINUE OVERNIGHT
ACROSS PARTS OF KS AND OK WITHIN A STRENGTHENING WAA REGIME
COINCIDENT WITH THE LLJ AXIS. THE STRONGER STORMS WILL BE CAPABLE
OF SOME HAIL WHICH MAY APPROACH SEVERE LEVELS.
...SNAKE RIVER VALLEY AND ERN PARTS OF THE GREAT BASIN INTO THE
CNTRL ROCKIES...
SIMILAR TO TUESDAY...STEEP LAPSE RATES...STRONG DYNAMIC FORCING AND
VERTICAL SHEAR MAY YIELD A FEW ORGANIZED STORMS ALONG THE PACIFIC
FRONT WITH THE PRIMARY SEVERE THREAT BEING DAMAGING WIND GUSTS.
THIS THREAT SHOULD BEGIN TO DIMINISH BY LATE EVENING AS THE BOUNDARY
LAYER COOLS AND STABILIZES.
..MEAD/SMITH.. 04/21/2010
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