SWODY1
SPC AC 201930
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0230 PM CDT TUE APR 20 2010
VALID 202000Z - 211200Z
...NO SVR TSTM AREAS FORECAST...
...GREAT BASIN...
EXIT REGION OF UPPER JET...AND ASSOCIATED ZONE OF FOCUSED
ASCENT...IS SPREADING ACROSS NRN CA/NWRN NV IN LINE WITH EARLIER
FORECASTS. ALONG THE LEADING EDGE OF THIS FORCING...STRONG UPDRAFTS
WITH LIGHTNING HAVE DEVELOPED FROM WASHOE COUNTY NV...SWD TO
CHURCHILL COUNTY NV. WITH SFC-3KM LAPSE RATES ROUGHLY DRY
ADIABATIC...HEAVIER RAIN SHOWERS BENEATH HIGH BASED THUNDERSTORMS
COULD PRODUCE MARGINALLY SEVERE WIND GUSTS WITHIN STRONGLY SHEARED
ENVIRONMENT. LARGE SCALE FORCING SEEMS SUPPORTIVE OF A LOOSELY
ORGANIZED SQUALL LINE SPREADING/DEVELOPING ENEWD INTO PARTS OF
ID/NERN NV INTO THE EARLY EVENING HOURS.
...HIGH PLAINS...
CONVECTION IS GRADUALLY DEEPENING ACROSS THE HIGHER TERRAIN OF
CO/NM...WITH GLACIATION AND LIGHTNING NOW OCCURRING WITH STRONGEST
UPDRAFTS. LATEST SATELLITE IMAGERY DEPICTS A RELATIVELY CLOUD-FREE
ZONE...ROUGHLY 100 MI WIDE...JUST DOWNSTREAM OF THE EAST SLOPES
WHICH CONTINUES TO WARM AND DESTABILIZE. LATEST OBSERVATIONAL DATA
SUGGESTS A NARROW AXIS OF SBCAPE VALUES ON THE ORDER OF 500-1000
J/KG WILL PROVE SUPPORTIVE OF GROWTH/MAINTENANCE OF MARGINALLY
SHEARED UPDRAFTS...PRIMARILY ACROSS THE HIGH PLAINS WEST OF THE
THICK STRATUS DECK. SOME HAIL AND GUSTY WINDS REMAIN POSSIBLE.
..DARROW.. 04/20/2010
.PREV DISCUSSION... /ISSUED 1127 AM CDT TUE APR 20 2010/
...SYNOPSIS...
A STRONG MIDLEVEL TROUGH WILL MOVE SEWD OVER CENTRAL/SRN CA THROUGH
THE PERIOD...WHILE A SPLIT FLOW REGIME PERSISTS DOWNSTREAM OVER MUCH
OF THE CONUS. THE RICHER MOISTURE AND ASSOCIATED INSTABILITY IS
LOCATED WELL TO THE S ACROSS THE GULF OF MEXICO IN ASSOCIATION WITH
A MEAN BAROCLINIC ZONE AND THE SUBTROPICAL JET. ONE EMBEDDED SPEED
MAX NOW OVER THE NW GULF WILL MOVE EWD TO FL BY TONIGHT...BUT MODEST
LOW-LEVEL MOISTURE AND POOR MIDLEVEL LAPSE RATES WILL LIMIT THE
THREAT FOR STRONG/SEVERE STORMS ACROSS FL THROUGH THE PERIOD.
...CENTRAL HIGH PLAINS THIS AFTERNOON/EVENING...
THE PRIMARY THREAT AREA FOR STRONG/SEVERE STORMS THIS AFTERNOON INTO
EARLY TONIGHT WILL BE ACROSS THE CENTRAL HIGH PLAINS IN ASSOCIATION
WITH A WEAK SURFACE LEE TROUGH/CYCLONE. EMBEDDED SPEED MAXIMA
/WITHIN AN INTERMEDIATE FLOW STREAM/ WILL PROGRESS SEWD FROM ERN WY
TO KS...AND ANOTHER WEAKER SPEED MAX WILL EJECT EWD ACROSS CO IN
ADVANCE OF THE CA TROUGH. AT THE SURFACE...A WEAK LEE CYCLONE
ACROSS SE CO WILL DRIFT SWD BY TONIGHT AS A REINFORCING COLD FRONTAL
SURGE PROGRESSES SWD ACROSS THE HIGH PLAINS IN ASSOCIATION WITH THE
MIDLEVEL SPEED MAX. THE COMBINATION OF THE SURFACE BOUNDARIES AND
MIDLEVEL TROUGH WILL HELP FOCUS THUNDERSTORM DEVELOPMENT ACROSS ERN
CO/SW NEB/WRN KS THIS AFTERNOON...AND CONVECTION WILL MOVE SEWD
ACROSS KS TO NW OK TONIGHT.
VISIBLE IMAGERY SHOWS SOME THINNING OF THE STRATUS CLOUDS ACROSS SE
CO...WHILE THE 12Z SOUNDINGS SUGGEST THAT CLOUDS WILL PERSIST AT
LEAST INTO EARLY AFTERNOON FARTHER E INTO SW KS TO THE ERN TX
PANHANDLE. THUS...THE STRONGER SURFACE HEATING WILL OCCUR NEAR THE
LEE TROUGH/CYCLONE ACROSS SE CO THIS AFTERNOON...WHERE MLCAPE WILL
APPROACH 1000 J/KG WITH TEMPERATURES IN THE LOW 70S AND BOUNDARY
LAYER DEWPOINTS IN THE MID-UPPER 40S. ADDITIONALLY...MIDLEVEL FLOW
WILL GRADUALLY INCREASE TO NEAR 30 KT ABOVE LOW-LEVEL SLY/SELY
FLOW...RESULTING IN EFFECTIVE BULK SHEAR OF 30-40 KT. THE
COMBINATION OF VERTICAL SHEAR AND INSTABILITY WILL BE AT LEAST
MARGINALLY SUFFICIENT FOR SUPERCELLS...WITH HAIL NEAR 1 INCH IN
DIAMETER POSSIBLE...ALONG WITH STRONG OUTFLOW WINDS. OVERALL...THE
SEVERE STORM THREAT STILL APPEARS TO BE A LITTLE TOO MARGINAL TO
JUSTIFY A CATEGORICAL UPGRADE.
...NRN GREAT BASIN THIS AFTERNOON/EVENING...
THOUGH LOW-LEVEL MOISTURE WILL BE SOMEWHAT LIMITED ACROSS THE GREAT
BASIN THIS AFTERNOON/EVENING...CONDITIONALLY UNSTABLE LAPSE RATES
AND FOCUSED ASCENT NE OF THE CA MIDLEVEL LOW WILL RESULT IN THE
DEVELOPMENT OF WEAK INSTABILITY FROM NRN NV INTO SW ID. A FEW
THUNDERSTORMS WILL FORM ALONG THE DEEP BAROCLINIC ZONE AND BELT OF
ASCENT BY MID-LATE AFTERNOON...WHEN INSTABILITY AND DEEP-LAYER SLY
VERTICAL SHEAR COULD SUPPORT STORMS WITH SMALL HAIL AND STRONG
OUTFLOW WINDS.
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