SPC AC 150530
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 AM CDT TUE SEP 15 2009
VALID 151200Z - 161200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A LARGE-SCALE BLOCKING PATTERN WILL BE MAINTAINED OVER N AMERICA
WITH THE PRIMARY BELT OF POLAR WESTERLIES CONFINED LARGELY TO
CANADA. DETACHED FROM THIS HIGHER MOMENTUM FLOW ARE TWO UPPER
LOWS...ONE WHICH WILL DRIFT SLOWLY SWD THROUGH UT INTO NRN AZ...AND
THE OTHER WHICH WILL REMAIN QUASI-STATIONARY OVER THE ARKLATEX.
...GREAT BASIN INTO CNTRL/SRN HIGH PLAINS...
15/00Z UPPER-AIR ANALYSIS SHOWED 500 MB TEMPERATURES OF -14 C
ASSOCIATED WITH UPPER LOW WHICH WERE CONTRIBUTING TO STEEP MIDLEVEL
LAPSE RATES OF AROUND 8 C/KM. MOISTURE WILL REMAIN MARGINAL AND
SIMILAR TO THAT OF MONDAY /PW VALUES OF .7-.8 INCH/...WITH THE STEEP
LAPSE RATES LARGELY CONTRIBUTING TO WEAK CONVECTIVE INSTABILITY OVER
THE COMPLEX TERRAIN OF UT/CO AS WELL AS ALONG LEE TROUGH OVER THE
HIGH PLAINS.
DYNAMIC FORCING FOR ASCENT ATTENDANT TO UPPER SYSTEM WILL LIKELY BE
WEAKER TODAY OWING TO DECELERATION AND NOW CLOSED NATURE OF MIDLEVEL
SYSTEM. BUT...WHEN COUPLED WITH OROGRAPHIC FORCING AND CONVERGENCE
ALONG LEE TROUGH...EXPECT ISOLATED TO SCATTERED DIURNAL STORM
DEVELOPMENT FROM VICINITY OF MIDLEVEL COLD POOL OVER UT/CO EWD/SEWD
ALONG LEE TROUGH. MARGINAL VERTICAL SHEAR AND INSTABILITY ARE
EXPECTED TO PRECLUDE AN ORGANIZED SEVERE THREAT. HOWEVER...BRIEFLY
SEVERE STORMS WILL BE POSSIBLE WITH THE THREAT FOR HAIL AND LOCALLY
STRONG WIND GUSTS THROUGH THIS EVENING.
...CNTRL GULF STATES...
SYNOPTIC PATTERN WILL REMAIN THE SAME AS PREVIOUS SEVERAL DAYS WHERE
VORTICITY MAXIMA ROTATING AROUND QUASI-STATIONARY UPPER LOW FOCUS
CLUSTERS OF STRONG TSTMS THROUGH THE AFTERNOON AND EVENING HOURS.
AIR MASS WILL REMAIN QUITE MOIST WITH PW VALUES AOA 2 INCHES...
SUPPORTING MLCAPE OF 1000-2000 J/KG. WHILE A LOW PROBABILITY THREAT
OF A BRIEF TORNADO OR WIND GUST WILL EXIST ACROSS SYSTEM WARM
SECTOR...THE MARGINAL VERTICAL SHEAR WILL PRECLUDE A MORE ROBUST
SEVERE THREAT.
..MEAD/JEWELL.. 09/15/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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