SPC AC 130543
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 AM CDT SUN SEP 13 2009
VALID 131200Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
OVER ERN MT...
...SYNOPSIS...
UPPER LOW CURRENTLY RETROGRADING NWWD INTO THE NRN HIGH PLAINS WILL
BEGIN TO LIFT MORE RAPIDLY NWD TODAY /THROUGH MT/ IN RESPONSE TO
APPROACH OF PROGRESSIVE...UPSTREAM SYSTEM MOVING ONTO THE PACIFIC
COAST. IN CONTRAST...A MORE STAGNANT AIRFLOW PATTERN WILL EXIST
OVER THE SRN STATES...PUNCTUATED BY UPPER LOW OVER TX/OK. A PV
ANOMALY IS FORECAST TO ROTATE AROUND THIS FEATURE FROM THE TX COAST
INTO THE LOWER MS VALLEY...LIKELY FOCUSING A LARGE AREA OF TSTMS
OVER THE CNTRL GULF STATES.
...NRN HIGH PLAINS...
13/00Z REGIONAL OBSERVED SOUNDINGS SHOW THAT LOW-LEVEL MOISTURE
REMAINS SOMEWHAT LIMITED WITH DEWPOINTS IN THE 40S TO LOWER 50S AND
LOWEST 100 MB MEAN MIXING RATIOS OF 6-8 G/KG. HOWEVER...STEEP
MIDLEVEL LAPSE RATES ASSOCIATED WITH COLD POOL /AROUND -16 C AT 500
MB/ OF UPPER SYSTEM WILL CONTRIBUTE TO POCKETS OF MODERATE
INSTABILITY BY AFTERNOON WITH MLCAPE OF AROUND 1000 J/KG.
PRIMARY FOCUS FOR STORM INITIATION APPEARS TO BE A WEAK SURFACE LOW
AND ATTENDANT FRONTAL BOUNDARY DEVELOPING FROM WY NWD INTO MT.
FORECAST SOUNDINGS SUGGEST THAT CAPPING ASSOCIATED WITH EML MAY
DELAY TSTM DEVELOPMENT UNTIL LATE AFTERNOON OR EARLY EVENING.
HOWEVER...WHEN STORMS DEVELOP...THE PRESENCE OF THE STEEP LAPSE
RATES...VEERING WINDS WITH HEIGHT AND 40-45 KT OF DEEP-LAYER SHEAR
SUGGEST THE POTENTIAL FOR ORGANIZED STORMS INCLUDING SUPERCELLS WITH
THE PRIMARY SEVERE THREAT BEING HAIL.
...WRN/CNTRL GULF COAST...
SYNOPTIC PATTERN WILL REMAIN QUITE SIMILAR TO THAT OF SATURDAY...
FEATURING AN IMPULSE ROTATING AROUND PRIMARY UPPER LOW WHICH WILL
SUPPORT WEAK CYCLOGENESIS OVER THE LOWER SABINE VALLEY. ATTENDANT
WARM FRONT MAY MOVE FURTHER INLAND /COMPARED TO SAT/...ALLOWING A
QUITE MOIST /DEWPOINTS IN THE LOWER TO MID 70S/ AIR MASS TO DEVELOP
NWD THROUGH THE I-10 CORRIDOR. LAPSE RATES WILL REMAIN AOB MOIST
ADIABATIC...THOUGH THE RICH BOUNDARY LAYER MOISTURE AND SOME HEATING
WILL CONTRIBUTE TO MLCAPE OF 1000-1500 J/KG.
MID AND HIGH-LEVEL FLOW WILL STRENGTHEN THROUGH THE DAY...HOWEVER
LOW-LEVEL WIND FIELDS AND RESULTANT NEAR-GROUND SHEAR WILL REMAIN
COMPARABLY WEAKER. AS SUCH...SETUP WILL FAVOR THE DEVELOPMENT OF
STRONG STORM CLUSTERS WHICH MAY EXHIBIT EPISODIC UPDRAFT ROTATION.
WHILE A BRIEF TORNADO AND/OR STRONG WIND GUST IS POSSIBLE...THIS
THREAT APPEARS TOO MARGINAL TO WARRANT A CATEGORICAL SLIGHT RISK.
..MEAD/JEWELL.. 09/13/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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