SWODY1
SPC AC 281956
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT SAT AUG 28 2010
VALID 282000Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF SWRN MT/SERN
ID/WRN WY AND NRN UT...
...SWRN MT/WRN WY/SERN ID/NRN UT...
STRONG TO SEVERE THUNDERSTORMS ARE CURRENTLY ONGOING AND A SEVERE
THUNDERSTORM WATCH IS EFFECT UNTIL 00Z. STORMS SHOULD SHIFT NEWD
THROUGH THE AFTERNOON AND EVENTUALLY INTO MT AS SHORTWAVE TROUGH
EJECTS NEWD FROM SRN ID INTO WRN/CENTRAL MT. WHILE THERE IS A
POTENTIAL OF SEVERE STORMS SPREADING INTO SWRN MT LATER THIS
AFTERNOON...THE THREAT APPEARS LOWER THAN IN CURRENT WW DUE TO DRIER
AND MORE STABLE BOUNDARY LAYER.
...AZ...
DRYING IS EVIDENT IN BOTH WATER VAPOR AND VISIBLE SATELLITE DUE TO
THE FLOW TURNING MOSTLY SWLY/WLY ABOVE THE BOUNDARY LAYER. DUE TO
THE DRIER AIR MASS...STORM COVERAGE SHOULD BE MUCH LESS THAN FRI.
HOWEVER...WITH ANY STORMS THAT DO DEVELOP...STEEPENING LOW LEVEL
LAPSE RATES AND DRIER BOUNDARY LAYER WOULD BE FAVORABLE FOR A FEW
STRONG WIND GUSTS.
...CENTRAL GULF COAST/LOWER MS VALLEY...
VSBY SATELLITE AND SURFACE OBSERVATIONS INDICATE A WEAK SURFACE LOW
PRESSURE SYSTEM WAS LOCATED ABOUT 80 NM SSW OF LFT. THE STRONGEST
LOW LEVEL CONVERGENCE AND MORE VIGOROUS CONVECTION HAS AND IS
GENERALLY EXPECTED TO REMAIN GENERALLY OFFSHORE THROUGH THIS
FORECAST PERIOD. HOWEVER...MOIST BOUNDARY LAYER AND 20 KT LOW LEVEL
SHEAR MIGHT RESULT IN A BRIEF TORNADO OR TWO...ESPECIALLY NEAR THE
IMMEDIATE COASTAL COUNTIES.
..IMY.. 08/28/2010
.PREV DISCUSSION... /ISSUED 1117 AM CDT SAT AUG 28 2010/
...SWRN MT/WRN WY/SERN ID/NRN UT...
EFFECTIVE FRONTAL ZONE HAS STALLED FROM SERN ID SSWWD INTO ERN NV AS
TROUGH CONTINUES TO AMPLIFY FROM WA/OR INTO CA/WRN NV TODAY.
SURFACE LOW ERN NV WILL GRADUALLY DEEPEN AND MOVE INTO SERN ID THIS
EVENING WHILE FRONT ONLY SLOWLY MOVES EWD INTO WRN UT. THE MOIST
MONSOON PLUME IN PLACE FROM AZ NWD THRU UT INTO SERN ID/WRN WY WILL
FUEL POTENTIAL FOR AN ACTIVE THUNDERSTORM PERIOD...IN ADVANCE OF THE
SURFACE LOW AND COLD FRONT. DRYING WILL SPREAD NEWD IN THE STRONG
SWLY FLOW IN ADVANCE OF THE FRONT INTO WRN UT THIS AFTERNOON.
HOWEVER MORE THAN SUFFICIENT INSTABILITY EXPECTED TO BE AVAILABLE
FROM WASATCH FRONT EWD FOR POTENTIAL OF A FEW SEVERE THUNDERSTORMS
GIVEN THE STRENGTH OF THE SHEAR...STEEP LAPSE RATES IN PLACE AHEAD
OF APPROACHING UPPER TROUGH.
THUS HAVE EXPANDED THE SLIGHT RISK SWD INTO NRN UT/SWRN WY FOR THIS
AFTERNOON AND EVENING.
FURTHER N ACROSS SERN ID/NWRN WY INTO SWRN MT...CONDITIONS STILL
APPEAR FAVORABLE FOR STRONG/SEVERE THUNDERSTORMS GIVEN THE POTENTIAL
FOR MLCAPES OF 1000 J/KG...40-50KT OF SHEAR COUPLED WITH STEEP MID
LAPSE RATES. WITH ENHANCED LOW LEVEL SHEAR AHEAD OF THE SURFACE LOW
MOVING INTO SERN ID LATER THIS AFTERNOON...SUPERCELL THUNDERSTORMS
ARE POSSIBLE AND HAVE INCREASED THE POTENTIAL FOR LARGE HAIL
ACCORDINGLY.
...AZ...
OVER THE SWRN DESERTS TODAY SOME LOW LVL MOISTURE WILL LINGER
BENEATH DRYING/STRENGTHENING SW FLOW ALOFT AHEAD OF APPROACHING
TROUGH. HOWEVER BOUNDARY LAYER FLOW REMAINS OUT OF S WRN AZ
PROVIDING A CONTINUED SHALLOW FEED OF MOISTURE THRU THE DAY.
SATELLITE/MODELS DO NOT SUGGEST PRESENCE OF AN UPR LVL FEATURE TO
FOCUS LARGE SCALE ASCENT OVER THE REGION. BUT SETUP APPEARS
POTENTIALLY SUPPORTIVE OF A CONDITIONAL HYBRID-TYPE SVR EVENT...AS
SWLY MID/UPR LVL FLOW WILL BE SUFFICIENT TO SUPPORT A
FEW SUSTAINED STORMS/POSSIBLE SUPERCELLS GIVEN SUFFICIENT LOW LVL
CONVERGENCE TO PRODUCE STRONG UPDRAFTS.
...CNTRL GULF CST/LWR MS VLY...
LOW LVL SHEAR HAS INCREASED SOMEWHAT OVER COASTAL REGIONS OF
LA...MS...AND AL AS WEAK SURFACE LOW REMAINS JUST OF CENTRAL LA
COAST. LOW LVL SPEED/DIRECTIONAL SHEAR SUFFICIENT TO POSE A THREAT
FOR ISOLATED BRIEF TORNADOES GIVEN HI PW OVER REGION AND OBSERVED
LOW LEVEL SHEAR. HOWEVER...WITH THE OVERALL MARGINAL NATURE OF
CONDITIONS WITH NO INTENSIFICATION EXPECTED HAVE OPTED TO REDUCE
TORNADO PROBABILITIES AND REMOVE THE SLIGHT RISK.
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