Heat Advisory 5, NWS Columbia, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
255 PM EDT WED AUG 6 2008

.SYNOPSIS...
A SLOW MOVING COLD FRONT WILL MOVE INTO THE FORECAST AREA THURSDAY
NIGHT. THE WEAKENING FRONT WILL LINGER NEAR THE REGION THROUGH
FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
WEAK CONVERGENCE ASSOCIATED WITH THE LEE TROUGH WAS OCCURRING EARLY
THIS AFTERNOON. INSTABILITY WAS MODERATE WITH LI/S AROUND -6.
HOWEVER...THE THUNDERSTORM CHANCE APPEARS VERY LOW BECAUSE OF THE
DRY AIR MASS. EARLY AFTERNOON SATELLITE IMAGERY SHOWED LITTLE
CUMULUS DEVELOPMENT. H7 TEMPERATURES WERE 10 TO 11 C. WATER VAPOR
IMAGERY SUPPORTS THE RUC/S FORECAST OF SHORTWAVE RIDGING OVER THE
REGION.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
MOISTURE WILL INCREASE ASSOCIATED WITH CONVERGENCE IN THE LEE TROUGH
AND APPROACHING COLD FRONT THURSDAY. ALL OF THE GUIDANCE HAS LOW POPS. THE
LOW VALUES APPEAR REASONABLE BECAUSE OF THE H85 NORTHWEST TO WEST
FLOW WITH LIMITED MOISTURE PLUS WEAK LOW-LEVEL CONVERGENCE. A
SIGNIFICANT UPPER-LEVEL FEATURE ALSO APPEARS LACKING. PLAN TO
FORECAST SLIGHT CHANCE POPS WHICH IS SUPPORTED BY THE
MAV...MET...AND FWC MOS. CONTINUED CONVERGENCE ASSOCIATED WITH THE
SLOW MOVING FRONT PLUS THE NAM AND GFS FORECAST OF AN H5
SHORTWAVE TROUGH SUPPORT A BETTER CHANCE OF THUNDERSTORMS THURSDAY
NIGHT...ESPECIALLY DURING THE EVENING AND CLOSER TO MAXIMUM
HEATING. USED THE GUIDANCE CONSENSUS POP AROUND 50 PERCENT. THE
LIKELY MAV POPS MAY BE TOO HIGH BASED ON THE WEST TO NORTHWEST H85
FLOW. MODERATE INSTABILITY SUPPORTS POSSIBLE SEVERE WIND GUSTS
WITH A FEW OF THE THUNDERSTORMS THURSDAY AFTERNOON AND EVENING.
THE SURFACE FRONT MAY LINGER IN THE FORECAST AREA BUT THE MODELS
INDICATE DEEPER MOISTURE SHIFTING EAST AND SOUTH OF THE AREA FOR
THURSDAY NIGHT AND FRIDAY. PLAN TO CONTINUE THE SMALL THUNDERSTORM
CHANCE.

USED THE MET MOS FOR THE TEMPERATURE FORECAST BECAUSE IT HAS
VERIFIED BEST LATELY. EXPECT HEAT ADVISORY CRITERIA OF 105 FOR 2 OR
MORE HOURS WILL OCCUR IN THE SOUTHEAST PART OF THE FORECAST AREA
THURSDAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
THE GFS SHOWS CONTINUED SURFACE TROUGHING BUT DEEPER MOISTURE
APPEARS TO REMAIN EAST AND SOUTH OF THE FORECAST AREA DURING MOST OF
THE EXTENDED PERIOD. MOST OF THE MOISTURE APPEARS TO STAY EAST AND
SOUTH OF THE REGION THROUGH MOST OF THE EXTENDED PERIOD. THE GFS
ENSEMBLE MEANS SUPPORT TEMPERATURES NEAR CLIMATOLOGY. POPS APPEAR
LOW...ESPECIALLY OVER THE WEEKEND.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
LATEST ANALYSIS INDICATES MODERATE TO STRONG SURFACE INSTABILITIES
OVER THE REGION...HOWEVER ATMOSPHERIC MOISTURE APPEARS
LIMITED...WITH HIGH CONVECTIVE TEMPS AND LEVELS OF FREE
CONVECTION. THIS SHOULD REDUCE AREAL TSRA COVERAGE OVER OUR FA.
HOWEVER...ANY TSRA THAT DOES DEVELOP COULD BE STRONG GIVEN DRY AIR
ALOFT AND RELATIVELY LOW WET BULB ZERO HEIGHT. AT THIS TIME...IT
APPEARS THAT THUNDER CHANCE IS TOO LOW TO INCLUDE ANY REFERENCE TO
IT IN THE 18Z TAFS. VFR CONDITIONS EXPECTED THROUGH THE 24 HOUR
TAF PERIOD...ALTHOUGH MVFR VSBYS IN HAZE OR FOG POSSIBLE THURSDAY
MORNING.

EXTENDED AVIATION OUTLOOK...ATMOSPHERIC MOISTURE WILL BE ON THE
INCREASE THURSDAY...ALONG WITH A SURFACE FRONT AND DEEPENING UPPER
TROUGH. THIS WILL ALLOW FOR A BETTER CHANCE OF TSRA THU AFTN/EVE...BUT
WILL EXPECT IT AFTER 18Z. A CHANCE OF THUNDER FRIDAY...THEN DRIER
AIR BEHIND THE FRONT IS EXPECTED TO PRECLUDE ANY SIGNIFICANT
CONVECTION SATURDAY AND SUNDAY.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...HEAT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR SCZ029>031-
     035>038-041.
     HEAT ADVISORY FROM 1 PM TO 7 PM EDT THURSDAY FOR SCZ031-
     035>038-041.
GA...HEAT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR GAZ063>065-077.
     HEAT ADVISORY FROM 1 PM TO 7 PM EDT THURSDAY FOR GAZ077.

&&

SYNOPSIS...JL
NEAR TERM...JL
SHORT TERM...JL
LONG TERM...JL
AVIATION...31

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