Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 201800
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
200 PM EDT WED AUG 20 2014

.SYNOPSIS...
DRIER AIR AND A BUILDING UPPER RIDGE JUST TO OUR WEST WILL REDUCE
THUNDERSTORM CHANCES THROUGH FRIDAY...AND LEAD TO HOTTER HIGH
TEMPERATURES. AN APPROACHING COLD FRONT AND INCREASING MOISTURE
WILL INCREASE THE THUNDERSTORM CHANCE OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
EARLY AFTERNOON SATELLITE IMAGES SHOWED LIMITED CUMULUS DEVELOPMENT.
MOISTURE OVER THE AREA WAS SHALLOW. THE EARLY AFTERNOON ANALYSIS HAD
A WEAK SURFACE TROUGH. THE WATER VAPOR IMAGERY INDICATED A SHORTWAVE
TROUGH APPROACHING IN THE NORTHWEST FLOW BUT MUCH OF THE LIFT
ASSOCIATED WITH THIS FEATURE WAS NORTH OF THE FORECAST AREA. THE
HIGH-RESOLUTION MODELS INDICATED JUST ISOLATED THUNDERSTORMS AND
THESE WERE MAINLY CONFINED TO A FEW LOCATIONS IN THE UPPER SAVANNAH
RIVER AREA CLOSER TO WHERE SATELLITE INDICATED MORE ENHANCED CUMULUS
AND DEEPER MOISTURE. THE FORECAST OF JUST SLIGHT CHANCE POPS STILL
APPEARS ON TRACK BASED ON SATELLITE AND RADAR TRENDS AND THE
FORECAST OF CONTINUED SHALLOW MOISTURE AND LITTLE CONVERGENCE INTO
THE WEAK SURFACE FEATURE.

MODERATE TO STRONG INSTABILITY HAS DEVELOPED. EARLY AFTERNOON
LI/S WERE -7 TO -8. DAMAGING WIND COULD POSSIBLY OCCUR WITH ANY
THUNDERSTORMS. TEMPERATURES WILL PEAK IN THE MIDDLE 90S.

THE THUNDERSTORM CHANCE SHOULD FURTHER DIMINISH OVERNIGHT WITH THE
LOSS OF HEATING AND MID-LEVEL SHORTWAVE RIDGING. NOCTURNAL COOLING
WITH DRY AIR ALOFT AND LIGHT WIND SHOULD HELP SUPPORT AREAS OF FOG
TOWARD SUNRISE. THE TEMPERATURE GUIDANCE WAS CONSISTENT WITH LOWS
IN THE LOWER AND MIDDLE 70S.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
UPPER RIDGE WILL BUILD JUST TO OUR WEST. THIS AND A LOW LEVEL
DOWNSLOPE FLOW WILL LEAD TO WARMING TEMPS. MODELS CONTINUE TO
INDICATE MAX TEMPS NEAR 100 DEGREES MOST AREAS...AND CONTINUE TO
INDICATES DEW POINTS MIXING DOWN INTO THE MID TO UPPER 60S ACROSS
THE NORTHERN AND WESTERN COUNTIES TO NEAR 70 OR LOWER 70S ACROSS
THE SOUTHEAST MIDLANDS. THIS KEEPS HEAT INDICES JUST BELOW OUR
HEAT ADVISORY CRITERIA OF 110F. ONLY SLIGHT CHANCE OF SHOWERS/TSTMS
EXPECTED DUE TO BUILDING RIDGE ALOFT...AND FAIRLY DRY LOW LEVEL
AIR LEADING TO AND HIGH LEVELS OF FREE CONVECTION/HIGH CONVECTIVE
TEMPS.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
UPPER RIDGE TO OUR WEST WITH UPPER TROUGH AND CLOSED LOW TO OUR
NE...PROVIDING A NW FLOW ALOFT FOR OUR FA. SOME TIMING
UNCERTAINTIES WITH A BACK DOOR FRONT. MODELS TRENDING A LITTLE
SLOWER WITH IT OF LATE...WITH POSSIBILITY THAT IT MAY NOT MAKE IT
TO OUR FA UNTIL SATURDAY AFTERNOON OR EVENING...SLOWLY PUSHING
SOUTH THROUGH SUNDAY. INCREASING POPS/THUNDER CHANCE ALONG AND
SOUTH OF THE BOUNDARY...WITH COOLER TEMPS NORTH OF IT. FRONT TO
PUSH TO OUR SOUTH EARLY NEXT WEEK...WITH SURFACE AND UPPER RIDGE
OVER THE EASTERN SEABOARD.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
EXPECT MAINLY VFR CONDITIONS THROUGH THE PERIOD.

THE LATEST ANALYSIS SHOWED SURFACE RIDGING TO OUR SOUTH WITH WEAK
TROUGHING IN THE FORECAST AREA. STRONG HEATING PLUS SOME SUPPORT
ASSOCIATED WITH THE SURFACE FEATURE AND A MID-LEVEL SHORTWAVE
TROUGH COULD HELP CAUSE THUNDERSTORMS. HOWEVER...MOISTURE WAS
SHALLOW AND CONVERGENCE INTO THE SURFACE FEATURE SHOULD REMAIN
WEAK. EARLY AFTERNOON SATELLITE TRENDS INDICATED LIMITED CUMULUS
DEVELOPMENT. MUCH OF THE LIFT ASSOCIATED WITH THE MID-LEVEL
SHORTWAVE TROUGH WILL STAY NORTH OF THE AREA. EXPECT JUST ISOLATED
THUNDERSTORM COVERAGE THIS AFTERNOON AND EVENING WITH THE CHANCE
TOO LOW TO INCLUDE IN THE TERMINAL FORECASTS AT THIS TIME. THE
ISOLATED COVERAGE WAS SUPPORTED BY THE HIGH RESOLUTION MODELS.
MODERATE TO STRONG INSTABILITY HAS DEVELOPED. SURFACE-BASED LI/S
WERE -7 TO -8 EARLY THIS AFTERNOON. THEREFORE...VERY STRONG WIND
MAY OCCUR NEAR ANY THUNDERSTORMS.

THE THUNDERSTORM CHANCE SHOULD FURTHER DIMINISH OVERNIGHT WITH THE
LOSS OF HEATING AND MID-LEVEL SHORTWAVE RIDGING. NOCTURNAL COOLING
WITH DRY AIR ALOFT AND LIGHT WIND SHOULD HELP SUPPORT AREAS OF FOG
TOWARD SUNRISE. THE NAM AND GFS MOS HAS TRENDED MORE OPTIMISTIC WITH
JUST MVFR FOG MAINLY AT THE RIVER VALLEY TERMINALS OF AGS AND
DNL. PREVIOUS RUNS INDICATED IFR CONDITIONS. WE CONTINUED THE
FORECAST OF A PERIOD OF IFR AT THE RIVER VALLEY TERMINALS AND MVFR
ELSEWHERE. HEATING AND MIXING SHOULD DISSIPATE ANY FOG BEGINNING
AROUND 13Z.

THE PRESSURE GRADIENT WILL REMAIN WEAK THROUGH THE TAF PERIOD.
GENERALLY LIGHT WIND WILL OCCUR.

EXTENDED AVIATION OUTLOOK...MVFR OR IFR CONDITIONS POSSIBLE IN LATE
NIGHT AND EARLY MORNING FOG THROUGH THE PERIOD. ISOLATED AFTERNOON
AND EVENING THUNDERSTORMS MAY ALSO BRING RESTRICTIONS.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.
&&

$$






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