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Area Forecast Discussion

883
FXUS62 KCAE 191559
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
1159 AM EDT TUE AUG 19 2014

.SYNOPSIS...
AN UPPER TROUGH AND STRONG HEATING WILL SUPPORT SCATTERED
THUNDERSTORMS THIS AFTERNOON INTO THE EVENING. DRIER AIR AND A
BUILDING UPPER RIDGE JUST TO OUR WEST WILL REDUCE THUNDERSTORM
CHANCES WEDNESDAY AND THURSDAY...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/...
THIS AFTERNOON...A WELL-DEFINED MID-LEVEL SHORTWAVE TROUGH WAS
SUPPORTING CLOUDINESS OVER MUCH OF THE FORECAST AREA AT MIDDAY. LIFT
ASSOCIATED WITH THIS FEATURE SHOULD BE MAINLY EAST OF THE FORECAST
AREA BY THE MIDDLE OF THE AFTERNOON. THE TROUGH PLUS HEATING AND
CONVERGENCE INTO THE LEE-SIDE SURFACE TROUGH SHOULD HELP SUPPORT
THUNDERSTORMS LATER TODAY. THE HIGH RESOLUTION MODELS INDICATE
SCATTERED COVERAGE. THE COVERAGE WILL PROBABLY REMAIN LIMITED
BECAUSE OF DIMINISHED UPPER-LEVEL SUPPORT. ALSO...CONVERGENCE
INTO THE SURFACE FEATURE SHOULD REMAIN WEAK AND FORECAST SOUNDINGS
SHOW WESTERLY FLOW THROUGH A DEEP LAYER WHICH SHOULD HELP KEEP
MOISTURE SOMEWHAT SHALLOW. SIGNIFICANT UNI-DIRECTIONAL WIND SHEAR
WITH 5000-FOOT WINDS NEAR 30 KNOTS MAINLY IN THE SOUTH PART AND
STEEP LOW-LEVEL LAPSE RATES MAY HELP SUPPORT STRONG WIND GUSTS
WITH ANY THUNDERSTORMS. STRONG MIXING WILL BRING GUSTY WINDS. USED
THE GFS LAMP AND NAM BUFKIT MOMENTUM-TRANSFER TOOL FOR THE WIND
GUST FORECAST. USED THE WARMER TEMPERATURE GUIDANCE BECAUSE OF THE
WESTERLY FLOW.

TONIGHT...THE MODELS MAINTAIN SURFACE TROUGHING. HOWEVER...BELIEVE
THE THUNDERSTORM CHANCE IS LOW BECAUSE OF SHALLOW MOISTURE IN THE
WAKE OF THE MID-LEVEL SHORTWAVE TROUGH AND NOCTURNAL COOLING. THE
NAM AND GFS MOS HAVE POPS 20 TO 30 PERCENT...MAINLY IN THE EVENING
CLOSER TO THE TIME OF HEATING. THE TEMPERATURE GUIDANCE WAS CLOSE.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
UPPER RIDGE WILL BUILD JUST TO OUR WEST WEDNESDAY AS THE UPPER
TROUGH MOVES OFF THE COAST. WARMING 850MB TEMPERATURES AND A LOW
LEVEL DOWNSLOPE FLOW WILL RESULT IN MAX TEMPERATURES PUSHING 100
DEGREES WEDNESDAY AND THURSDAY. GUIDANCE INDICATES DEW POINTS
MIXING DOWN INTO THE MID TO UPPER 60S ACROSS THE NORTHERN AND
WESTERN COUNTIES TO NEAR 70 ACROSS THE SOUTHEAST MIDLANDS. THIS
SHOULD KEEP HEAT INDICES JUST BELOW OUR HEAT ADVISORY CRITERIA OF
110F. ONLY SLIGHT CHANCE OF SHOWERS/TSTMS EXPECTED BOTH WEDNESDAY
AND THURSDAY DUE TO DRIER AIR AND BUILDING RIDGE ALOFT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
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...BUT MODELS SUGGEST A BACK DOOR FRONT WILL MOVE
DOWN THE EAST COAST...REACHING OUR FA SOME TIME THIS WEEKEND. THIS
WOULD INCREASE POPS ALONG AND SOUTH OF THE BOUNDARY...AND LEAD TO
COOLER TEMPS NORTH OF IT. WILL MAINTAIN TREND IN THE ONGOING
FORECAST OF POPS TRENDING HIGHER AND TEMPS TRENDING LOWER DURING
THAT TIME.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
EXPECT MAINLY VFR CONDITIONS DURING THE TAF PERIOD.

SCATTERED SHOWERS WERE IN THE FORECAST AREA EARLY AT MIDDAY ASSOCIATED
WITH A MID-LEVEL SHORTWAVE TROUGH. THE TROUGH PLUS HEATING AND
CONVERGENCE INTO THE LEE-SIDE SURFACE TROUGH SHOULD HELP SUPPORT
THUNDERSTORMS LATER THIS AFTERNOON. THE HIGH RESOLUTION MODELS
INDICATE SCATTERED COVERAGE. THE COVERAGE WILL PROBABLY REMAIN
LIMITED BECAUSE MUCH OF THE UPPER-LEVEL LIFT ASSOCIATED WITH THE
SHORTWAVE TROUGH WILL LIKELY OCCUR EARLY AND BEFORE MAXIMUM
HEATING. ALSO...CONVERGENCE INTO THE SURFACE FEATURE SHOULD REMAIN
WEAK AND FORECAST SOUNDINGS SHOW WESTERLY FLOW THROUGH A DEEP
LAYER WHICH SHOULD HELP KEEP MOISTURE SOMEWHAT SHALLOW. THE
THUNDERSTORM CHANCE IS TOO LOW TO INCLUDE IN THE TERMINAL
FORECASTS AT THIS TIME BECAUSE OF THE SCATTERED COVERAGE AND
TIMING UNCERTAINTY. SIGNIFICANT UNI-DIRECTIONAL WIND SHEAR WITH
5000-FOOT WINDS NEAR 30 KNOTS MAINLY IN THE SOUTH PART AND STEEP
LOW-LEVEL LAPSE RATES MAY HELP SUPPORT STRONG WIND GUSTS NEAR ANY
THUNDERSTORMS. STRONG MIXING WILL BRING GUSTY WINDS. USED THE GFS
LAMP AND NAM BUFKIT MOMENTUM-TRANSFER TOOL FOR THE WIND GUST
FORECAST. DRYING ALOFT AND LINGERING LOW-LEVEL MOISTURE PLUS
NOCTURNAL COOLING MAY HELP SUPPORT FOG TONIGHT. MOST OF THE NAM
AND GFS MOS INDICATE MVFR FOG. FOG WILL LIKELY BE LIMITED BY SOME
MIXING.

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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