043
FXUS62 KCHS 242000
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
400 PM EDT THU JUL 24 2008
SYNOPSIS
A WEAK COLD FRONT WILL DISSIPATE NEAR OR JUST NORTHWEST OF THE
AREA TONIGHT. OTHERWISE...ATLANTIC HIGH PRESSURE WILL BUILD OVER
THE REGION THROUGH THE MIDDLE OF NEXT WEEK WHILE A TROUGH OF LOW
PRESSURE SETS UP WEST OF THE AREA.
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
WATER VAPOR IMAGERY DEPICTS VERY DRY CONDITIONS IN THE MID LEVELS
OF THE ATMOSPHERE OVER THE REGION THIS AFTERNOON BEHIND AN UPPER
LEVEL TROUGH AXIS WHICH CONTINUES TO PUSH OFFSHORE. MEANWHILE AT
THE SURFACE...A COLD FRONT OVER THE SOUTH CAROLINA MIDLANDS AND
CENTRAL GEORGIA CONTINUES TO MAKE SLOW PROGRESS TOWARD THE COAST...
BUT SHOULD STALL AND DISSIPATE AS IT NEARS THE WESTERN EDGE OF THE
FORECAST AREA TONIGHT. THEREFORE...DO NOT ANTICIPATE DEWPOINTS
FALLING INTO THE MID TO UPPER 50S LIKE THEY HAVE UPSTREAM.
EVEN THROUGH THERE IS PLENTY OF DRY AIR IN THE MID LEVELS OF THE
ATMOSPHERE...A SCATTERED TO BROKEN CUMULUS FIELD HAS MANAGED TO
DEVELOP ACROSS THE AREA AND ISOLATED SHOWERS HAVE EVEN FORMED NEAR
THE ALTAMAHA RIVER VALLEY THIS AFTERNOON. APPARENTLY THERE IS
SUFFICIENT MOISTURE BENEATH A LOW LEVEL INVERSION TO CAUSE THIS TO
OCCUR. THE SHOWERS WILL REMAIN RATHER LOW TOPPED...DUE TO THE
SHALLOW NATURE OF THE MOISTURE AND THE CAP THAT IS IN PLACE.
ANY SHOWER ACTIVITY WILL QUICKLY COME TO AN END THIS EVENING WITH
THE LOSS OF DAYTIME HEATING. HOWEVER...HIGH LEVEL CLOUDINESS
RACING IN FROM THE NORTHWEST WILL OVERSPREAD THE AREA RESULTING IN
MOSTLY CLEAR SKIES THROUGH THE NIGHT.
THE THIN HIGH LEVEL CLOUD COVER...SHALLOW MOISTURE AT THE SURFACE
WITH DRY AIR ALOFT AND DECOUPLED WINDS WILL COMBINE TO PRODUCE
PATCHY GROUND FOG ACROSS MUCH OF THE AREA OVERNIGHT.
TEMPERATURES COULD FALL INTO THE UPPER 60S TO LOWER 70S AWAY FROM
THE IMMEDIATE COAST...BUT SHOULD NOT MAKE IT BELOW THE MID 70S
RIGHT AT THE BEACHES.
SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
THE FORECAST AREA WILL GENERALLY BE BETWEEN AN UPPER LEVEL RIDGE
OVER THE SOUTHERN PLAINS...A TROUGH EXTENDING DOWN THE MID-
ATLANTIC REGION FROM THE GREAT LAKES/NORTHEASTERN STATES AND
ANOTHER RIDGE OVER THE WESTERN ATLANTIC ON FRIDAY. A WEAK LOW
LEVEL ONSHORE FLOW WILL BE IN PLACE...WITH NORTH OR NORTHWEST
WINDS ABOVE 750 MB. WHILE THERE WILL BE SOME MOISTURE IN
PLACE...IT APPEARS TO REMAIN RATHER SHALLOW. THEREFORE...EXPECT
ANOTHER GOOD CUMULUS FIELD TO DEVELOP. THE FORECAST WILL NOT SHOW
ANY PRECIPITATION...BUT ISOLATED CONVECTION IS CERTAINLY POSSIBLE
IF THE MOISTURE IS DEEPER THAN CURRENTLY FORECAST BY THE MODELS.
HIGH TEMPERATURES ARE EXPECTED TO BE IN THE LOWER TO MID 90S AWAY
FROM THE IMMEDIATE COAST.
DRY CONDITIONS ARE EXPECTED FRIDAY NIGHT...ALONG WITH MAINLY CLEAR
SKIES. PATCHY FOG COULD DEVELOP DEPENDING ON HOW MUCH RESIDUAL LOW
LEVEL MOISTURE IS IN PLACE...BUT WILL NOT MENTION IN THE FORECAST
AT THIS TIME.
LONG TERM /SATURDAY THROUGH THURSDAY/
A MEAN UPPER LEVEL TROUGH WILL PERSIST FROM EASTERN CANADA SOUTHWARD
INTO THE CAROLINAS...WHILE MEAN UPPER LEVEL RIDGING LINGERS ACROSS
THE SOUTHWEST AND SOUTHERN PLAINS STATES. A SERIES OF WEAK
SHORTWAVES WILL REGULARLY ROUND THE BASE OF THE UPPER TROUGH
THROUGH THE EXTENDED PERIOD. THIS SHORTWAVE ACTIVITY WILL COMBINE
WITH TYPICAL SUMMERTIME INSTABILITY AND SEABREEZE FORCING TO
PRODUCE A SLIGHT CHANCE TO A CHANCE OF CONVECTION EACH AFTERNOON
AND EVENING.
SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA WILL REMAIN ON THE
WESTERN PERIPHERY OF AN ATLANTIC SURFACE HIGH THROUGH NEXT
WEEK...WHILE SURFACE TROUGHING STRETCHES FROM VIRGINIA INTO SOUTHERN
GEORGIA. DEEP LAYER MOISTURE APPEARS A BIT LIMITED ON
SATURDAY...WITH GFS AND NAM BOTH INDICATING BEST THUNDERSTORM
CHANCES ACROSS HIGHER MOISTURE AREAS OF SOUTHEAST GEORGIA. HAVE THUS
MAINTAINED LOWEST POPS OF THE PERIOD ON SATURDAY...AROUND 20 PERCENT
OR LESS.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON SUNDAY...THEN STALL
WITHIN THE INLAND TROUGH TO THE WEST AND NORTH. MODELS SUGGEST THAT
SEVERAL WAVES OF LOW PRESSURE COULD DEVELOP ALONG THE
FRONT...INCREASING MOISTURE AND CONVERGENCE FOR THE REGION. LACKING
ANY FRONTAL PASSAGE...SHOWER AND THUNDERSTORM ACTIVITY IS EXPECTED
TO REMAIN MOSTLY DIURNAL IN NATURE. HAVE INDICATED AROUND A 30
PERCENT CHANCE FOR CONVECTION WITHIN SEABREEZE FORCING AND
INSTABILITY DURING THE AFTERNOONS AND EVENINGS FROM SUNDAY THROUGH
THURSDAY...DIMINISHING TO A SLIGHT CHANCE OR LESS DURING THE
OVERNIGHT HOURS.
EXPECT A SLIGHT WARMING TREND FROM THE WEEKEND INTO THE MIDDLE OF
NEXT WEEK. HIGHS IN THE LOWER 90S AWAY FROM THE COAST ON SATURDAY
WILL INCREASE TO THE LOWER TO MID 90S MONDAY THROUGH MID WEEK. LOW
LEVEL MOISTURE WILL ALSO INCREASE THROUGH THE PERIOD...THUS HEAT
INDICES WILL RANGE FROM 100 TO 105 DEGREES AFTER SATURDAY.
AVIATION /19Z THURSDAY THROUGH TUESDAY/
EXTENSIVE STRATOCU WILL DISSIPATE WITH THE LOSS OF HEATING THIS
EVENING. THE MAINLY CLEAR SKIES COMBINED WITH DECOUPLED WINDS AND
LOW LEVEL MOISTURE TRAPPED UNDERNEATH AN INVERSION WILL ENHANCE
THE FOG POTENTIAL AT BOTH TERMINALS OVERNIGHT. THE FORECAST
REFLECTS TEMPORARY MVFR VISIBILITIES FROM 09-12Z BUT WILL STILL
NEED TO EVALUATE THE POTENTIAL FOR LOWER VISIBILITIES AT THE
NEXT TAF ISSUANCE. OTHERWISE VFR CONDITIONS WILL PREVAIL.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL.
MARINE
WINDS AS HIGH AS 10-15 KT WILL BE POSSIBLE INTO THIS EVENING
ACROSS THE OUTER GEORGIA WATERS...BUT OVERALL EXPECT A SOUTHERLY
COMPONENT TO THE WINDS WITH SPEEDS OF 10 KT OR LESS THROUGH FRIDAY
NIGHT. SEAS WILL REMAIN 3 FT OR LESS.
THE MARINE ZONES WILL REMAIN ON THE WESTERN PERIPHERY OF ATLANTIC
HIGH PRESSURE THROUGH THE EXTENDED PERIOD. SURFACE FLOW WILL BE
DOMINATED BY SEABREEZE CIRCULATION...AS SOUTHWEST WINDS DURING THE
NIGHTTIME AND MORNING HOURS BACK TO THE SOUTH EACH AFTERNOON. WIND
SPEEDS WILL REMAIN AT OR BELOW 15 KNOTS...WITH SEAS 2 TO 3 FT
NEARSHORE WATERS AND 3 TO 4 FT OFFSHORE ZONES.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
JAQ/WMM/REB
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