Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 261949
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
349 PM EDT SUN APR 26 2015

.SYNOPSIS...
A BACKDOOR COLD FRONT WILL DROP SOUTH THROUGH THE AREA TONIGHT.
DRY HIGH PRESSURE WILL PREVAIL MONDAY INTO TUESDAY. A GULF OF
MEXICO STORM SYSTEM WILL IMPACT THE REGION MID WEEK WITH DRY HIGH
PRESSURE EVENTUALLY RETURNING LATER THIS WEEK AND LASTING THROUGH
THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE BACKDOOR COLD FRONT IS CLEARLY EVIDENT ON MID-AFTERNOON
SATELLITE DATA AND SURFACE OBSERVATIONS. THE FRONT WILL CONTINUE
TO DRIFT SOUTH TONIGHT...CLEARING THE CHARLESTON TRI-COUNTY AREA
LATE THIS AFTERNOON...SOUTHERN SOUTH CAROLINA LATER THIS EVENING
AND SOUTHEAST GEORGIA EARLY MONDAY MORNING.

THE CUMULUS FIELD ALONG AND JUST AHEAD OF THE FRONT IS BECOMING
INCREASINGLY AGITATED (PER GOES-EAST RSO IMAGERY) AS SURFACE
TEMPERATURES APPROACH CONVECTIVE THRESHOLDS. HIGH RESOLUTION MODEL
DATA HAVE BEEN CONSISTENT IN PUSHING SCATTERED SHOWERS/TSTMS INTO
THE CHARLESTON TRI-COUNTY AREA OVER THE NEXT SEVERAL HOURS SO POPS
WILL BE INCREASED TO 40 PERCENT IN THIS AREA WITH 20-30 PERCENT
POPS ELSEWHERE ACROSS SOUTHEAST SOUTH CAROLINA. SOUTHEAST GEORGIA
LOOKS TO REMAIN DRY AS INSTABILITY WILL WANE SIGNIFICANTLY BEFORE
THE FRONT REACHES AREAS SOUTH OF THE SAVANNAH RIVER. LOWS MONDAY
MORNING WILL RANGE FROM THE LOWER-MID 50S NORTHERN AREAS TO THE
UPPER 50S-LOWER 60S CENTRAL/SOUTH WITH MID 60S ALONG COASTAL
MCINTOSH COUNTY.

0-6KM BULK SHEAR IS SUPPORTIVE OF SUPERCELLS...ALTHOUGH THE DEGREE
OF INSTABILITY IS BEING TEMPERED SOMEWHAT FROM DEWPOINTS MIXING
OUT INTO THE UPPER 50S/LOWER 560S IN THE WARM/WESTERLY FLOW AHEAD
OF THE FRONT. MODIFIED SOUNDINGS STILL SUPPORT MODEST INSTABILITY
WITH SBCAPE APPROACHING 2000 J/KG...WHICH WILL BE MORE AND
ADEQUATE TO SUPPORT TSTMS IF UPDRAFTS CAN BE SUSTAINED GIVEN THE
MARGINALLY MOIST ENVIRONMENT. A MORE SUBSTANTIAL RISK FOR SEVERE
TSTMS MAY EVOLVE IF TSTMS CAN BE SUSTAINED GIVEN THE LEVEL OF BULK
SHEAR THAT IS IN PLACE. DCAPES ARE PROGGED TO MAX OUT IN THE
1200-1500 J/KG RANGE ACROSS THE TRI-COUNTY AREA AND WBZ HEIGHTS
REMAIN FAIRLY LOW...BOTH SUPPORTIVE OF A DAMAGING WIND AND LARGE
HAIL THREAT.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
MONDAY AND TUESDAY...DRY HIGH PRESSURE WILL BUILD FROM THE NORTH AND
NORTHWEST BEHIND A COLD FRONT WELL TO OUR SOUTH AND OFFSHORE. AS A
RESULT...TEMPS WILL BE MUCH COOLER WITHIN A NORTHERLY FLOW. IN
GENERAL...MONDAY AFTERNOON HIGHS WILL RANGE FROM THE LOW TO MID
70S...THEN COOL A FEW MORE DEGREES ON TUESDAY AS HIGH PRESSURE
BECOMES CENTERED JUST TO OUR NORTH WHILE CLOUDS BEGIN TO DEVELOP
WITH MOISTURE RETURN TO OUR SOUTH. BY TUESDAY EVENING...SUFFICIENT
MOISTURE WILL RETURN WITH AN ONSHORE FLOW DEVELOPING WELL AHEAD OF
LOW PRESSURE SHIFTING OVER THE NORTHERN GULF OF MEXICO. A FEW
SHOWERS WILL BE POSSIBLE...MAINLY SOUTH OF INTERSTATE 16 BEFORE
SUNSET.

TUESDAY NIGHT INTO WEDNESDAY...LOW PRESSURE WILL STRENGTHEN/DEEPEN
OVER THE NORTHERN GULF OF MEXICO WITH A WARM FRONT EXTENDING
EASTWARD OVER THE NORTHERN FLORIDA PENINSULA. THE WARM FRONT IS
EXPECTED TO LIFT NORTH AND EVENTUALLY REACH SOUTHERN AREAS BY
WEDNESDAY MORNING...BRINGING INCREASING SHOWER COVERAGE AND PERHAPS
A FEW THUNDERSTORMS OVER SOUTHEAST GEORGIA. PRECIP COVERAGE WILL
LIKELY EXPAND OVER THE ENTIRE FORECAST AREA LATE WEDNESDAY MORNING
INTO WEDNESDAY EVENING AS THE MAIN SFC LOW TRACKS OVER THE
SOUTHEAST...THEN OFFSHORE. HAVE THEREFORE MAINTAINED 60-70 POPS OVER
MOST AREAS. TEMPS WILL BE HIGHLY DEPENDENT ON THE TRACK OF THE SFC
LOW AND THE NORTHERN EXTENT OF THE WARM FRONT. AT THIS TIME...TEMPS
SHOULD PEAK IN THE UPPER 60S INLAND TO LOW/MID 70S CLOSER TO THE
COAST IN SOUTHEAST GEORGIA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
A BIT BETTER MODEL AGREEMENT NOW REGARDING THE LOW PRESSURE SYSTEM
MOVING UP THE SOUTHEAST COAST WEDNESDAY NIGHT...ALTHOUGH THE ECMWF
CONTINUES TO BE SLOWER AND STRONGER THAN THE GFS. EITHER WAY IT
LOOKS LIKE RAIN CHANCES WILL BE DIMINISHING FROM SOUTHWEST TO
NORTHEAST WITH THE BEST CHANCES OVER SOUTHERN SOUTH CAROLINA. CANNOT
RULE OUT SOME LINGERING SHOWERS THURSDAY/FRIDAY AS THE UPPER LOW IS
SLOW TO MOVE THROUGH WITH TEMPS REMAINING BELOW NORMAL IN THE 70S.
IT LOOKS DRY FOR SATURDAY THROUGH SUNDAY LOOK DRIER AS HIGH PRESSURE
RETURNS WITH TEMPS GETTING BACK TO NEAR OR JUST ABOVE NORMAL.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
KCHS...VFR THROUGH LATE AFTERNOON AS A BACKDOOR COLD FRONT
APPROACHES. RISK FOR ISOLATED SHOWERS/TSTMS TO IMPACT THE TERMINAL
ROUGHLY 23-01Z. WILL INCLUDE A TEMPO GROUP FOR MVFR CONDITIONS IN
TSRA FOR NOW. AFTER 02Z...RISK FOR LOW CLOUDS FILLING BEHIND THE
FRONT INCREASES. DATA LOOKS MARGINAL FOR IFR CIGS SO CIGS WILL BE
LIMITED TO LOW-END MVFR. IFR CIGS MAY EVENTUALLY BE NEEDED. CIGS
WILL SLOWLY LIFT THROUGH THE NIGHT AS THE FRONT SAGS SOUTH. VFR
EXPECTED MONDAY.

KSAV...VFR. THERE WILL BE A RISK FOR MVFR CIGS AS THE COLD FRONT
CLEARS THE TERMINAL...BUT WILL KEEP CIGS VFR FOR NOW.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL MONDAY AND
TUESDAY BEFORE SHOWERS AND POSSIBLY A FEW THUNDERSTORMS RETURN
TUESDAY EVENING AND ESPECIALLY TUESDAY NIGHT THROUGH WEDNESDAY
NIGHT. SOME RAIN WILL BE MODERATE SO IFR OR LOWER CONDITIONS ARE
LIKELY ON WEDNESDAY. VFR CONDITIONS SHOULD THEN PREVAIL THURSDAY AND
FRIDAY.

&&

.MARINE...
TONIGHT...WEATHERFLOW SENSORS NEAR THE HARBOR ENTRANCE ARE
AVERAGING 15-20 KT WITH GUSTS TO 25 KT AT TIMES. WINDS ARE
HIGHER IN THE OPEN AREAS OF THE CHARLESTON HARBOR WHERE WESTERLY
FLOW IS MAXIMIZED. THE SMALL CRAFT ADVISORY WILL REMAIN IN FORCE
THROUGH EARLY EVENING. OTHERWISE...WEST/SOUTHWEST WINDS WILL TURN
NORTH/NORTHEAST THIS EVENING AND OVERNIGHT AS A BACKDOOR COLD
FRONT DROPS SOUTH THROUGH THE WATERS. BOTH WINDS AND SEAS LOOKS TO
REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS.

MONDAY THROUGH FRIDAY...HIGH PRESSURE WILL CONTINUE BUILDING FROM
THE NORTH ON MONDAY...THEN BECOME CENTERED OVER THE AREA ON
TUESDAY...LEADING TO A WEAKENING PRESSURE GRADIENT THROUGH THE
PERIOD AND IMPROVED WINDS/SEAS. CONDITIONS SHOULD THEN DETERIORATE
ON WEDNESDAY AS A LOW PRESSURE SYSTEM APPROACHES FROM THE SOUTHWEST
AND PASSES OVER THE COASTAL WATERS WEDNESDAY NIGHT. A PERIOD OF
SMALL CRAFT ADVISORIES IS POSSIBLE FOR ALL WATERS WEDNESDAY NIGHT
BEHIND THE DEPARTING LOW PRESSURE SYSTEM...WITH BEST CHANCES
OCCURRING IN NORTHERN SC WATERS OFF THE CHARLESTON COUNTY COAST AND
IN OFFSHORE GEORGIA WATERS. WINDS/SEAS SHOULD THEN SLOWLY IMPROVE ON
THURSDAY AS THE LOW PRESSURE SYSTEM SHIFTS NORTH/NORTHEAST AND AWAY
FROM THE AREA...BEFORE IMPROVING FURTHER AS WEAK HIGH PRESSURE
SETTLES OVER THE WATERS ON FRIDAY.

&&

.CLIMATE...
RECORD HIGHS FOR 26 APRIL...
KCHS 92/1989...
KCXM 89/1989...
KSAV 92/1989...

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR AMZ330.

&&

$$

ST/DPB



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