Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 261651
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1251 PM EDT SUN APR 26 2015

.SYNOPSIS...
A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH TODAY THEN DROP
ACROSS THE AREA THIS EVENING INTO THE EARLY OVERNIGHT HOURS. 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 /UNTIL 6 PM THIS EVENING/...
THE FORECAST PHILOSOPHY REMAINS UNCHANGED. ONLY MINOR TWEAKS WERE
MADE TO HOURLY GRIDDED PARAMETERS FOR THE EARLY AFTERNOON UPDATE.

MID-MORNING VISIBLE SATELLITE DATA SHOW A WELL-PRONOUNCED BACKDOOR
COLD FRONT MOVING SOUTH OUT OF NORTH CAROLINA AND INTO THE SOUTH
CAROLINA PEE DEE...NORTHERN MIDLANDS AND UPSTATE. TEMPERATURES ARE
WARMING QUICKLY AHEAD OF THE FRONT WHILE TEMPERATURES ARE STILL
IN THE 40S AND 50S BEHIND IT. THE BOUNDARY WILL CONTINUE TO MOVE
SLOWLY SOUTH THIS AFTERNOON...REACHING THE SOUTH SANTEE RIVER BY
LATE AFTERNOON. DEEP WESTERLY FLOW COUPLED WITH STRONG PRE-FRONTAL
COMPRESSION...NEAR FULL INSOLATION...A PINNED SEA BREEZE
CIRCULATION AND 850 HPA TEMPERATURES RISING TO 16C WILL SUPPORT A
TOASTY DAY WITH HIGHS REACHING INTO THE UPPER 80S TO LOWER 90S FOR
MOST LOCATIONS. THE HOTTEST TEMPERATURES WILL OCCUR BETWEEN I-95
AND THE INTRACOASTAL WATERWAY GIVEN STRONG WESTERLY FLOW REGIME.
TODAY CERTAINLY HAS THE POTENTIAL TO BE THE HOTTEST DAY SO FAR IN
2015.

THE DEEP WESTERLY FLOW WILL KEEP THE ATMOSPHERE CAPPED FOR MUCH OF
THE DAY UNTIL THE BACKDOOR COLD FRONT DRAWS CLOSER. THERE LOOKS TO
BE JUST ENOUGH PRE-FRONTAL LIFT AND LOW-LEVEL MOISTURE POOLING
TO SUPPORT ISOLATED TO PERHAPS SCATTERED SHOWERS/TSTMS FROM LATE
AFTERNOON INTO EARLY THIS EVENING ACROSS NORTHERN PARTS OF
SOUTHEAST SOUTH CAROLINA. RAP/H3R MODIFIED SOUNDINGS SUGGEST ANY
TSTMS THAT ARE ABLE TO INITIATE AND MAINTAIN SUSTAINED UPDRAFTS
WILL HAVE THE ABILITY TO BECOME SEVERE WITH DAMAGING WINDS AND
FREQUENT CLOUD-TO-GROUND LIGHTNING. DCAPES ARE PROGGED TO REACH
1500 J/KG BY MID-AFTERNOON WHICH WILL FURTHER SUPPORT A DAMAGING
WIND THREAT. THE THREAT FOR SEVERE WEATHER LOOKS TO REMAIN FAIRLY
ISOLATED ATTM GIVEN THE VERY MARGINAL MOISTURE ENVIRONMENT...
ALTHOUGH 0-6KM BULK SHEAR NEAR 70 KT SUGGESTS A POTENTIAL FOR
ORGANIZATION SHOULD ENOUGH CONVECTIVE CLUSTERS DEVELOP. THIS WILL
HAVE TO BE WATCHED CAREFULLY THROUGH THE DAY. THE CAP LOOKS TO
COLD FARTHER TO THE SOUTH SO DRY CONDITIONS WILL PREVAIL THERE.

MORNING LOW CLOUDS AFFECTING THE WESTERN ZONES WILL MIX OUT
SHORTLY YIELDING SUNNY TO MOSTLY SUNNY SKIES FOR THE REST OF THE
DAY. CLOUD COVER WILL INCREASE FROM THE NORTH LATE AS THE BACKDOOR
COLD FRONT DESCENDS INTO THE AREA. BREEZY CONDITIONS ARE LIKELY
FOR MANY AREAS WITH DEEP MIXING PROFILES DEVELOPING. GUSTS COULD
APPROACH 30 MPH AT TIMES ACROSS THE SOUTH CAROLINA COASTAL ZONES
WHERE LOW-LEVEL WIND FIELDS WILL BE THE STRONGEST.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
OVERNIGHT...THE BACKDOOR COLD FRONT WILL DROP SOUTH OF THE AREA
DURING THE EARLY OVERNIGHT HOURS...WITH MUCH COOLER/DRIER HIGH
PRESSURE BUILDING INTO THE REGION FROM THE NORTHWEST. LOWS ARE
EXPECTED TO RANGE FROM THE MID AND UPPER 50S ACROSS NORTH AND
NORTHWEST PORTIONS OF THE FORECAST AREA...WITH LOWER 60S CLOSER TO
NORTH COASTAL GEORGIA.

MONDAY...HIGH PRESSURE TO THE NORTHEAST WILL PREVAIL WITH DRY
WEATHER AND TEMPERATURES DIPPING BELOW NORMAL INTO THE LOWER TO MID
70S. COULD SEE SOME UPPER 40S MONDAY NIGHT...MAINLY OVER INTERIOR
SOUTHEAST SC WHERE THE BEST RADIATIONAL COOLING IS EXPECTED.

TUESDAY...HIGH PRESSURE WILL CONTINUE FROM THE NORTH AS LOW PRESSURE
BEGINS TO DEVELOP OVER THE NORTHERN GULF OF MEXICO. COULD SEE SOME
LATE LIGHT SHOWERS SOUTH OF I-16 BUT MOST AREAS SHOULD REMAIN DRY
GIVEN THE LINGERING LOW-LEVEL DRY AIR IN PLACE. TEMPERATURES WILL BE
COOLER THAN MONDAY GIVEN THE INCREASED CLOUD COVER...PROBABLY MORE
LIKE 70-74. RAIN CHANCES WILL INCREASE TUESDAY NIGHT AS DEEP
MOISTURE MOVES INTO THE AREA AHEAD OF THE APPROACHING LOW PRESSURE
SYSTEM AND DEVELOPING WARM FRONT AROUND THE FLORIDA
PANHANDLE/SOUTHERN GEORGIA. SOME OF THE RAIN COULD BE HEAVY AT TIMES
BUT CHANCES FOR THUNDER WILL BE LOW AND MAINLY LATE AS IT WILL TAKE
A WHILE FOR SUFFICIENT INSTABILITY TO DEVELOP.

WEDNESDAY...PROBABLY THE WORST...OR AT LEAST THE WETTEST...WEATHER
OF THE WEEK AS LOW PRESSURE MOVES THROUGH SOUTHEAST GEORGIA BRINGING
WIDESPREAD MODERATE TO OCCASIONALLY HEAVY RAINFALL. BEST CHANCE FOR
THUNDERSTORMS WILL BE OVER SOUTHEAST GEORGIA AND ALONG THE SOUTHERN
SC COAST. COULD EVEN SOME STRONGER T-STORMS IF THE WARM FRONT CAN
MAKE IT INTO THE AREA AND ALLOW FOR SUFFICIENT INSTABILITY GIVEN
PLENTY OF DEEP LAYER SHEAR IN PLACE. TEMPS WILL BE HIGHLY DEPENDENT
ON THE TRACK OF THE LOW AND WARM FRONT WITH A BIG SPREAD POSSIBLE
FROM NORTHWEST /MID TO UPPER 60S/ TO SOUTHEAST LOWER TO MID 70S/.

&&

.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 /18Z 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 MON INTO
TUE BEFORE SHOWERS AND POSSIBLY A FEW TSTMS RETURN LATER TUE AND
ESPECIALLY TUE NIGHT INTO WED NIGHT. SOME OF THE RAIN WILL BE
MODERATE TO HEAVY SO IFR OR LOWER CONDS ARE LIKELY DURING THIS
TIME. VFR SHOULD PREVAIL THU/FRI.

&&

.MARINE...
TODAY...DEEP MIXING AROUND THE CHARLESTON HARBOR SHOULD SUPPORT
FREQUENT WIND GUSTS NEAR 25 KT THIS AFTERNOON. A SMALL CRAFT
ADVISORY HAS THEREFORE BEEN ISSUED. ELEVATED WINDS WILL PERSIST
OVER THE COASTAL WATERS...BUT BELOW SMALL CRAFT ADVISORY
THRESHOLDS.

TONIGHT...A BACKDOOR COLD FRONT WILL DROP THROUGH THE WATERS THIS
EVENING INTO THE EARLY OVERNIGHT HOURS...CAUSING WINDS TO VEER
NORTH-NORTHEAST AND INCREASE IN SPEED UPWARDS OF 15-20 KT AS THE
GRADIENT TIGHTENS AND A COOLER AIRMASS SPREADS INTO THE AREA AS
HIGH PRESSURE BUILDS FROM THE NORTHWEST. COULD NOT RULE OUT SMALL
CRAFT ADVISORY CONDITIONS DEVELOPING...BUT AT THIS TIME MODEL
CONSENSUS KEEPS WINDS JUST BELOW CRITERIA.

MONDAY THROUGH FRIDAY...HIGH PRESSURE BUILDING FROM THE NORTH SHOULD
LEAD TO A WEAKENING PRESSURE GRADIENT AND THUS WINDS AS WELL INTO
MONDAY NIGHT BEFORE CONDITIONS GO BACK DOWNHILL AS DEVELOPING LOW
PRESSURE APPROACHES FROM THE SOUTHWEST TUESDAY/WEDNESDAY BEFORE
PASSING THROUGH THE AREA WEDNESDAY NIGHT. BEST SHOT AT SMALL CRAFT
ADVISORIES WILL BE BEYOND 20 NM AND OVER THE NEARSHORE WATERS OFF
CHARLESTON COUNTY. EXPECT IMPROVING CONDITIONS THU AND ESPECIALLY BY
FRI.

&&

.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



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