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Area Forecast Discussion

981
FXUS62 KCHS 252115
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
415 PM EST SUN JAN 25 2015

.SYNOPSIS...
A COLD FRONT ASSOCIATED WITH LOW PRESSURE PASSING NORTH OF THE
REGION WILL SWING THROUGH LATE TONIGHT INTO EARLY MONDAY. THE LOW
WILL MOVE OFF THE MID-ATLANTIC COAST ON MONDAY...WITH A REINFORCING
COLD FRONT THEN MOVING THROUGH LATE TUESDAY INTO TUESDAY NIGHT. HIGH
PRESSURE WILL THEN PREVAIL THROUGH THURSDAY...BEFORE ANOTHER COLD
FRONT PUSHES THROUGH THE AREA FRIDAY. HIGH PRESSURE WILL THEN
PREVAIL THROUGH NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
AFTER A MAINLY CLEAR AND MILD EVENING...WITH TEMPERATURES HELD UP
BY SOUTH/SOUTHWEST WINDS...AN APPROACHING/AMPLIFYING UPPER TROUGH
ADVANCING THROUGH THE MID-MISSISSIPPI RIVER VALLEY SUNDAY
AFTERNOON WILL PUSH EAST AND WILL DRIVE A SURFACE COLD FRONT
TOWARD THE SOUTHEAST COAST TONIGHT. GUIDANCE CONTINUES TO DEPICT A
SPLIT BETWEEN PRECIPITATION DRIVEN BY THE UPPER TROUGH/COLD FRONT
NORTH/WEST OF THE REGION AND A PLUME OF LOW/MID LEVEL MOISTURE
AND ASSOCIATED SHOWERS THAT WILL SURGE NORTH/NORTHEAST FROM THE
GULF OF MEXICO AHEAD OF THE FRONT AFTER MIDNIGHT. LATEST GUIDANCE
CONFIRMS A CONTINUATION OF PREVIOUS THINKING THAT THE SOUTHERN
BAND OF SHOWERS WILL BYPASS MOST LAND ZONES AND REMAIN MAINLY OVER
COASTAL WATERS. THUS...SLIGHT CHANCE/CHANCE POPS ARE STILL
LIMITED TO FAR SOUTHERN COUNTIES AND TO MARINE ZONES LATE TONIGHT.
THIS REMAINS A MODERATE CONFIDENCE FORECAST...DEPENDING ON THE
ORIENTATION AND DEGREE OF AMPLIFICATION OF THE UPPER TROUGH
AND THE TIMING OF THE COLD FRONT WHICH WILL ARRIVE LATE
TONIGHT...CANNOT RULE OUT A BAND OF SHOWERS DEVELOPING SOMEWHAT
FARTHER NORTH/WEST THAN CURRENTLY FORECAST...MAINLY ALONG/EAST OF
I-95.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY AND MONDAY NIGHT...A POTENT SHORT WAVE WILL CROSS THE AREA
EARLY AS IT ROUNDS THE BASE OF A LONGWAVE TROUGH BECOMING NEGATIVELY
TILTED OVER THE EASTERN UNITED STATES. MEANWHILE AT THE
SURFACE...LOW PRESSURE WILL MOVE OFF THE MID-ATLANTIC COAST MONDAY
THEN RAPIDLY INTENSIFY AS IT LIFTS NORTHEAST TOWARD THE NEW ENGLAND
COAST MONDAY NIGHT. MOISTURE IN THE 3-6K FT LAYER COMBINED WITH THE
COLD POOL ALOFT COULD RESULT IN THE DEVELOPMENT OF ISOLATED SHOWERS
ACROSS THE CHARLESTON TRI-COUNTY AREA AND COLLETON COUNTY BEGINNING
AROUND MIDDAY AND LASTING WELL INTO THE AFTERNOON. THERE IS A
SMALL POSSIBILITY THAT SOME SMALL GRAUPEL COULD OCCUR AS WELL
GIVEN THE STEEP LAPSE RATES ASSOCIATED WITH THE COLD POOL
ALOFT...BUT REALLY NO GOOD WAY TO CONVEY THIS IN THE GRIDDED
FORECASTS. AN ISOLATED THUNDERSTORM COULD ALSO NOT BE ENTIRELY
RULED OUT...BUT THE POTENTIAL FOR IT TO OCCUR IS JUST TOO LOW TO
INCLUDE IN THE FORECAST. STRONG COLD AIR ADVECTION WILL OCCUR
MONDAY AND MONDAY NIGHT...WITH BREEZY CONDITIONS EXPECTED ACROSS
THE AREA IN THE AFTERNOON DURING PEAK HEATING. THE IMPACTS OF THE
COLD AIR ADVECTION ON TEMPERATURES SHOULD BE OFFSET SOMEWHAT BY
THE DOWNSLOPE FLOW...WITH DAYTIME HIGHS IN THE UPPER 50S TO AROUND
60 UNDER PARTLY SUNNY SKIES. TEMPERATURES MONDAY NIGHT SHOULD COOL
INTO THE MID 30S AWAY FROM THE IMMEDIATE COAST.

TUESDAY AND TUESDAY NIGHT...THE REGION WILL BE LOCATED ALONG THE
SOUTHWEST PERIPHERY OF AN INTENSE VERTICALLY STACKED LOW PRESSURE
SYSTEM/NOREASTER OFF THE SOUTHERN NEW ENGLAND COAST. A DRIER
WEST-NORTHWEST FLOW ACROSS THE AREA WILL RESULT IN RAIN-FREE
CONDITIONS...EVEN WITH A REINFORCING COLD FRONT DROPPING THROUGH
LATE TUESDAY INTO TUESDAY NIGHT. HOWEVER...WITH SOME OF THE COLD
POOL LINGERING ALOFT THE POTENTIAL EXISTS FOR SOME SCATTERED CLOUD
COVER. HIGHS WILL GENERALLY BE IN THE LOWER TO MID 50S ACROSS
SOUTHEAST SOUTH CAROLINA AND MID TO UPPER 50S ACROSS SOUTHEAST
GEORGIA. ADDITIONAL COLD AIR ADVECTION BEHIND THE COLD FRONT SHOULD
DROP LOWS INTO THE LOWER TO MID 30S TUESDAY NIGHT.

WEDNESDAY...THE LONGWAVE TROUGH WILL PUSH OFF THE COAST...ALLOWING
UPPER LEVEL RIDGING AND ASSOCIATED HIGH PRESSURE AT THE SURFACE TO
BUILD INTO THE REGION FROM THE WEST. DESPITE SUNNY SKIES...HIGHS
WILL ONLY WARM TO AROUND 50 OR THE LOWER 50S.

LAKE WINDS...STRONG COLD AIR ADVECTION AND A POTENT LOW LEVEL JET
OVER THE AREA COULD RESULT IN STRONG WINDS OVER LAKE MOULTRIE
TUESDAY INTO TUESDAY NIGHT. MIXING PROFILES WILL BE POOR OVER THE
OPEN LAKE WATERS...BUT GUSTY WINDS COULD OCCUR NEAR THE LAKE
SHORE... ESPECIALLY IN THE AFTERNOON. A LAKE WIND ADVISORY MAY BE
NEEDED.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
SFC HIGH PRESSURE WILL BUILD FROM THE NORTH/NORTHWEST WEDNESDAY
NIGHT...BECOME CENTERED OVER THE SOUTHEASTERN UNITED STATES EARLY ON
THURSDAY...THEN CONTINUE TO SHIFT OFFSHORE AHEAD OF ANOTHER LOW
PRESSURE SYSTEM PASSING OVER THE MIDWEST. THE PATTERN WILL FAVOR A
SLIGHT WARMING TREND THROUGH EARLY THURSDAY NIGHT AS WEAK MID LVL
RIDGING OCCURS AND A LIGHT SOUTHERLY FLOW DEVELOPS WELL AHEAD OF THE
LOW PRESSURE SYSTEM PASSING TO THE NORTH. IN GENERAL...AFTERNOON
HIGH TEMPS SHOULD PEAK IN THE UPPER 50S TO AROUND 60 ON THURSDAY. A
COLD FRONT EXTENDING SOUTHWARD FROM THE LOW PRESSURE SYSTEM PASSING
OVER THE NORTHEAST WILL THEN SHIFT OVER THE SOUTHEASTERN UNITED
STATES THURSDAY NIGHT INTO EARLY FRIDAY. MOISTURE IS RATHER LACKING
DURING THE TIME OF FROPA...SO HAVE MAINTAINED A DRY FORECAST AT THIS
POINT...BUT A FEW SHOWERS ARE NOT OUT OF THE QUESTION. DRY AND
SLIGHTLY BELOW NORMAL TEMPS ARE THEN ANTICIPATED AS HIGH PRESSURE
BUILDS FROM THE NORTH BEHIND THE DEPARTING COLD FRONT ON
FRIDAY...BUT A WEAK COASTAL TROUGH COULD DEVELOP OFF THE SOUTHEAST
COAST DURING THE WEEKEND...THUS INCREASING PRECIP CHANCES ALONG THE
COASTAL AREAS.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
VFR. LOW PROBABILITY FOR MVFR CEILINGS AS A COLD FRONT PASSES
LATE TONIGHT/EARLY MONDAY. PROBABILITY FOR LOW-LEVEL WIND SHEAR
JUSTIFIES A MENTION OVERNIGHT/EARLY MONDAY.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL
AT KCHS AND KSAV. BREEZY CONDITIONS WILL OCCUR AT BOTH TERMINALS
MONDAY AFTERNOON. IN ADDITION...ISOLATED SHOWERS AND/OR SMALL HAIL
COULD OCCUR IN THE VICINITY OF KCHS MONDAY AFTERNOON AS AN UPPER LOW
PASSES NORTH OF THE AREA.

&&

.MARINE...
TONIGHT...AHEAD OF AN APPROACHING COLD FRONT...WINDS WILL VEER
TOWARD THE SOUTHWEST AND WILL ACCELERATE AT AT LEAST 15-20 KNOTS.
GUSTS TO 25 KNOTS SHOULD REMAIN CONFINED TO AREAS BEYOND 20 NM
FROM THE COAST. SEAS WILL BUILD TO 2-4 FT WITHIN NEARSHORE WATERS
AND TO AT LEAST 4-5 FT BEYOND 20 NM.

MONDAY AND MONDAY NIGHT...LOW PRESSURE WILL PASS NORTH OF THE AREA
WHILE ITS TRAILING COLD FRONT MOVES OFFSHORE EARLY MONDAY. STRONG
COLD AIR ADVECTION WILL DEVELOP OVER THE AREA BEHIND THE FRONT
MONDAY AFTERNOON AND MONDAY NIGHT...ALLOWING STRONG WINDS ALOFT TO
MIX TO THE OCEAN SURFACE. SMALL CRAFT ADVISORIES TAKE EFFECT FOR ALL
NEAR SHORE WATERS MONDAY MORNING...IN ADDITION TO THE ONGOING SMALL
CRAFT ADVISORY FOR THE OUTER GEORGIA WATERS. A GALE WATCH HAS ALSO
BEEN POSTED FOR THE OUTER GEORGIA WATERS LATE MONDAY AFTERNOON AND
MONDAY NIGHT DUE TO BETTER MIXING NEAR THE GULF STREAM.
FORTUNATELY...THE LIMITED FETCH DUE TO THE OFFSHORE FLOW SHOULD
LIMIT SEAS TO 3-5 FT ACROSS THE NEAR SHORE WATERS AND 5-7 FT ACROSS
THE OUTER GEORGIA WATERS.

TUESDAY AND TUESDAY NIGHT...CONDITIONS WILL GRADUALLY IMPROVE OVER
THE WATERS AS COLD AIR ADVECTION WANES AND THE SURFACE PRESSURE
GRADIENT WEAKENS SOME. HOWEVER...ANOTHER SURGE IS POSSIBLE TUESDAY
NIGHT AS A REINFORCING COLD FRONT DROPS THROUGH. WINDS SHOULD FALL
BELOW SMALL CRAFT ADVISORY LEVELS BY AFTERNOON ACROSS THE NEAR SHORE
WATERS...BUT SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY TO LINGER
THROUGH TUESDAY NIGHT FOR THE OUTER GEORGIA WATERS DUE TO THE
PASSAGE OF THE REINFORCING COLD FRONT.

WEDNESDAY THROUGH SATURDAY...HIGH PRESSURE WILL BUILD OVER THE
WATERS BEHIND A DEPARTING COLD FRONT...WITH MUCH QUIETER CONDITIONS
OVER THE COASTAL WATERS THROUGH THURSDAY. A COLD FRONT WILL THEN
SHIFT OVER THE AREA THURSDAY NIGHT INTO EARLY FRIDAY...CHANGING A
SOUTHERLY WIND TO NORTH/NORTHWEST AS HIGH PRESSURE BUILDS IN BEHIND
IT. A WEAK COASTAL TROUGH COULD DEVELOP OFFSHORE NEXT WEEKEND...WITH
A FEW SHOWERS EVENTUALLY SHIFTING OVER NEARSHORE WATERS.
HOWEVER...WINDS/SEAS ARE EXPECTED TO REMAIN WELL BELOW SMALL CRAFT
ADVISORY LEVELS DURING THIS TIME FRAME.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM MONDAY TO 11 AM EST TUESDAY FOR
     AMZ350-352-354.
     GALE WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING FOR
     AMZ374.
     SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 2 PM EST
     MONDAY FOR AMZ374.

&&

$$

NEAR TERM...SPR
SHORT TERM...JAQ
LONG TERM...
AVIATION...JAQ/SPR
MARINE...JAQ/SPR






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