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Area Forecast Discussion

364
FXUS62 KCHS 301049
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
549 AM EST FRI JAN 30 2015

.SYNOPSIS...
A COLD FRONT WILL PUSH OFFSHORE THIS MORNING. HIGH PRESSURE WILL
BUILD INTO THE REGION THROUGH SATURDAY. A WEAK COASTAL TROUGH WILL
DEVELOP SUNDAY AND LIFT NORTH AHEAD OF A COLD FRONT PASSING OVER
THE AREA MONDAY. HIGH PRESSURE WILL THEN RETURN TO THE REGION
TUESDAY BEFORE SHIFTING OFFSHORE AHEAD OF ANOTHER STORM SYSTEM
APPROACHING FROM THE GULF OF MEXICO LATE IN THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A COLD FRONT WAS MOVING QUICKLY ACROSS CENTRAL SOUTH CAROLINA AND
GEORGIA THIS MORNING. SHOWER ACTIVITY IS RAPIDLY EXPANDING OVER
THE CHARLESTON TRI-COUNTY AREA IN RESPONSE TO THE APPROACHING
SHORTWAVE TROUGH. THIS ACTIVITY WILL PUSH OFF THE COAST OVER THE
NEXT 1-2 HOURS AS THE COLD FRONT APPROACHES THE BEACHES. HAVE
ADJUSTED POPS UP TO 30 PERCENT FOR PARTS OF THE CHARLESTON TRI-
COUNTY AREA THROUGH 13Z. DRY CONDITIONS WILL PREVAIL ELSEWHERE.

DRY AND GUSTY CONDITIONS WILL PREVAIL ACROSS THE REGION TODAY AS
THE UPPER TROUGH SHIFTS OFFSHORE AND SURFACE HIGH PRESSURE BEGINS
TO MOVE IN FROM THE WEST AND NORTHWEST. THE WINDS WILL BE THE MOST
GUSTY THIS MORNING /UP TO 25 MPH/ WITH CONDITIONS DIMINISHING
THIS AFTERNOON AS WEAK COLD AIR ADVECTION AND ISALLOBARIC
INFLUENCES DIMINISH. DESPITE A MODEST DROP IN 850 HPA
TEMPERATURES INTO THE +1C TO +4C RANGE...A SOLID DOWNSLOPE
COMPONENT IN THE LEE OF THE SOUTHERN APPALACHIANS WILL ALLOW HIGHS
TO RECOVER INTO THE UPPER 50S FOR MOST LOCATIONS UNDER FULL
INSOLATION. THE OFFSHORE WIND TRAJECTORIES WILL PREVENT THE
FORMATION OF A SEA BREEZE CIRCULATION THIS AFTERNOON.

LAKE WINDS...THE LAKE WIND ADVISORY FOR LAKE MOULTRIE WILL BE
CANCELLED. POOR MIXING PROFILES ARE EXPECTED OVER THE OPEN LAKE
WATERS TODAY DESPITE WEAK COLD AIR ADVECTION IN THE WAKE OF A
COLD FRONT THIS MORNING. MODEL SOUNDINGS SUGGEST THE MIXING
PROFILE WILL BE STAGNATED QUITE A BIT BY WATER TEMPERATURES IN THE
UPPER 40S WITH SUSTAINED WINDS LIKELY RISING NO HIGHER THAN 15 KT.
IT WILL BE GUSTY ALONG THE LAKESHORE WITH GUSTS POSSIBLY
APPROACHING 25 KT AT TIMES...BUT THERE DOES NOT APPEAR TO BE
ENOUGH EVIDENCE TO MAINTAIN THE CURRENT LAKE WIND ADVISORY FOR THE
OPEN LAKE WATERS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
TONIGHT...A LINGERING PRESSURE GRADIENT BETWEEN INLAND HIGH
PRESSURE AND THE OFFSHORE COLD FRONT WILL LIKELY KEEP THE BOUNDARY
LAYER SOMEWHAT MIXED THROUGH MUCH OF THE EVENING HOURS BEFORE
DECOUPLING AFTER MIDNIGHT AS THE NOCTURNAL INVERSION DEEPENS AND
THE CORE OF THE SURFACE HIGH DRAWS CLOSER. WITH SOLID RADIATIONAL
CONDITIONS EXPECTED BETWEEN MIDNIGHT AND SUNRISE SATURDAY...HAVE
LEANED CLOSER TO THE COOLER SIDE OF THE GUIDANCE ENVELOP TO
CONSTRUCT OVERNIGHT LOWS. LOWS WILL RANGE FROM THE UPPER 20S WELL
INLAND TO THE LOWER-MID 30S ELSEWHERE...EXCEPT UPPER 30S ALONG
PARTS OF THE GEORGIA COAST. NORTHERLY WINDS OVER LAKE MOULTRIE
WILL ALSO KEEP AREAS IMMEDIATELY DOWNWIND OF THE LAKE A BIT
WARMER...INCLUDING THE MONCKS CORNER AREA.

SATURDAY...SURFACE HIGH PRESSURE WILL STEADILY TRACK OVER THE EAST
COAST STATES DURING THE DAYTIME HOURS...EVENTUALLY MOVING INTO THE
NEARBY ATLANTIC WATERS OVERNIGHT. A COOLER AIR MASS AND NORTHEAST
FLOW WILL REMAIN IN PLACE FOR THE FIRST HALF OF THE DAY...SUPPORTING
HIGH TEMPERATURES SLIGHTLY BELOW NORMAL. TEMPERATURES WILL PEAK IN
THE LOW 50S NORTH TO THE UPPER 50S SOUTH...WHILE MAINLY HIGH CLOUDS
BEGIN TO INTRUDE FROM THE WEST DURING THE LATE AFTERNOON TIME FRAME.
THE INCREASING CLOUD COVER...COMBINED WITH MORE EAST/SOUTHEAST
SURFACE FLOW...WILL MODERATE NIGHTTIME TEMPERATURES A FEW DEGREES
COMPARED TO THE PREVIOUS NIGHT. EXPECT LOW TEMPERATURES TO STAY
ABOVE FREEZING...RANGING FROM THE LOW/MID 30S INLAND TO THE UPPER
30S/AROUND 40 SOUTH AND COAST.

SUNDAY...SURFACE HIGH PRESSURE WILL HAVE SETTLED OVER THE ATLANTIC
BY DAYBREAK...WITH THE NEXT LOW PRESSURE SYSTEM TAKING SHAPE ACROSS
THE MISSISSIPPI VALLEY. A WEAK COASTAL TROUGH ON THE PERIPHERY OF
THE ATLANTIC HIGH COULD GENERATE ISOLATED SHOWERS OVER THE MARINE
ZONES IN THE MORNING. THE COASTAL TROUGH WILL THEN DISSIPATE AND/OR
MOVE ONSHORE AS THE DAY PROGRESSES...AHEAD OF THE DEEPENING LOW
PRESSURE SYSTEM AND TRAILING COLD FRONT MOVING TOWARD THE
APPALACHIANS OVERNIGHT. SHOWERS WILL SPREAD ACROSS THE FORECAST AREA
FROM WEST TO EAST MAINLY BEGINNING IN THE LATE AFTERNOON/EARLY
EVENING. COVERAGE IS THEN EXPECTED TO PEAK BETWEEN MIDNIGHT AND
DAYBREAK MONDAY MORNING...WHEN THE COLD FRONT SHIFTS INTO THE
WESTERN FORECAST AREA. DESPITE THICKENING SKY COVER...EXPECT WARMER
TEMPERATURES SUNDAY AS A RESULT OF INCREASING SOUTHERLY FLOW IN THE
WARM SECTOR OF THE APPROACHING SYSTEM. HIGH TEMPERATURES WILL BE IN
THE LOW TO MID 60S...WHILE LOW TEMPERATURES ONLY FALL INTO THE UPPER
40S TO LOW 50S.

MONDAY...THE COLD FRONT WILL BE CROSSING OVER THE FORECAST AREA
DURING THE MORNING HOURS...AND LIKELY MOVING OFFSHORE NO LATER THAN
EARLY AFTERNOON. SCATTERED SHOWERS ARE THUS STILL EXPECTED THROUGH
THE MORNING...BEFORE DISSIPATING FROM WEST TO EAST IN THE WAKE OF
THE DEPARTING SYSTEM. HIGH TEMPERATURES WILL RETURN TO MORE SEASONAL
NORMALS WITHIN BREEZY WEST FLOW...REACHING THE UPPER 50S TO LOWER
60S AS CLOUD COVER STEADILY DECREASES.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
RAIN CHANCES WILL DROP BELOW 10 PERCENT BY MONDAY EVENING. LOW
TEMPERATURES MONDAY NIGHT WILL REFLECT THE COOLER AIR MASS IN
PLACE...FALLING INTO THE LOW 30S WEST AND NORTH TO THE MID TO UPPER
30S COAST AND SOUTH. TRANSIENT HIGH PRESSURE WILL MOVE QUICKLY
ACROSS THE EASTERN UNITED STATES IN THE WAKE OF THE DEPARTING LOW
SYSTEM ON TUESDAY. NUMERICAL MODEL SOLUTIONS THEN INDICATE SOUTHERN
STREAM SHORTWAVE ENERGY MOVING INTO THE GULF OF MEXICO AND
GENERATING A LOW PRESSURE SYSTEM ON WEDNESDAY. STRENGTH AND TIMING
DIFFERENCE BETWEEN MODELS ARE STILL QUITE SIGNIFICANT. THERE REMAINS
AT LEAST A 6 HOUR VARIANCE BETWEEN THE FASTER AND SLOWER SOLUTIONS
REGARDING WHEN THE DEEPENING LOW WILL HAVE TRACKED UP TO THE
SOUTHEAST COAST. WILL REMAIN SOMEWHAT GENERIC AND CONSERVATIVE
REGARDING RAIN CHANCES UNTIL THERE IS BETTER MODEL AGREEMENT. AT
THIS POINT...WILL REINTRODUCE RAIN CHANCES BY WEDNESDAY AS A COASTAL
TROUGH DEVELOPS ALONG THE PERIPHERY OF THE SURFACE HIGH OVER THE
ATLANTIC. HAVE THEN INDICATED INCREASING COVERAGE/POTENTIAL OF RAIN
WEDNESDAY NIGHT INTO EARLY THURSDAY...WHEN THE FASTER MODEL SOLUTION
TRACKS THE GULF LOW UP THE SOUTHEAST COASTLINE. ALTHOUGH COVERAGE IS
EXPECTED TO DECREASE FROM WEST TO EAST LATER THURSDAY INTO
FRIDAY...WILL MAINTAIN SLIGHT CHANCE POPS TO ACCOUNT FOR A FEW
SHOWERS THAT COULD BE INITIATED AS AN UPPER TROUGH MOVES ACROSS THE
EAST COAST BEHIND THE DEPARTING LOW SYSTEM.

HIGH TEMPERATURES EACH AFTERNOON WILL GENERALLY BE IN THE 50S.
MONDAY NIGHT WILL BE THE COOLEST...WITH LOW TEMPERATURES EACH NIGHT
THEREAFTER GENERALLY IN THE MID 30S INLAND TO LOW 40S NEAR THE COAST.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
VFR. THE RISK FOR LOW-LEVEL WIND SHEAR WILL END BY 13Z WITH THE
PASSAGE OF A COLD FRONT.

EXTENDED AVIATION OUTLOOK...VFR TO PREVAIL UNTIL SUNDAY NIGHT INTO
MONDAY WHEN MVFR OR POSSIBLY LOWER CONDS ARE POSSIBLE DUE TO A
PASSING COLD FRONT. BREEZY CONDS ALSO LIKELY SUN NIGHT/MON.

&&

.MARINE...
TODAY...MARGINAL SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED TO
DEVELOP THIS MORNING IN THE WAKE OF A COLD FRONT. FREQUENT GUSTS
TO 25 KT BEING DRIVEN BY WEAK COLD AIR ADVECTION AND MODEST
ISALLOBARIC AFFECTS ARE EXPECTED OVER ALL LEGS WITH THE EXCEPTION
OF THE GEORGIA NEARSHORE WATERS. SMALL CRAFT ADVISORIES WILL BE
MAINTAINED FOR ALL SOUTH CAROLINA MARINE ZONES...INCLUDING THE
CHARLESTON HARBOR AND THE GEORGIA OFFSHORE ZONE. OFFSHORE WIND
TRAJECTORIES WILL LIMIT SEAS TO 2-3 FT NEARSHORE WATERS WITH 3-5
FT OFFSHORE WATERS.

SATURDAY THROUGH TUESDAY...HIGH PRESSURE WILL BUILD INTO THE REGION
AND EVENTUALLY SHIFT OFFSHORE OVER THE WEEKEND. A STRENGTHENING LOW
PRESSURE SYSTEM WILL TRACK NORTH OF THE AREA MONDAY...WITH ITS
TRAILING COLD FRONT SWEEPING THROUGH THE MARINE ZONES MONDAY
MORNING. INCREASING SOUTHERLY FLOW AHEAD OF THE FRONT...AS WELL AS
NORTHWEST FLOW IN ITS WAKE...COULD SUPPORT SMALL CRAFT ADVISORY
CONDITIONS OVER THE LOCAL WATERS LATE SUNDAY NIGHT INTO MONDAY
NIGHT. HIGH PRESSURE BUILDING INTO THE REGION TUESDAY WILL THEN LEAD
TO IMPROVING CONDITIONS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR AMZ330-
     350-352-374.

&&

$$

ST/WMS



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