Area Forecast Discussion
Issued by NWS Charleston, SC

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000 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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