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Area Forecast Discussion

541
FXUS62 KCHS 022125
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
425 PM EST MON MAR 2 2015

.SYNOPSIS...
A BACKDOOR COLD FRONT WILL DROP SOUTH THROUGH THE AREA TONIGHT...THEN
STALL JUST SOUTH OF THE AREA EARLY TUESDAY. THE FRONT WILL LIFT BACK
NORTH AS A WARM FRONT LATE TUESDAY INTO WEDNESDAY. A COLD FRONT WILL
APPROACH FROM THE NORTHWEST WEDNESDAY NIGHT...PASSING THROUGH THE
REGION THURSDAY. COLDER HIGH PRESSURE WILL BUILD OVER THE AREA INTO
EARLY SATURDAY...WITH A COASTAL TROUGH TO DEVELOP OFFSHORE INTO SUNDAY.
ANOTHER COLD FRONT COULD IMPACT THE AREA EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
LATE THIS AFTERNOON...WATER VAPOR IMAGERY DEPICTS A NEARLY ZONAL
FLOW ALOFT. MEANWHILE...SURFACE OBSERVATIONS AND SATELLITE
IMAGERY INDICATE A BACKDOOR COLD FRONT POSITIONED JUST NORTH OF
THE AREA ACROSS THE SOUTHERN PEE DEE AND GRAND STRAND.
TEMPERATURES HAVE WARMED CONSIDERABLY ACROSS THE AREA...MID 70S IN
MOST PLACES...WITH ABUNDANT SUNSHINE AND A WESTERLY FLOW IN PLACE
AHEAD OF AN APPROACHING BACKDOOR COLD FRONT.

TONIGHT...THE REGION WILL REMAIN ALONG THE NORTHERN PERIPHERY OF
UPPER LEVEL RIDGING CENTERED OVER THE GULF OF MEXICO...MAINTAINING
A NEARLY ZONAL FLOW ALOFT. AT THE SURFACE...THE BACKDOOR COLD
FRONT WILL MAKE STEADY PROGRESS SOUTHWARD INTO SOUTHEAST SOUTH
CAROLINA THIS EVENING THEN THROUGH SOUTHEAST GEORGIA OVERNIGHT.
HIGH PRESSURE CROSSING THE CENTRAL APPALACHIANS WILL THEN WEDGE
SOUTHWARD INTO THE REGION IN WAKE OF THE BACKDOOR COLD FRONT.

A SHORT WAVE DISTURBANCE EMBEDDED WITHIN THE WESTERLY FLOW ALOFT
WILL INTERACT WITH THE BAROCLINIC ZONE/OVERRUNNING REGIME AND
PRODUCE INCREASING CHANCES FOR LIGHT RAIN TONIGHT. RAIN
PROBABILITIES WILL BE GREATEST...IN THE CHANCE TO LIKELY
CATEGORY...ACROSS NORTHWEST AND NORTHERN PORTIONS OF THE FORECAST
AREA OVERNIGHT.

A STRENGTHENING LOW LEVEL INVERSION WITHIN THE DEVELOPING WEDGE
WILL RESULT IN EXTENSIVE LOW STRATUS FORMATION. MEANWHILE...SOUTH
OF THE BOUNDARY ABUNDANT LOW LEVEL MOISTURE AND A WARMER AIRMASS
WILL SUPPORT THE FORMATION OF AREAS OF FOG TONIGHT...MAINLY SOUTH
OF THE I-16 CORRIDOR...WHICH COULD BECOME LOCALLY DENSE AT TIMES.

LOWS ARE FORECAST TO RANGE FROM THE MID TO UPPER 40S IN THE
CHARLESTON TRI-COUNTY AREA...TO THE LOWER AND MID 50S FARTHER
SOUTH.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
TUESDAY...THE BACKDOOR FRONT WILL BE SOUTH OF THE ALTAMAHA RIVER IN
SOUTHEAST GEORGIA BY DAYBREAK...WITH A WELL-DEFINED WEDGE OF HIGH
PRESSURE BUILDING DOWN THE LEE OF THE APPALACHIANS IN ITS WAKE. THIS
PATTERN WILL SUPPORT A STRONG INVERSION THAT WILL TRAP LOW LEVEL
MOISTURE FOR MUCH OF THE DAY AND ALLOW THICK CLOUDS TO PERSIST.
PATCHY FOG IN THE EARLY MORNING HOURS WILL DISSIPATE OVER
LAND...WHILE POSSIBLY LINGERING OVER THE COASTAL WATERS THROUGH THE
AFTERNOON. LIGHT RAIN/DRIZZLE WILL HOLD THE WEDGE IN PLACE THROUGH
AT LEAST EARLY AFTERNOON...ESPECIALLY ACROSS FAR INLAND AND NORTHERN
LOCATIONS. MUCH OF THE SENSIBLE WEATHER IMPACTS FOR THE
AFTERNOON/EARLY EVENING WILL BE HIGHLY DEPENDENT ON WHERE THE WARM
FRONT/SOUTHERN PERIPHERY OF THE WEDGE SETS UP...BEFORE THE FEATURE
EVENTUALLY LIFTS NORTH OVERNIGHT. AS IS TYPICAL IN AN INLAND WEDGE
PATTERN...HAVE INDICATED A RATHER NOTABLE HIGH TEMPERATURE GRADIENT
FROM NORTHWEST TO SOUTHEAST. TEMPERATURES WILL LIKELY BE SUPPRESSED
TO A RANGE FROM THE MID 50S NEAR THE SANTEE RIVER TO THE LOWER 70S
NEAR THE ALTAMAHA RIVER. HOWEVER ANY CHANGE IN THE LOCATION OF THE
SOUTHERN PERIPHERY OF THE WEDGE COULD GREATLY IMPACT TEMPERATURES.

TUESDAY NIGHT... THE WEDGE IS EXPECTED TO GRADUALLY ERODE
OVERNIGHT...ALLOWING A SOLID SOUTHERLY FLOW TO SET UP IN ITS WAKE.
ANY LIGHT PRECIPITATION CHANCES WILL END FROM SOUTH TO NORTH BY THE
EVENING HOURS. THE ADVECTION OF HIGHER DEWPOINT AIR AND THE BUILD-
DOWN OF STRATUS WILL SUPPORT FOG DEVELOPMENT OVERNIGHT...WITH DENSE
FOG ADVISORIES QUITE LIKELY. LOW TEMPERATURES WILL RANGE FROM THE
MID 50S TO AROUND 60 DEGREES.

WEDNESDAY...THE SOUTHEAST WILL BE WITHIN SOLID SOUTHERLY FLOW
BETWEEN ATLANTIC HIGH PRESSURE AND A COLD FRONT FAR UPSTREAM. THE
COMBINED EFFECTS OF WARM ADVECTION AND DEEP LAYER RIDGING FROM THE
ATLANTIC SUGGESTS A CONSIDERABLY WARMER DAY THAN SEEN IN QUITE SOME
TIME FOR THE FORECAST AREA. INLAND TEMPERATURES WILL PEAK IN THE
UPPER 70S NORTH TO LOWER 80S SOUTH. THE COASTAL AREAS WILL BE
NOTABLY COOLER...A RESULT OF BOTH THE PROXIMITY OF COOLER MARINE AIR
AND POSSIBLY SOME INTRUSION OF SEA FOG FROM THE NEARSHORE WATERS.
ALTHOUGH A FEW FORECAST MODELS INDICATE SOME LIGHT PRECIPITATION
INLAND...PREFER TO KEEP RAIN CHANCES BELOW 15 PERCENT CONSIDERING
DEEP LAYER RIDGING AND NEGATIVE VORTICITY ADVECTION ACROSS THE AREA.

WEDNESDAY NIGHT...THE COLD FRONT WILL BE APPROACHING FROM THE
WEST...YET REMAIN JUST UPSTREAM BY DAYBREAK THURSDAY. ASSOCIATED
RAIN WILL ALSO REMAIN OUTSIDE OF THE FORECAST AREA OVERNIGHT...AND
HAVE KEPT RAIN CHANCES BELOW THE MENTIONABLE 15 PERCENT ACCORDINGLY.
FOG IS POSSIBLE AGAIN...HOWEVER INCREASING LOW LEVEL FLOW COULD
PREVENT FOG FROM BECOMING AS DENSE AS TUESDAY NIGHT. SEA FOG COULD
STILL PERSIST AND SLIP LOCALLY ONSHORE.

THURSDAY...LATEST GFS AND ECMWF MODEL RUNS SUPPORT THE COLD FRONT
BEING JUST TO OUR NORTH AND WEST AT NOON ON THURSDAY AND THEN
QUICKLY MOVING THROUGH THE AREA DURING THE AFTERNOON. THIS WOULD
SUPPORT SLIGHTLY HIGHER TEMPERATURES AND RAISED HIGHS A LITTLE...BUT
I AM STILL SEVERAL DEGREES BELOW GUIDANCE AND THE ENSEMBLE MEANS.
12Z NAM IS EVEN SLOWER WITH THE FRONT AND IF THIS IS CORRECT AND I
THINK IT IS OVERDONE...BUT WOULD RESULT IN HIGHS WELL INTO THE 70S.
FOR NOW HAVE HIGHS MAINLY IN THE MID TO UPPER 60S. IF THE MODEL
TRENDS CONTINUE THOUGH...LATER FORECASTS WILL NEED TO RAISE HIGHS ON
THURSDAY FURTHER. CANNOT RULE OUT A FEW SHOWERS THURSDAY
MORNING...BUT BEST CHANCES WILL BE DURING THE AFTERNOON. STILL THINK
THAT UPPER END CHANCE LEVELS LOOK REASONABLE...BUT BASED ON THE BEST
LIFT AND MOISTURE SHIFT BY TO THE NORTH AND WEST OF THE AREA...WOULD
NOT BE SURPRISED IF THE THREAT FOR SHOWERS WOULD NEED TO BE LOWERED
A LITTLE IN FUTURE FORECASTS...ESPECIALLY IF THE FRONT IS SLOWER.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
THE COLD FRONT SLIDES INTO THE ATLANTIC THURSDAY NIGHT WITH COLDER
CANADIAN HIGH PRESSURE ARRIVES BEHIND THE FRONT INTO SATURDAY. THE
HIGH THEN PROGRESSES INTO THE ATLANTIC AS A COASTAL TROUGH DEVELOPS
OUT NEAR THE WESTERN WALL OF THE GULF STREAM. THE TROUGH MAY CLOSE
OFF SUNDAY...BUT IT DOES LIFT OFF TO THE NE AND EAST...BEFORE
ANOTHER COLD FRONT LOOKS TO APPROACH EARLY NEXT WEEK. CONDITIONS
WILL BE COLDER INTO THE WEEKEND...BEFORE SOME MODERATING TEMPS COULD
DEVELOP BY EARLY NEXT WEEK. RETURN FLOW OF MOISTURE OFF THE ATLANTIC
WILL PRODUCE A SLOWLY INCREASING CHANCE FOR SHOWERS FRIDAY INTO THE
WEEKEND. UNLESS THIS PROGRESSION IS FASTER THAN NOW ANTICIPATED
THERE DOESN/T APPEAR TO BE ANY P-TYPE ISSUES.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL AT BOTH KCHS AND KSAV THROUGH THE
REMAINDER OF THE AFTERNOON. A BACKDOOR COLD FRONT WILL DROP IN
FROM THE NORTH THIS EVENING...WITH DETERIORATING CONDITIONS IN ITS
WAKE AS ABUNDANT MOISTURE BECOMES TRAPPED BENEATH A STRONG LOW
LEVEL INVERSION. CEILINGS WILL EVENTUALLY FALL TO IFR OR LOWER
LEVELS OVERNIGHT...WITH SOME REDUCED VISIBILITIES AS WELL.
EXPECT MVFR OR LOWER CONDITIONS TO THEN PREVAIL AT THE TERMINALS
THROUGH 18Z TUESDAY.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS MUCH OF THE TIME
THROUGH THURSDAY. POTENTIAL FOR SOME VFR CONDITIONS WEDNESDAY AND
AGAIN THURSDAY NIGHT AND FRIDAY.

&&

.MARINE...
TONIGHT...A BACKDOOR COLD FRONT WILL DROP THROUGH THE WATERS THIS
EVENING INTO THE OVERNIGHT HOURS...WITH WINDS SHIFTING NE/E AND
SURGING IN ITS WAKE. WINDS APPEAR STRONGEST ACROSS THE CHARLESTON
COUNTY WATERS WHERE A SMALL CRAFT ADVISORY TAKES EFFECT BEGINNING
AT 10 PM FOR 20 KT WINDS AND GUSTS TO 25 KT. CONDITIONS COULD
ALSO APPROACH SMALL CRAFT ADVISORY CRITERIA IN CHARLESTON HARBOR
BUT CONFIDENCE IS TOO LOW TO ISSUE ANY ADVISORIES AT THIS TIME.
ACROSS THE REMAINDER OF THE WATERS...WINDS SHOULD PEAK UPWARDS OF
15-20 KT. SEAS WILL BUILD WITHIN STRENGTHENING WINDS AND A
FAVORABLE FETCH...REACHING 4-6 FT ACROSS THE CHARLESTON COUNTY
WATERS AND 3-5 FT ELSEWHERE.

SEA FOG REMAINS A CONCERN FOR THE WATERS TONIGHT. FOG FROM EARLIER
THIS AFTERNOON APPEARS TO HAVE LIFTED INTO A LOW STRATUS DECK AS
OFFSHORE WINDS ADVECTED IT FARTHER AWAY FROM THE COAST.
HOWEVER...CONDITIONS APPEAR FAVORABLE FOR SEA FOG TO REDEVELOP
TONIGHT ALONG AT LEAST THE GEORGIA NEAR SHORE WATERS IF NOT THE
FAR SOUTHERN SOUTH CAROLINA NEAR SHORE WATERS AS WELL. DENSE FOG
ADVISORIES MAY BE NEEDED ONCE AGAIN FOR THESE AREAS. FARTHER
NORTH...INCREASING WINDS SHOULD LIMIT FOG/STRATUS BUILD DOWN SO
REDUCED VISIBILITIES ARE LESS OF A CONCERN THROUGH DAYBREAK.

TUESDAY...ANOTHER INLAND WEDGE OF HIGH PRESSURE WILL BE
THE PROMINENT FEATURE BEHIND A STATIONARY FRONT JUST SOUTH OF THE
LOCAL WATERS. THERE IS ENOUGH PINCHING BETWEEN THESE TWO SYSTEMS TO
PRODUCE A SMALL CRAFT ADVISORY FOR AT LEAST AMZ350 INTO MIDDAY. IN
ADDITION...LATE NIGHT AND MORNING FOG FROM BOTH THE WATER AND LAND
SOURCES COULD LINGER INTO THE AFTERNOON OVER THE COOLER SHELF WATERS.

TUESDAY NIGHT AND WEDNESDAY...THE STATIONARY FRONT WILL HAVE
TRANSITIONED INTO A NORTHWARD MOVING WARM FRONT...PUTTING THE AREA
INTO THE SO-CALLED WARM SECTOR...AS A SUB-TROPICAL ATLANTIC RIDGE
FILLS IN BEHIND THE FRONT. WINDS AND SEAS WILL BE BELOW ANY ADVISORY
CRITERIA DURING THIS TIME AS THEY VEER AROUND TO THE SOUTH AND SW.
HOWEVER...THIS FAVORABLE FLOW WILL OVERSPREADS THE CONSIDERABLY
COOLER CONTINENTAL SHELF WATERS...LEADING TO AT LEAST AREAS OF SEA
FOG. DENSE FOG ADVISORIES APPEAR A GOOD BET...AND THE PORTS OF
CHARLESTON AND SAVANNAH CERTAINLY COULD BE CLOSED FOR AN EXTENDED
LENGTH OF TIME.

WEDNESDAY NIGHT AND THURSDAY...THE ATLANTIC RIDGING GIVES WAY TO A
COLD FRONT THAT APPROACHES FROM THE NW AND MOVES INTO THE WATERS
THURSDAY AFTERNOON AND EVENING. FOG WILL CONTINUE TO BE A CONCERN IN
ADVANCE OF THE COLD FRONT...BEFORE THE ARRIVAL OF STRONGER WINDS AND
AT LEAST SCATTERED SHOWERS. WINDS REACHING OR EXCEEDING 20 KNOTS ARE
LIKELY BY LATE IN THE DAY ACROSS THE NORTHERN WATERS. AS A
RESULT...A SMALL CRAFT ADVISORY MAY BE NEEDED FOR AT LEAST AMZ350
BY LATE THURSDAY.

THURSDAY NIGHT THROUGH SATURDAY...A STRONG CONTINENTAL HIGH WILL
BUILD FROM THE NW BEHIND THE COLD FRONT...AND THE COMBINATION OF
COLD ADVECTION AND A TIGHT PRESSURE PATTERN AS A COASTAL TROUGH
EVENTUALLY FORMS LATE IN THE PERIOD SHOULD LEAD TO AT LEAST SMALL
CRAFT ADVISORIES. THERE IS EVEN A LOW RISK FOR GALES FOR ESPECIALLY
THE OUTER GA WATERS THURSDAY NIGHT INTO FRIDAY IF THE COLD ADVECTION
IS STRONG ENOUGH.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 1 PM EST
     TUESDAY FOR AMZ350.

&&

$$
SYNOPSIS...
NEAR TERM...JAQ
SHORT TERM...WMS/MTE
LONG TERM...
AVIATION...JAQ/WMS
MARINE...JAQ/WMS/MTE



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