Area Forecast Discussion
Issued by NWS Columbia, SC

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000
FXUS62 KCAE 221954
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
254 PM EST MON DEC 22 2014

.SYNOPSIS...
A FRONTAL ZONE WILL REMAIN NEAR THE SOUTHEAST COAST THROUGH
TUESDAY. A SERIES OF LOW PRESSURE SYSTEMS WILL MOVE NORTHEASTWARD
ALONG THE FRONT...KEEPING WEATHER UNSETTLED. A STRONG COLD FRONT
APPROACHING FROM THE WEST WILL MOVE THROUGH THE FORECAST AREA
WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
DEEP UPPER TROUGH OVER THE CENTRAL CONUS WILL CONTINUE TO PROMOTE
SOUTHWESTERLY FLOW ALOFT. AT THE SURFACE...HIGH PRESSURE CENTERED
OVER NEW ENGLAND WILL CONTINUE RIDGING INTO THE FORECAST AREA PROMOTING
A STRONG COLD AIR DAMMING SETUP. SURFACE ANALYSIS SHOWS AN AREA OF
LOW PRESSURE CENTERED OVER THE NORTH CAROLINA COAST WHICH IS
PROMOTING INCREASED MOISTURE INTO THE AREA. MESOSCALE BRIEFING
INDICATES THE HIGHEST PRECIPITABLE WATER AND BEST MOISTURE
TRANSPORT ACROSS THE EAST. ISENTROPIC LIFT OVER THE WEDGE RIDGE
WILL SUPPORT RAIN OR DRIZZLE INTO THE OVERNIGHT PERIOD. REGIONAL
RADAR COMPOSITE SHOWS AN AREA OF SHOWERS MOVING NORTHEAST ACROSS
THE CENTRAL AND EASTERN PART OF THE FORECAST AREA THIS AFTERNOON
WITH MORE WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS FURTHER
SOUTH AND EAST ALONG COASTAL SC/GA AND ACROSS THE FLORIDA
PANHANDLE. HAVE SEEN SOME LIGHTNING IN THE EASTERN MIDLANDS DUE
TO INSTABILITY ALOFT. FOR MOST OF THE FORECAST AREA...THE MAIN
PRECIPITATION TYPE WILL BE OCCASIONAL DRIZZLE. MODELS INDICATE
0.15 INCH OF RAIN OR LESS WITH THE HIGHEST AMOUNTS EAST.
TEMPERATURES WILL REMAIN STEADY IN THE 40S THROUGH THE AFTERNOON
AND WILL MAKE LITTLE CHANGE OVERNIGHT UNDER CLOUD COVER.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
VERY ACTIVE WEATHER EXPECTED DURING THIS PERIOD AS 500MB FLOW
BECOMES HIGHLY AMPLIFIED WITH LOW PRESSURE DEVELOPING ALONG THE
WESTERN GULF COAST BY TUESDAY AFTERNOON AND LIFTING NORTHWARD INTO
THE OHIO VALLEY ON WEDNESDAY...WHICH WILL DRIVE A COLD FRONT
ACROSS OUR AREA WEDNESDAY EVENING.

THERE SHOULD BE A RELATIVE BREAK IN THE PRECIPITATION TUESDAY
MORNING AS THE AREA REMAINS IN BETWEEN WAVES OF ENERGY ROTATING
THROUGH THE LONGWAVE TROUGH. THE CAD WEDGE CONDITIONS WILL PERSIST
AND THINK MODELS ARE TOO AGGRESSIVE IN ERODING THE WEDGE BY
TUESDAY AFTERNOON SO HAVE GONE WELL BELOW MOS GUIDANCE FOR MAX
TEMPS...HEAVILY LEANING TOWARDS OUR LOCAL WEDGE EQUATION WHICH
GIVES MAX TEMPS SIMILAR TO TODAY IN THE MID TO UPPER 40S...EXCEPT
SOME LOWER 50S POSSIBLE IN THE EASTERN MIDLANDS LATE IN THE DAY.
EXPECT PATCHY DRIZZLE WITH SCATTERED RAIN SHOWERS THROUGH THE
MORNING HOURS THEN POPS RAMP UP TO CATEGORICAL BY AFTERNOON AS
ANOTHER SHORTWAVE TROUGH MOVES INTO THE REGION FROM THE SOUTH
COINCIDING WITH STRONG ISENTROPIC LIFTING OVER THE AREA.

AS THE STORM SYSTEM MATURES AND DEEPENS TUESDAY NIGHT...850MB
FLOW OVER THE FORECAST AREA INCREASES AND MOISTURE TRANSPORT OVER
BECOMES MAXIMIZED. PRECIPITABLE WATER VALUES INCREASE TO OVER 1.75
INCHES WHICH IS NEAR THE CLIMATOLOGICAL MAXIMUM FOR OUR AREA AND
EXPECT WIDESPREAD RAINFALL...MODERATE AT TIMES...AND CANNOT RULE
OUT SOME ISOLATED THUNDER. THE WEDGE WILL BREAK DOWN AS LOW LEVEL
FLOW BECOMES MORE SOUTHEASTERLY AND EVENTUALLY SOUTHERLY BY
WEDNESDAY MORNING ALLOWING TEMPERATURES TO WARM UP THROUGH THE
NIGHT. USED A NON-DIURNAL TEMPERATURE TREND TUESDAY AND TUESDAY
NIGHT. SIGNIFICANT RAINFALL IS EXPECTED DURING THE TUESDAY EVENING
THROUGH WEDNESDAY AFTERNOON PERIOD WITH QPF BETWEEN 1-2 INCHES
ACROSS THE AREA.

THE AREA IS FORECAST TO FALL WITHIN THE WARM SECTOR ON WEDNESDAY
WITH A WARM FRONT LIFTING NORTH OF THE REGION WITH STRONG
SOUTHERLY FLOW SUPPORTING ABOVE NORMAL TEMPERATURES. FORECAST
INSTABILITY IS WEAK WITH LI VALUES STRUGGLING TO RISE ABOVE ZERO.
STRONG SHEAR IS EXPECTED WITH LOW LEVEL JET AROUND 55-60 KNOTS AND
COULD SUPPORT AN ISOLATED DAMAGING WIND THREAT DESPITE THE WEAK
FORECAST INSTABILITY. FRONT WILL CROSS THE AREA SOMETIME WEDNESDAY
EVENING WITH HIGH PRESSURE BUILDING IN FROM THE SOUTHWEST LATE
WEDNESDAY NIGHT. STRONG WINDS ARE EXPECTED BEHIND THE FRONT WITH
SOME GUSTS TO 15 TO 25 MPH DUE TO INCREASED PRESSURE GRADIENT.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
AN ACTIVE AND GENERALLY MERIDIONAL UPPER LEVEL FLOW PATTERN
PERSISTS ACROSS THE COUNTRY DURING THE EXTENDED FORECAST PERIOD.

THE STRONG STORM SYSTEM THAT WILL BRING SIGNIFICANT RAINFALL TO
THE REGION MID WEEK WILL LIFT INTO SOUTHEASTERN CANADA ON
CHRISTMAS DAY THURSDAY AS MID LEVEL 500MB FLOW BECOMES ZONAL BY
THURSDAY EVENING ACROSS THE SOUTHEASTERN STATES. MUCH DRIER AIR
WILL BUILD OVER THE FORECAST AREA THURSDAY BEHIND A COLD FRONT
WITH COOLER TEMPERATURES AND BREEZY CONDITIONS EXPECTED. NEAR
NORMAL TO SLIGHTLY BELOW NORMAL TEMPERATURES ARE EXPECTED ON
THURSDAY WITH HIGHS IN THE 50S AND LOWS THURSDAY NIGHT IN THE
LOWER TO MID 30S.

TRANQUIL WEATHER UNDER MOSTLY CLEAR SKIES WITH MODERATING
TEMPERATURES ARE FORECAST FOR FRIDAY AND SATURDAY AS SURFACE HIGH
PRESSURE SETTLES OVER THE AREA ON FRIDAY AND SHIFTS OFF THE COAST
ON SATURDAY WITH A RETURN SOUTHERLY FLOW DEVELOPING. TEMPERATURES
DURING THIS PERIOD WILL BE SLIGHTLY ABOVE NORMAL WITH HIGHS IN THE
UPPER 50S TO LOWER 60S AND ABOVE NORMAL OVERNIGHT LOWS IN THE
UPPER 30S TO 40S.

MORE UNCERTAINTY EXISTS IN THE LATER PART OF THE EXTENDED FORECAST
PERIOD DUE TO DIFFERENCES AMONG THE MEDIUM RANGE MODELS LEADING TO
LOWER CONFIDENCE IN THE FORECAST. THE GFS DEPICTS AN UPPER TROUGH
CROSSING THE OHIO VALLEY AND MID ATLANTIC WHICH PUSHES A COLD
FRONT THROUGH THE FORECAST AREA SATURDAY NIGHT. HOWEVER...LITTLE
MOISTURE IS AVAILABLE WITH THE SYSTEM. THE ECMWF IS A BIT SLOWER
THAN THE GFS AND BRINGS A STRONGER SHORTWAVE TROUGH ACROSS THE
APPALACHIANS ON SUNDAY WITH BETTER MOISTURE RETURN AND INFLOW
INTO THE FRONT RESULTING IN A BETTER CHANCE OF PRECIPITATION LATE
SATURDAY NIGHT AND SUNDAY. WILL LEAN TOWARDS THE HPC GUIDANCE
REGARDING POPS AND SINCE THERE IS REASONABLE CONSENSUS ON
SATURDAY BEING DRY WILL REMOVE POPS SATURDAY AND INCLUDE POPS ON
SUNDAY. TEMPERATURES WILL BE DETERMINED BY WHEN THE COLD FRONT
ACTUALLY PASSES THROUGH WITH COOLER TEMPERATURES EXPECTED BEHIND
THE FRONTAL PASSAGE.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
IFR CONDITIONS EXPECTED THROUGH THE 24 HOUR TAF PERIOD.

LIGHT RAIN/DRIZZLE STILL CONTINUING AT THE TAF SITES THIS
AFTERNOON. REGIONAL RADAR COMPOSITE SHOWS PATCHY LIGHT RAIN
MOVING NORTHEAST ACROSS SOUTHEASTERN GEORGIA WHICH WILL REACH THE
TAF SITES LATE THIS AFTERNOON. CONDITIONS NOT EXPECTED TO IMPROVE
AS NORTHEASTERLY FLOW CONTINUES TO PROMOTE WEDGE CONDITIONS.
EXPECT LIGHT RAIN/DRIZZLE TO REDUCE VSBYS INTO THE MVFR RANGE
WITH CIGS MAINLY IFR THROUGH THE AFTERNOON...AND IFR CIGS/VSBYS
THIS EVENING. MODELS INDICATE LIFR CIGS LATE TONIGHT THROUGH THE
END OF THE TAF PERIOD. MAY SEE IMPROVEMENT FROM LIFR TO IFR
TOWARD THE END OF THE TAF PERIOD ALTHOUGH MODELS OFTEN SHOW
IMPROVEMENT TOO QUICKLY SO HAVE KEPT LIFR CONDITIONS THROUGH 18Z
TUESDAY. WINDS THROUGH THE PERIOD WILL BE NORTHEASTERLY AT 7
KNOTS OR LESS FOR MUCH OF THE PERIOD.

EXTENDED AVIATION OUTLOOK...WIDESPREAD MVFR TO IFR CONDITIONS
EXPECTED TUESDAY THROUGH WEDNESDAY EVENING AS A SERIES OF SYSTEMS
CROSS THE REGION. BREEZY CONDITIONS POSSIBLE WEDNESDAY AFTERNOON
INTO THURSDAY MORNING.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.
&&

$$




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