Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 201944
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
244 PM EST SAT DEC 20 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. A STRONG COLD FRONT APPROACHING
FROM THE WEST WILL MOVE THROUGH THE FORECAST AREA WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
RAIN HAS ALMOST CLEARED THE FORECAST AREA WITH SOME LINGERING RAIN
OVER THE EASTERN MIDLANDS BUT THIS TOO SHOULD SHIFT OUT BY 2 PM.
TEMPERATURES HAVE NOT MOVED MUCH TODAY DUE TO EXTENSIVE CLOUDS AND
LIGHT RAIN BUT MAY RISE A DEGREE OR TWO BEFORE SUNSET NOW THAT THE
RAIN HAS CLEARED. LOW CLOUDS EXTEND WELL BACK INTO ALABAMA AND
WITH MODEL TIME HEIGHTS AND CROSS SECTIONS SHOWING SIGNIFICANT
MOISTURE IN THE LOWER LEVELS DO NOT THINK THE LOW CLOUDS WILL
BREAK OVERNIGHT. WITH THE FORECAST AREA IN THE WAKE OF THE
DEPARTING SHORTWAVE TROUGH AND THEREFORE LACK OF UPWARD VERTICAL
MOTION DO NOT THINK THERE WILL BE SIGNIFICANT DRIZZLE OVERNIGHT
BUT DO THINK THERE WILL BE AREAS OF FOG THAT DEVELOPS AND POSSIBLY
SOME DENSE FOG IN TYPICAL LOW LYING AREAS. OVERNIGHT LOWS TONIGHT
SHOULD FALL INTO THE MID 30S ACROSS THE FORECAST AREA.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
THE MID/UPPER FLOW WILL BECOME INCREASINGLY SOUTHWEST DURING THE
DAY ON SUNDAY INTO SUNDAY NIGHT AS A S/W TROUGH MOVES INTO  THE MS
VALLEY. MODEL TIME SECTIONS SHOW INCREASING LOW LEVEL MOISTURE AND
ISENTROPIC LIFT THROUGH THE PERIOD AS WEAK LOW PRESSURE DEVELOPS
IN THE GULF AND MOVES NORTHEAST ACROSS FLORIDA AND OFF THE
SOUTHEAST COAST. DURING THE PERIOD...PRECIPIATION AMOUNTS LOOK TO
BE LESS THAN ONE QUARTER INCH AS THE LIGHT RAIN/DRIZZLE IS
EXPECTED. WILL CONTINUE WITH SOME PATCHY FOG SUNDAY MORNING WITH
POPS AROUND 10 PERCENT OR LESS. HOWEVER...THROUGH THE AFTERNOON
WITH INCREASING ISENTROPIC LIFT FROM S TO N EXPECT A GRADUAL
INCREASE IN POPS. POPS GO FROM SLIGHT CHANCE SUNDAY TO CATEGORICAL
BY LATER SUNDAY NIGHT. AS FOR TEMPERATURES...EXPECT LITTLE DIURNAL
RANGE GIVEN CLOUD COVER AND PRECIPITATION POTENTIAL. HAVE TRENDED
TOWARD JUST BELOW CONSENSUS FOR HIGHS AND JUST ABOVE FOR LOWS.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
A MORE VIGOROUS S/W WILL DIG A DEEP TROUGH ACROSS THE EASTERN HALF
OF THE COUNTRY BY MID WEEK AS MID LEVEL LOW CLOSES OFF ACROSS THE
UPPER PLAINS/UPPER MIDWEST. MOISTURE ACROSS THE REGION WILL REMAIN
RATHER HIGH THROUGH MIDWEEK WITH PW VALUES INCREASING TO OVER 1.5
INCHES BY LATE TUESDAY NIGHT/INTO WEDNESDAY. AHEAD OF THIS SYSTEM
A WEDGE WILL DEVELOP ACROSS THE AREA ON MONDAY AND MODELS INDICATE
THIS FEATURE HOLDING INTO TUESDAY. HAVE TRENDED WITH LOWER
TEMPERATURES THROUGH THE PERIOD AS ECMWF/GFS/NAM INDICATE NE LOW
LEVEL FLOW AND VERY STABLE AIRMASS IN PLACES OVER THE REGION.
HOWEVER...BY LATE TUESDAY AFTERNOON/TUESDAY NIGHT BOTH ECMWF AND
GFS LIFT THE WARM FRONT NORTHWARD ACROSS THE AREA. TEMPERATURES
WILL LIKELY RISE SLOWLY TUESDAY NIGHT AS LOW LEVEL FLOW SHIFTS
FROM NE AND E TO A MORE SOUTHERLY DIRECTION. THE GFS AND ECMWF
MODELS HAVE CONTINUED WITH THE TREND OF THE SLOWER COLD FRONTAL
PASSAGE ON WEDNESDAY. THE AREA WILL REMAIN UNDER ISENTROPIC LIFT
THROUGH MUCH OF THE PERIOD FROM MONDAY INTO EARLY WEDNESDAY WITH
AN INCREASING WIND FIELD TUESDAY NIGHT INTO WEDNESDAY. THE GFS
SHOWS A 50 TO 60 KT H8 JET ASSOCIATED WITH THE SYSTEM EARLY
WEDNESDAY. WITH THE DELAY OF THE FRONTAL PASSAGE AND AREA BECOMING
INCREASINGLY UNSTABLE BY WEDNESDAY HAVE CONTINUED THE MENTION OF
THUNDERSTORMS IN THE FORECAST. ALSO EXPECT INCREASING SURFACE
WINDS WITH TIGHT PRESSURE GRADIENT AND STRONG LOW LEVEL WINDS ON
WEDNESDAY.

THE INCREASING SHEAR AND POTENTIAL FOR SUFFICIENT INSTABILITY
INDICATES A POSSIBILITY OF STRONG/SEVERE THUNDERSTORMS.

EXPECT A DIMINISHED SHOWER CHANCE WEDNESDAY NIGHT BEHIND THE
FRONT WITH BREEZY CONDITIONS. THE MODELS HAVE BEEN CONSISTENT
SHOWING A DRY WEST FLOW BETWEEN HIGH PRESSURE NEAR THE GULF COAST
AND LOW PRESSURE LIFTING NORTH OF THE GREAT LAKE REGION FOR
CHRISTMAS DAY. BREEZY CONDITIONS MAY CONTINUE DURING THE DAY...BUT
THE MODEL TREND HAS BEEN TO SHOW THE RIDGE FARTHER NORTHWARD WITH
LESS OF A PRESSURE GRADIENT IN THE FORECAST AREA.

MOISTURE MAY INCREASE AHEAD OF ANOTHER COLD FRONT APPROACHING
FRIDAY NIGHT INTO SATURDAY. HAVE CONTINUED THE MENTION OF A SMALL
POP FRIDAY NIGHT AND SATURDAY. EXPECT TEMPERATURES TO BE COOLER
THAN NORMAL MONDAY AND TUESDAY...ABOVE NORMAL WEDNESDAY AND THEN
RETURNING TO MORE NORMAL TEMPERATURES FOR THE REMAINDER OF THE
PERIOD.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
MVFR/IFR CIG RESTRICTIONS EXPECTED THROUGH MUCH OF THE 24 HOUR
FORECAST PERIOD.

REGIONAL RADAR SHOWING THE RAIN ASSOCIATED WITH THE PASSING
SHORTWAVE TROUGH HAS SHIFTED EAST OF THE TERMINALS AND DO NOT
EXPECT ANY ADDITIONAL RAIN. SUBSIDENCE BEHIND THE SHORTWAVE HAS
STRENGTHENED THE INVERSION AND LOW LEVEL MOISTURE TRAPPED BELOW IT
SO AM EXPECTING THE MVFR/IFR CIGS TO CONTINUE THROUGH THE FORECAST
PERIOD. HRRR GUIDANCE HAS BEEN TO OPTIMISTIC WITH CIGS THUS FAR
TODAY AND MET GUIDANCE HAS BEEN DOING WELL WITH THE LOW CIGS SO
HAVE LEANED TOWARD THAT GUIDANCE AND THE LAV GUIDANCE LOWERING
CIGS TO IFR ALL TERMINALS AFTER 04Z WITH POSSIBLE LIFR CIGS
OGB/AGS/DNL. VSBYS ALSO LIKELY TO DROP INTO MVFR AND POSSIBLY IFR
04Z-12Z TIME FRAME. SOME IMPROVEMENT IS EXPECTED AFTER 13Z BUT LOW
CONFIDENCE THAT VFR CONDITIONS WILL RETURN.

EXTENDED AVIATION OUTLOOK...WIDESPREAD LOW CLOUDS AND
PRECIPITATION EXPECTED LATE SUNDAY NIGHT INTO MONDAY WITH ANOTHER
GULF COAST SYSTEM CROSSING THE REGION. YET ANOTHER SYSTEM WILL
AFFECT THE AREA TUESDAY NIGHT BRINGING POSSIBLE RESTRICTIONS WITH
WINDY CONDITIONS EXPECTED WEDNESDAY.

&&

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

$$
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