Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 221747
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1247 PM EST MON DEC 22 2014

.SYNOPSIS...
A MOIST AIRMASS WILL REMAIN ATOP THE REGION BEFORE A COLD FRONT
CROSSES BY WEDNESDAY NIGHT. DRY HIGH PRESSURE WILL ARRIVE FOR
CHRISTMAS DAY AND LINGER INTO FRIDAY. ANOTHER COLD FRONT WILL CROSS
THE AREA ON SATURDAY...FOLLOWED BY HIGH PRESSURE ON SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1245 PM...ALTHOUGH THE RAIN HAS ENDED...LOW CLOUDS DRIZZLE AND
FOG CONTINUE IN THE COPIOUS LOW LEVEL MOISTURE AND ISENTROPIC UPGLIDE
OVER THE CAD DOME. RAIN CHC INCREASES FROM SOUTH TO NORTH ACROSS THE
AREA LATE THIS AFTERNOON AND INTO THE EVENING. SKIES HAVE CLEARED
SOMEWHAT ALONG THE TN BORDER...SO THE HIGHER TEMPS AND LOWER PRECIP
CHC STILL LOOKS GOOD THERE. ONLY MINOR CHANGES WERE NEEDED TO THE
GOING FCST...MAINLY FOR CURRENT CONDITIONS.

AS OF 935 AM...LIGHT RAIN QUICKLY ENDING ACROSS THE CWFA. HOWEVER...
WIDESPREAD DRIZZLE AND LOW CLOUDS REMAIN. SHOULD ONLY SEE PATCHY
VERY LIGHT RAIN FOR THE REST OF THE DAY...BUT LOW CLOUDS AND DRIZZLE
WILL LINGER...WITH PATCHY FOG OF VARYING VISIBILITY DEPENDING ON
THE AMOUNT OF DRIZZLE. NELY WIND WITH OCCASIONAL LOW END GUSTS WILL
CONTINUE OUTSIDE OF THE MTNS...WITH GENERALLY LIGHT SLY WINDS ACROSS
THE MTNS. MAY SEE SOME BREAKS IN THE CLOUDS NEAR THE TN BORDER THRU
THE DAY WHICH WOULD ALLOW TEMPS TO INCREASE SIGNIFICANTLY THERE.
ELSEWHERE...ONLY A SMALL INCREASE IN TEMPS IS EXPECTED WITH THE
CONTINUED LOW CLOUDS AND DRIZZLE. THAT SAID...TEMPS COULD RISE A
LITTLE HIGHER IF DRIZZLE ENDS...ALLOWING A LITTLE MORE INSOLATION
EVEN WITH THE CLOUDS REMAINING.

AS OF 630 AM EST...FAIRLY HIGH COVERAGE OF MAINLY VERY LIGHT RAIN
AND DRIZZLE ARE INDICATED ON RADAR AND IN OBS AROUND DAYBREAK ACROSS
THE AREA. PRECIP INTENSITY/COVERAGE WILL LIKELY CONTINUE TO SLOWLY
DWINDLE THROUGH THE DAY AS WEAK UPGLIDE RELAXES OVER THE CAD
STRETCHING FROM 1027 MB HIGH PRES CENTERED OVER ERN NY DOWN THROUGH
THE WRN CAROLINAS. ANY LINGERING SPOTTY FREEZING DRIZZLE ALONG THE
NRN BLUE RIDGE SHOULD BE ENDING AS TEMPS RISE THROUGH THE MIDDLE
30S. THE CAD WILL REMAIN IN PLACE THROUGH THE DAY DESPITE THE
GRADUALLY WEAKENING ISENTROPIC LIFT. THIS SHOULD HOLD TEMPERATURES
IN THE UPPER 30S TO MIDDLE 40S THROUGHOUT THE REGION TODAY...EXCEPT
FOR SOME LOWER 50S IN THE SW MTNS OUTSIDE THE CAD REGIME.

MEANWHILE...A DEEP TROUGH STRETCHING FROM THE NRN PLAINS TO E TX
WILL SEE HEIGHTS CLOSING OFF OVER THE CENTRAL CONUS THROUGH TONIGHT.
THE MAIN DOWNSTREAM RESULT OF THIS WILL BE RESURGENT UPGLIDE TONIGHT
ALONG WITH SLIGHTLY DEEPER MOISTURE. WILL ALLOW POPS TO REBOUND TO
HIGH CHC TO LIKELY FOR MAINLY LIGHT RAIN...AND TEMPERATURES WILL
GENERALLY REMAIN STEADY THROUGH THE NIGHT.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AT 200 PM EST MONDAY..12Z MODEL RUNS INDICATE THAT SOME SEMBLANCE OF
A WEDGE WILL REMAIN THROUGH MOST IF NOT ALL OF TUE NIGHT. THE NAM
DOES SUGGEST THAT PERHAPS THE SOUTHERN UPSTATE MAY GET UNCOVERED BY
12Z WED. THE UPSHOT FOR TUE NIGHT IS THAT ISENTROPIC LIFT WILL
CONTINUE OVER THE WEDGE WITH WIDESPREAD LIGHT TO EVEN MODERATE RAIN.
BEST RAINFALL RATES ARE EXPECTED TO BE OVER THE WESTERN UPSTATE...NE
GA MOUNTAINS AND THE WESTERN ESCARPMENT WHERE BEST FORCING WILL
BECOME ESTABLISHED. RAINFALL IN THOSE AREAS IS LIKELY TO BE UPWARDS
OF AN INCH. ON WED...THE CONSENSUS IS THAT THE REMAINDER OF THE
WEDGE WILL GRADUALLY BE UNCOVERED...BUT AS USUALL IT COULD LINGER
WELL INTO THE AFTERNOON FROM THE CENTRAL UPSTATE EASTWARD.
RAIN/DRIZZLE WILL BECOME SHOWERY AS WEDGE DISSIPATES. THE NEXT ISSUE
IS THE COLD FRONT THAT WILL TRANSLATE ACROSS THE AREA FROM THE WEST
AS LOW PRESSURE MOVES FROM CENTRAL TN TO THE LOWER GREAT LKAES ON
WED. THE 12Z MODELS ARE TRENDING SLOWER WITH THE FRONTAL PASSAGE...
WITH THE NAM THE SLOWEST OF THE OPERATIONAL RUNS....A GOOD 6 HOURS
SLOWER THAN THE GLOBAL MODELS. THE 09Z SREF SUPPORTS THE SLOWER NAM.
IN REGARD TO TIMING WILL USE A CONSENSUS APPROACH WHICH WILL MOVE
THE FRONT INTO WESTERN SECTIONS DURING WED AFTERNOON AND THEN ACROSS
THE REMAINDER OF THE AREA WED EVENING. THE MAIN CONCERN WITH THE
FRONTAL PASSAGE WILL BE THE THREAT FOR SOME SORT OF QLCS EVENT. ALL
THE MODELS SHOW SOME LOW END CAPE UPWARDS OF 200 J/KG AHEAD OF THE
FRONT. SHEAR/HELICITY IS ADEQUATE ALTHOUGH NOT THROUGH THE ROOF.
WHAT IS LACKING WILL BE THE UPPER FORCING COINCIDENT WITH THE FRONT.
THE UPPER TROUGH IS FORECAST TO TRAIL THE SURFACE FRONT WITH THE
MAIN UPPER FORCING GOING WELL NORTH OF THE REGION. HENCE...CHANCES
FOR SEVERE CONVECTTION IS ON THE LOW END AND WILL NOT MENTION IN THE
HWO. DRYER AIR AND DOWNSLOPING WINDS WILL FINALLY SCOUR CLOUDS OUT
EAST OF THE MOUNTAINS WED NIGHT WITH PERHAPS A PERIOD OF SOME NW
FLOW SNOW/RAIN SHOWERS EARLY CHRISTMAS IN THE MOUNTAINS.

TEMPERATURES WILL BE A CHALLENGE AS A NON-DIURNAL TREND WILL OCCUR
TUE NIGHT WHERE THE WEDGE ERODES. THIS WOULD MOST LIKELY BE ACOSS
THE SOUTHERN PERIPHEREY OF THE FORECAST AREA. TEMPS ON WED SHOULD
SURGE WELL INTO THE 60S AS THE WEDGE DISSIPATES. COOLER TEMPS WILL
THEN OCCUR WED NIGHT WITH MAX TEMPS THU NEAR CLIMO.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AT 230 AM EST MONDAY...ON THURSDAY MORNING UPPER TROUGHS WILL BE
OVER THE EAST AND THE WEST...WITH A LOW AMPLITUDE UPPER RIDGE OVER
THE PLAINS. BY FRIDAY MORNING THE RIDGE AXIS WILL HAVE PROGRESSED TO
THE EAST COAST...WHILE THE TROUGH UPSTREAM WILL HAVE REACHED THE
EAST SLOPES OF THE ROCKIES. THE TROUGH WILL CROSS THE PLAINS ON
SATURDAY. BY SUNDAY THE ECMWF AND GFS ARE OUT OF PHASE...WITH THE
FORMER PLACING ITS HIGHLY AMPLIFIED TROUGH OVER THE MS RIVER VALLEY
     AND THE LATER HAVING ITS DEAMPLIFIED TROUGH OVER THE EAST
COAST...WITH A LOW AMPLITUDE RIDGE OVER THE MS RIVER VALLEY...AND
ANOTHER LOW AMPLITUDE TROUGH OVER THE PLAINS...WITH NEARLY ZONAL
FLOW OVER THE SOUTHERN TIER OF STATES.

A COLD FRONT WILL BE DEPARTING THE EAST COAST ON THURSDAY...WITH
DRYING DOWNSLOPE FLOW IN THE LEE OF THE MOUNTAINS...AND SOME
LINGERING UPSLOPE FLOW SNOW SHOWERS IN THE NC MOUNTAINS BORDERING
TN. THE UPSLOPE/DOWNSLOPE REGIME ENDS LATE THURSDAY AS HIGH PRESSURE
CROSSES THE GULF...AND BY FRIDAY MORNING....GULF INFLOW SETS UP ON
THE BACK SIDE OF THIS HIGH AHEAD OF THE NEXT FRONT. THIS FRONT
CROSSES THE MOUNTAINS LATE FRIDAY NIGHT...BUT GULF INFLOW WEAKENS
BEFORE IT ARRIVES...LIMITING PRECIPITATION. THE FRONT MOVES OFF THE
EAST COAST BY SUNDAY MORNING....WITH ANOTHER ROUND OF NW UPSLOPE
FLOW INTO THE NC MOUNTAINS...SUPPORTING ANOTHER BATCH OF SNOW
SHOWERS. BY MONDAY...DRY HIGH PRESSURE MOVES INTO THE TN VALLEY.

TEMPERATURES WILL WARM FROM NEAR NORMAL THURSDAY TO SLIGHTLY ABOVE
NORMAL FRIDAY IN WARM ADVECTION AHEAD OF THE NEXT FRONT...COOLING TO
SLIGHTLY BELOW NORMAL BEHIND THE FRONT.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
AT KCLT...EVEN THO RAIN ENDED...LOW LEVEL MOISTURE REMAINS HIGH AND
CONTINUED UPGLIDE OVER THE SFC CAD LAYER HAS KEPT IFR VSBY IN
DRIZZLE AND LOW CLOUDS ACROSS THE AREA. THIS WILL CONTINUE THRU THE
AFTERNOON...SO HAVE GONE PESSIMISTIC WITH THE TAF AND KEEP CURRENT
CONDITIONS THRU THE EARLY EVENING. CONDITIONS WILL BE AT LEAST LIFR
OVERNIGHT IN CIGS AND POSSIBLY VSBY AS DRIZZLE CONTINUES AND RAIN
DEVELOPS. IMPROVEMENT OF IFR IS POSSIBLE TUE MORN...BUT LIFR IS MOST
LIKELY TO CONTINUE ALONG WITH RAIN AND DRIZZLE. NELY WIND 10 KTS OR
LESS CONTINUES THRU THE PERIOD.

ELSEWHERE...SIMILAR CONDITIONS TO KCLT. THE BIGGEST DIFFERENCE IS
THE VFR VSBY AND IFR CIG AT KAND. THESE MAY CONTINUE THRU THE
AFTERNOON...BUT DETERIORATION IS EXPECTED THERE BY EVENING AS WELL.
KAVL ALSO DIFFERENT WITH SLY WINDS THRU THE PERIOD...BUT LIFR
CONDITIONS AS WELL.

OUTLOOK...DEEP MOISTURE CONTINUES THROUGH TUESDAY NIGHT AHEAD OF THE
NEXT APPROACHING COLD FRONT. LOW RESTRICTIONS AND WIDESPREAD RAIN
SHOWERS ARE EXPECTED. A COLD FRONT WILL CROSS THE REGION FROM THE
WEST ON WED. DRY HIGH PRESSURE WILL RETURN THROUGH LATE WEEK.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       MED   62%     MED   75%     MED   75%     HIGH  80%
KGSP       MED   62%     HIGH 100%     MED   75%     HIGH  80%
KAVL       MED   75%     HIGH 100%     HIGH  83%     HIGH  90%
KHKY       HIGH 100%     HIGH  83%     HIGH  83%     HIGH  90%
KGMU       MED   62%     HIGH 100%     MED   75%     HIGH  80%
KAND       MED   62%     MED   75%     MED   75%     MED   70%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JAT
NEAR TERM...HG/RWH
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...RWH



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