Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 190232
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
932 PM EST THU DEC 18 2014

.SYNOPSIS...
WEAK HIGH PRESSURE OVER THE REGION ON FRIDAY WILL GIVE WAY TO A
BRIEF INCREASE IN MOISTURE ALONG WITH CHILLY TEMPERATURES ON
SATURDAY. DRIER HIGH PRESSURE THEN RETURNS FOR SUNDAY BEFORE AN AREA
OF LOW PRESSURE BRINGS RAIN CHANCES BACK FOR MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
915 PM UPDATE...CLOUD COVER CROSSING THE MTNS FROM THE TENN VALLEY
IS BREAKING UP UPSTREAM AS MODELS SUGGESTED...BEING IN THE WAKE
OF THE SHORTWAVE NOW OVER THE CENTRAL APPALACHIANS. DOWNSLOPING
HAS HAD SOMEWHAT OF AN IMPACT...AS THE CLOUDS THAT FILLED IN OVER
THE CWFA AFTER SUNSET NOW ARE BEGINNING TO DISSOLVE. SKIES WILL
REMAIN MOSTLY CLOUDY OVERALL FOR A COUPLE MORE HRS BUT SHOULD
BECOME MOSTLY CLEAR BY EARLY MRNG. REVISED SKY GRIDS TO ACCOUNT FOR
THIS. TEMPS THRU THE LATE EVENING SHOULD BE UNAFFECTED...BUT
PREVIOUS MINS APPEAR TO BE ON TRACK.

630 PM UPDATE...IN COLLABORATION WITH NEIGHBORING
OFFICES...REVISED POPS FOR LATE FRI NIGHT AND SATURDAY TO BETTER
REFLECT GUIDANCE DEPICTION OF THE PRECIP ASSOCIATED WITH THE PASSING
SRN STREAM WAVE. CATEGORICAL POPS SEEMED TOO HIGH OVER THE NRN
UPSTATE AND SRN NC PIEDMONT/FOOTHILLS...SO WE REDUCED THEM TO LKLY
RANGE.

AS OF 220 PM...A VORT MAX WILL STREAK WEST TO EAST FROM THE OHIO
VALLEY TO THE MID ATLANTIC TONIGHT...WITH THE ONLY REAL EFFECT THIS
FAR SOUTH BEING A REINFORCING VEERING NWLY LLVL FLOW IN ITS WAKE. SO
WHILE THERE IS STILL A FAIR AMOUNT OF MID CLOUDS TRYING TO MAKE
INROADS FROM THE TN VALLEY AND THE GULF STATES...MOST OF THE CLOUDS
WILL BE FROM PERIODS OF CIRRUS WITHIN A STRONG SUBTROPICAL JET THRU
FRIDAY. WINDS WILL BE LIGHT AND THE AIR FAIRLY DRY. MIN TEMPS WILL
BE A CATEGORY OR TWO ABOVE NORMAL (MID-UPR 20S MTNS AND LWR-MID 30S
PIEDMONT).

ON FRIDAY...ANOTHER POTENT SOUTHERN STREAM SHORTWAVE WILL ENTER THE
SOUTHERN PLAINS...WITH INCREASING HIGH CLOUDS FOR THE AFTN ATOP THE
CWFA. LLVL FLOW WILL WEAKEN AND BEGIN TO BACK TO SWLY...WHILE SFC
HIGH PRES LINGERS ACRS THE GREAT LAKES AND OHIO VALLEY. TEMPS ARE
EXPECTED TO BE NEAR NORMAL IN THE MTNS...AND A CATEGORY OR TWO ACRS
THE PIEDMONT.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 245 PM...BEGINNING FRIDAY NIGHT...SHORT RANGE MODELS INDICATE
THAT A WEAK INVERTED SURFACE TROUGH WILL DEVELOP NEAR THE
MISSISSIPPI DELTA. BY 12Z SAT...THE CENTER OF SFC HIGH PRESSURE IS
FORECAST TO REACH THE GREAT LAKES REGION...RIDGING SOUTHWARD ACROSS
THE WESTERN CAROLINAS. A H5 TROUGH IS EXPECTED TO RIPPLE ACROSS THE
DEEP SOUTH...MOISTURE AHEAD OF THE DISTURBANCE WILL ADVECT NORTH
FROM THE GULF OF MEXICO TO TN. AS THE MID LEVEL WAVE
APPROACHES...MOISTURE WILL BUILD ACROSS THE SOUTHERN APPALACHIAN
REGION. HOWEVER...LLVL FLOW WILL REMAIN FROM THE SW AND MODEL
ISENTROPIC LIFT APPEARS VERY WEAK. AS A RESULT...12Z MODEL RUNS HAVE
CONTINUED A DRIER TREND. I WILL DELAY POPS UNTIL BETTER MID FORCING
ARRIVES AROUND SUNRISE SATURDAY. AT THE TIME OF PRECIP
ARRIVAL...TEMPERATURES ARE FORECAST TO RANGE FROM THE MID TO LOW 30S
ACROSS THE MTNS TO MID TO UPPER 30S EAST. BASED ON FORECAST
SOUNDINGS...PRECIP SHOULD FALL AS A MIX OF RA AND SNOW ACROSS THE
MTNS DURING THE EARLY MORNING HOURS...WITH A COLD RAIN EAST. IN
ADDITION...FOLLOWING MODEL TRENDS...I HAVE DECREASED QPF ACROSS THE
CWA ON SATURDAY. SNOWFALL BETWEEN A HALF INCH TO INCH IS STILL
POSSIBLE ACROSS THE NRN MTNS...ELSEWHERE...LITTLE TO NO ACCUMS.
HIGHS WILL BE TWEAKED A LITTLE WARMER FROM PREVIOUS
FORECAST...RANGING IN THE LOW TO MID 40S.

SUNDAY...S/W RIDGING WILL RIPPLE ACROSS REGION AHEAD OF THE NEXT
AMPLIFYING TROUGH. MIN TEMPERATURES UNDER PARTLY CLOUDY SKY SHOULD
RANGE FROM THE L30S ALONG I-40 TO U30 ACROSS THE UPPER SAVANNAH
RIVER VALLEY. MOISTURE WILL SURGE ACROSS THE REGION DURING THE
AFTERNOON. LLVL WINDS SHOULD BACK FROM THE SOUTH-
SOUTHEAST...PROVIDING MARGINAL UPSLOPE FLOW. I WILL INCREASE POPS TO
SCHC ACROSS THE PIEDMONT FOR RAIN. HIGHS SHOULD REMAIN AROUND 3-5
DEGREES BELOW NORMAL.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 225 PM THURSDAY...THE MEDIUM RANGE WILL FEATURE A TRANSITION
TO A HIGHLY AMPLIFIED AND ACTIVE UPPER FLOW PATTERN...AS A DEEP
EASTERN TROUGH IS EXPECTED TO BECOME ESTABLISHED IN RESPONSE TO A
SERIES OF POTENT SHORT WAVE TROUGHS DIVING OUT OF THE NORTHERN
ROCKIES. THE GLOBAL MODELS GENERALLY AGREE IN INITIATING WEAK
CYCLOGENESIS OFF THE SOUTHEAST COAST ON MONDAY IN ADVANCE OF THE
FIRST SHORT WAVE. THE GFS AND THE ECMWF RESPOND WITH QPF ACROSS THE
WESTERN CAROLINAS AND NORTH GEORGIA BY MONDAY MORNING...ALTHOUGH THE
STRENGTH AND POSITION OF THE CONSENSUS LOW CENTER SUGGESTS PRECIP IS
HARDLY A SLAM DUNK...THUS POPS WILL BE MAINTAINED IN THE CHANCE
RANGE IN MOST AREAS. PARTIAL THICKNESS PROGS FROM THE GFS AND ECMWF
SUGGEST AN ALL-LIQUID EVENT OVER THE VAST MAJORITY OF THE AREA.
HOWEVER...WITH IN SITU COLD AIR DAMMING POSSIBLY DEVELOPING IN
RESPONSE TO LIGHT PRECIP FALLING OVER COOL/DRY SURFACE RIDGE...
LOCATIONS ALONG THE EASTERN BLUE RIDGE ESCARPMENT...PARTICULARLY THE
NORTHERN MTNS...COULD SEE A BRIEF PERIOD OF FZRA EARLY MONDAY.

THE NEXT WEATHER MAKER APPEARS TO ARRIVE IN THE TUE NIGHT/EARLY WED
TIME FRAME...WHEN A MORE SUBSTANTIVE WAVE DIVES INTO THE
SOUTHEAST...POTENTIALLY RESULTING IN A STRONGER SURFACE RESPONSE
(ALTHOUGH THIS IS NOT ENTIRELY CERTAIN...ESP GIVEN THE DETERMINISTIC
GFS SOLUTION...WHICH SUGGESTS MORE OF AN OPEN WAVE OVER THE
SOUTHEAST). HIGHER POPS WILL BE FEATURED DURING THIS TIME FRAME.
ONCE AGAIN...IT APPEARS THE COLD AIR WILL HOLD OFF UNTIL AFTER THE
AREA OF DEEP FORCING EXITS THE FORECAST AREA. HOWEVER...POST FRONTAL
NORTHWEST FLOW COULD RESULT IN SNOW SHOWERS ACROSS THE MTNS WED INTO
WED NIGHT. THERE WILL ALSO BE THE POTENTIAL FOR SOME THUNDER ACROSS
THE PIEDMONT AS THE COLD FRONT PASSES THROUGH THE AREA EARLY WED.
TEMPS WILL GENERALLY BE NEAR-TO-BELOW NORMAL THROUGH THE PERIOD...
WITH MONDAY EXPECTED TO BE THE COOLEST DAY THANKS TO THE POTENTIAL
FOR IN SITU CAD.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...VFR. PATCHY CLOUDS AROUND 050 WILL PASS THRU
THE REGION THIS EVENING AS A POCKET OF LLVL MOISTURE ARRIVES.
PERIODS OF CIGS WILL BE SEEN UNTIL THESE CLOUDS MOVE OUT. THE BULK
OF THE CLOUD COVER OVER THE TENN VALLEY IS EXPECTED TO BE ERODED BY
THE MOUNTAINS AS IT PUSHES EAST...BUT SCT 050-070 CLOUDS WILL LIKELY
STILL BE SEEN THRU MRNG. WINDS WILL PREVAIL NW-N BY LATE EVENING AS
MIXING CEASES...VEERING SLIGHTLY FOR FRIDAY BUT REMAINING LIGHT THRU
THE DAY. KAVL IS AN EXCEPTION...REMAINING BREEZY OVERNIGHT. CIRRUS
WILL THICKEN AHEAD OF SHORTWAVE RISING OUT OF THE GULF STATES LATE
FRI.

OUTLOOK...A MORE ORGANIZED SYSTEM WILL APPROACH FROM THE WEST EARLY
SATURDAY BRINGING ELEVATED PRECIP/RESTRICTION CHANCES. SOME WINTRY
PRECIP IS POSSIBLE ACROSS THE NC MTNS AND FOOTHILLS AFFECTING
KAVL/KHKY SATURDAY MORNING. WINTRY PRECIP IS NOT EXPECTED AT THIS
TIME FOR ANY OTHER TAF SITES. A WETTER SYSTEM WILL TRACK INTO THE
AREA FOR MONDAY LIKELY BRINGING SOME RESTRICTIONS.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

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...CSH
NEAR TERM...ARK/WIMBERLEY
SHORT TERM...NED
LONG TERM...JDL
AVIATION...WIMBERLEY



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