Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 292027
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
327 PM EST THU JAN 29 2015

.SYNOPSIS...
IN THE WAKE OF A COLD FRONTAL PASSAGE...HIGH PRESSURE WILL BUILD
INTO THE REGION LATER ON FRIDAY. THE HIGH WILL LINGER OVER THE AREA
INTO SUNDAY BEFORE MOISTURE RETURNS OUT AHEAD OF A DEVELOPING
LOW PRESSURE SYSTEM. DRY CANADIAN HIGH MOVES BACK INTO THE AREA BY
TUESDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 230 PM EST THURSDAY...THIS AFTERNOON AND EVENING...A RATHER
FAST MOVING LIGHT BAND OF PRECIP ASSOCIATED WITH AN UPPER WAVE WAS
MOVING EASTWARD ACROSS THE NC PIEDMONT AND UPSTATE SC. THERE HAVE
BEEN NUMEROUS REPORTS OF A MIX OF RAIN AND SLEET AS THIS BAND MOVED
ACROSS THE NC MTNS/VALLEYS AND INTO THE PIEDMONT DUE TO WET-BULB
COOLING EFFECT. HENCE...HAVE CARRIED A CHANCE OF RAIN AND SLEET
ACROSS THE PIEDMONT WHERE THE BAND WAS PUSHING EASTWARD. AS THIS
FEATURE PUSHES OFF TO THE EAST...THERE WILL BE A LULL IN PRECIP
THROUGH THIS EVENING.

TONIGHT AND TOMORROW...ANOTHER ROUND OF PRECIP IS EXPECTED MAINLY
ACROSS THE NC MTNS ZONES AS AN UPPER LEVEL TROUGH AXIS ASSOCIATED
WITH A SURFACE COLD FRONT PUSHES THROUGH THE REGION. AS OVERNIGHT
TEMPS PLUMMET WELL BELOW FREEZING...SNOW SHOULD BE A DOMINANT
P-TYPE. LATEST MESO-SCALE MODELS AGREE THAT THE BEST CHANCE OF NW
SNOW WILL OCCUR BETWEEN 3Z-12Z WHEN THE BEST UPPER FORCING...MOIST
LLVL LAYER (SURFACE TO 700MB) WILL BE PRESENT WITHIN STRONG CAA NW
UPSLOPE FLOW REGIME. THEREFORE...USING A BLEND OF CAMPOP AND OTHER
GUIDANCE...CATEGORICAL POPS WERE MENTIONED ALONG THE TN LINE WITH
SOLD CHANCE TO LIKELY POPS ELSEWHERE IN THE MTNS/VALLEYS.
HOWEVER...GIVEN RELATIVELY SHORT DURATION OF SNOW AND LESS FAVORING
H85 WSWLY WINDS...TOTAL SNOW ACCUMS WILL BE LESS THAN 2 INCHES WHICH
IS BELOW THE ADVISORY CRITERIA. SO NO WSW WILL BE ISSUED AT THIS
TIME. STRONG CAA NWLY WINDS WILL DEVELOP BY LATE TONIGHT AND
CONTINUE THROUGH TOMORROW AFTERNOON AS A TIGHT SURFACE PRESSURE
GRADIENT SETS UP. WILL ISSUE A WIND ADVISORY ACROSS THE NORTHERN NC
MTNS TONIGHT INTO TOMORROW AFTERNOON WHERE GUSTY NW WINDS OF
45-50MPH WILL OCCUR. CONDITIONS SHOULD DRY OUT ALONG THE TN LINE
TOWARD FRI MIDDAY AS DRY HIGH PRESSURE BUILDS IN FROM THE NW.
ELSEWHERE WILL SEE CONTINUED DRY WEATHER. TEMPS OVERNIGHT WILL BE
AROUND NEAR CLIMO FOR MOST LOCATIONS. DAYTIME TEMPS ON FRI WILL STAY
5-7 DEGREES BELOW NORMAL OVER THE MTNS/VALLEYS WITH 2-3 DEGREES
BELOW NORMAL ELSEWHERE.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 230 PM THURSDAY...FORECAST TRENDS IMPROVING FOR THE WEEKEND
WEATHER. SHORT RANGE MODELS AGREE THAT THE CENTER OF A CANADIAN HIGH
PRESSURE WILL APPROACH THE REGION EARLY SATURDAY...WITH THE CENTER
PASSING OVER THE SOUTHERN APPALACHIANS SATURDAY AFTERNOON AND
EVENING. A BLEND OF MOS GUIDANCE FAVORS TEMPERATURES 5 TO 7 DEGREES
BELOW NORMAL FOR SATURDAY. AFTERNOON RH VALUES ARE FORECAST TO RANGE
FROM THE MID 20S TO LOWER 30S.

ON SUNDAY...MODELS HAVE TRENDED SIGNIFICANTLY SLOWER WITH ARRIVAL OF
DEEP MOISTURE AND FORCING...NOW ARRIVING DURING THE LATE AFTERNOON.
NAM...GFS...AND ECMWF INDICATE THAT GREATEST POTENTIAL FOR THE ONSET
OF MEASURABLE PRECIP WILL OCCUR BETWEEN 18Z TO 0Z. TEMPERATURES
ACROSS THE MTNS ARE FORECAST TO RANGE GENERALLY IN THE MID 30S TO
LOW 40S. I WILL INDICATE IN THE FORECAST THAT PRECIP WILL FALL AS
RAIN WITH HIGH ELEVATION SNOW...LITTLE TO NO ACCUM BEFORE 0Z MON.
SUN HIGHS WILL LIKELY RANGE FROM LOW TO MID 40S ACROSS THE MTNS TO
AROUND 50 EAST OF I-85.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 255 PM THURSDAY...GOOD AGREEMENT IN THE OVERALL PATTER FOR THE
MEDIUM RANGE...BUT CONSIDERABLE DISAGREEMENT REMAINS IN THE DETAILS
AND EXPECTED SENSIBLE WX. A NRN STREAM SHORT WAVE CROSSES THE AREA
MONDAY WITH A FLAT TROF IN PLACE ON TUE. AN UPPER LOW THAT STARTS
THE PERIOD OVER THE BAJA PENINSULA OPENS UP AND MOVES EAST INTO THE
AREA WED OR WED NITE WITH SOME DEGREE OF PHASING WITH A NRN STREAM
SHORT WAVE DROPPING INTO THE TROF AT THAT SAME TIME. THE WAVE THEN
MOVES EAST OF THE AREA THURSDAY.

AT THE SFC...PRECIP WILL LIKELY BE ONGOING AT THE START OF THE
PERIOD IN THE MOIST SLY FLOW AHEAD OF A LOW PRESSURE SYSTEM MOVING
NE TO THE WEST OF THE APPALACHIANS. THE LOW THEN SLIDES EAST NEAR
THE VA/NC BORDER AND DRAGS A COLD FRONT ACROSS THE AREA. THIS WILL
KEEP THE AREA OUTSIDE OF THE MTNS TOO WARM FOR ANYTHING BUT RAIN.
HOWEVER...TEMPS WILL BE COLD ENUF FOR SNOW TO DEVELOP ACROSS THE
HIGH ELEVATIONS...THEN FALL TO THE VALLEY FLOORS TOWARD DAYBREAK
MON. PRECIP ENDS AS A BRIEF NW FLOW SNOW MON AFTERNOON. QPF AMOUNTS
WILL BE HIGH ENUF FOR A HIGH END ADVISORY ACROSS THE HIGHER
ELEVATIONS AND A LOW END ADVISORY IN THE VALLEYS FROM HAYWOOD NORTH.
HOWEVER...THE TEMPS REMAINING QUESTION AS THE COOLING COULD BE
DELAYED DEPENDING ON THE MOVEMENT AND SPEED OF THE LOW AND
ASSOCIATED COLD FRONT. COLD AND DRY HIGH PRESSURE BUILDS IN MON NITE
AND TUE. TEMPS MON NITE ABOVE NORMAL WITH BELOW NORMAL TEMPS THRU
TUE.

THE NEXT WX SYSTEM MOVES IN DURING THE WED TIME FRAME. THE ECMWF IS
FASTER AND HAS A MORE COHERENT MILLER A TYPE GULF LOW...WHILE THE
GFS IS SLOWER AND HAS MORE OF AN ELONGATED FRONTAL ZONE CROSSING THE
AREA WITH A LOW IN QUEBEC AND A WEAKER MILLER A FARTHER SOUTH IN THE
GULF. HAVE USED A MODEL BLEND FOR TIMING. IF THE PRECIP MOVED IN
FAST ENUF AND OUT SLOW ENUF...THEN THERE COULD BE SOME SNOW OUTSIDE
OF THE MTNS AT ONSET AND BEFORE DISSIPATION. HOWEVER...THIS REMAINS
HIGHLY UNCERTAIN. IT IS ALSO QUESTIONABLE HOW MUCH SNOW WOULD FALL
ACROSS THE HIGH ELEVATIONS OF THE MTNS...RIGHT NOW IT LOOKS SUB-
ADVISORY. DRY CONDITIONS EXPECTED OUTSIDE OF THE MTNS THU AS HIGH
PRESSURE BUILDS IN. TEMPS REMAIN BELOW NORMAL FROM TUE NITE THRU
THU.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
AT KCLT...EXPECT VFR CONDITIONS TO PERSIST THROUGH 18Z FRIDAY. A
LIGHT BAND OF PRECIP ASSOCIATED WITH A WEAK UPPER WAVE WILL CROSS
THE NC MTNS THROUGH THIS AFTERNOON. HOWEVER...LATEST MESO-MODELS
INDICATE THAT THIS FEATURE WILL WEAKEN CONSIDERABLY AS IT ENTERS THE
NC FOOTHILLS/PIEDMONT BY EARLY THIS AFTERNOON. SO NO PRECIP WAS
MENTIONED IN THE TAF. SW WINDS SHOULD PERSIST WITH OCCASIONAL GUSTS
TO AROUND 15-20KTS POSSIBLE THRU THIS AFTERNOON. TONIGHT...SW WINDS
SHOULD TO VEER TO THE NW AS A SURFACE COLD FRONT PUSHES THROUGH THE
REGION. AS SURFACE PRESSURE TIGHTENS UP BEHIND THE FRONT...GUSTY NW
WINDS OF 15-20KTS WILL DEVELOP BY AROUND 15Z. CLOUD CIGS WILL BOTTOM
OUT AROUND 8K FT DURING THE FROPA TONIGHT.

ELSEWHERE...VFR THROUGH THE PERIOD EXCEPT KAVL WHERE MVFR CLOUDS
WILL SPREAD IN FROM THE NORTH TONIGHT DUE TO THE FROPA. A LIGHT BAND
OF PRECIP WILL MOVE ACROSS THE NC MTN ZONES THROUGH THIS AFTERNOON.
HOWEVER...THE PRECIP APPEARS TO BE VERY LIGHT AND IT WILL BE MAINLY
CONFINED TO THE RIDGE TOPS OF THE MTNS. HENCE...NO PRECIP WAS
MENTIONED IN KAVL. OTHERWISE...EXPECT MOSTLY CLOUDY SKIES WITH SW
WINDS PERSISTING THROUGH LATE THIS EVENING ACROSS MUCH OF THE
REGION. WINDS WILL VEER THE NW TONIGHT AS A SURFACE COLD FRONT
PUSHES THROUGH THE AREA. AGAIN...PRECIP CHANCES ARE TOO LOW TO
MENTION IN THE TAF. TIGHT PRESSURE GRADIENT BEHIND THE FRONT WILL
RESULT IN GUSTY NW WINDS ACROSS MUCH OF THE REGION BY FRI MORNING.

OUTLOOK...A PAIR OF CLIPPER SYSTEMS WILL BRING CHANCES FOR RAIN OR
SNOW SHOWERS TO THE NC MTNS FRI. MOST OF THESE SHOWERS WILL REMAIN
WEST AND NORTH OF KAVL...BUT BRIEF PERIODS OF RESTRICTIONS CANNOT BE
RULED OUT. OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED ACROSS THE
AREA UNTIL MOISTURE BEGINS TO RETURN SUNDAY. DRYING IS EXPECTED ON
MONDAY.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  98%     HIGH  80%     LOW   58%
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...WIND ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT EST FRIDAY
     NIGHT FOR NCZ033-049-050.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...JOH
SHORT TERM...NED
LONG TERM...RWH
AVIATION...JOH



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