Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 300609
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
109 AM EST FRI JAN 30 2015

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

&&

.NEAR TERM /THROUGH TODAY/...
1245 AM UPDATE...A LOW-MIDLEVEL CLOUD DECK /NOT WELL HANDLED BY
GUIDANCE/ HAS SPREAD OVER MUCH OF THE AREA DUE TO ELEVATED MOISTURE
IN THE PRESENCE OF THE FRONTAL CONVERGENCE. A POCKET OF STRONGER
RADAR RETURNS FROM PRECIP ENCOUNTERING THE MTNS OF EAST TN HAS NOW
EVIDENTLY PUSHED INTO THE MTNS LEAVING MAINLY NW FLOW PRECIP. A FEW
SPRINKLES ARE LIKELY FALLING FROM THE CLOUD DECK OVER THE BLUE RIDGE
AREA OF WNC WITH FLEETING VERY LIGHT RETURNS. TRENDS SUGGEST THESE
WON/T MAKE IT MUCH FARTHER EAST EVEN AS THE FRONT SLIDES ACROSS.
TEMPS ARE REMAINING STEADY OR EVEN WARMING SLIGHTLY AHEAD OF THE
FRONT...WHICH HAS SEEMINGLY SLOWED NOCTURNALLY. IT IS STILL PROGGED
TO EXIT THE AREA BEFORE SUNRISE. REVISED HRLY TEMPS OVERNIGHT BUT
MAY NOT HAVE ACCOUNTED FOR THE CLOUD COVER ENOUGH. DOWNSLOPING IS
EXPECTED TO EVENTUALLY ERODE IT BUT THAT MAY TAKE SOME TIME. RAPID
COOLING IS LIKELY ONCE WINDS FLIP AND SKIES CLEAR.

AS OF 230 PM EST THURSDAY...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 /TONIGHT 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 /06Z FRIDAY THROUGH TUESDAY/...
AT KCLT...GUIDANCE SUGGESTS FROPA WILL OCCUR EARLY THIS AM...BUT
ALREADY SEEMS A LITTLE TOO FAST WITH TIMING OF WSHFT. NO PRECIP
EXPECTED TO MAKE IT THIS FAR EAST OF THE MTNS IN DOWNSLOPING FLOW
ALOFT. WINDS SHOULD BEGIN TO FAVOR NWLY AFTER 08Z WITH SOLIDLY NW
WINDS NOT ARRIVING UNTIL A LITTLE LATER. A MIDLEVEL CIG WILL LIKELY
PERSIST UNTIL AFTER SUNRISE UNLESS DOWNSLOPING IS MORE EFFECTIVE
THAN ANTICIPATED. NW WINDS WITH FREQUENT LOW-END GUSTS AS SOON AS
MIXING BEGINS TODAY. CAN/T RULE OUT A COUPLE GUSTS TO NEAR 30KT
THOUGH. GENERALLY CALMER AND CONTINUED CLEAR TONIGHT UNDER BUILDING
HIGH PRESSURE AND DRY SFC CONDS.

ELSEWHERE...A LOW VFR CIG WILL PERSIST THRU THE EARLY AM DUE TO
MIDLEVEL MOISTURE AND ENHANCED LIFT FROM FROPA. NW FLOW WILL DRIVE
MTN PRECIP ALONG THE TENN BORDER. PCPN CHANCES AT KAVL ARE TOO LOW
TO MENTION BUT SOME LIGHT SPRINKLES OR FLURRIES COULD OCCUR.
GUIDANCE HAS BACKED OFF EARLIER EXPECTATION OF AN MVFR CIG AT KAVL
BUT A FEW CLOUDS AT THAT LEVEL ARE LIKELY TO BE SEEN. WSHFT TO NW
WILL OCCUR POST FROPA GENERALLY IN THE 08-10Z TIMEFRAME WITH THE
CIGS SCOURING IN THE WAKE OF THE FRONT...THOUGH CIGS MAY NOT CLEAR
COMPLETELY UNTIL AFTER DAYBREAK. FREQUENT GUSTS OF 20-25KT ACRS MUCH
OF THE REGION THIS AFTN...WITH THE MTNS GUSTING HIGHER. KAVL MIGHT
SEE SOME GUSTS OF 30-35KT. INCOMING HIGH PRESSURE TONIGHT WILL ALLOW
WINDS TO RELAX AND SKIES TO REMAIN MCLR.

OUTLOOK...MAINLY VFR CONDITIONS ARE EXPECTED ACROSS THE AREA
SATURDAY. MOISTURE THEN BEGINS TO RETURN SUNDAY AHEAD OF ANOTHER LOW
PRESSURE SYSTEM...WHICH IS LIKELY TO BRING PRECIP AND RESTRICTIONS.
DRYING IS EXPECTED BY LATE MONDAY IN THE WAKE OF THAT SYSTEM.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  88%     LOW   56%     HIGH 100%     HIGH  93%
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 UNTIL MIDNIGHT EST TONIGHT FOR NCZ033-049-050.
SC...NONE.

&&

$$
SYNOPSIS...WIMBERLEY
NEAR TERM...JOH/WIMBERLEY
SHORT TERM...NED
LONG TERM...RWH
AVIATION...WIMBERLEY


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