Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 240836
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
336 AM EST SAT JAN 24 2015

.SYNOPSIS...
LOW PRESSURE WILL MOVE UP THE EAST COAST TODAY. HIGH PRESSURE WILL
BRIEFLY BUILD IN ON SUNDAY...BEFORE A LOW PRESSURE SYSTEM AND
TRAILING UPPER LEVEL DISTURBANCE AFFECT THE AREA SUNDAY NIGHT
THROUGH TUESDAY. HIGH PRESSURE WILL BUILD OVER THE AREA DURING THE
MIDDLE TO LATE PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
SPORADIC BANDS OF LIGHT TO MODERATE RAIN...ASSOCIATED WITH LOW-TO-
MID LEVEL FRONTOGENESIS WILL CONTINUE TO PUSH EAST ACROSS THE
PIEDMONT THIS MORNING...WITH PRECIP CHANCES ENDING FOR MOST AREAS
EAST OF THE MTNS...AS MID/UPPER LEVEL DRYING OCCURS ON THE AC SHEAR
SIDE OF THE UPPER JET. MEANWHILE...DEFORMATION ZONE BAND CONTINUES
TO PROGRESS STEADILY ACROSS THE TENN VALLEY AND CUMBERLAND PLATEAU
AREA THIS MORNING...WITH PRIMARILY LIGHT RETURNS INDICATED ON
REGIONAL 88DS. TEMPS HAVE BEGUN TO FALL SLOWLY ACROSS THE HIGHER
ELEVATIONS OF THE NC MTNS THIS MORNING...AND BY THE TIME THIS BAND
OF PRECIP REACHES WESTERN NC (BY AROUND DAYBREAK)...AREAS ABOVE 3000
FEET OR SO SHOULD BE COLD ENOUGH FOR SNOW. IN FACT...SNOW LEVELS
WILL FALL RATHER QUICKLY AFTER 09Z...AND I EXPECT MOST OF THE
MTNS... EVEN THE LOWER VALLEYS WILL SEE AT LEAST A FEW FLAKES BEFORE
THE DEFORMATION BAND PUSHES EAST AROUND MID-MORNING. STILL EXPECT
THE MORE SIGNIFICANT ACCUMS (2-3 INCHES TO BE CONFINED TO AREAS
ABOVE 3500 FEET...BUT SOME VALLEY LOCATIONS COULD PICK UP A QUICK
DUSTING TO AN INCH...ESP NEAR THE TENN BORDER.

SHORT TERM GUIDANCE INDICATES MOISTURE WILL DRY UP VERY QUICKLY
LATER THIS MORNING IN THE W/NW FLOW REGIME...SO POPS FALL TO LESS
THAN SLIGHT CHANCE BY 18Z...BY WHICH TIME SKIES SHOULD BE CLEAR IN
MOST AREAS...EXCEPT PERHAPS THE IMMEDIATE TENN BORDER. GUSTY NW
WINDS CAN BE EXPECTED OVER THE MTNS TODAY...WITH GUSTS OF AROUND 40
MPH LIKELY IN THE HIGH ELEVATIONS. TEMPS WILL REBOUND TO NEAR NORMAL
THANKS TO DOWNSLOPE WARMING EAST OF THE MTNS...WHILE MOST OF THE
HIGH TERRAIN WILL SEE MAXES 5-10 DEGREES BELOW CLIMO.

MOISTURE MAKES A BRIEF RETURN TO THE SOUTHERN APPALACHIANS
TONIGHT...AS A WEAK VORT MAX DROPS INTO THE BASE OF THE DEVELOPING
BROAD LONG WAVE TROUGH. HOWEVER...IT/S DEBATABLE WHETHER MOISTURE
WILL BE DEEP ENOUGH TO SUPPORT ADDITIONAL SNOW SHOWERS. A TOKEN
SLIGHT CHANCE WILL BE MAINTAINED...BUR PRIMARILY LIMITED TO THE NRN
MTNS.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AT 230 AM EST SATURDAY...ON SUNDAY MORNING A MEAN UPPER TROUGH WILL
BE OVER THE EASTERN PORTION OF THE CONTINENT...WHILE AN UPPER RIDGE
WILL BE OVER THE NW USA...AND A CLOSED LOW WILL BE OFF BAJA CA. ONE
SHORTWAVE WILL BE EXITING THE EAST COAST...WHILE A CLOSED LOW DIVES
SE ACROSS THE PLAINS AND MID MS RIVER VALLEY INTO THE BASE OF THE
TROUGH. THE UPPER LOW OPENS UP SUNDAY NIGHT AS IT REACHES THE
SOUTHERN APPALACHIANS...WHILE WHAT WAS CHANNELED VORTICITY TO ITS
SOUTH...BECOMES ADVECTED VORTICITY FROM NC TO LA. THE LOW CROSSES
THE CAROLINAS ON MONDAY... MOVING OFF THE COAST MONDAY NIGHT...
FOLLOWED BY A SLUG OF CHANNELED VORTICITY TOWARD DAWN.

AT THE SURFACE...A COLD FRONT WILL APPROACH THE SOUTHERN
APPALACHIANS FROM THE WEST ON SUNDAY...SPREADING PRECIPITATION EAST
ACROSS THE AREA IN THE AFTERNOON. THICKNESS VALUES WILL BE RATHER
LOW ACROSS THE AREA...BUT MODEL SOUNDINGS SUGGEST PRECIPITATION WILL
START AS RAIN AT ALL BUT THE HIGHEST MOUNTAIN ELEVATIONS.
PRECIPITATION WILL CONTINUE SUNDAY NIGHT BEHIND THE FRONT UNDER THE
UPPER LOW...WITH SNOW LEVELS DROPPING TO THE MOUNTAIN VALLEY
FLOORS...WHILE RAIN CONTINUES IN THE LEE OF THE MOUNTAINS. AS THE
UPPER LOW MOVES OFF TO THE EAST ON MONDAY...RAIN WILL SLOWLY DIMINISH
FROM THE WEST IN THE LEE OF THE MOUNTAINS...WHILE A NW FLOW SNOW
EVENT SETS UP IN THE NC MOUNTAINS...WHICH CONTINUES THROUGH MONDAY
NIGHT. TEMPERATURES WILL START OUR SLIGHTLY ABOVE NORMAL AHEAD OF
THE FRONT...FALLING TO SLIGHTLY BELOW NORMAL BEHIND IT.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AT 230 AM EST SATURDAY...ON TUESDAY MORNING AN UPPER TROUGH WILL BE
OVER THE EASTERN USA...WITH A RIDGE OVER THE EASTERN ROCKIES...AND
AND UPPER LOW NEAR THE CA COAST. THE MODELS VARY ON THE DEGREE OF
DEAMPLIFICATION THAT OCCURS OVER THE EAST INTO TUESDAY...BUT
BASICALLY AGREE ON A MORE ZONAL UPPER FLOW OVER THE SOUTHEAST BY
LATE THURSDAY. THERE IS GOOD MODEL AGREEMENT ON REAMPLFICATION OF
THE EASTERN TROUGH FROM FRIDAY INTO SATURDAY.

A COLD FRONT WILL BE MOVING SOUTH OVER THE GULF OF MEXICO TUESDAY
MORNING...WHILE MOIST NW FLOW PERSISTS INTO THE NC MOUNTAINS. SNOW
SHOWERS ASSOCIATED WITH THIS FLOW WILL GRADUALLY DIMINISH...AS HIGH
PRESSURE MOVES FROM THE PLAINS TO THE OH RIVER VALLEY BY WEDNESDAY.
THIS HIGH DRIFTS TOE THE EAST COAST BY THURSDAY...WHILE A PAIR OF
COLD FRONTS MOVE SE THROUGH THE MS RIVER VALLEY. THE FRONTS CROSS
OUR AREA FROM THE NW ON THURSDAY NIGHT...ACCOMPANIED BY MODEST
MOISTURE AND LIMITED POTENTIAL FOR RAINFALL. SOME LINGERING MOISTURE
ALONG THE TN BORDER MAY RESULT IN NW FLOW SNOW SHOWERS IN THE NC
MOUNTAINS ON THURSDAY NIGHT AND FRIDAY...BRIEFLY CHANGING TO RAIN
BEFORE ENDING FRIDAY NIGHT.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIFR CONDITIONS ARE EXPECTED TO PERSIST...ALONG WITH OCCL
-RA AND/OR -DZ THROUGH THE OVERNIGHT HOURS. AS SURFACE LOW PRESSURE
LIFTS UP THE SOUTHEAST COAST...THE FLOW WILL TURN TOWARD THE NW
LATER THIS MORNING...AND DRIER AIR WILL BEGIN TO OVERSPREAD THE
PIEDMONT...ALLOWING CIGS TO LIFT TO IFR BY MID-MORNING...THEN TO VFR
BY EARLY AFTERNOON. GENERALLY LIGHT N WINDS OVERNIGHT WILL BECOME
LIGHT NW BY SUNRISE...THEN INCREASE TO AROUND 10 KTS BY EARLY
AFTERNOON.

ELSEWHERE...THE FORECAST FOR THE NEXT 6 HOURS OR SO IS NOT AS EASY
AS IT WOULD APPEAR...AS IT IS NOT AN ABSOLUTE SLAM DUNK THAT CURRENT
IFR/LIFR CIGS WILL REMAIN LOCKED IN THROUGH THIS TIME. IN FACT...
MOST OF THE UPSTATE SC TERMINALS AND KHKY HAVE SEEN OR ARE SEEING
PERIODS OF MVFR CONDITIONS...PRESUMABLY IN ASSOCIATION WITH SOME
SPOTTY RAIN SHOWERS MIXING OUT THE LOWER CIGS. THE PRIMARY FLY IN
THE OINTMENT FOR THE REMAINDER OF THE OVERNIGHT IS THE DOWNSLOPE FLOW
THAT IS EXPECTED TO GRADUALLY DEVELOP ABOVE THE SHALLOW COLD AIR
DAMMING LAYER. IN FACT...I WOULDN/T RULE OUT THE POSSIBILITY THAT
THESE PERIODS OF IMPROVING CONDITIONS MAY BE TIED TO THAT
PHENOMENON. WHILE I DIDN/T HAVE THE INTESTINAL FORTITUDE TO SHOW A
DRAMATIC IMPROVING TREND OVERNIGHT...I DO INDICATE AN IMPROVEMENT TO
THE UPPER END OF IFR...OR MVFR W/ TEMPOS FOR IFR AT MOST TERMINALS
BY AROUND 10Z. OTHERWISE...A BRIEF PERIOD OF RA MIXED WITH IP/SN
WILL BE POSSIBLE AT KAVL AS TEMPS BEGIN TO FALL ACROSS THE MTNS
LATER THIS MORNING. CIGS SHOULD THEN IMPROVE RATHER QUICKLY
THROUGHOUT THE DAYLIGHT HOURS SATURDAY...WITH VFR CONDITIONS
EXPECTED NO LATER THAN EARLY AFTERNOON.

OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING SNOW CHANCES TO THE
AREA EARLY IN THE WEEK...MAINLY TO THE MTNS NORTH AND WEST OF KAVL.
VFR IS LIKELY ELSEWHERE.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       MED   69%     LOW   57%     HIGH 100%     HIGH 100%
KGSP       HIGH  86%     MED   70%     HIGH 100%     HIGH 100%
KAVL       HIGH  90%     MED   73%     HIGH 100%     HIGH 100%
KHKY       MED   72%     MED   68%     HIGH 100%     HIGH 100%
KGMU       MED   76%     MED   73%     HIGH 100%     HIGH 100%
KAND       MED   78%     HIGH  96%     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...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ033-
     048>052-058-059-501-503-505.
SC...NONE.

&&

$$
SYNOPSIS...JAT
NEAR TERM...JDL
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...JDL



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