Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240241
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
941 PM EST FRI JAN 23 2015

.SYNOPSIS...
LOW PRESSURE WILL TRACK ALONG THE CAROLINA COAST TONIGHT...BEFORE
CONTINUING UP THE EAST COAST...ALLOWING PRECIPITATION TO TAPER OFF
IN OUR AREA ON SATURDAY. 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...BRINGING
PRECIPITATION CHANCES MAINLY TO THE MOUNTAINS. HIGH PRESSURE WILL
BUILD OVER THE AREA FOR THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 930 PM EST...WATER VAPOR IMAGERY SHOWS THE APPROACHING UPPER
TROUGH AXIS OVER THE MS RIVER VALLEY THIS EVENING...AND DEEP LAYER Q
VECTOR CONVERGENCE SHOULD STEADILY RAMP UP FROM THE WEST THROUGH THE
OVERNIGHT HOURS AS THE TROUGH SWINGS EAST. KGSP RADAR REFLECTIVITIES
HAVE RECENTLY IMPROVED OVER THE HEART OF THE FORECAST AREA AS A
DECENT BAND OF DEFORMATION FORMS NW OF THE COASTAL SFC LOW PRES
SYSTEM...AND DEEPER MOISTURE FILLS IN THE SHALLOW DRY SLOT THAT
CURTAILED RATES EARLIER THIS EVENING. ALL TOLD...PRECIPITATION RATES
SHOULD BE FAIRLY MODEST FOR THE OVERNIGHT HOURS...BUT IMPROVING LATE
NEAR THE TN BORDER WHERE THERMAL PROFILES ARE MOST TROUBLING.
FORTUNATELY...MOST OF THE FORECAST AREA HAS SFC TEMPS A FEW DEGREES
ABOVE FREEZING...WITH JUST ISOLATED FREEZING POCKETS AT LOCATIONS
ALONG AND NEAR THE BLUE RIDGE. PROFILES WILL START COOLING AGAIN
OVERNIGHT...AND A MIXED BAG OF FREEZING RAIN...SLEET...AND THEN SNOW
RETURNING FROM THE WEST. USING THE TOP DOWN TECHNIQUE WITH CONSENSUS
18Z MODEL PROFILES REFLECTS THIS TREND...WITH TOTAL SNOWFALL OF 1 TO
2 INCHES EXPECTED IN THE FAR WRN MTNS THROUGH SAT MORNING...EXCEPT
FOR SOME 3 INCH TOTALS ON TOP OF THE SMOKIES...MIXED WITH A LITTLE
SLEET THROUGHOUT. ADDITIONAL FREEZING RAIN ACCUMULATIONS OF A FEW
HUNDREDTHS TO PERHAPS A TENTH OF AN INCH ARE EXPECTED OVERNIGHT
THROUGHOUT THE ADVISORY AREA...WITH THE GREATEST ICING IN NRN MTN
LOCATIONS BEFORE THE CHANGEOVER TO SNOW OCCURS SAT MORNING. ALL
TOLD...THE CURRENT ADVISORY AREA HAS THIS WELL CAPTURED. THE POCKETS
OF FREEZING NEAR THE FRENCH BROAD VALLEY REMAIN TROUBLING...BUT
NEARLY ALL MESONET SITES ARE SHOWING MID 30S THERE...SO NO ADVISORY
CHANGES ARE EXPECTED.

THE UPPER TROUGH AXIS WILL SWING THROUGH THE REGION VERY QUICKLY
FROM 12Z TO 18Z...WITH WESTERLY FLOW DRYING ALLOWING FOR STEADY
EROSION OF ANY LINGERING SFC CAD LAYER EAST OF THE MTNS. ANY
RESIDUAL NW FLOW SNOW SHOWERS WILL DRY UP QUICKLY IN THE WESTERN
MOUNTAINS BY EARLY AFTERNOON. EXPECT MAXES TO RANGE FROM ONE
CATEGORY BELOW NORMAL IN THE PIEDMONT TO AS MUCH AS 5 TO 10 DEGREES
BELOW CLIMO IN THE MTNS.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 230 PM FRIDAY...ANOTHER VORTMAX WILL CROSS THE CWFA SATURDAY
EVENING...AS IT ROUNDS THE BASE OF A BROAD 500 MB ERN CONUS TROF.
THE NAM AND GFS AGREE THAT THERE WILL BE A BRIEF SHOT OF SHALLOW
MOISTURE WITHIN REINFORCING 850 MB NWLY FLOW. ENUF SO THAT A FEW
FLURRIES/LGT SNOW SHWRS MAY DEVELOP ALONG THE TN BORDER...PRIMARILY
IN THE NRN NC MTNS. I HAVE POPS RAMPING BACK UP TO CHC IN THE NRN
FOUR TN BORDER ZONES LATE EVENING...THEN TAPERING OFF TO LESS THAN
15 PCT BY 12Z SUN. THE REST OF THE AREA SHUD SEE MOSTLY CLEAR SKIES.
TEMPS WILL BE NEAR NORMAL.

SUNDAY THRU MONDAY...A POTENT CLIPPER SYSTEM WILL DIVE INTO THE OHIO
VALLEY ON SUNDAY...THEN CROSS THE SOUTHERN APPALACHIANS SUNDAY
NIGHT. THE SYSTEM WILL HAVE STRONG DEEP-LAYER Q-VECTOR
CONVERGENCE...COUPLED WITH DECENT RH. A CROSS SECTION OF THE NC MTNS
SHOWS PEAK LLVL LIFT WITH THE QG FORCING WILL BE AROUND 06Z. OF
COURSE...GIVEN THE FAST MOVING NATURE...EXACT TIMING IN THE MODELS
MAY BE OFF BY A FEW HOURS. IN ANY CASE...HAVE POPS RAMP UP TO HIGH-
END LIKELY ALONG THE TN BORDER OVERNIGHT...WITH EVEN A BIT OF SLGT
CHC TO LOW-END CHC OF LIGHT RAIN ACRS THE NC PIEDMONT AND ERN
UPSTATE...AS THE STRONG FORCING MAY ALLOW FOR A FEW STRAY SHWRS TO
/BREAK CONTAINMENT/. FCST SNDGS SHOW STEEP LLVL LAPSE RATES WITH
PROGRESSIVELY BETTER NW UPSLOPE COMPONENT ALONG THE TN LINE (30-35
KTS). THE SFC-BASED WARM LAYER LOOKS TOO DEEP FOR ANY SNOW OR SLEET
EAST OF THE MTNS. HOWEVER...GIVEN THE OVERNIGHT TIMING...CANNOT RULE
OUT A VERY BRIEF AND SPOTTY MIX ACRS MAINLY THE NC FOOTHILLS AND NW
PIEDMONT MONDAY MORNING. FOR NOW...I WILL KEEP ONLY RAIN MENTION
OUTSIDE THE HIGH TERRAIN. SNOW AMTS LOOK SOLIDLY ADVISORY LVL...AND
COULD APPROACH WARNING...IF THE UPSLOPE FLOW CAN OVERLAP THE BEST
LAPSE RATES AND MID LVL FORCING. WILL CONTINUE TO MENTION SNOW
POSSIBLE IN THE NW FLOW AREAS IN THE HWO. TEMPS WILL BE NEAR NORMAL
ON SUNDAY...WITH SLIGHTLY ABOVE NORMAL LOWS MONDAY MORNING...THEN
NEAR OR SLIGHTLY BELOW NORMAL HIGHS MONDAY AFTN...AS CAA AND
LINGERING CLOUDS LIMIT HEATING.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 200 PM FRI...LATEST GLOBAL MODEL RUNS SHOW A SECOND NRN STREAM
SHORTWAVE DIVING OUT OF CANADA EARLY NEXT WEEK...THRU THE UPPER OH
VALLEY AND THEN ACROSS THE CAROLINAS MON NIGHT AND TUE. THE MODELS
HAVE TRENDED A LITTLE STRONGER WITH THIS WAVE...WITH EARLIER RUNS
GENERALLY SUGGESTING ONLY A WEAK POCKET OF VORT CROSSING THE AREA IN
THE WAKE OF MONDAY/S CLIPPER. THE IMPLICATION FOR THE FCST IS MORE OR
LESS TO PROLONG THE EFFECTS OF AN ERN CONUS TROUGH...MAINTAINING
CHANCES OF NW FLOW PRECIP IN THE MTNS AND BRINGING SLIGHT CHANCES TO
SOME AREAS EAST OF THE MTNS AS THE SHORTWAVE PASSES. POPS DIMINISH BY
EARLY WED AS SHORTWAVE RIDGING RETURNS TO THE SRN APPALACHIAN REGION
FOR WED AND WED NIGHT. HOWEVER THIS RESULTS FROM THE BREAKDOWN OF THE
REX BLOCK OVER THE WEST COAST...AND THE REMNANT SHORTWAVE FROM THE
BLOCKING LOW MOVES IN BEHIND THAT RIDGE...WHICH COULD BRING SOME
PRECIP BACK TO THE AREA BY THU NIGHT. GUIDANCE SUGGESTS THIS
SHORTWAVE COULD PHASE WITH A CLIPPER AND DRIVE A COLD FRONT INTO THE
UPPER OH/TN VALLEYS. THAT MIGHT BEAR WATCHING. TEMPS WILL REMAIN A
LITTLE BELOW CLIMO MON NIGHT THRU WED MRNG...WHEN THICKNESSES APPEAR
TO BOTTOM OUT. A GENTLE WARMING TREND IS EXPECTED THEREAFTER.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIGHT RAIN AND IFR CONDITIONS WILL CONTINUE THIS EVENING
AND LIKELY LOWER TO FREQUENT LIFR WITH LIGHT RAIN/DRIZZLE OVERNIGHT.
NELY WINDS WILL BECOME NLY OVERNIGHT. WINDS TURN NWLY AFTER DAYBREAK
AND MOISTURE BEGINS TO THIN AND LIFT. EXPECT A RISE TO MVFR BY MID
MORNING THEN SCATTERING OUT TO VFR BY EARLY AFTERNOON. NWLY WINDS
SHOULD BECOME GUSTY BY EARLY AFTERNOON AS WELL.

AT KAVL...IFR TO LIFR CONDITIONS SHOULD PERSIST ALONG WITH LIGHT
RAIN AND DRIZZLE FOR MOST OF THE NIGHTTIME HOURS. TEMPERATURES
APPEAR TO BE STEADY JUST ABOVE THE FREEZING MARK. BRIEF SLEET CANNOT
BE RULED OUT COMPLETELY...BUT PTYPES LOOK TO BE MOSTLY RAIN ALL
NIGHT. THE RAIN MAY BECOME MORE SHOWERY LATE TONIGHT THROUGH SAT
MORNING AS THE UPPER TROUGH MOVES THROUGH. THE RAIN SHOWERS COULD
BRIEFLY MIX WITH SLEET OR SNOW SHOWERS BEFORE ENDING LATE SAT
MORNING. EXPECT LIGHT SRLY WINDS THIS EVENING TO TURN NW OVERNIGHT
AND BECOME GUSTY THROUGH THE DAY ON SATURDAY.

ELSEWHERE...SIMILAR CONDITIONS TO KCLT ARE EXPECTED AT THE FOOTHILL
TAF SITES. WIDESPREAD IFR TO LIFR CONDITIONS ARE EXPECTED OVERNIGHT
INTO SAT MORNING WITH LINGERING LIGHT RAIN/DRIZZLE. EXPECT WINDS TO
TURN AROUND THE DIAL FROM NE TO NW LATE TONIGHT AND THEN WESTERLY
WITH PERHAPS LOW END GUSTS SAT AFTERNOON ONCE CLEARING/MIXING
OCCURS.

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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       MED   62%     MED   73%     MED   78%     HIGH 100%
KGSP       MED   62%     MED   65%     MED   78%     HIGH 100%
KAVL       MED   73%     MED   76%     MED   74%     HIGH 100%
KHKY       MED   62%     MED   64%     MED   75%     HIGH 100%
KGMU       MED   62%     MED   67%     MED   79%     HIGH 100%
KAND       MED   64%     MED   73%     HIGH  88%     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 SATURDAY FOR NCZ033-
     048>052-058-059-501-503-505.
SC...NONE.

&&

$$
SYNOPSIS...WIMBERLEY
NEAR TERM...HG
SHORT TERM...ARK
LONG TERM...WIMBERLEY
AVIATION...HG



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