Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 240014
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
714 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 645 PM EST...A WEAK PUNCH OF MID LEVEL DRY AIR HAS WRAPPED
ATOP THE FORECAST AREA THIS EVENING...TRANSITIONING PTYPES TO A
LIGHT RAIN/DRIZZLE MIXTURE EAST OF THE MOUNTAINS...AND MAKING ICE
CRYTAL GROWTH NUCLEI SLIGHTLY MORE SCARCE OVER THE MTNS. WHILE
SPOTTY MOUNTAIN SLEET CONTINUES TO MIX IN WITH THE RAIN...THE MAIN
IMMEDIATE CONCERN IS THAT A VERY FEW LOCATIONS...ESPECIALLY FROM ERN
BUNCOMBE COUNTY UP THE BLUE RIDGE TO NEAR LITTLE SWITZERLAND...HAVE
GOTTEN LOCKED IN AROUND THE FREEZING MARK. ADDITIONAL ICE GLAZING
THIS EVENING SHOULD BE CONFINED TO MAINLY THE TREES...AND SOME
MELTING/LATENT HEATING HAS MANAGED TO KEEP ACCRUAL GENERALLY BELOW
WARNING LIMITS EVEN IN THESE AREAS. THE ADVISORY WILL THUS BE
MAINTAINED AS IT THIS EVENING.

OTHERWISE...THE UPPER LOW PRES SYSTEM OVER TX/LA IS EXPECTED TO OPEN
AND MOVE EAST ALONG THE GULF COAST OVERNIGHT...THEN INTO THE
ATLANTIC SAT. AT THE SFC...A MILLER TYPE A LOW PRESSURE SYSTEM IS
TRANSITIONING FROM THE GULF COAST TO THE SE ATLANTIC COASTLINE THIS
EVENING...AND SHOULD PULL UP THE ATLANTIC COAST SATURDAY. THE AFORE
MENTIONED DRY SLOT WILL PERSIST OVER THE CENTER OF THE CWFA
OVERNIGHT BETWEEN THE DEPARTING WARM CONVEYOR BELT AND THE
APPROACHING DEFORMATION ZONE. PTYPES SHOULD REMAIN ALL RAIN UNTIL
PRECIP ENDS SAT MORNING OUTSIDE OF THE MTNS. CANNOT RULE OUT SOME
SNOW MIXING IN ACROSS THE LOWER ELEVATIONS OF THE NRN FOOTHILLS/NW
PIEDMONT BEFORE ENDING. NO ACCUMS ARE EXPECTED EVEN IF THAT DOES
OCCUR. SKIES CLEAR SAT WITH GUSTY NW WINDS DEVELOPING. LOWS TONIGHT
WILL BE 5 TO 10 DEGREES ABOVE NORMAL...WITH HIGHS SAT A FEW DEGREES
BELOW NORMAL.

A DIFFERENT STORY EXISTS ACROSS THE MTNS. MOST LOCATIONS ARE ABOVE
FREEZING...EXCEPT FOR THE HIGHEST ELEVATIONS OF THE NRN MTNS. THE
GOOD NEWS THERE IS THAT PRECIP REMAINS VERY LIGHT...SO ONLY LIGHT
ADDITIONAL ICE ACCRETION IS EXPECTED BEFORE PRECIP PICKS BACK UP
ACROSS THE MTNS OVERNIGHT AS A DEFORMATION ZONE MOVES IN FROM THE
WEST AND NWLY FLOW DEVELOPS. THE WARM NOSE CURRENTLY OVER THE AREA
WILL ONLY SLOWLY ERODE OVERNIGHT AS THE COLDER H85 LEVEL AIR IS SLOW
TO MOVE IN AS THIS IS NOT A TYPICAL NW FLOW EVENT. THEREFORE...WHERE
TEMPS FALL BACK BELOW FREEZING...MAINLY ABOVE 3500 FEET...PRECIP
WILL CHANGE BACK OVER TO FREEZING RAIN. ONCE THE COLD AIR ARRIVES
TOWARD DAYBREAK...THEN THE PRECIP WILL CHANGE OVER TO SNOW...WITH
SNOW LEVELS DROPPING TO OR NEAR THE VALLEY FLOORS. BY THEN...PRECIP
WILL BE TAPERING OFF AS THE DEFORMATION ZONE MOVES NE OF THE AREA
AND THE LOW LEVEL MOISTURE BECOMES MORE SHALLOW. IN FACT...PRECIP
WILL END RATHER QUICKLY SAT MORNING WITH ONLY SOME LINGERING CLOUDS
ACROSS THE NRN MTNS FOR THE AFTERNOON. THEREFORE...GIVEN THE LIGHT
ADDITIONAL ACCUMS OF ICE AND SNOW ACROSS THE NC MTNS...WILL LEAVE
THE WINTER WX ADV IN PLACE. THERE WILL BE SOME LIGHT ACCUMS IN THE
VALLEYS OF THE CENTRAL AND SRN MTNS. HOWEVER...THEY SHUD BE AN INCH
OR LESS WITH NO ICING... PRECLUDING THE NEED FOR AN ADV. DO EXPECT
GUSTY WINDS TO DEVELOP OVERNIGHT AND CONTINUE THRU THE DAY. LOWS
TONIGHT WILL BE 5 TO 10 DEGREES ABOVE NORMAL WITH HIGHS SAT 5 TO 10
DEGREES BELOW NORMAL.

&&

.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 /00Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIGHT RAIN AND IFR CONDITIONS WILL CONTINUE THIS EVENING
AND LIKELY LOWER TO FREQUENT LIFR WITH DRIZZLE AS A SLIGHTLY DRIER
PATCH OF AIR WORKS IN ALOFT. 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 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. PRECIPITATION WILL LIKELY SLACKEN TO DRIZZLE A BIT
SOONER...BUT WITH WIDESPREAD IFR TO LIFR CONDITIONS EXPECTED
OVERNIGHT INTO SAT MORNING. 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...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       MED   66%     MED   69%     MED   75%     HIGH 100%
KGSP       MED   68%     MED   65%     MED   69%     HIGH 100%
KAVL       MED   76%     MED   70%     MED   68%     HIGH 100%
KHKY       MED   65%     MED   63%     MED   72%     HIGH 100%
KGMU       MED   69%     MED   64%     MED   73%     HIGH 100%
KAND       MED   75%     MED   68%     HIGH  83%     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/RWH
SHORT TERM...ARK
LONG TERM...WIMBERLEY
AVIATION...HG/RWH



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