Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 271731
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1231 PM EST TUE JAN 27 2015

.SYNOPSIS...
DRY HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH WEDNESDAY.
ON THURSDAY...A COLD FRONT WILL CROSS THE FORECAST AREA WITH ANOTHER
HIGH PRESSURE SYSTEM BUILDING IN FRIDAY THROUGH SATURDAY. A MOIST
LOW PRESSURE SYSTEM IS EXPECTED TO AFFECT THE REGION ON SUNDAY INTO
MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1225 PM EST TUESDAY...OPTED TO EXTENDED CURRENT WW ADVISORY
THROUGH THE AFTERNOON WITH A NEW EXPIRATION TIME OF 6PM THIS EVENING
DUE TO CONTINUED UPSTREAM DEVELOPMENT PER KMRX RADAR.  IN
ADDITION...NEW GFS GUIDANCE AGREES FAIRLY WELL WITH THE 12Z NAM WITH
BOTH YIELDING SUBSTANTIAL LOW LEVEL MOISTURE POOLING ALONG THE
WESTWARD FACING SLOPES OF THE SW MTNS INTO THE EVENING.
OTHERWISE...BAND OF LIGHT FLURRIES OVER THE WESTERN NC PIEDMONT HAVE
FADED LEADING TO SLOW IMPROVEMENT IN SKY CONDITIONS.  FCST CONTINUES
TO FEATURE GRADUAL CLEARING OF SKIES THROUGH THE EVENING ACROSS MUCH
OF THE LOW TERRAIN.  ALSO MADE TWEAKS TO TEMPERATURES AND DEWPOINTS
IN THE EXTREME NEAR TERM TO REFLECT LATEST OBSERVATIONS.

PREVIOUS DISCUSSION...

AT 230 AM EST TUESDAY...AN UPPER LOW WILL REMAIN ALONG THE EAST
COAST TODAY AND TONIGHT...WHILE AN UPPER LOW MOVES NE ALONG THE NEW
ENGLAND COAST. STRONG CHANNELED VORTICITY ROUNDING THE TROUGH WILL
PERSIST THROUGH TODAY...WEAKENING TONIGHT. A SOMEWHAT TIGHT SURFACE
PRESSURE GRADIENT WILL REMAIN OVER OUR AREA BETWEEN A DEPARTING COLD
FRONT OVER THE ATLANTIC...AND HIGH PRESSURE OVER THE GREAT LAKES.
THIS WILL KEEP A MOIST NW FLOW DIRECTED INTO THE MOUNTAINS BORDERING
TN...WHERE SNOW WILL PERSIST INTO THIS EVENING. DUE TO THE SHALLOW
NATURE OF THE MOIST LAYER...SNOWFALL ACCUMULATIONS ARE EXPECTED TO
REACH NO HIGHER THAN ADVISORY CRITERIA. THE CURRENT ADVISORY WILL BE
LEFT IN PLACE THROUGH MIDDAY.

HIGH TEMPERATURES TODAY WILL RUN SLIGHTLY BELOW NORMAL IN THE LEE OF
THE MOUNTAINS...WHERE NW DOWNSLOPE FLOW WILL PARTIALLY OFFSET COLD
ADVECTION. HIGH TEMPERATURES WILL RUN AROUND 10 DEGREES BELOW NORMAL
IN THE MOUNTAINS. LOW TEMPERATURES TONIGHT WILL RUN AROUND SEVEN
DEGREES BELOW NORMAL.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 310 AM TUESDAY...THE FIRST HALF OF THE SHORT TERM WILL BE
RATHER QUIET...SEASONABLY COOL AND DRY...AS THE EASTERN LONG WAVE
TROUGH BEGINS TO FLATTEN A BIT IN RESPONSE TO PROGRESSIVE SHORT WAVE
RIDGING. HOWEVER...BY THE END OF THE PERIOD...THE TROUGH WILL DEEPEN
AGAIN AS A COUPLE OF SHORT WAVE TROUGHS PASS OVER THE OHIO VALLEY
AND MID-ATLANTIC....SIGNALING THE BEGINNING OF ANOTHER COOL DOWN AT
THE END OF THE WEEK.

IN THE INTERIM...MOISTURE ASSOCIATED WITH APPROACHING COLD FRONT
WILL BE RATHER MARGINAL THURSDAY THROUGH THURSDAY EVENING. IN
FACT...MOST OF THE MOISTURE IS POST-FRONTAL...SUGGESTING THAT
DESPITE DECENT DIVERGENCE IN THE LRQ OF A 125-PLUS KT UPPER JET
MAX...MOST OF THE IMPETUS FOR PRECIP CHANCES DURING THIS TIME FRAME
MAY WELL BE NORTHWEST/UPSLOPE FLOW. THE HIGHEST POPS (50-60) WILL
THEREFORE BE FEATURED ACROSS THE NORTHERN NC MTNS...TAPERING TO ONLY
A SLIGHT CHANCE ACROSS THE PIEDMONT. THERMO PROFILES SUGGEST A
PRIMARILY RAIN EVENT...WITH AN OUTSIDE OF FREEZING RAIN ACROSS THE
MTNS IF PRECIP BEGINS EARLY ENOUGH IN THE DAY THURSDAY. A TRANSITION
TO NORTHWEST FLOW SNOW SHOWERS WILL THEN OCCUR IN THE COLD ADVECTION
REGIME THU NIGHT...WITH SOME LIGHT ACCUMS POSSIBLE IN THE TYPICAL
AREAS.

GUSTY NW WINDS WILL OCCUR ACROSS THE MTNS THU NIGHT...AS GRADUALLY
DEEPENING SURFACE LOW MOVES FROM THE GREAT LAKES INTO NEW ENGLAND.
THE PROGGED PRESSURE GRADIENT...AND 40-50 KTS OF H8 FLOW SUGGEST A
DECENT POTENTIAL FOR AN ADVISORY LEVEL EVENT...BUT WILL WAIT TO
EVALUATE ANOTHER COUPLE OF CYCLES OF MODEL DATA BEFORE TALKING THIS
UP IN ANY OUTLOOK PRODUCTS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 325 AM TUESDAY...THE MAIN STORY OF THE MEDIUM RANGE WILL
REVOLVE AROUND THE PATTERN SHIFT OVER THE EAST...AS A RATHER DEEP
TROUGH ACROSS THE SOUTHWEST STATES FORCES HEIGHT RISES ALONG THE
ATLANTIC SEABOARD. THE LATEST GLOBAL MODEL GUIDANCE IS IN
CONSIDERABLY BETTER AGREEMENT REGARDING THE DETAILS OVER THE
WEEKEND...AS A MAJOR SHORT WAVE TROUGH IS EXPECTED TO EJECT OUT OF
THE PLAINS BY SUNDAY NIGHT...INITIATING CYCLOGENESIS IN THE MID-
MISS/TENN/OHIO VALLEY ALONG STRENGTHENING BAROCLINIC ZONE. WHILE
THERE WAS SOME POTENTIAL FOR A (POTENTIALLY SIGNIFICANT) WINTER
WEATHER EVENT SUGGESTED IN PREVIOUS MODEL RUNS...THE GROWING
CONSENSUS OF THE SURFACE CYCLONE PASSING WEST OF THE APPALACHIANS...
AND SURFACE HIGH PRESSURE IN AN UNSUITABLE LOCATION FOR STRONG COLD
AIR DAMMING...IS NOT AT ALL FAVORABLE FOR MUCH OF ANYTHING OTHER
THAN RAIN (WITH THE EXCEPTION OF THE USUAL TRANSIENT P-TYPE
POTENTIAL ACROSS THE HIGH TERRAIN AT PRECIP INSET). PER
COLLABORATION WITH NEIGHBORING OFFICES...NO MAJOR CHANGES WERE MADE
TO THE FORECAST FOR SUNDAY AND SUNDAY NIGHT (RAIN/SNOW MTNS...RAIN
ELSEWHERE)...BUT IF THE LATEST MODEL TRENDS CARRY TO THE NEXT
CYCLE...A TRANSITION TOWARD A /RAIN ONLY/ FORECAST MAY BE NECESSARY.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD.  MID
LEVEL STRATUS WILL LINGER THROUGH THE FIRST FEW HOURS OF THE TAF
CYCLE BEFORE SCT OUT TOWARDS SUNSET.  NORTHWEST WINDS WILL REMAIN
BRISK WITH GUSTS NEAR 20KTS LIKELY THROUGH THE AFTERNOON BEFORE
MIXING AND PGFS RELAX.  OTHERWISE...TAFS FEATURE LIGHT NORTHWESTERLY
WINDS THROUGH THE OVERNIGHT INTO WEDNESDAY MORNING AMIDST CLEAR
SKIES.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH VFR PREVAILING WITH THE
EXCEPTION OF AT KAVL WHERE UPSTREAM SNOW SHOWERS ADVECT MVFR CIGS UP
THE FRENCH BROAD VALLEY INTO KAVL.  THUS...KAVL TAF FEATURES BRIEF
WINDOW OF MVFR AT INITIALIZATION BEFORE INCREASING TO LOW VFR
THROUGH THE REMAINDER OF THE DAY.  OTHERWISE...GUSTY NW WINDS WILL
PREVAIL AT ALL SITES WITH MID LEVEL CIGS SCT OUT INTO THE EVENING
LEADING TO SKC THROUGH PERIODS END.  WINDS WILL SUBSIDE AFTER SUNSET
YIELDING LIGHT NORTHWEST FLOW FOR THE REMAINDER OF THE TAF CYCLE.

OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING PERIODIC CHANCES
FOR RAIN OR SNOW SHOWERS...MAINLY TO THE MOUNTAINS LATE IN THE WEEK.
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.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       LOW   58%     HIGH 100%     HIGH 100%     HIGH 100%
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...WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS EVENING FOR NCZ048-
     051-052-058-059.
SC...NONE.

&&

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



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