Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 202117
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
417 PM EST SAT DEC 20 2014

.SYNOPSIS...
LOW LEVEL MOISTURE WILL LINGER ATOP A WEDGE OF HIGH PRESSURE...AS A
SERIES OF WEAK WAVES TRACK BY TO OUR SOUTH TONIGHT THROUGH MONDAY.
DEEPER MOISTURE ARRIVES ON TUESDAY AHEAD OF A SHARP COLD FRONT. THE
COLD FRONT WILL CROSS THE AREA FROM THE WEST ON WEDNESDAY. COLD AND
WINDY CONDITIONS WILL SET UP IN THE MOUNTAINS THROUGH THURSDAY...
WITH DRIER CONDITIONS EXPECTED EAST OF THE MOUNTAINS.

&&

.NEAR TERM /THROUGH SUNDAY/...
400 PM UPDATE...THE WINDOW FOR SKIES TO BEGIN CLEARING BEFORE SUNSET
IS CLOSING...WITH LLVL MOISTURE HOLDING STRONG DESPITE MINIMAL
UPGLIDE ATOP THE WEDGE. STRATUS DECK IS BREAKING UP A LITTLE BIT
OVER THE CENTRAL TENN VALLEY...BUT IT DOES NOT LOOK LIKELY SUCH
EROSION WILL BE ABLE TO OCCUR THIS FAR EAST. SUBSIDENCE IN THE WAKE
OF THE SHORTWAVE IS APPARENTLY JUST TOO WEAK TO REALLY DRIVE MUCH
CLEARING. WILL INCREASE SKY COVER INTO EVENING. AS FAR AS POP...NO
RETURNS SEEN ON RADAR OR PCPN ON SFC OBS OVER THE UPSTATE SO I WILL
LET THOSE POPS TRAIL OFF. WILL CONTINUE TO ADVERTISE THE DRIZZLE
NEAR THE BLUE RIDGE TONIGHT.

AS OF EARLY SAT AFTN...MODEL SOUNDINGS AND TIME HEIGHTS INDICATE
THAT LOW LEVEL FLOW WILL REMAIN MOSTLY NE-E THROUGH SUNDAY AS WEAK
CAD CONDITIONS CONTINUE. BOUNDARY LAYER ALSO IS FORECAST TO REMAIN
MOIST. HENCE...EXPECT CLOUDS TO STUBBORNLY HANG IN. ALSO AS THE
BOUNDARY LAYER COOLS OVERNIGHT AND UPPER LEVELS DRY... EXPECT
WIDESPREAD FOG TO DEVELOP. RIGHT NOW IT DOES NOT LOOK LIKE VSBYS
WILL LOWER ENOUGH TO WARRANT AN ADVISORY...BUT THIS WILL BE
REACCESSED THROUGH THE EVENING FORECAST UPDATES. A WEAK UPSLOPE
COMPONENT INTO THE BLUE RIDGE MAY PRODUCE PATCHY DRIZZLE THERE
OVERNIGHT. SOME OF THE HIGHER EVELATIONS COULD COOL ENOUGH FOR SOME
FREEZING DRIZZLE...BUT AGAIN NOT WIDESPREAD ENOUGH FOR ANY ADVISORY.

ON SUNDAY...LITTLE CHANGE IS EXPECTED AS WEAK CAD PERSISTS. SUNDAY
SHOULD BE A MOSTLY CLOUDY DAY WITH TEMPS PERHAPS RECOVERING A
CATEGORY ABOVE TODAY AS CLOUDS THIN SOME DURING THE AFTERNOON.
HOWEVER...MAX TEMPS WILL BE BELOW CLIMO OUTSIDE OF THE MOUNTAINS.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 200 PM EST SAT...SUN NIGHT THRU MONDAY NIGHT...A SOUTHWESTERLY
UPPER DIFFLUENT FLOW REGIME WILL SET UP ACROSS THE REGION BY MON
NIGHT AS A SOUTHERN STREAM UPPER SHORTWAVE APPROACHES FROM THE SW
AND A WEAK UPPER RIDGE AXIS PUSHES OFF THE EAST COAST. AHEAD OF THIS
UPPER FEATURE...BEST 290K ISENTROPIC LIFT WILL OCCUR BETWEEN 00Z AND
12Z MON. THE UPPER WAVE IS FORECAST TO LIFT NE ACROSS THE CWA
BETWEEN 12Z AND 18Z MON...OFF THE NC/VA COAST BY 00Z TUE. AT THE
SURFACE...COLD AIR DAMMING WEDGE WILL PERSIST ACROSS THE REGION AS
1030MB HIGH REMAINS CENTERED OVER THE NE STATES. MEANWHILE...A
CYCLOGENESIS WILL TAKE PLACE JUST OFF THE SE COAST ON
MONDAY...OVERSPREADING DEEP MOISTURE FROM THE SE. THE COMBINATION OF
THE BEST 290K ISENTROPIC LIFT AND DEEP LAYER MOISTURE ADVECTION WILL
SUPPORT LIKELY POPS OVER THE PIEDMONT AND SOLID CHANCE POPS IN THE
MTN ZONES LATE SUN NIGHT INTO MON MORNING. GIVEN ABOVE FREEZING
SURFACE TEMPS AND WARM NOSE ALOFT...FROZEN PRECIP IS NOT EXPECTED AT
THIS TIME. POPS RAMP DOWN TO THE CHANCE RANGE THRU MON AFTERNOON AS
THE LOW PULLS FARTHER NE AWAY AND THE UPPER FORCING EJECTS TO THE
NE. MON NIGHT AND TUE...A RESIDUAL CAD AND MOIST SWLY FLOW ALOFT
OVER THE AREA WILL KEEP LOW END CHANCE POPS OVER THE PIEDMONT WITH
SLIGHT CHANCE POPS OVER THE MTNS ZONES. WITH ONGOING PRECIP AND
CAD...TEMPS WILL REMAIN 3-7 DEGREES BELOW NORMAL.

TUESDAY...A RATHER STRONG SSWLY UPPER DIFFLENT WILL DEVEP OVER THE
SE AS A HIGH-AMPLITUDE UPPER TROUGH WILL DIG INTO THE WESTERN GULF
STATES. AT THE SURFACE...A LOW OVER THE GREAT PLAINS WILL LIFT NE
INTO THE WESTERN GREAT LAKES REGION...PUSHING AN ASSOCIATED SHARP
SURFACE COLD FRONT INTO THE MISSISSIPPI VALLEY BY 00Z WED.
MEANWHILE...THE HIGH CENTERED OVER THE NE STATES WILL SHIFT
OFFSHORE...WITH NE FLOW BECOMING EASTERLY OVER THE FORECAST AREA BY
TUE AFTERNOON IN ITS WAKE. POPS THEN RAMP UP TO CATEGORICAL OVER THE
ESCARPMENT OF THE BLUE RIDGE AND LIKELY RANGE ELSEWHERE THRU LATE
TUE AFTERNOON/EVENING AS STRONG UPPER SSWLY DIFFLUENT FLOW ALOFT
DEVELOPS WHILE ATLANTIC MOISTURE ADVECTION INCREASES IN EASTERLY
FLOW REGIME. TEMPS WILL WARM INTO NEAR NORMAL RANGE ON TUE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 130 PM SATURDAY...A DEEP UPPER TROUGH AND ASSOCIATED CYCLONE
WILL MOVE ACROSS THE EASTERN CONUS EARLY IN THE MEDIUM RANGE
PERIOD...LIKELY RESULTING IN WIDESPREAD RAIN ACROSS THE FORECAST
AREA EARLY ON CHRISTMAS EVE. QPF WILL BE THE PRIMARY CHALLENGE
SURROUNDING THIS PERIOD OF THE FORECAST OVER THE NEXT COUPLE OF
DAYS...AS THERE APPEARS TO BE A GOOD CASE FOR A CONSIDERABLE AMOUNT
OF GULF COAST CONVECTION POTENTIALLY INTERRUPTING TRANSPORT OF THE
RICHEST GULF MOISTURE INTO THE AREA. NEVERTHELESS...MOST AREAS
SHOULD SEE RAIN LATE TUE NIGHT/EARLY WED...AND HIGH-END LIKELY TO
CATEGORICAL POPS WILL BE CARRIED DURING THIS TIME. ANOTHER
POTENTIALLY PROBLEMATIC FACET TO THE FORECAST IS THE POTENTIAL FOR
CONVECTION ACROSS OUR AREA WITHIN HIGH SHEAR/LOW CAPE REGIME WED
MORNING...AS STRONG/DEEP MERIDIONALLY-ORIENTED FORCING ACCOMPANIES
THE COLD FRONT INTO THE AREA. THE LATEST GFS HAS BECOME A LITTLE
MORE PRONOUNCED WITH ITS SURFACE-BASED INSTABILITY DURING THIS
TIME...AND A SLIGHT CHANCE FOR THUNDER WILL BE CARRIED...MAINLY
ACROSS THE PIEDMONT.

ALTHOUGH A BRIEF NORTHWEST FLOW SNOW EVENT MAY UNFOLD LATER WED INTO
WED NIGHT...THE LOW LEVEL FLOW REMAINS QUITE BACKED AS SNOW LEVELS
START TO FALL...OWING TO A CONSIDERABLE AMOUNT OF UPPER LEVEL SHORT
WAVE ENERGY REMAINING UPSTREAM OF THE REGION. MEANWHILE...THE UPPER
TROUGH AXIS IS EXPECTED TO LIFT QUICKLY OFF THE COAST INTO EARLY
THURSDAY...SO MOISTURE DOES NOT LINGER FOR VERY LONG ONCE THE FLOW
FINALLY TURNS NORTHWEST. THIS SPELLS A LOW IMPACT EVENT.

CHRISTMAS WILL BE UNSEASONABLY COOL BUT DRY UNDER ANOMALOUSLY LOW
HEIGHTS...BUT TEMPS WILL BEGIN TO MODERATE BY FRIDAY AS HEIGHTS RISE
OVER THE EAST IN RESPONSE TO DEPARTING TROUGH...AND A NEW ROUND OF
HEIGHT FALLS ACROSS THE WESTERN CONUS. THIS AREA OF HEIGHT FALLS AND
ATTENDANT FRONTAL ZONE MAY BRING THE NEXT CHANCE FOR PRECIP TO THE
AREA BY DAY 7.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
AT KCLT...MAIN AREA OF PRECIP HAS MOVED EAST OF THE AIRFIELD ALONG
WITH VORT MAX THAT TRIGGERED IT. IN ITS WAKE...A MOIST BOUNDARY
LAYER WILL REMAIN AS LIGHT NE FLOW CONTINUES. EXPECT CIGS TO HOVER
AROUND 025 AND THEN SLOWLY LOWER OVERNIGHT AS BOUBNDARY LAYER COOLS.
PLAYED IT CONSERVATIVE FOR NOW AND JUST LOWERED CIGS TO 015
OVERNIGHT AND VSBY TO 4SM IN BR. WOULD NOT BE SURPRISED IF IT WENT A
BIT LOWER THAN THAT. ONLY A SLOW IMPROVEMENT AFTER SUNRISE SUNDAY.

ELSEWHERE...FOR THE SC TAF SITES LOW MVFR TO IFR CONDITIONS ARE
EXPECTED TO PREVAIL DUE TO THE VERY MOIST BOUNDARY LAYER AND WINDS
REMAINING LIGHT E-NE. DRIZZLE SHOULD GRADUALLY END BY 00Z...BUT THEN
VSBYS WILL GRADUALLY LOWER TO AT LEAST 3SM IN BR BY 12Z.

OUTLOOK...LINGERING LOW LEVEL MOISTURE IS LIKELY TO KEEP LOW STRATUS
AND NIGHT TIME FOG AROUND THRU MONDAY...WITH SOME IMPROVEMENT DURING
THE DAYLIGHT HOURS. A COLD FRONT WILL APPROACH ON TUESDAY FROM THE
WEST AND MOVE THROUGH ON WED. WIDESPREAD SHOWERS WITH RESTRICTIONS
SHOULD ARRIVE TUESDAY AFTERNOON AND WILL CONTINUE UNTIL THE FRONT
CLEARS THE AREA LATE WEDNESDAY.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-18Z
KCLT       MED   75%     HIGH  83%     HIGH  91%     HIGH  90%
KGSP       HIGH  94%     HIGH  94%     HIGH 100%     HIGH  86%
KAVL       HIGH  94%     HIGH  88%     HIGH  83%     HIGH  96%
KHKY       MED   75%     HIGH  94%     HIGH  86%     HIGH  96%
KGMU       HIGH  94%     HIGH  94%     HIGH 100%     HIGH  86%
KAND       HIGH  97%     HIGH  80%     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...NONE.
SC...NONE.

&&

$$
SYNOPSIS...ARK
NEAR TERM...LG/WIMBERLEY
SHORT TERM...JOH
LONG TERM...JDL
AVIATION...LG/WIMBERLEY



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