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Area Forecast Discussion

623
FXUS62 KGSP 110549
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1249 AM EST THU FEB 11 2016

.SYNOPSIS...
CANADIAN HIGH PRESSURE WILL BUILD ACROSS THE REGION TODAY AND REMAIN
THROUGH THE WEEKEND. HOWEVER...DEVELOPING COASTAL SYSTEMS WILL BRING
CHANCES OF PRECIPITATION FRIDAY AND THEN AGAIN EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1230 AM THU...RADAR RETURNS FROM UPSLOPE SNOW ON THE TENN
BORDER ARE DIMINISHING AS MORE BROKEN CLOUDINESS MOVES OVER EAST
TENN ON GOES FOG PRODUCT. MOST OF THE CAM GUIDANCE INDICATES A
SLOW DECLINE IN HOURLY QPF THRU DAYBREAK. SNOW SHOWERS SHOULD
BECOME LESS FREQUENT OVER THE NEXT FEW HOURS...SO THE LOW POP WE
HAVE LOOKS GOOD. REVISED SKY/WIND THRU TODAY/TONIGHT...WITH NO
SIGNIFICANT CHANGES. THINKING A STRATUS DECK IS LIKELY TO DEVELOP
BEFORE MIDNIGHT TONIGHT OVER THE UPSTATE IN AREA OF WARM UPGLIDE
AHEAD OF WEAK CLIPPER-LIKE SHORTWAVE MOVING TOWARD THE CAROLINAS.

AS OF 230 PM EST WED...THE WX PATTERN ACROSS NORTHEAST GA AND THE
WESTERN CAROLINAS IS FINALLY STARTING TO MODIFY AS THE PARENT
LONGWAVE UPPER TROF AXIS SHIFTS EAST THIS AFTERNOON ALLOWING
FOR THE EVENTUAL DEGRADATION OF THE PROLONGED NWFS ACROSS THE
NC/GA MTNS INTO LATE EVENING.  MEANWHILE...ANOTHER FAST MOVING
CLIPPER TYPE DISTURBANCE WILL DIVE DOWN THE DESCENDING BRANCH OF
THE LONGWAVE TROF INTO THE OH/TN VALLEYS TONIGHT.  MODELS DONT
SEEM TO BE TOO THRILLED ABOUT ADDITIONAL PRECIPITATION...WHICH
WOULD FALL AS SNOW ACROSS THE WESTERN TIER OF THE FCST AREA.
HOWEVER...WOUDLDNT BE SHOCKED IF A FEW WEAK SN SHOWERS DID RAMP
BACK UP ALONG THE TN LINE...WITH FLURRIES POSSIBLE ACROSS THE SW
NC AND NORTHEAST GA MTNS AS WELL AS PORTIONS OF THE NW UPSTATE.
NOT EXPECTING ANY ACCUMULATION OUTSIDE OF THE HIGH TERRAIN WHERE
ONLY AN ADDITIONAL HALF TO ONE INCH IS FCST.  BRISK WNW FLOW
POSSIBLY GUSTING UPWARDS OF 40-50MPH FOR LOCALES ABOVE 3-3.5KFT
WILL COMBINE WITH OVERNIGHT LOWS IN THE TEENS TO SINGLE DIGITS TO
YIELD ANOTHER EVENING OF BITTERLY COLD WIND CHILL VALUES...SOME AS
LOW AS -5 TO -10 DEGREES.  THUS...OTHER THAN EXPIRATION OF CURRENT
WWY FOR THE TN LINE ZONES AT 7PM...NOT EXPECTING ANY CHANGES TO
CURRENT WSW AS WCY SHOULD VERIFY WITHOUT ISSUE.

OTHERWISE...WEAK/MODERATE DOWNSLOPING FLOW HAS ALLOWED FOR MOSTLY
SUNNY SKIES TO PREVAIL OVER THE PIEDMONT REGIONS WITH THE EXCEPTION
OF A FEW SCT STRATOCU NEAR/ALONG THE I77 CORRIDOR WHERE SOUNDINGS
INDICATE THE BEST OVERALL LLV MOISTURE.  STILL EXPECTING SUCH TO
ERODE AROUND SUNSET HOWEVER TO BE REPLACED WITH A FEW MID/HIGH
CIRRUS ASSOCIATED WITH THE ABOVE MENTIONED H5 IMPULSE THROUGH
AT LEAST THE EARLY/MID MORNING HOURS.  LOWS TONIGHT WILL FALL
INTO THE LOWER/MID 20S...WITH UPPER 20S LIKELY OVER THE LAKELANDS
REGION...WHICH WILL BE A TAD WARMER THAN YESTERDAY MORNING LIKELY
BECAUSE OF SAID CIRRUS.  THURSDAY LOOKS TO BE A RATHER NICE AND
PLEASANT DAY ACROSS THE REGION AS MOSTLY SUNNY SKIES DOMINATE
AMIDST BACKED WSW FLOW AT THE SURFACE.  THEREFORE GUIDANCE FAVORS
HIGHS IN THE MID 40S ACROSS THE PIEDMONT AND MID/UPPER 30S FOR THE
MAJORITY OF THE MTNS...WITH 20S FAVORED AT THE HIGHEST ELEVATIONS.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
AS OF 215 PM WEDNESDAY...RISING HEIGHTS AND INCREASING CLOUDS NEAR
THE EXIT REGION OF THE NEXT UPPER JET MAX/CHANNELED SHORT WAVE
TROUGH WILL RESULT IN SOMEWHAT OF A TEMPERATURE MODERATION THU
NIGHT...ALTHOUGH MINS ARE STILL EXPECTED TO BE AS MUCH AS 10 DEGREES
BELOW CLIMO. NUMERICAL GUIDANCE IS COMING INTO BETTER AGREEMENT
REGARDING THE INTENSITY AND LOCATION OF SURFACE DEVELOPMENT
ASSOCIATED WITH THE SHORT WAVE ACROSS THE SOUTHEAST FRIDAY...WITH A
WEAK SURFACE WAVE INDICATED ACROSS SOUTHERN GA BY AROUND 06Z
FRIDAY...PUSHING OFF THE COAST AND DEEPENING WELL OFF SHORE DURING
THE DAY. AS A RESULT...GUIDANCE BY AND LARGE KEEPS THE CWA DRY
THROUGH MUCH OF THE DAY...WITH THE NAM AND THE ECMWF SKIRTING THE
SOUTHEAST PART OF THE CWA WITH SOME VERY LIGHT QPF. THUS...SLIGHT
CHANCE POPS WILL BE RETAINED. FOR THE TIME BEING...THE P-TYPE WILL
BE CODED AS RAIN IN THOSE ZONES...BUT SOME FLURRIES COULD MIX
IN...OR BE THE PRIMARY P-TYPE IF PRECIP DEVELOPS EARLY ENOUGH IN THE
DAY. THERE COULD ALSO BE FLURRIES AND/OR SPRINKLES FALLING FROM
MID-LEVEL CLOUD COVER ACROSS THE REMAINDER OF THE CWA FRIDAY.

OTHERWISE...AS STRONG COLD ADVECTION AND MOISTURE SURGE INTO THE
SOUTHERN APPALACHIANS...NW FLOW SNOW VERSION 2.0 WILL WIND UP
BRIEFLY FRI NIGHT. THE INGREDIENTS LOOK TO BE PRETTY DECENT FOR
ADDITIONAL ACCUMS...AT LEAST FOR A FEW HOURS...WITH VERY STRONG NW
LOW LEVEL FLOW 40-50 KTS AT H8...MOISTURE DEPTH EXTENDING ABOVE
H8...AND TEMPS AS COLD AS -10C IN THE MOIST LAYER. SOME LIGHT ACCUMS
WILL THEREFORE BE LIKELY IN THE LOCATIONS TYPICALLY IMPACTED BY NW
FLOW SNOW SHOWERS...BUT DUE TO THE SHORT DURATION OF THE EVENT THIS
MAY PROVE TO BE SUB-ADVISORY IN NATURE.

THE REMAINDER OF THE SHORT TERM WILL BE CHARACTERIZED BY VERY COLD
AND DRY CONDITIONS...AS SPRAWLING 1040+ ARCTIC HIGH PRESSURE BUILDS
INTO THE REGION. MAX TEMPS WILL BE 15-20 DEGREES BELOW CLIMO ON
SATURDAY. ADVISORY LEVEL WIND CHILL VALUES WILL BE POSSIBLE ACROSS
THE MTNS FRI NIGHT AND SATURDAY...AS HAS BEEN MENTIONED IN THE HWO
FOR A COUPLE OF DAYS NOW. THE POTENTIAL FOR A COLD WAVE WILL ALSO BE
MENTIONED ACROSS THE PIEDMONT AND FOOTHILLS.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 235 PM WEDNESDAY...NOT MUCH HAS CHANGED RELATIVE TO FORECAST
CONFIDENCE...WHICH STARTS OUT HIGH AS THE FCST IS DRY FOR
SUNDAY...BUT RAPIDLY GOES DOWNHILL AS THE NEXT SYSTEM APPROACHES
SUNDAY NIGHT.

THE MAIN PROBLEM IS THAT THE DETERMINISTIC GUIDANCE OUT BEYOND 00Z
MONDAY HAS SIGNIFICANT DIFFERENCES WITH REGARD TO HOW DEEP/STRONG
THE NEXT SYSTEM WILL BE AS IT COMES OUT OF THE PLAINS AND ACROSS THE
TN VALLEY/SOUTHEAST ON MONDAY AND INTO TUESDAY. THE ECMWF DIGS THE
UPPER TROF THE MOST AND CLOSES OFF A LOW AT 500 MB. WITH ITS
STRONGER SYSTEM...THERE IS MORE OF A CHANCE FOR STRONG WARM
ADVECTION OUT AHEAD OF THE SYSTEM TO PULL UP CONSIDERABLY MORE WARM
AIR...AND MOISTURE...ACROSS THE CAROLINAS MONDAY NIGHT INTO TUESDAY.
THE ECMWF MIGHT EVEN SUGGEST A HEAVY RAIN/FLOODING THREAT ACROSS THE
PIEDMONT IF IT WORKS OUT. MEANWHILE...THE OPERATIONAL GFS IS MUCH
LESS AMPLIFIED...AS IS THE CANADIAN. THE GFS HAS ONLY A WEAK SURFACE
LOW MOVING ALONG AN OLD FRONT ACROSS THE SOUTHEAST. WHILE THIS LOOKS
LESS IMPRESSIVE DYNAMICALLY...IT COULD ACTUALLY BE MORE OF A
PROBLEM...AS THE WEAKER SYSTEM WOULD HAVE LESS WARM ADVECTION ALOFT
AND WOULD KEEP A COLDER TEMP PROFILE ACROSS THE REGION. THE GFS
PATTERN IS ACTUALLY A FAVORABLE ONE FOR HEAVY SNOW ACROSS THE
WESTERN CAROLINAS AS COLD ENOUGH AIR WOULD STAY IN PLACE WHILE
ISENTROPIC LIFT AND LOW/MID LEVEL FRONTOGENESIS PROVIDE THE FORCING.

CONFIDENCE IS HIGHEST IN PRECIP ONSET AND PROBABILITY. THINK THAT
PRECIP SHOULD BEGIN TO DEVELOP FROM THE WEST AFTER 00Z MONDAY...AND
WILL SPREAD EAST ACROSS THE MTNS OVERNIGHT...AND THEN E OF THE BLUE
RIDGE MONDAY MORNING. THE PREPONDERANCE OF THE GUIDANCE SUGGESTS
THAT WE SHOULD RAISE THE PRECIP PROBABILITY INTO THE LIKELY RANGE
FROM WEST TO EAST MONDAY AFTERNOON AND THEN KEEP IT LIKELY MONDAY
NIGHT. THAT BEING SAID...CONFIDENCE IS MODERATE THAT WE WILL HAVE A
PRECIP-TYPE PROBLEM AT ONSET MONDAY EVEN IF THE ECMWF IS CORRECT
WITH ITS MORE AMPLIFIED PATTERN AND EVENTUAL CHANGEOVER TO RAIN. IT
SHOULD BE NOTED THAT WE WILL BEGIN THE EVENT WITH A COLD AIR MASS IN
PLACE...AND THAT SHOULD HELP ELEVATE THE WINTRY PRECIP TYPE THREAT.
THIS MAY CAUSE PROBLEMS ACROSS THE REGION THAT WILL HAVE TO BE
ADDRESSED IN LATER ISSUANCES. AT LEAST THE IMPACT MIGHT BE LESSENED
BY THE PRESIDENTS DAY HOLIDAY. WILL MENTION THIS IN THE HWO. WE ARE
LEAST CONFIDENT IN THE PRECIP TYPE FOR MONDAY NIGHT...WHICH IS KEY
TO WHETHER OR NOT WE HAVE A WINTER STORM OR JUST A NUISANCE EVENT.
THE GEFS PLUME DIAGRAMS ARE MOST INDICATIVE OF THE PROBLEM...WITH
QPF GREATER THAN 1.5 INCHES LIQUID IN MANY ENSEMBLE MEMBERS...BUT
OTHER ENSEMBLE MEMBERS WITH MERE HUNDREDTHS. EVEN THOUGH UNCERTAINTY
IS HIGH...IT SEEMS MOST LIKELY THAT PRECIP WILL GRADUALLY CHANGE
OVER TO RAIN ON TUESDAY MORNING. STAY TUNED.

THE REST OF THE MEDIUM RANGE LOOKS RELATIVELY BENIGN. THERE WILL
LIKELY BE A PERIOD OF NW FLOW SNOW ON THE BACK SIDE OF THE SYSTEM
LATE TUESDAY AND TUESDAY NIGHT. KEPT WEDNESDAY DRY AS HIGH PRESSURE
MOVES ACROSS THE SOUTHEAST AND THE NEXT NRN STREAM CLIPPER STAYS
WELL TO THE N.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AT KCLT...VFR THRU THE TAF PERIOD. UPPER JET OVER THE REGION WILL
BRING A FEW HIGH CLOUDS THRU TODAY. EARLY ON SOME MIDLEVEL CLOUDS
WILL ALSO BE SEEN OVER THE MTNS...BUT THESE WILL DISSIPATE THIS
MORNING. AS LOW PRESSURE MOVES OFF THE EAST COAST AND HIGH PRESSURE
REPLACES IT FROM THE NW...INITIALLY WESTERLY WINDS WILL BACK TO SW
DURING THE DAYTIME...THEN VEER AROUND TO NE TONIGHT AT ALL SITES
EXCEPT KAVL. A LOWER VFR DECK IS EXPECTED TO DEVELOP TONIGHT AS
WARM ADVECTION DEVELOPS AHEAD OF A SHORTWAVE MOVING OUT OF THE
MID-MISSISSIPPI VALLEY.

OUTLOOK...A LOW PRESSURE SYSTEM CENTERED NEAR THE MOUTH OF THE
SAVANNAH RIVER MAY SPREAD RESTRICTIVE CEILINGS OVER THE PIEDMONT
ON FRIDAY. AN ARCTIC AIR MASS WILL BUILD OVER THE REGION THIS
WEEKEND...RESULTING IN UPSLOPE CLOUDS ALONG THE WEST SIDE OF THE
APPALACHIANS. TEMPERATURES WELL BELOW NORMAL ARE FORECAST FOR
SATURDAY AND SUNDAY.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     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 SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WIND CHILL ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ033-
     048>052-058-059-062>064.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...NED/WIMBERLEY
SHORT TERM...JDL
LONG TERM...PM
AVIATION...WIMBERLEY



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