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Area Forecast Discussion

817
FXUS62 KGSP 040838
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
338 AM EST WED MAR 4 2015

.SYNOPSIS...
VERY WARM AND MOIST AIR WILL RETURN TO THE AREA TODAY AHEAD OF AN
APPROACHING COLD FRONT. THIS FRONT IS FORECAST TO PASS THROUGH THE
AREA ON THURSDAY...WITH COOL AND DRY HIGH PRESSURE RETURNING FOR
FRIDAY AND INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
DENSE FOG IS SLOWLY BUT SURELY EXPANDING ACROSS THE PIEDMONT THIS
MORNING WITHIN WARM/MOIST ADVECTIVE/DECAYING WEDGE REGIME. AS
SUCH...THE DENSE FOG ADVISORY APPEARS TO BE VERY WELL PLACED...AND
WILL REMAIN IN EFFECT UNTIL 15Z.

THE BULK OF SHOWER ACTIVITY CONTINUES TO DEVELOP ACROSS THE GREAT
TENN VALLEY AND CUMBERLAND PLATEAU AREAS THIS MORNING...LIFTING
PRIMARILY WEST OF THE APPALACHIANS WITHIN DEEP SW FLOW ALOFT. THIS
PROBABLY ISN/T GOING TO CHANGE A WHOLE LET OVER THE NEXT 12-18
HOURS...AS THIS IS WHERE THE BETTER FORCING AND MOISTURE PROFILES
WILL REMAIN THROUGH THE DAY...UNDER PERSISTENT DEEP SW FLOW.
STILL...CHANCE POPS APPEAR WARRANTED ALONG THE TENN BORDER THROUGH
THE DAY...WITH 50-60 POPS RESERVED PRIMARILY FOR THE SMOKIES AND
SURROUNDING AREAS...WHICH IS SLIGHTLY MORE ALONG THE TRAJECTORY OF
THE SHOWER GENERATION AREA...AND STANDS THE BEST CHANCE OF SEEING
SHOWERS INITIATE IN RESPONSE TO MECHANICAL LIFT ASSOCIATED WITH THE
SW FLOW.

THE AIR MASS ABOVE THE DRAINING COOL POOL IS VERY WARM...WITH H8
TEMPS OF +10 TO +13 REPORTED ACROSS THE REGION AT 00Z. ONCE THE FOG
AND LOW STRATUS BURN OFF...TEMPS WILL SOAR ACROSS THE AREA...LIKELY
REACHING THE 70S ACROSS MUCH OF THE PIEDMONT THIS AFTERNOON . IN
FACT...IF THE GRUNGE DISSIPATES EARLIER THAN CURRENTLY
ANTICIPATED...EVEN THIS MAY PROVE TO BE TOO COOL...AND WOULD NOT BE
SURPRISED TO SEE EXTREME SOUTHERN PIEDMONT AREAS TOP OUT NEAR 80.

POPS WILL GRADUALLY RAMP UP ACROSS THE MTNS THIS EVENING...AS
COLD/ANAFRONT GRADUALLY BUILDS INTO THE FORECAST AREA. DUE TO THE
ANAFRONT NATURE OF THE BOUNDARY...TIMING OF THE WIND SHIFT INTO THE
AREA WILL DICTATE HOW SOON LIKELY/CATEGORICAL CHANCES FOR RAIN WILL
DEVELOP OVER THE FORECAST AREA...AND THESE THINGS NEVER SEEM TO MOVE
AS FAST AS THE MODELS SUGGEST. THEREFORE...THE HIGHEST POPS HAVE
BEEN DELAYED UNTIL AFTER MIDNIGHT...CATEGORICAL ACROSS THE
MTNS...TAPERING TO HIGH CHANCE/LIKELY ACROSS THE PIEDMONT BY
DAYBREAK THU.

COLD AIR MAY BEGIN FILTERING INTO THE FAR WESTERN MTN VALLEYS BY
DAYBREAK THU...WITH PROFILES EXHIBITING A TREMENDOUS WARM NOSE...AND
FREEZING RAIN BEING THE PRIMARY WINTRY P-TYPE. WHILE IT APPEARS THAT
FREEZING RAIN WILL BE LIKELY AT SOME POINT DURING THIS EVENT ACROSS
THE WESTERN MTN VALLEYS...TIMING OF THE ARRIVAL OF COLD AIR IS STILL
HIGHLY UNCERTAIN...AND SUSPECT DAYBREAK THURSDAY IS THE
EARLIEST THAT THIS WOULD OCCUR. THEREFORE...NO ADVISORIES WERE
ENTERTAINED ON THIS SHIFT.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AT 300 AM EST WEDNESDAY...ON THURSDAY MORNING AN UPPER TROUGH WILL
EXTEND FRONT EASTERN CANADA TO THE SOUTHERN PLAINS...WITH A WELL
DEFINED SHORTWAVE MOVING THROUGH IT OVER THE UPPER MS RIVE VALLEY
AND SOUTHERN PLAINS. THE TROUGH DEAMPLIFIES SOMEWHAT BY
FRIDAY...WHILE AN UPPER LOW CLOSES OFF IN NW MEXICO. THE SHORTWAVE
MOVING THROUGH BECOMES MORE CHANNELED...APPROACHING THE SOUTHERN
APPALACHIANS IN THE MORNING. A SECOND AND MORE ROBUST SHORTWAVE
APPROACHES THE MOUNTAINS LATER IN THE DAY...CROSSING THE MOUNTAINS
BY FRIDAY EVENING...AND MOVING TO THE SOUTHERN EDGE OF OUR AREA LATE
SATURDAY NIGHT.

AT THE SURFACE...ON THURSDAY MORNING A STRONG COLD FRONT WILL BE
LOCATED JUST SE OF OUR AREA...WITH A SURFACE WAVE MOVING ALONG IT
OVER SC. MOISTURE WILL EXTEND WELL BEHIND THE FRONT INTO THE MS
RIVER VALLEY...AND POST FRONTAL PRECIPITATION. THE NAM EVEN SHOWS
SOME INSTABILITY AND SHEAR BEHIND THE BOUNDARY OVER UPSTATE SC AT
MIDDAY. AS THE FRONT MOVES SE DURING THE DAY...COLD ADVECTION WILL
SPREAD OVER THE NC MOUNTAINS. MODEL SOUNDINGS ARE INITIALLY TO WARM
AT THE TOP OF THE MOIST LAYER TO SUPPORT ICE NUCLEATION...AND
FREEZING RAIN IS EXPECTED BY LATE IN THE DAY. DRYING FROM THE TOP
DOWN WILL RAPIDLY LESSEN THE CHANCE OF PRECIPITATION IN THE
EVENING...BUT RAPID COOLING WILL BRING THE TOP OF THE MOIST LAYER TO
THE POINT OF ICE NUCLEATION...SUPPORTING A CHANGEOVER FROM FREEZING
RAIN TO SNOW BEFORE PRECIPITATION ENDS LATE THURSDAY NIGHT. FRIDAY
AND FRIDAY NIGHT FEATURE DRY AND COOL CONDITIONS.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AT 300 AM EST WEDNESDAY...ON SATURDAY MORNING A WELL AMPLIFIED UPPER
TROUGH WILL EXTEND FROM NE CANADA TO THE SOUTHERN APPALACHIANS...
WHILE A CLOSED UPPER LOW WILL BE OVER NW MEXICO. THE TROUGH LOSES
SOME AMPLITUDE BY SUNDAY...WHILE THE UPPER LOW FILLS AND CROSSES
NORTHERN MEXICO. THE REMAINS OF THE UPPER LOW CROSS THE SOUTHERN
PLAINS ON MONDAY...RESULTING IN LOW AMPLITUDE RIDGING OVER THE
SOUTHERN APPALACHIANS...WHILE NORTHERN STREAM FLOW BECOMES ZONAL. ON
TUESDAY THE ECMWF AND GFS DIVERGE...WITH THE FORMER HAVING ZONAL
FLOW OVER THE SE...AND THE LATER MAINTAINING A TROUGH IN THE LOWER
MS RIVER VALLEY AND A RIDGE TO THE EAST.

AT THE SURFACE...ON SATURDAY DRY HIGH PRESSURE WILL EXTEND FROM
CHESAPEAKE BAY TO TX...WHILE A STATIONARY FRONT WILL EXTEND FROM S FL
TO NEAR THE YUCATAN PENINSULA. MOISTURE AND PRECIPITATION ASSOCIATED
WITH THIS FRONT IS EXPECTED TO REMAIN SOUTH OF OUR AREA. A DRY COLD
FRONT RAPIDLY CROSSES OUR AREA SATURDAY NIGHT...REACHING THE GA
COAST BY SUNDAY MORNING...WHILE THE STATIONARY FRONT REMAIN OVER S
FL. ON MONDAY A SURFACE WAVE DEVELOPS ON THE STATIONARY FRONT IN THE
WESTERN GULF OF MEXICO. MOISTURE IS EXPECTED TO SPREAD FARTHER NORTH
OVER THE FRONT IN FL...PERHAPS SUPPORTING SMALL POPS AS FAR N AS OUR
AREA. BY TUESDAY THE SURFACE WAVE REACHES THE SC COAST...WITH
PRECIPITATION IN ISENTROPIC UPGLIDE EXTENDING BACK THE THE SOUTHERN
APPALACHIANS.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT AND ELSEWHERE (EXCEPT KAVL)...LIFR CONDITIONS AND LIGHT
SOUTH WINDS WILL PERSIST THROUGH THE OVERNIGHT AND MUCH OF THE
MORNING...WITH PERIODS OF VLIFR BECOMING MORE LIKELY TOWARD
DAYBREAK. VERY STRONG WINDS ABOVE ABOUT 3000 FEET WILL RESULT IN
LLWS LATER THIS MORNING AT ALL TERMINALS. OTHERWISE...COOL WEDGE IS
EXPECTED TO COMPLETELY SCOUR ACROSS THE REGION BY AFTERNOON...WITH
VFR CONDITIONS EXPECTED. AS THIS OCCURS...WINDS WILL BECOME MORE
SW...AND INCREASE TO 10-15 KTS...WITH GUSTS IN THE LOWER 20S LIKELY
DURING THE AFTERNOON. A STRAY SHOWER OR TWO WILL BE POSSIBLE AT JUST
ABOUT ANYTIME DURING THE PERIOD...BUT THE PROBABILITY APPEARS TOO
LOW FOR A TAF MENTION ATTM.

AT KAVL...THE BULK OF THE OVERNIGHT SHOULD SEE CONDITIONS REMAINING
NO WORSE THAN MVFR. HOWEVER...DO EXPECT PERIODS OF IFR CIGS TOWARD
DAYBREAK IN THE INCREASING MOIST SOUTHERLY FLOW. A STRAY SHOWER OR
TWO WILL BE POSSIBLE AT JUST ABOUT ANYTIME OVER THE NEXT 18 HOURS OR
SO...BUT THE PROBABILITY APPEARS TOO LOW FOR A TAF MENTION...UNTIL
WED EVENING...WHEN CHANCES FOR RAIN AND FLT RESTRICTIONS WILL
INCREASE AS A COLD FRONT APPROACHES FROM THE TENN VALLEY.

OUTLOOK...A COLD FRONT WILL MOVE SLOWLY THROUGH THE REGION WEDNESDAY
NIGHT THROUGH THURSDAY...BRINGING CHANCES FOR HEAVIER RAINFALL AND
LOW CIGS/VSBYS TO THE AREA. VFR CONDITIONS ARE EXPECTED TO RETURN
FOR FRIDAY THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     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...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR GAZ010-017-
     018-026-028-029.
NC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ035>037-
     056-057-068>072-082-502-504-506-508-510.
SC...DENSE FOG ADVISORY UNTIL 10 AM EST THIS MORNING FOR SCZ001>014-
     019.

&&

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



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