Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 012100
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
500 PM EDT WED APR 1 2015

.SYNOPSIS...
HIGH PRESSURE WILL MOVE EAST OF THE AREA THURSDAY AS MOIST SOUTHERLY
FLOW RETURNS. A COLD FRONT WILL PUSH THROUGH NORTHEAST GEORGIA AND
THE WESTERN CAROLINAS ON FRIDAY EVENING AHEAD OF DRIER HIGH PRESSURE
FOR THE WEEKEND. MOISTURE WILL RETURN FOR THE START OF THE NEXT WORK
WEEK AS SOUTHERLY FLOW INCREASES PRECIPITATION CHANCES.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 445 PM EDT...RIDGETOP WINDS WERE INCREASED SLIGHTLY FOR THE
OVERNIGHT HOURS AS SLIGHTLY BETTER 850 MB FLOW DEVELOPS LATE.
OTHERWISE...THE CURRENT FORECAST REMAINS ON TRACK. CLOUDS WILL
GRADUALLY INCREASE OVER WESTERN SECTIONS AS FLOW TURNS SE AND
MOISTURE ADVECTION DEVELOPS. A PROGRESSIVE UPPER PATTERN WILL ALLOW
FOR THE RIDGE OVER THE REGION LATE TODAY TO MOVE OFF THE EAST COAST
TONIGHT. A SHORT WAVE WILL THEN MOVE EAST ACROSS THE AREA ON
THURSDAY. AT THE SAME TIME...THE RETURN FLOW ON THE WEST SIDE OF THE
SURFACE HIGH MOVING OUT INTO THE ATLANTIC WILL PROMOTE MOISTURE
ADVECTION...ESPECIALLY IN THE LOWER LEVELS. THE COMBINATION OF WEAK
PVA...ISENTROPIC LIFT AND UPSLOPE FLOW WILL PRODUCE AT LEAST
SCATTERED SHOWERS DURING THURSDAY...MOST NUMEROUS ALONG THE WESTERN
ESCARPMENT. BOTH THE NAM AND GFS HINT AT A WEAK IN SITU TYPE WEDGE
DEVELOPING AS PRECIP BEGINS ON THU. HENCE...NO SBCAPE IS FORECAST
ACROSS THE AREA UNTIL LATE IN THE DAY OVER SOUTHERN SECTIONS OF THE
PIEDMONT. HENCE...ONLY THE SOUTHERN PORTIONS OF THE PIEDMONT WILL
GET A MENTION OF THUNDER.

IN REGARD TO TEMPS...IT WILL BE MILD OVERNIGHT OVER WESTERN SECTIONS
AS CLOUDS INCREASE. MINIMUM TEMPS OVER EASTERN AREAS WILL BE COOLER
AND CLOSER TO CLIMO AS RADIATIONAL COOLING WILL OCCUR AT LEAST UNTIL
MIDNIGHT OR SO. HEDGED MAX TEMPS ON THURSDAY TOWARD THE COOLER GFS
GUIDANCE WHICH KEEPS TEMPS BELOW CLIMO EXCEPT FOR THE SOUTHERN
PIEDMONT.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 245 PM EDT WEDNESDAY...SHORT TERM BEGINS WITH SHORTWAVE
PUSHING THROUGH THE SOUTHEAST AND GRADUALLY DAMPING INTO THE OVERALL
LONGWAVE PATTERN. FINGER OF STABILITY ALONG THE LEE OF THE
APPALACHIANS REMAINS IN PLACE AT THE BEGINNING OF THE PERIOD WITH
BEST THUNDER CHANCES IN THE SOUTHERN AND SOUTHWEST PORTIONS OF THE
FORECAST AREA...DIMINISHING LATE THURSDAY EVENING. NOT ENOUGH DEEP-
LAYER SHEAR TO SUPPORT MUCH OF ANYTHING IN THE WAY OF ORGANIZED
CONVECTION.

EXPECT A BIT OF A BREAK DURING THE DAY ON FRIDAY BEHIND THE
SHORTWAVE. HIGHS ON FRIDAY AFTERNOON SHOULD SOAR BACK WELL ABOVE
SEASONAL NORMALS IN RESPONSE TO INCREASING LOW-LEVEL WAA AHEAD OF
THE NEXT FRONT TO APPROACH FRIDAY NIGHT INTO EARLY SATURDAY. GFS AND
ECMWF HAVE COME INTO MUCH BETTER AGREEMENT WITH THE PAST COUPLE OF
RUNS AND BESIDES THE POTENTIAL FOR A FEW UPSLOPE SHOWERS EARLY
MORNING FRIDAY...THE MAIN AREA OF PRECIPITATION SHOULD BE PUSHING
INTO THE MOUNTAINS FRIDAY LATE MORNING INTO EARLY AFTERNOON. BEST
AREA OF CONVECTION WILL BE MORE FRIDAY LATE EVENING AND NIGHT WHEN
OF COURSE DIURNAL TRENDS WOULD MINIMIZE CAPE POTENTIAL...BUT EVEN
THE MORE CONSERVATIVE GFS DOES BRING A BAND OF SBCAPE BETWEEN 100-
300 J/KG INTO THE LOWER APPALACHIANS. THE CONCERN IS THAT THIS
INSTABILITY...ALBEIT WEAK...IS COLLOCATED WITH 60+KT 0-6KM SHEAR...
AND 30-40KT 0-1KM SHEAR. SHERB VALUES OVERALL REMAIN BELOW 1 BUT
SREF SHERB PLUME FORECASTS FOR THE AREA DO SHOW AT LEAST SOME SREF
MEMBERS CREEPING ABOVE 1. SPC DAY3 OUTLOOK OVERNIGHT DID INTRODUCE
MARGINAL RISK INTO THE MOUNTAINS SO CANNOT RULE OUT AN ISOLATED
SEVERE STORM OR TWO AT THIS TIME...WILL HAVE TO MONITOR THE FORECAST
EVOLUTION.

ONLY OTHER MINOR ISSUE IS THAT DEPENDING ON TIMING OF FALLING
TEMPERATURES BEHIND THE FRONT...IT IS POSSIBLE THAT SOME OF THE
HIGHEST PEAKS MAY SEE A BRIEF CHANGEOVER TO SNOW EARLY SATURDAY
MORNING. CONFIDENCE NOT PARTICULARLY HIGH WITH THIS AND EVEN IF IT
WERE TO OCCUR NO ACCUMULATIONS WOULD BE EXPECTED.

AFTER THE FRONT PUSHES THROUGH...ALL POPS MOVE OUT OF THE AREA BY
18Z SATURDAY LEAVING THE REST OF THE DAY TO BE PRETTY NICE WITH
TEMPERATURES BELOW SEASONAL NORMALS. THE DRY CONDITIONS CONTINUE
INTO THE EXTENDED.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 300 PM EDT WEDNESDAY...EXTENDED BEGINS WITH TEMPERATURES BELOW
SEASONAL NORMALS AND CLEAR CONDITIONS BEHIND SATURDAY/S FRONT...WITH
SURFACE HIGH PRESSURE IN PLACE AND WEAK NORTHWEST FLOW ALOFT...
LEADING TO A NICE EASTER SUNDAY. PRECIPITATION SPREADS ACROSS THE
MIDSOUTH AND DEEP SOUTH LATE SUNDAY INTO EARLY MONDAY IN RESPONSE TO
A WEAK SHORTWAVE AND ISENTROPIC LIFT ON THE WESTERN PERIPHERY OF THE
SURFACE HIGH THAT BY THIS POINT HAS PUSHED OFF INTO THE ATLANTIC.
STILL SOME QUESTION ABOUT QPF VALUES AS WELL AS HOW WIDESPREAD THE
PRECIPITATION WILL BE...WITH GFS A LITTLE MORE ROBUST ON MONDAY THAN
THE ECMWF...AND HAVE CONTINUED TREND OF GENERALLY LOW CHANCE POPS
ESPECIALLY WEST DURING THE DAY ON MONDAY.

LATE IN THE PERIOD...ANOTHER DEEP TROUGH IN THE ROCKIES PUSHES INTO
THE PLAINS. WEAK RIDGING ALOFT OVER THE GULF COMBINED WITH THE
DEEPENING TROUGH WILL PRODUCE SOUTHWEST FLOW ALOFT ACROSS THE
SOUTHEAST BUT AGAIN SIGNIFICANT UNCERTAINTY REMAINS IN EXACTLY WHERE
THE SUBTROPICAL JET MIGHT SET UP. GFS WANTS TO KEEP A BAND OF
PRECIPITATION ACROSS THE SOUTHEAST WITH THE ASSOCIATED FRONT PUSHING
INTO THE MID-ATLANTIC REGION TUESDAY EVENING WHEREAS THE ECMWF HAS
THE MOIST FETCH A BIT FARTHER NORTH MORE IN THE OHIO VALLEY...WITH
THE FRONT LINGERING ACROSS THE UPPER MIDWEST. WITH THESE DIFFERENCES
AND RESULTING FAIRLY LOW CONFIDENCE...HAVE KEPT TREND OF SLIGHT TO
LOW CHANCE POPS WITH A BIT OF A DIURNAL TREND IN THUNDER POTENTIAL.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
AT KCLT...LOOKS LIKE VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD. HOWEVER...MOISTURE WILL INCREASE ACROSS THE AREA THURSDAY
MORNING AS HIGH PRESSURE MOVES WELL OFF THE COAST AND GULF MOISTURE
ADVECTS INTO THE REGION. LOOKS LIKE DEEPER MOISTURE AND BEST
ISENTROPIC LIFT STAYS WEST OF CLT...SO ONLY LOWERING VFR CEILINGS
ARE ANTICIPATED AFTER 12Z. LIGHT NE WINDS WILL SHIFT TO SE CIRCA
00Z.

ELSEWHERE...VFR CONDITIONS WITH LIGHT WINDS WILL HOLD FOR THE
OVERNIGHT. DEEPENING MOISTURE AND ISENTROPIC LIFT WILL DEVELOP CIRCA
12Z WITH VFR CEILINGS LOWERING TO MVFR AND EVEN IFR AT KAVL BY 17Z.
THE EXCEPTION WILL BE KHKY WHICH SHOULD REMAIN VFR. SCT RAIN SHOWERS
ARE ALSO EXPECTED TO BE AROUND THE AIRFIELDS AFTER 12Z EXCEPT AT
KHKY.

OUTLOOK...MOIST SOUTHEAST UPSLOPE FLOW WILL CONTINUE THURSDAY NIGHT
INTO FRIDAY MORNING WHICH WILL PROMOTE MVFR TO IFR CEILINGS.
CONDITIONS WILL IMPROVE TO VFR BY FRIDAY AFTERNOON. A COLD FRONT
WILL AFFECT THE AREA FRIDAY NIGHT INTO EARLY SATURDAY...BRINGING
ANOTHER ROUND OF RAIN/POSSIBLE THUNDERSTORMS AND RESTRICTIONS. VFR
WILL RETURN FOR THE REST OF THE WEEKEND.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  91%
KAVL       HIGH 100%     HIGH 100%     HIGH  80%     HIGH  86%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  94%
KAND       HIGH 100%     HIGH 100%     HIGH  97%     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...RWH
NEAR TERM...HG/LG
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...HG/LG



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