Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 012353
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
753 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 745 PM EDT...STRONG MODEL CONSENSUS CONTINUES ON THE 18Z RUNS
DEPICTING IMPROVING MOIST UPGLIDE IN THE 4000 TO 6000 FT AGL LAYER
FROM THE SW DURING THE OVERNIGHT HOURS. THIS SHOULD LEAD TO
INCREASING CLOUDS...WITH MIN TEMPS SLIGHTLY WARMER THAN A CONSENSUS
OF GUIDANCE. AS THE WEAK UPGLIDE AND SRLY UPSLOPE FLOW IMPROVES
TOWARD DAYBREAK...ISOLD TO SCATTERED RAIN SHOWERS SHOULD DEVELOP IN
THE SRN MTNS.

RETURN FLOW MOISTURE WILL DEEPEN IN PROFILES THROUGH THU...GRADUALLY
EXPANDING OVER MOST OF THE AREA. THE HIGHEST PRECIPITATION CHANCES
WILL REMAIN FOCUSED ON THE SRLY UPSLOPE AREAS OF THE SRN MTNS AND
IMMEDIATELY ADJACENT FOOTHILLS...BUT WITH ISOLATED SHOWER CHANCES
EVENTUALLY EXPANDING OUT EAST TO INTERSTATE 77. THE SOLIDIFYING
CLOUD DECK SHOULD KEEP MAXES BELOW GUIDANCE THU AFTN...ESPECIALLY IF
IN SITU SHALLOW COLD AIR DAMMING DEVELOPS EAST OF THE BLUE RIDGE. IN
ADDITION TO THE MOIST UPGLIDE...A PHASING SHORTWAVE MOVING EAST FROM
THE PLAINS WILL CROSS THE REGION DURING THE AFTN. HIGHER DEWPOINTS
AND SLIGHTLY MORE INSTABILITY IN SRN SECTIONS MAY PERMIT ISOLD TO
SCT TSTMS TO CROSS THE SRN TIER DURING THE AFTN HOURS.

&&

.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 /00Z THURSDAY THROUGH MONDAY/...
AT KCLT...MOISTURE WILL RETURN AT VFR LEVELS OVERNIGHT...WITH A
STRATOCUMULUS CIG LIKELY BY MID MORNING ON THURSDAY. DEEPENING MOIST
UPGLIDE WILL ALLOW CIGS TO LOWER INTO THE MVFR RANGE THROUGH THE
AFTN HOURS. SPOTTY LIGHT SHOWERS CANNOT BE RULED OUT...BUT CHANCES
LOOK TOO LOW TO MENTION IN THE TAF AT PRESENT. LIGHT ESE FLOW WILL
GRADUALLY BECOME MORE SRLY WITH TIME THROUGH THE TAF PERIOD.

ELSEWHERE...VFR LEVEL STRATOCUMULUS WILL DEVELOP FROM S TO N ACROSS
THE MTN AND FOOTHILL TAFS TONIGHT. MVFR CIGS WILL THEN BECOME
INCREASINGLY LIKELY THROUGH THU MORNING AT KAVL AND THE SC SITES AS
THE MOIST UPGLIDE DEEPENS. THERE IS GENERAL CONSENSUS AMONG THE
MODELS/MOS ON IFR CIGS FROM KAVL TO KGSP AND POINTS S BY EARLY
AFTN...BUT THE IFR CIGS COULD BE TEMPO MVFR ALL AFTN. WILL MENTION
VCSH WITH THE DEEPEST MOISTURE THROUGHOUT...AND LIMIT PROB30 FOR
TSRA TO KAND WITH THE UPPER SHORTWAVE INTERACTING WITH MORE UNSTABLE
AIR ACROSS THE SRN PART OF THE TERMINAL AREA LATE DAY. EXPECT
EASTERLY WINDS TO TOGGLE SOUTHERLY OVER TIME...BUT PERHAPS ADJUST
BACK TO EASTERLY IN ANY WEAK CAD REGIONS FROM KGMU TO 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...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  80%
KGSP       HIGH 100%     HIGH  98%     HIGH  85%     MED   73%
KAVL       HIGH 100%     HIGH  85%     HIGH  82%     HIGH  91%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  94%
KGMU       HIGH 100%     HIGH  86%     MED   65%     MED   73%
KAND       HIGH 100%     HIGH  88%     MED   75%     HIGH  82%

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
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...HG/LG


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