Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 292317
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
717 PM EDT SAT AUG 29 2015

.SYNOPSIS...
WEAK SURFACE HIGH PRESSURE WILL LINGER OVER THE REGION THROUGH THE
WEEKEND...BUT WITH MOISTURE GRADUALLY INCREASING FROM THE SOUTHWEST.
THE REMNANTS OF TROPICAL STORM ERIKA ARE EXPECTED TO MOVE SLOWLY
NORTHWARD THROUGH THE EASTERN GULF OF MEXICO ON MONDAY AND TUESDAY.
THE FATE OF ERIKA WILL BECOME MUCH MORE UNCERTAIN FROM MID WEEK
ONWARD...BUT TROPICAL MOISTURE COULD GRADUALLY REACH THE WESTERN
CAROLINAS AND NORTHEAST GEORGIA THROUGH THE UPCOMING WORK WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
2315 UTC UPDATE...POPS HAVE BEEN REDUCED IN THE UPPER SAVANNAH RIVER
VALLEY PER RADAR TRENDS. WINDS WERE UPDATED WITH A BLEND OF THE
LATEST MODEL DATA. SKY COVER WAS UPDATED FROM VISIBLE SATELLITE
IMAGERY.

2040 UTC UPDATE...POPS HAVE BEEN ADJUSTED PER RADAR TRENDS...
FAVORING THE CENTRAL TN BORDER AREA. SKY COVER WAS UPDATED FROM
VISIBLE SATELLITE IMAGERY.

AS OF 230 PM EDT SATURDAY...BROAD UPPER RIDGE OVER THE FOUR CORNERS
COMPLIMENTS A CLOSED UPPER LOW ATOP THE NORTH CENTRAL GULF THIS
AFTERNOON.  AT THE SURFACE...HIGH PRESSURE REMAINS CENTERED OVER THE
MID ATLANTIC YIELDING PREDOMINATE ENE/ESE FLOW AND THUS DEWPOINTS IN
THE MID 50S UNDER PARTLY/MOSTLY CLOUDY SKIES.  EXPECTING SAID UPPER
LOW TO ADVECT NORTHWARD THROUGH THE PERIOD ALL THE WHILE ENHANCING
GULF/ATL MOISTURE FLUX INTO THE REGION TONIGHT AND TOMORROW.
IN RESPONSE...LIGHT SHOWERS CURRENTLY ONGOING ACROSS EASTCENTRAL
GA ARE FCST TO MOVE NORTHWARD OVER PORTIONS OF THE UPPER SAVANNAH
RIVER VALLEY AND THE NC HIGH TERRAIN THIS AFTERNOON/TONIGHT.
SLIGHT/CHANCE POPS ARE FEATURED FOR SUCH THROUGH THE REMAINDER OF
THE FIRST PERIOD BEFORE ALL POPS ARE REMOVED BRIEFLY AFTER MIDNIGHT
OUTSIDE OF THE SW NC MTNS WHERE SLIGHT CHANCES WILL PERSIST.

AS THE DEEPER MOISTURE PLUME ADVANCES NORTHWARD BY DAYBREAK
SUNDAY...POPS WILL INCREASE FROM THE SOUTHWEST.  THE FCST FEATURES
SLIGHT CHANCES OVER WEST EARLY...INCREASING WITH TIME TO HIGH
END CHANCES OVER THE WEST...AND SLIGHT CHANCES EAST IN CLOSER
PROXIMITY TO LESS MOIST AIRMASS ADJACENT TO DEPARTING SURFACE RIDGE.
NOT EXPECTING ANY HAZARDOUS WX AS THE PWATS REMAIN BELOW CLIMO AND
INSTABILITY WILL BE DAMPENED THANKS TO MOSTLY CLOUDY TO OVERCAST
SKIES ON SUNDAY.  AS A RESULT OF SAID SKY COVER...EXPECTING
TEMPERATURES TO REMAIN NEAR OR JUST ABOVE NORMAL FOR OVERNIGHT
LOWS AND 3-4 DEGREES BELOW NORMAL FOR HIGHS ON SUNDAY AFTERNOON.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 230 PM EDT SATURDAY...THE MEAN PATTERN WILL TRANSITION TO
UPPER RIDING ALOFT WITH A PIECE OF ENERGY STILL BROKEN OFF OVER THE
SOUTH. A PORTION OF THIS ENERGY WILL CONTINUE TO SLIDE SOUTHWESTWARD
TOWARD THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY...WHILE
ANOTHER PIECE OF UPPER ENERGY WILL DRIFTING NORTHEAST ACROSS OUR
AREA THROUGH THE SHORT TERM. 250-300MB JET WILL BE PUSHING NORTH
ACROSS GEORGIA AND THE CAROLINAS WITH A DECENT VORT MAX WITH IT.
BEST PRECIPITATION ASSOCIATED WITH THE SYSTEM WILL REMAIN ACROSS
CENTRAL SOUTH CAROLINA BUT SHOULD PUSH INTO PORTIONS OF OUR UPSTATE
ZONES. WILL GET TO THE REMNANTS OF ERIKA MORE BELOW...BUT THIS FIRST
SLUG OF MOISTURE MOVING THROUGH MIGHT BE TRENDING MORE TOWARD A
PREDECESSOR RAINFALL EVENT /PRE/...AS MENTIONED IN THE OVERNIGHT
DISCUSSION...BUT BY DEFINITION COULD ONLY BE A PRE IF WE ACTUALLY
GET IMPACTED BY THE REMNANTS OF ERIKA. AGAIN...MORE ON THAT BELOW.

THE WAVE PUSHES RAPIDLY EAST AND OFFSHORE BY MIDDAY MONDAY AS
MOISTURE ASSOCIATED WITH THE REMNANTS OF ERIKA ARE PROGGED TO PUSH
NORTH ACROSS FLORIDA. STILL SOME UNCERTAINTY THERE FOR SURE BUT AT
LEAST INCREASING CONFIDENCE BASED ON LATEST GUIDANCE THAT THROUGH
THE SHORT TERM SHOULD NOT SEE ANY IMPACTS FROM THE REMNANTS ACROSS
OUR AREA. UPPER RIDGING BUILDS ACROSS THE SOUTHEAST SO WE SEE A
RETURN TO CLIMATOLOGICAL POPS AND A SLIGHT INCREASING TREND IN
TEMPS...BUT STILL WITH HIGHS HOVERING JUST BELOW SEASONAL NORMALS
ESPECIALLY ON MONDAY GIVEN THE UPPER WAVE MOVING THROUGH AND
CORRESPONDING AMOUNT OF BOUNDARY LAYER MOISTURE IN PLACE AND CLOUD
COVER.

TOWARD THE END OF THE SHORT TERM...MODELS BEGIN TO DIVERGE MORE WITH
THE 12Z GFS BRINGING THE REMNANTS OF ERIKA INTO GEORGIA AND SOUTHERN
PORTIONS OF SOUTH CAROLINA...AND THE ECMWF KEEPING THE MOISTURE
FARTHER TO THE SOUTH. THE SOUTHERN PLAINS WEAKNESS IS A LITTLE MORE
PRONOUNCED ON THE GFS WHICH IS LIKELY THE CULPRIT...AS THE UPPER
FLOW AROUND THE CUTTING OFF LOW PULLS MORE MOISTURE NORTH ON THE
GFS. AS MENTIONED ABOVE...SHOULD NOT REALLY START TO SEE ANY IMPACTS
OF THIS ACROSS OUR AREA THROUGH THE SHORT TERM...BUT THINGS GET MORE
COMPLICATED AS WE GO INTO THE EXTENDED.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 245 PM EDT SATURDAY...AFOREMENTIONED MOISTURE FROM THE
REMNANTS OF ERIKA WILL BE THE MAIN PLAYER AT LEAST THROUGH THE FIRST
PART OF THE EXTENDED. THE PROBLEM IS THAT THERE IS NO CLEAR
CONSENSUS ON WHAT THIS MOISTURE WILL DO. THE 12Z GFS HAS THE DEEP
LAYER MOISTURE /PW VALUES BETWEEN 2-2.25 INCHES/ HOVERING RIGHT ON
OUR DOORSTEP ACROSS GEORGIA AND CENTRAL/SOUTHERN SOUTH CAROLINA. THE
SLUG OF MOISTURE WILL CONTINUE TO SPIN AROUND ITSELF /IT IS THE
REMNANT OF A TROPICAL SYSTEM AFTER ALL/ BUT ITS DIRECTION WILL BE
FORCED BETWEEN THE CUTOFF LOW ACROSS THE LOWER MISSISSIPPI VERSUS
THE UPPER RIDGING DOMINATING THE EASTERN HALF OF THE COUNTRY. THE
12Z GFS KEEPS ABUNDANT MOISTURE ACROSS THE SOUTHEAST...WITH THE
LOWER MISSISSIPPI UPPER LOW ABSORBING THE REMNANTS AND KEEPING IT
GENERALLY WET ACROSS THE SOUTHEAST AND SOUTHERN APPALACHIANS PRETTY
MUCH THROUGH THE END OF THE PERIOD. 12Z ECMWF HOWEVER KEEPS THE
LOWER MISSISSIPPI LOW ITS OWN ENTITY AND THE REMNANTS OF ERIKA PHASE
WITH A SLOWLY DEEPENING UPPER TROUGH DOWN THE EASTERN SEABOARD...
NOT ABSORBING THE LOWER MISSISSIPPI LOW UNTIL SOMETIME ON FRIDAY.
MOISTURE IS ANEMIC WITH THE ECMWF AND REMAINS EITHER OFFSHORE OR TO
OUR SOUTH...WITH BASICALLY JUST CLIMO POPS ACROSS THE AREA.

RECONCILING THESE TWO FORECASTS...ONE VERY WET WITH INCREASING
POTENTIAL FOR HYDRO PROBLEMS...AND THE OTHER MUCH DRIER /RELATIVELY
SPEAKING OF COURSE/ WITH MORE OF A CLIMO PATTERN...IS DIFFICULT AT
BEST. ADD TO THIS THE RAIN POTENTIAL /PRE POTENTIAL AT THAT/ DURING
THE SHORT TERM AND THE FORECAST IS RIDDLED WITH LOWER CONFIDENCE
THAN USUAL. IF ONE WERE TO BELIEVE THE GFS...SEVERAL INCHES OF RAIN
WOULD BE POSSIBLE...AT LEAST SOMEWHERE...ASSOCIATED WITH THE
REMNANTS OF ERIKA. FOR NOW THAT SOMEWHERE IS GENERALLY CENTRAL AND
SOUTHERN GEORGIA BUT WITH A PROLONGED PERIOD OF ABOVE-NORMAL PW
VALUES ACROSS THE SOUTHEAST IN GENERAL...BUT AS WITH ANY FORECAST
COULD EASILY CHANGE. THE ECMWF NOT SO EXCITED.  WITH LACK OF MORE
CONSISTENT GUIDANCE...TRIED TO TAKE A BIT OF A MIDDLE-OF-THE-ROAD
SOLUTION WITH GENERALLY AN ENHANCED DIURNAL TREND TO POPS AND A
REDUCED DIURNAL TREND IN TEMPERATURES. STAY TUNED THOUGH AS THE
FORECAST COULD EASILY SWING...MAYBE EVEN MARKEDLY SO...IN ONE
DIRECTION OR THE OTHER.

&&

.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
AT KCLT...VFR. MODEL TIME HEIGHTS SUGGEST INCREASING HIGH CLOUDS
FORMING A HIGH VFR CIG FOR MUCH OF THE EVENING...WITH SCATTERED LOW
VFR CLOUDS MOVING IN UNDERNEATH. BY MID MORNING SUNDAY LOW VFR CIGS
ARE EXPECTED. DAYBREAK FOG IS NOT SUPPORTED BY MODEL DATA. LIGHT
WINDS WILL FAVOR THE SSE. CONVECTIVE CHANCES WILL INCREASE TOWARD
MIDDAY SUNDAY...BUT NOT ENOUGH TO WARRANT A MENTION IN THE TAF BY
AFTERNOON.

ELSEWHERE...A DAYBREAK MVFR FOG RESTRICTION IS POSSIBLE AT KAVL SUNDAY
MORNING. HIGH VFR CIGS AREA EXPECTED AT ALL SITES OVERNIGHT...WHILE
SCATTERED LOW VFR CLOUDS MOVE IN UNDERNEATH. BY MIDDAY LOW VFR CIGS
ARE EXPECTED...LOWERING TO MVFR AT KAVL BY AFTERNOON. LIGHT WINDS
WILL BECOME VARIABLE OVERNIGHT...FAVORING THE S IN NC ON SUNDAY...
AND THE EAST IN SC. CONVECTIVE CHANCES INCREASES ENOUGH TO WARRANT A
MENTION ON SUNDAY AFTERNOON.

OUTLOOK...THE SOUTHEAST REGION IS FORECAST TO REMAIN UNDER A PLUME
OF GULF AND ATLANTIC MOISTURE THROUGH THE MIDDLE OF NEXT WEEK. IN
ADDITION...MOISTURE ASSOCIATED WITH THE REMNANTS OF ERIKA COULD
REACH THE SOUTHERN APPALACHIANS DURING THE MID WEEK. RESTRICTIONS
ARE POSSIBLE DURING PERIODS OF RAIN AND WITH THE MTN VALLEY FOG
AROUND DAWN.

CONFIDENCE TABLE...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     MED   66%     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 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

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...TDP
NEAR TERM...CDG/JAT
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JAT



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