Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 182043
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
443 PM EDT SAT APR 18 2015

.SYNOPSIS...
A VERY MOIST WARM FRONT WILL LIFT NORTHEAST ACROSS THE AREA TONIGHT
INTO SUNDAY. A COLD FRONT WILL THEN CROSS THE AREA ON
MONDAY...USHERING IN SEASONABLE TEMPERATURES AND DRY CONDITIONS.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 430 PM EDT SATURDAY...ONLY MINOR TWEAKS TO THE NEAR TERM
FORECAST AT THIS TIME. UPDATED HOURLY TEMP/DEWPOINT/SKY TRENDS TO
LINE UP WITH OBSERVATIONS. NO CHANGES TO POPS AT THIS TIME AS LATE
AFTERNOON AND EVENING TRENDS LOOK GOOD PER RADAR AND HIRES
REFLECTIVITY FORECASTS...BUT SOME OF THE LATTER BRING MORE
WIDESPREAD PRECIPITATION INTO NORTHEAST GEORGIA AND THE UPSTATE
BETWEEN 03-06Z. WILL CONTINUE TO WATCH TRENDS BUT MAY NEED TO BUMP
UP POPS FOR THAT TIMEFRAME IN SUBSEQUENT UPDATES.

AS OF 300 PM EDT SATURDAY...PRIMARY FCST CONCERN THROUGH THE NEAR
TERM PERIOD WILL BE THE POTENTIAL FOR HEAVY RAIN ACROSS MUCH OF THE
AREA ON SUNDAY.  AS FOR TODAY...EXPECTING CONVECTION TO CONTINUE TO
INITIATE...ESPECIALLY ACROSS THE EASTERN UPSTATE AND NC PIEDMONT
WHERE BEST DIFFERENTIAL HEATING HAS OCCURRED.  LATEST SPC MESO
ANALYSIS INDICATES ROUGHLY 500K/KG SBCAPE SPREAD ACROSS THESE ZONES
WITH FURTHER EXPANSION EXPECTED ALONG WITH ADDITIONAL
DESTABILIZATION.

BEYOND THAT...CONVECTION WILL DIMINISH THIS EVENING WITH HEATING
LOSS MAKING WAY FOR INCOMING SHORTWAVE AND ASSOCIATED SURFACE WARM
FRONT.  THUS...FCST FEATURES CHANCE POPS ACROSS MUCH OF THE AREA
THIS AFTERNOON TO ACCOUNT FOR ISOLATED/SCATTERED THUNDERSTORMS...
WITH FURTHER INCREASES ACROSS NORTHEAST GA...SOUTHWEST NC...AND THE
WESTERN UPSTATE OVERNIGHT.  EXPECTING THE UPPER VORT MAX TO PASS
THROUGH THE REGION AFTER MIDNIGHT WITH ENHANCED H85 LLJ OUT AHEAD.
NEARLY 40-50KTS SOUTHERLY H85 FLOW WILL HELP PROMOTE ENHANCED
UPSLOPING ALONG THE SOUTHWEST NC...AND WESTERN NC ESCARPMENT.
FURTHERMORE...ANTECEDENT CONDITIONS FROM PREVIOUS DAYS RAINFALL OVER
THE UPSTATE AND PORTIONS OF NORTHEAST GA WILL YIELD ENHANCED
FLOODING CONCERNS AS A RESULT OF NEARLY 2-4 INCHES OF QPF IN THE
FCST.  THUS...OPTED TO ISSUE FLOOD WATCH FOR THESE ZONES STARTING
TONIGHT AT MIDNIGHT RUNNING THROUGH 8PM SUNDAY.

IN ADDITION...EXPECTING CONVECTION ALONG THE WARM FRONT AS IT SWEEPS
THROUGH ON SUNDAY.  MODELS INDICATE NEARLY 500-1000J/KG SBCAPE WITH
MODEST SHEAR AT 30-40KTS BULK.  THUS...FCST FEATURES CAT POPS
THROUGH THE DAY ON SUNDAY WITH HEAVY RAIN MENTION DUE TO WIDESPREAD
SHOWERS/THUNDERSTORMS.  NEW SPC DAY2 OUTLOOK PLACES THE REGION IN
THE SLIGHT RISK FOR SEVERE WEATHER...WHICH SEEMS TO FIT WELL WITH
THE FCST.  THEREFORE EXPECTING ADDITIONAL THREATS OF DAMAGING
WINDS...AND PERHAPS ANY ISOLATED TORNADO ON SUNDAY.  TEMPERATURES
THROUGH THE PERIOD WILL REMAIN ABOVE NORMAL.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM SATURDAY...PRECIP CHANCES WILL BE WINDING DOWN SUNDAY
EVENING...AS WARM CONVEYOR BELT ZONE SHIFTS INTO THE MID-ATLANTIC.
LOW LEVEL MOISTURE WILL LINGER THROUGH THE OVERNIGHT WITHIN DEEP SW
FLOW...AND TOKEN SLIGHT/LOW CHANCE POPS WILL BE RETAINED THROUGH
MONDAY MORNING.

A POTENTIALLY VERY INTERESTING SITUATION THEN EVOLVES FOR MONDAY
AFTERNOON...AS HEIGHT FALLS AND ATTENDANT FRONTAL ZONE OVERSPREAD
THE REGION FROM THE TENN VALLEY. IT SEEMS THAT THE MODELS ARE
DEPICTING AN INCREASINGLY WELL-FORCED FRONT WITH EACH SUCCESSIVE
RUN...SWINGING A FAIRLY SUBSTANTIVE SHORT WAVE TROUGH ACROSS THE
AREA DURING THE AFTERNOON. IN RESPONSE...THE LOW LEVEL FLOW IS MORE
BACKED THAN IN EARLIER RUNS...RESULTING IN BETTER SHEAR PROFILES AS
WELL AS IMPROVED FRONTAL CONVERGENCE. SHORT TERM MODELS CONTINUE TO
DEPICT ROBUST BUOYANCY...AS ADVECTION OF ELEVATED MIXED LAYER AIR
INTO THE SOUTHEAST SUPPORTS MID-LEVEL LAPSE RATES OF AROUND 7 C/KM.
BASED UPON A MODEL AND ENSEMBLE CONSENSUS...CAPE OF AROUND 2000 J/KG
APPEARS LIKELY ACROSS MUCH OF THE AREA DURING THE AFTERNOON. A
CONSIDERABLE DEGREE OF DRY MID-LEVEL AIR...MODEST FORCING...AND DEEP
LAYER SHEAR IN EXCESS OF 40 KTS MAY LEAD TO MORE IN THE WAY OF
SCATTERED/DISCRETE CELLS AS OPPOSED TO LINEAR ORGANIZATION. VERY DRY
AIR ALOFT AND A RELATIVELY DRY/DEEP BOUNDARY LAYER WOULD SUPPORT
DAMAGING WINDS AND LARGE HAIL AS THE PRIMARY THREATS.

POPS LINGER INTO MONDAY EVENING...AS THE MAIN UPPER TROUGH AXIS
LINGERS TO OUR WEST...AND FRONTAL BOUNDARY TAKES A BIT OF TIME
PUSHING EAST OF THE AREA. THE REMAINDER OF THE PERIOD WILL BE DRY
AND SEASONABLY MILD...AS CP HIGH PRESSURE OVERSPREADS THE AREA IN
THE WAKE OF THE FRONT.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM SATURDAY...WEDNESDAY THROUGH SATURDAY...A LARGE MID
LEVEL CLOSED LOW IS EXPECTED TO ROTATE OVER THE U.S./CANADA BORDER
FROM THE GREAT LAKES EAST...AS A RIDGE REMAINS ACROSS THE SOUTHERN
PLAINS. THE HEIGHTS ACROSS THE CWA SHOULD PERSIST GENERALLY ZONAL
THROUGH THE MEDIUM RANGE. THE PERIOD SHOULD BEGIN DRY WITH POPS
INCREASING TO CHC TO SCHC THURSDAY AND FRIDAY. THE GREATEST CHC FOR
RAIN WILL OCCUR ON SATURDAY AS SFC LOW PRESSURE SYSTEM ORGANIZES
OVER THE SOUTHERN MISSISSIPPI RIVER VALLEY AND TRACKS EAST...WITH A
WARM FRONT RUNNING ACROSS THE SOUTHERN APPALACHIANS. I WILL
INDICATES SOLID CHC POPS WITH LIKELY ACROSS THE MTN RIDGES. AS THE
CASE OVER THE PAST SEVERAL DAYS...THE GFS IS MUCH WETTER THAN THE
ECMWF...I WILL USE A BLEND. TEMPERATURES THROUGH THE PERIOD SHOULD
RANGE WITHIN SEVERAL DEGREES OF NORMAL.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
AT KCLT /21Z UPDATE/...SBCAPE VALUES BEGINNING TO DECREASE
ACROSS THE AREA AND NOT REALLY MUCH IN THE WAY OF TSRA SO FOR NOW
WILL DROP TSRA FROM THE TEMPO AND JUST GO TEMPO -SHRA WITH MVFR
CIGS. OTHERWISE...VFR/MVFR AND IFR CONDITIONS WILL HIGHLIGHT THE TAF
CYCLE THROUGH THE PERIOD.  CIGS WILL LOWER AS UPPER WAVE AND
SUBSEQUENT WARM FRONT SLIDE NORTHEAST OVERNIGHT.  FCST FEATURES IFR
CIGS AROUND THE 08Z TIMEFRAME AS SHRA INTRUDES...WITH FURTHER
LOWERING TO LIFR BY MID MORNING AS PRECIP INTENSIFIES.  CARRIED
MODERATE SHRA FROM THAT POINT ON AS SHOWERS COULD BE HEAVY AT TIMES.
 LASTLY...ADDED PROB30 ONTO THE LAST FM GROUP FOR ANY CONVECTION
EARLY IN THE AFTERNOON.  WINDS WILL BE QUITE GUSTY AS POTENT LOW
LEVEL WINDS MIX DOWN WITH 20-25KT SOUTHEASTERLY GUSTS POSSIBLE.

ELSEWHERE...SIMILAR TO KCLT ABOVE AS LOW VFR CU WILL PREVAIL THROUGH
THE AFTERNOON AS THE ATM DESTABILIZES.  MODELS CONTINUE TO PROG
CURRENT PRECIP BAND EXPANDING INTO THE UPSTATE AND WESTERN
NC...ALONG WITH ADDITIONAL CONVECTIVE SHOWERS/STORMS THIS
AFTERNOON.  THUS ALL TAF SITES FEATURE VCTS WITH MVFR/VFR CIGS.
WINDS WILL GRADUALLY VEER TO THE SOUTH THROUGH THE AFTERNOON AHEAD
OF ARRIVING WARM FRONT OVERNIGHT.  SHRA WILL SPREAD THROUGH THE AREA
FROM THE SOUTHWEST WITH SHOWERS BEING HEAVY AT TIMES.  VISB/CIGS
WILL LIKELY FALL TO IFR/LIFR LEVELS BY MORNING AS PRECIP OVERTAKES
EACH AIRFIELD.  LOW LEVEL WINDS WILL MIX TO THE SURFACE YIELDING
GUTSY CONDITIONS AT NEARLY ALL SITES.  ADDITIONALLY...INSTABILITY
WILL INCREASE BY MID/LATE MORNING WARRANTING REINTRODUCTION OF
THUNDER IN THE TAFS.

OUTLOOK...A COLD FRONT WILL SWEEP THROUGH THE REGION ON MONDAY WITH
STRONG TO SEVERE THUNDERSTORMS BEING A POSSIBILITY.  RESTRICTIONS
WILL BE LIKELY AT TIMES ON MONDAY FOR ALL SITES.  HIGH PRESSURE WILL
BUILD IN BEHIND THE COLD FRONT LEADING TO LOWER PRECIP/RESTRICTION
CHANCES.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH 100%     HIGH  91%     HIGH  88%     MED   77%
KGSP       HIGH 100%     HIGH  87%     HIGH  94%     MED   77%
KAVL       HIGH 100%     HIGH  93%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH  81%     HIGH  92%     HIGH  85%
KGMU       HIGH 100%     HIGH  95%     HIGH  94%     MED   77%
KAND       HIGH  84%     MED   76%     HIGH  98%     HIGH  90%

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...FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH SUNDAY EVENING
     FOR GAZ010-017-018-026-028.
NC...FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH SUNDAY EVENING
     FOR NCZ033-035>037-049-050-053-056-057-062>065-068>072-
     501>510.
SC...FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH SUNDAY EVENING
     FOR SCZ001>010.

&&

$$
SYNOPSIS...CSH
NEAR TERM...CDG/TDP
SHORT TERM...JDL
LONG TERM...NED
AVIATION...CDG/TDP


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