Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 181801
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
201 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 TONIGHT/...
AS OF 155 PM EDT SATURDAY...LATEST SPC MESO ANALYSIS INDICATES
INCREASING SBCAPE ACROSS THE NC PIEDMONT THIS AFTERNOON WHERE AMPLE
HEATING HAS RESIDED ALL MORNING.  IN RESPONSE...STARTING TO SEE SOME
ISOLATED CONVECTIVE INITIATION ALONG THE I40 CORRIDOR.  EXPECTING
THIS TREND TO CONTINUE INTO THE REMAINDER OF THE AFTERNOON...THUS
TWEAKED POPS A BIT TO BETTER ALIGN WITH CURRENT COVERAGE TO INCLUDE
INTRUDING SHRA ACTIVITY SOUTH OF INTERSTATE 85.  OTHERWISE LEFT THE
REMAINDER OF THE FCST AS IS.  FULL FCST DISCUSSION TO FOLLOW WITHIN
THE HOUR.

PREVIOUS DISCUSSION...

AS OF 645 AM...AFTER AN INCREASE IN PRECIP COVERAGE OVERNIGHT...
SHRA IS SCATTERING OUT AS A SHORT WAVE MOVES EAST OF THE AREA AND
ISENTROPIC LIFT ENDS. THE PATCHY FOG AND LOW CLOUDS WILL BURN OFF
THIS MORNING AND BREAKS IN THE CLOUDS WILL ALLOW HEATING. THIS WILL
LEAD TO WEAK INSTABILITY AND SCT SHRA AND ISOLATED TSRA FOR THE
AFTERNOON. CURRENT FCST LOOKS ON TRACK WITH CHANGES MAINLY FOR
CURRENT CONDITIONS.

AS OF 345 AM...A SHORT WAVE CURRENTLY OVER THE AREA MOVES EAST
TODAY. ISENTROPIC LIFT OVER THE AREA COMES TO AN END AS WELL. THIS
WILL HELP BRING AN END TO THE SCT SHRA ACROSS THE AREA THIS MORNING.
FOG...SOME DENSE...WILL DEVELOP AS THE PRECIP ENDS. LOW CLOUDS WILL
ERODE THRU THE DAY AS THE ISENTROPIC LIFT ENDS AND THE LOW LEVEL
MOISTURE MIXES OUT. HOWEVER...THIS WILL ALLOW HEATING TO DEVELOP...
WHICH COMBINED WITH THE HIGH SFC DEW POINTS...WILL CREATE WEAK
INSTABILITY. THEREFORE...EXPECT SCT SHRA AND ISOLATED TSRA TO
DEVELOP THRU THE AFTERNOON. PRECIP WILL GENERALLY BE LIGHT...BUT
COULD BE BRIEFLY HEAVY IN ANY STORMS THAT DO DEVELOP. HIGHS WILL END
UP AS MUCH AS 5 DEGREES ABOVE NORMAL.

SHORT WAVE RIDGING MOVES EAST OF THE AREA TONIGHT AS SHORT WAVES
ROTATING AROUND AN UPPER LOW OVER THE SRN PLAINS MOVE INTO THE AREA.
THIS WILL PUSH A WARM FRONT INTO THE AREA FROM THE SW. LOW LEVEL
FLOW BECOMES SELY OVERNIGHT BRINGING AN INCREASE IN LOW LEVEL
MOISTURE...ISENTROPIC LIFT AND UPSLOPE FLOW. THIS WILL CREATE
STEADILY INCREASING PRECIP CHC THRU THE NITE...WITH CAT POPS ACROSS
THE AREA BY DAYBREAK. PRECIP WILL GENERALLY BE LIGHT UNTIL AFTER
MIDNIGHT WHEN MODERATE QPF DEVELOPS ALONG AND NEAR THE NC/SC/GA
BORDERS. LOWS WILL BE 10 TO 15 DEGREES ABOVE NORMAL.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 300 AM SATURDAY...THE MAIN CONCERNS FOR THE SHORT TERM WILL BE
HEAVY RAIN AND LOCALIZED FLOODING ON SUNDAY...AND SEVERE TSTMS ON
MONDAY.

NOT MUCH CHANGE IN THINKING FOR THE HEAVY RAIN THREAT ON SUNDAY.
EXCEPT THAT GUIDANCE HAS TRENDED A LITTLE FASTER WITH THE WARM
FRONT...AND ALLOW FOR DECENT INSTBY ON BACK EDGE OF THE EXPECTED
PRECIP SHIELD SUNDAY AFTN. THE NEW DAY 2 SPC CONVECTIVE OUTLOOK HAS
EXPANDED THE MRGL RISK INTO THE CWFA FOR SUNDAY. GOING CLOSE TO THE
LATEST WPC QPF...EXPECT A SOLID 1.5-2" ACRS NEARLY THE ENTIRE CWFA
BY SUNDAY EVENING...WITH 2-3" ALONG THE BLUE RIDGE ESCARPMENT WHERE
STRONG SELY LLVL JET ENHANCES RAIN RATES. PWATS OF 1.5-1.7" WITHIN
THIS WARM CONVEYOR BELT OF LIFT AND PRECIP IS NEAR RECORDS FOR APRIL
19TH PER THE GSO/FFC SOUNDING CLIMATOLOGY...AND ARE 3-4 SD
ANOMALIES. SO WILL MENTION HEAVY RAIN IN THE GRIDS. A FLOOD WATCH
MAY BE NEEDED...AT LEAST FOR THE BLUE RIDGE ESCARPMENT.
HOWEVER...THE TWO THINGS LIMITING MORE WIDESPREAD FLOODING WILL BE
FAIRLY HIGH FFG VALUES (NEED 2+" IN 1 HOUR TO 3.5-4.5" IN 12
HOURS)...AND THE PRECIP BAND LOOKS PRETTY PROGRESSIVE IN THE
GUIDANCE. TEMPS WILL BE TRICKY ON SUNDAY...AS TIMING OF THE PRECIP
MAY AFFECT HIGHS SUNDAY AFTN. GIVEN THE SLIGHTLY FASTER TIMING...I
DID BUMP UP HIGHS SLIGHTLY...ESP IN THE UPPER SAVANNAH VALLEY. TEMPS
WILL REMAIN ELEVATED SUNDAY NIGHT WELL ABOVE NORMAL...AS PRECIP
TAPERS OFF BUT CLOUDS LINGER.

ON MONDAY...A COLD FRONT CROSS THE AREA DURING THE DAY...AS A LOW
PRES SYSTEM LIFTS NE INTO THE GREAT LAKES. MODELS IN PRETTY GOOD
AGREEMENT THAT THE WARM SECTOR AHEAD OF THE FRONT SHUD DESTABILIZE
TO 1000-2000 J/KG OF SBCAPE BY MID AFTN. THE 0-6KM BULK SHEAR LOOKS
TO BE ABOUT 40-50 KTS...PLENTY FOR ORGANIZED STORMS. THE NEW DAY 3
CONVECTIVE OUTLOOK HAS A SLGT RISK ACRS THE MID ATLANTIC TO SE
GA...INCLUDING THE CLT METRO AREA. A MRGL RISK AROUND THE SLGT
INCLUDES THE BLUE RIDGE AND REST OF THE PIEDMONT. THERE WILL BE A
SOLID SHORTWAVE CROSSING THE AREA...AS AN UPPER TROF APPROACHES FROM
THE WEST. SO DEPENDING ON HOW STRONG THE FRONTAL FORCING IS...THERE
MAY BE A LINE OF STORMS OR MORE DISCRETE STORMS. WILL MENTION THE
SEVERE THREAT IN THE HWO. HIGHS ON MONDAY SHUD BE IN THE 70S TO LWR
80S...WITH BREEZY SW WINDS.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 330 AM SATURDAY...AN UPPER LOW WILL PERSIST ACRS EASTERN
CANADA AND THE GREAT LAKES...KEEPING OUR AREA UNDER CONFLUENT
QUASI-ZONAL FLOW. HIGH PRES WILL BUILD IN UNDER THE CONFLUENT
FLOW...AND SHUD RESULT IN SEASONABLE TEMPS AND DRY CONDITIONS FOR
THE MIDDLE OF THE WEEK. THE GFS IS STILL TRYING TO SQUEEZE OUT A FEW
SHWRS WITH A REINFORCING DRY COLD FRONT ON WEDNESDAY...AND AGAIN ON
THURSDAY. WHILE...THE ECMWF IS GENERALLY DRIER. SLGT CHC TO CHC POPS
START RAMPING UP FRIDAY...ALTHO CONFIDENCE IS BELOW AVERAGE...AS
MODELS DIVERGE ON WHEN TO BRING SOUTHERN STREAM ENERGY BACK INTO THE
AREA LATE NEXT WEEK.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT...VFR/MVFR AND IFR CONDITIONS WILL HIGHLIGHT THE TAF CYCLE
THROUGH THE PERIOD.  TAF INITIALIZES WITH LIGHT NE WINDS BEFORE
VEERING JUST SOUTH OF EAST AROUND MID AFTERNOON ALONG WITH LOW VFR
CU DEVELOPMENT.  CURRENT PRECIP SLIDING THROUGH THE UPSTATE WILL
PUSH INTO THE NC PIEDMONT REGION IN A FEW HOURS WITH ENOUGH
INSTABILITY PRESENT TO WARRANT TEMPO FOR MVFR TSRA.  BEYOND
THAT...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.  RESTRICITONS
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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH  95%     HIGH  93%     HIGH  81%
KGSP       HIGH 100%     HIGH  89%     HIGH  89%     HIGH  90%
KAVL       HIGH 100%     HIGH  95%     HIGH  97%     HIGH 100%
KHKY       HIGH 100%     HIGH  87%     HIGH  96%     HIGH  88%
KGMU       HIGH  99%     HIGH  92%     HIGH  89%     HIGH  90%
KAND       HIGH  87%     MED   79%     HIGH  98%     HIGH  93%

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...ARK
NEAR TERM...CDG/RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...CDG


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