Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 181445
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1045 AM EDT SAT APR 18 2015

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

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1035 AM EDT SATURDAY...SKIES CONTINUE TO SCT ACROSS MUCH OF
THE FCST AREA...PARTICULARLY ALONG AND NORTH OF INTERSTATE 85 WHERE
BEST LOW LEVEL DRYING IS OCCURRING.  FURTHER SOUTH ACROSS EAST
CENTRAL GA AND THE MIDLANDS A BAND OF LIGHT PRECIP CONTINUES TO
SLIDE NORTH TOWARD THE LAKELANDS.  LATEST GUIDANCE FAVORS THE
SURVIVAL OF SAID SHOWERS AS THEY ADVANCE INTO THE UPSTATE AND
NORTHEAST GA LATER THIS MORNING.  MODELS ALSO CONTINUE TO INDICATE
AT LEAST MODEST DESTABILIZATION THIS AFTERNOON AS THE BOUNDARY LAYER
WARMS AND LAPSE RATES STEEPEN.  WOUDLNT BE SURPRISED TO SEE SCATTERED
CONVECTION...BUT STILL EXPECT UPPER SHORT WAVE RIDGE AXIS TO PROVIDE
SOME SUBSIDENCE.  THUS FOR THE FCST ADJUSTED
POPS/SKY/TEMPS/DEWPOINTS TO REFLECT THESE TRENDS/OBS AND LEFT THE
REMAINDER UNCHANGED.  ANALYSIS OF LATEST GUIDANCE CONTINUES
REGARDING HEAVY RAIN AND POSSIBLE STRONG/SEVERE THUNDERSTORM THREAT
ON SUNDAY.

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 /15Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...MVFR FOG AND PATCHY LIGHT RAIN WILL END QUICKLY AFTER
DAYBREAK...LEAVING VFR FOR THE REST OF THE DAY. THERE IS A SMALL CHC
OF CONVECTION THIS AFTERNOON...BUT CHC TOO LOW FOR TAF. CONDITIONS
DETERIORATE AFTER MIDNIGHT TONIGHT AS LOW LEVEL MOISTURE AND
ISENTROPIC LIFT MOVE BACK INTO THE AREA. EXPECT MVFR BECOMING IFR
WITH PRECIP DEVELOPING. NLY WIND THIS MORNING BECOMES ENE THIS
AFTERNOON...THEN ESE AFTER MIDNIGHT.

ELSEWHERE...AFTER MORNING FOG AND LOW CLOUDS BURN OFF...SIMILAR
CONDITIONS TO KCLT...EXCEPT AN EARLIER ONSET IN GENERAL. KAVL WILL
SEE NLY WIND THIS MORNING WITH SSE WIND FOR THE AFTERNOON INTO THE
OVERNIGHT.

OUTLOOK...DEEPER MOISTURE WILL RETURN ALONG A WARM FRONT THROUGH
SUNDAY...WITH HEAVY RAINFALL AND WIDESPREAD RESTRICTIONS LIKELY ONCE
AGAIN. THUNDERSTORMS WILL THEN BE POSSIBLE THROUGH MONDAY AS A COLD
FRONT REACHES THE AREA FROM THE WEST.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       HIGH  97%     HIGH 100%     HIGH  93%     HIGH  88%
KGSP       HIGH  87%     HIGH  98%     HIGH  86%     HIGH  95%
KAVL       HIGH  83%     HIGH 100%     MED   77%     HIGH 100%
KHKY       LOW   48%     HIGH 100%     MED   74%     HIGH  85%
KGMU       HIGH  86%     HIGH  98%     HIGH  83%     HIGH  95%
KAND       MED   73%     HIGH  81%     MED   68%     HIGH  87%

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...RWH



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