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Area Forecast Discussion

457
FXUS62 KGSP 180750
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
350 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 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 /08Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...CANNOT RULE OUT A BRIEF MVFR VSBY OR CIG AS SHRA MOVE
ACROSS THE AIR FIELD EARLY THIS MORNING. HOWEVER...DO EXPECT
CONDITIONS TO FALL TO MVFR THEN IFR TOWARD DAYBREAK AFTER THE PRECIP
ENDS. EXPECT LOW VFR BY NOON OR SO AS FORCING ENDS AND LOW LEVEL
MOISTURE MIXES OUT. MVFR COULD RETURN BY THE END OF THE PERIOD...BUT
MORE LIKELY TOWARD THE END OF THE NEXT TAF ISSUANCE. LIGHT NORTH OR
CALM WIND EARLY THIS MORNING BECOMES LIGHT NE...THEN ENE THRU THE
DAY.

ELSEWHERE...PRECIP WILL SOON MOVE EAST OF THE AREA AND CONDITIONS
WILL FALL TO IFR BEFORE DAYBREAK. IN FACT...LIFR LIKELY...LIKE THE
CURRENT CONDITIONS AT KAND. EXPECT A SLOW IMPROVEMENT TO LOW VFR
THRU THE MORNING. MVFR AND PRECIP MOVE BACK IN FROM THE WEST
TONIGHT. CALM WIND BECOMES NE THIS MORNING...THEN ENE TONIGHT. KAVL
WILL SEE NLY WIND BECOMING SLY TODAY...REMAINING THERE TONIGHT.

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...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       MED   78%     HIGH  85%     HIGH 100%     HIGH  92%
KGSP       MED   66%     MED   62%     HIGH 100%     HIGH  86%
KAVL       MED   62%     MED   77%     HIGH 100%     HIGH  82%
KHKY       MED   62%     HIGH  85%     HIGH 100%     HIGH  94%
KGMU       MED   72%     LOW   57%     HIGH 100%     HIGH  90%
KAND       LOW   54%     LOW   56%     HIGH  86%     MED   70%

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...RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...RWH



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