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Area Forecast Discussion

404
FXUS62 KGSP 301542
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1142 AM EDT SAT MAY 30 2015

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL PERSIST ACROSS THE REGION INTO EARLY NEXT
WEEK...WITH MOIST SOUTHERLY FLOW SUPPORTING SCATTERED AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS. A COLD FRONT APPROACHES THE AREA
ON TUESDAY AND IS EXPECTED TO BECOME STATIONARY THROUGH THE MIDDLE
OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1055 AM...CU/STRATOCU EXPANDED RAPIDLY ACROSS THE PIEDMONT/
FHILLS ONCE THE BOUNDARY LAYER BEGAN TO WARM THIS MORNING...AND IN
LIGHT OF PERSISTENCE OF RELATIVELY MOIST SE LOW LEVEL FLOW...SKY
COVER WAS INCREASED ACROSS MUCH OF THE AREA...MAINLY FROM THE
ESCARPMENT SOUTH AND EAST THROUGH THE AFTERNOON. A FEW SMALL SHOWERS
WERE MOVING ACROSS THE SC MIDLANDS LATE THIS MORNING...LIKELY
ASSOCIATED WITH ANOTHER IN A SERIES OF SUBTLE BOUNDARIES ORIGINATING
FROM THE COAST. ALTHOUGH INSTABILITY WILL BE QUITE MUTED THIS
AFTERNOON...OWING LARGELY TO ABOVE-CLIMO MID-LEVEL TEMPS RESULTING
FROM RISING HEIGHTS...THE COMBINATION OF TERRAIN EFFECTS/WEAK
UPSLOPE/DIFFERENTIAL HEATING AND SUBTLE BOUNDARIES SHOULD ALLOW FOR
ISOLATED DEEP CONVECTION TO FORM JUST ABOUT ANYWHERE THIS
AFTERNOON...MAINLY IN THE FORM OF SHOWERS. THE EXTENSIVE CU FIELD
SHOULD HINDER INSOLATION ENOUGH TO KEEP MAX TEMPS CLOSE TO CLIMO.

AS OF 645 AM...FOG AND LOW CLOUDS HAVE BEEN QUITE COMMON WITHIN THE
MTN VALLEYS AND ACROSS THE NC NRN MTNS AND FOOTHILLS. I WILL UPDATE
THE FORECAST TO ADJUST VIS LOWER AND INDICATE GREATER COVERAGE OF
FOG. OTHERWISE...THE CURRENT FORECAST APPEARS IN GREAT SHAPE.

AS OF 245 AM...NEAR TERM MODELS AGREE THAT THE FORECAST AREA WILL
REMAIN UNDER MID LEVEL RIDGING WITH BROAD SFC HIGH PRESSURE. RETURN
FLOW WILL CONTINUE THROUGH THE DAYLIGHT HOURS AS A WELL ORGANIZED
LOW PRESSURE SYSTEM TRACKS NORTHEAST ACROSS THE MID MISSISSIPPI
RIVER VALLEY. USING A BLEND OF MOS...AFTERNOON DEWPOINT VALUES ARE
FORECAST TO RANGE IN THE LOW TO MID 60S. HIGH TEMPERATURES MAY RISE
A DEGREE OR TWO OVER VALUES OBSERVED ON FRIDAY. FORECAST SOUNDINGS
SHOW RATHER SHALLOW MID LEVEL LAPSE RATES...WITH OVERALL CAPES
GENERALLY REMAINING LESS THAN 500 J/KG. GIVEN WEAK FLOW FROM 0 TO 15
KFT AND LFC AROUND 5 KFT...IT APPEARS THAT SHRA AND TSRA WILL BE
LOW. I WILL FORECAST 20 TO 30 POPS ACROSS THE MTNS AND ADJACENT
FOOTHILLS...WITH 20 POPS EAST OF I-85.

TONIGHT...CONVECTION ACROSS THE PIEDMONT AND FOOTHILLS SHOULD
QUICKLY DISSIPATE AFTER SUNSET. HOWEVER...THE SFC LOW IS EXPECTED TO
TRACK NE ALONG THE OHIO RIVER...RESULTING IN STRENGTHENING OF H925
AND H850 SOUTH WINDS ACROSS THE MTNS. I WILL KEEP 20 POPS ACROSS THE
MTNS TO HIGHLIGHT THE POTENTIAL FOR ISO UPSLOPE SHRA AND POSSIBLY
THE ARRIVAL OF A FADING LINE OF CONVECTION FROM THE WEST. LOW
TEMPERATURES ARE FORECAST TO RANGE FROM THE L60S ACROSS THE MTNS
VALLEYS TO THE MID 60S EAST.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 2 AM SATURDAY MORNING...THE SHORT TERM FCST PICKS UP AT 12Z ON
SUNDAY WITH UPPER RIDGING LINGERING OVER THE REGION AND A LOW
AMPLITUDE UPPER TROF SLOWLY MAKING ITS WAY TOWARDS THE CWFA. OVER
THE REMAINDER OF THE PERIOD...THE RIDGE AXIS SLIDES FARTHER OFF THE
ATLANTIC COAST WHILE THE TROF AXIS WILL EVENTUALLY OVER OVER THE
CAROLINAS BY THE END OF THE PERIOD EARLY TUES.

AT THE SFC...A LOW THAT SPINS UP ON THE SOUTHERN END OF AN ELONGATED
FRONTAL ZONE WILL SLIDE JUST NORTH OF THE FCST AREA ON
SUN...HOWEVER...THE MODELS ARE SLOW TO BRING THE BULK OF THE MOIST
AIR SOUTHWARD AND INTO THE CWFA. ITS STILL LOOKING LIKE MOST OF THE
DEEPER MOISTURE WONT OVERSPREAD OVER THE AREA UNTIL MON. WE SHOULD
STILL SEE FAVORABLE UPSLOPE FLOW ON SUN ALONG WITH GREATER UPPER LVL
SUPPORT FOR LIFT...ESP OVER THE NC/TENN BORDER REGION. AS WE MOVE
THRU MON...WIDESPREAD SHOWERS AND TS ARE LOOKING LIKELY WITH SLY
FLOW TO OUR SOUTH AND NLY FLOW ASSOCIATED WITH THE GREAT LAKES HIGH
TO OUR NORTH. BY TUES MORNING SOME OF THE MODEL GUIDANCE...ESP THE
00Z GFS...HAS THE HIGH PUSHING MOST OF THE SLY FLOW TO OUR SOUTH
WITH NLY WINDS OVER THE BULK OF THE CWFA...HOWEVER THIS IS THE MOST
AGGRESSIVE SCENARIO. ITS MORE LIKELY THAT THE WE WILL REMAIN
SANDWICHED IN BETWEEN THE NLY AND SLY FLOW INTO WED. AS FOR THE
SENSIBLE FCST...NO SIG CHANGES WERE NEEDED FOR SUN WITH POPS RAISED
TO WIDESPREAD LIKELY FOR MON AFTERNOON/EARLY EVENING. THEY REMAIN AT
HIGH END CHANCE THRU 12Z TUES WITH LINGERING DEEP MOISTURE OVER THE
AREA. MODEL PROFILES CONTINUE TO SHOW HEALTHY AMOUNTS OF SFC BASED
CAPE BOTH SUN AND MON WITH SPC INCLUDING OUR CWFA UNDER A SLIGHT
RISK AREA BOTH DAYS. SUFFICE TO SAY...CONDITIONS LOOK FAVORABLE FOR
WIDESPREAD TS ACTIVITY WITH SOME STORMS BECOMING SEVERE.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 305 AM SATURDAY MORNING...THE MEDIUM RANGE FCST PICKS UP AT
12Z ON TUESDAY WITH AN UPPER TROF AXIS TO OUR NORTH AND BROAD UPPER
RIDGING OVER THE CENTRAL CONUS. OVER THE NEXT 24 TO 48 HRS THE TROF
AXIS LIFTS NE OF THE AREA WHILE THE UPPER RIDGE BUILDS OVER THE SE
REGION IN THE TROFS WAKE. AT THE SFC...A LARGE PLUME OF DEEP LYR
MOISTURE ASSOCIATED WITH A DISSIPATING FRONTAL ZONE WILL KEEP THE
FCST AREA UNDER FAVORABLE CONDITIONS FOR WIDESPREAD SHOWERS AND TS
ON TUES. ON WED SOME DRYING IS LIKELY...ESP OVER THE NW ZONES...AS
THE DEEPER MOISTURE MOVES FARTHER EAST AND THE GREAT LAKES HIGH
SLIDES FARTHER SE. ON THURS...THE HIGH TRIES TO SET UP WEDGE TYPE
SFC PATTERN OVER THE FCST AREA...BUT IT ISNT LOOKING AS COHERENT
COMPARED TO PREVIOUS MODEL RUNS. ALSO OF NOTE...THE GFS NOW
GENERATES A TROPICAL SYSTEM OVER CUBA ON WED AND MOVES THE LOW
DIRECTLY OVER THE CWFA BY DAY 7 ON SAT. THIS KIND OF RAPID
CYCLOGENESIS IS NOT SEEN ON THE OTHER LONG RANGE GUIDANCE AND IS
UNLIKELY TO MATERIALIZE. DIURNALLY DRIVEN POPS REMAIN IN THE 20 TO
40% RANGE EACH DAY/EVENING WITH TEMPS LOWERED A BIT ON DAYS
5...6...AND 7 TO REFLECT THE COOLER GUIDANCE.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...A WELL ORGANIZED LOW PRESSURE SYSTEM WILL TRACK NORTHEAST
OVER THE MID MISSISSIPPI RIVER VALLEY...REACHING THE THE OHIO RIVER
VALLEY THIS EVENING. BROAD HIGH PRESSURE IS EXPECTED TO REMAIN OFF
THE MID ATLANTIC COAST THROUGH THE PERIOD. THIS PRESSURE PATTERN
SHOULD YIELD STEADY SOUTH WINDS BETWEEN 5 TO 10 KTS THROUGH THE 12Z
TAF FORECAST. THE PRIMARY FORECAST CHALLENGE WILL BE THE POSSIBLE
DEVELOPING LAYER OF IFR TO MVFR STRATUS LATE TONIGHT. THE LATEST NAM
FORECAST SOUNDING INDICATES THAT THE LAYER OF CONDENSATION WILL
DEEPEN AFTER 6Z TONIGHT I WILL HIGHLIGHT THE POTENTIAL FOR
RESTRICTIVE CEILINGS WITH MVFR FROM 6Z-8Z...THEN FALLING TO IFR BY
11Z. THIS TIMING IS SUPPORTED BY THE NAM FORECAST SOUNDING FOR KCLT
AND SREF GUIDANCE. OTHERWISE...THE TAF WILL FEATURE NONRESTRICTIVE
VIS AND SCT TO BKN CU AROUND 040 DURING THE AFTERNOON. THE GREATEST
COVERAGE OF SHRA AND TSRA SHOULD REMAIN OVER THE NC FOOTHILLS AND
MTNS.

ELSEWHERE...CONDITIONS WILL FOLLOW KCLT CLOSELY. HOWEVER...KAVL HAS
ALREADY SEEN SEVERAL HOURS OF LIFR CEILINGS AND RESTRICTIVE FOG. I
WILL INDICATE IN THE TAF THAT CONDITIONS WILL REMAIN LIMITED UNTIL
MIX OCCURS AFTER 14Z. ALTHOUGH KAVL AND KHKY WILL SEE THE GREATEST
CHC FOR CONVECTION THIS AFTERNOON AND EVENING...COVERAGE APPEARS TOO
LIMITED TO MENTION WITHIN THE TAFS AT THIS TIME. THE WESTERN
CAROLINA TAFS SHOULD SEE IFR VIS AND CEILINGS LATE TONIGHT...I WILL
HIGHLIGHT FROM 6Z THROUGH 12Z.

OUTLOOK...MOIST SW FLOW WILL CONTINUE TO AFFECT THE TERMINAL
FORECAST AREA THROUGH THIS WEEKEND...AS A COLD FRONT LAYS OVER TO
THE NORTH OF THE AREA. EXPECT POCKETS OF MORNING FOG AND/OR STRATUS
MOST DAYS...WITH CONTINUED CHANCES OF AFTN/EVENING SHRA/TSRA EACH
DAY.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     MED   67%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  88%     HIGH  89%
KHKY       HIGH  96%     HIGH 100%     HIGH  85%     HIGH  84%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  98%     MED   70%     HIGH 100%     MED   79%

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...LEV/NED
NEAR TERM...JDL/NED
SHORT TERM...JPT
LONG TERM...JPT
AVIATION...NED



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