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Area Forecast Discussion

484
FXUS62 KGSP 200509
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
109 AM EDT WED AUG 20 2014

.SYNOPSIS...
A BROAD UPPER LEVEL RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE
MISSISSIPPI RIVER VALLEY OVER THE NEXT FEW DAYS AND LINGER FOR THE
REST OF THE WORK WEEK...RESULTING IN ABOVE NORMAL TEMPERATURES. A
WEAK COLD FRONT WILL THEN PUSH INTO THE AREA FROM NORTHEAST LATE
FRIDAY INTO SATURDAY AND BRING SOME MINOR RELIEF FROM THE HEAT.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...WINDS WERE UPDATED FROM THE LATEST NAM AND ADJMAV.
SKY COVER WAS UPDATED FROM INFRARED SATELLITE IMAGERY. MORE CLOUD
COVER WAS ADDED TO THE NW NC MOUNTAINS AROUND DAYBREAK ...WHERE AND
ADVANCING MCS WILL MAKE A CLOSE PASS...IF NOT HIT DIRECTLY. POPS
WERE INITIALLY LOWERED PER RADAR TRENDS...THEN RAISED ON THE TN
BORDER TO ACCOUNT FOR THE MCS.

AS OF 1030 PM...ONE FINAL UPDATE THIS EVENING BASED ON RADAR TRENDS.
AREA OF THUNDERSTORMS THAT MOVED DOWN FROM SW VA INTO THE NRN
FOOTHILLS AND NW PIEDMONT SHOULD RAIN ITSELF OUT NEAR KHKY THROUGH
04Z. A FEW OTHER ISOLATED SHOWERS NOTED OVER UPSTATE SC AND THE
UPPER FR BROAD VALLEY SHOULD ALSO DISSIPATE...ALTHO ONE OR TWO MORE
STRAYS CANNOT BE RULED OUT OVER THE SAVANNAH RIVER BASIN OWING TO
RESIDUAL CAPE AROUND 1000 J/KG. BACKED OFF ON POP ALONG TN BORDER
BASED ON LACK OF UPSTREAM CONVECTION. TEMPS LOOK OK.

REMAINDER OF PREVIOUS DISCUSSION...

DEEP LAYER DRYING ASSOCIATED WITH EASTWARD SHIFT OF A MID-LEVEL
SHORT WAVE TROUGH SHOULD RESULT IN DIMINISHING OF CONVECTION FAIRLY
QUICKLY THIS EVENING. THE ONLY EXCEPTION MAY BE ALONG THE TENN
BORDER. LATE TONIGHT...ATTENTION TURNS TO SHORT WAVE TROUGH AND/OR
ASSOCIATED (POSSIBLY ORGANIZED) CONVECTION APPROACHING THE AREA IN
VEERING UPPER FLOW. THE SHORT TERM MODELS...DESPITE PICKING UP ON
THIS SHORT WAVE...DO NOT DEVELOP MUCH IN THE WAY OF CONVECTION
ACROSS THE AREA EARLY WEDNESDAY.

BY WED AFTERNOON...DRIER AIR ALOFT/STEEPER LAPSE RATES IS RESULTING
IN APPRECIABLY STRONGER BUOYANCY IN FORECAST SOUNDINGS ACROSS THE
AREA. NEVERTHELESS...THE SHORT TERM MODELS ARE RATHER MUTED IN THEIR
QPF RESPONSE WED AFTERNOON. NEVERTHELESS...BASED UPON THE DEGREE OF
INSTABILITY...AND THE POTENTIAL FOR WEAK WAVES RIPPLING THROUGH THE
NW FLOW...WILL FEATURE 30-50 POPS ACROSS MUCH OF THE AREA...WITH THE
HIGHEST FAVORED ACROSS THE WESTERN MTNS...IN LIGHT OF PERSISTENT LOW
LEVEL W/NW FLOW ACTING ON A POTENTIALLY VERY UNSTABLE AIR MASS
ACROSS THE TENN VALLEY. THE POTENTIAL FOR SEVERE CONVECTION SHOULD
BE A BIT HIGHER WED OWING TO THE DRIER AIR ALOFT/MORE UNSTABLE
SCENARIO.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AS OF 215 PM TUE...A STRONG UPPER RIDGE AXIS WILL BLOSSOM OVER THE
MIDDLE AND LOWER MS RIVER VALLEY WED NIGHT THROUGH THU...AND THEN
EXPAND EASTWARD TOWARD THE APPALACHIANS THROUGH FRI. A 90 KT 250 MB
JET STREAK RIDING OVER THE BUILDING RIDGE AXIS ON THU WILL PRODUCE
INCREASED UPPER DIVERGENCE SWD ALONG THE APPALACHIAN CHAIN...BUT
THERE IS CONSIDERABLE UNCERTAINTY WHETHER OR NOT THE BEST FORCING
WITH THIS WILL REACH FAR ENOUGH S TO AFFECT OUR AREA. WHAT IS MORE
CERTAIN IS THAT INSTABILITY IN THE DEEP LAYER NW FLOW SHOULD BE
SUFFICIENT FOR UPSTREAM MCS GENERATION THU...BUT WITH THE BULK OF
THE ACTIVITY LIKELY PASSSING N AND E OF OUR AREA. A GENERAL HIGHER
CHC N TO LOWER CHC S POP PATTERN WILL BE NEEDED FOR OUR FORECAST
AREA THU AFTN AND EVENING. TEMPS SHOULD WARM TO A COUPLE OF
CATEGORIES ABOVE NORMAL...BUT WILL KEEP MAX VALUES BELOW MOS AND
LEAN TOWARD THE BIAS CORRECTED MOS MAXES WHICH HAVE BEEN
CONSISTENTLY COOLER THIS SUMMER.

THE DEEP LAYER FLOW COMPONENT MAY BECOME MORE NRLY AROUND THE
STRENGTHENING RIDGE ON FRI...WHICH COULD DRIVE ANY UPSTREAM
CONVECTION FARTHER TO THE SOUTH FROM IT/S GENESIS REGION IN THE OH
VALLEY AND SRN GREAT LAKES. IN ADDITION...THE STEEPER LAPSE RATES
THAT DEVELOPED ON THE ERN PERIPHERY OF THE RIDGE THU WILL PERSIST
THROUGH FRI. A SIMILAR PATTERN OF DIURNAL...HIGHER N/LOWER S POPS
WILL BE FEATURED FOR FRI ALONG WITH CONTINUED ABOVE CLIMO/BELOW MOS
MAX TEMPS IN THE 90S.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 140 PM EDT TUESDAY...THE MEDIUM RANGE PICKS UP AT 00Z ON
SATURDAY WITH THE UPPER RIDGE AXIS NEARLY STATIONARY AND JUST TO OUR
WEST AND BROAD UPPER TROFFING JUST OFF THE ATLANTIC SEABOARD. FOR
THE REMAINDER OF THE PERIOD...THE RIDGE AXIS REMAINS LARGELY IN
PLACE WHILE THE UPPER TROF BECOMES NEARLY STATIONARY AND MORPHS INTO
A CLOSED H5 LOW OVER THE WEEKEND. THE LATEST MODEL GUIDANCE
CONTINUES TO SUGGEST THAT SOME FLATTENING OF THE UPPER RIDGE IS
LIKELY TOWARDS THE END OF THE PERIOD...YET THIS IS EXPECTED TO BE
MINIMAL.

AT THE SFC...A STRONG HIGH CENTERED OVER FAR EASTERN QUEBEC AND A
DEEPENING LOW MOVING INTO THE NORTH ATLANTIC WILL ESTABLISH A COOLER
AIR WEDGE PATTERN JUST TO OUR NORTH ON SAT. THIS PROVIDES FOR MORE
PERSISTENT NELY LOW LVL FLOW OVER THE FCST REGION AS THE HIGH IS
SLOW TO MOVE EASTWARD AND THE LOW REMAINS OFF THE NORTHEAST COAST
THRU EARLY NEXT WEEK. PREVIOUS MODEL RUNS HAD THE WEDGE PATTERN
BREAKING DOWN BY EARLY NEXT WEEK...HOWEVER THE LATEST RUNS SUGGEST
THAT THE CANADIAN SFC HIGH WILL ACTUALLY MOVE SOUTHWARD EARLY NEXT
WEEK AND MAINTAIN THE WEDGE THRU THE END OF THE MEDIUM RANGE. THIS
SOLUTION IS BETTER SUPPORTED BY THE 00Z ECMWF...WITH THE LATEST 12Z
GFS ACTUALLY SPINNING UP A TROPICAL CYCLONE AND MOVING IT INTO THE
GULF OF MEX BY NEW DAY 7. THIS CAUSES THE FLOW TO BECOME MORE SELY
OVER THE CAROLINAS BY THAT TIME. AS FOR THE SENSIBLE WX...I KEPT A
SOLID CHANCE POP FOR MOST OF THE ZONES ON SAT AND SUN WITH THE
DEEPER MOISTURE EXPECTED TO REMAIN OVER THE AREA AND SOME WEAK
SHORTWAVE ACTIVITY PROVIDING SOME DEGREE OF UPPER SUPPORT EACH
AFTERNOON/EVENING. THE DEEPER MOISTURE IS EXPECTED TO SHIFT EASTWARD
ON MON AND TUES AND THE WEDGE WEAKENS AND THUS WIDESPREAD SHOWER AND TS
ACTIVITY IS NOT AS LIKELY OVER THE WESTERN CAROLINAS. TEMPS START
OUT ABOVE NORMAL ON SAT AND COOL THRU THE WEEKEND...WITH VALUES
EXPECTED TO REBOUND A FEW DEGREES BY EARLY NEXT WEEK.

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...RAIN EARLIER TODAY WILL FAVOR FOG FORMATION BY DAWN. MVFR
CIG AND VSBY WILL BE INTRODUCED BEFORE DAYBREAK. MODEL TIME HEIGHTS
SHOW LOW VFR CLOUDS LINGERING THROUGH THE FORECAST. ALTHOUGH A COLD
FRONT WILL APPROACH FORM THE NE OVERNIGHT...IT IS UNCLEAR IF THE
FRONT WILL REACH KCLT OR NOT...AND SERVE AS A FOCUSING MECHANISM FOR
BOTH CLOUDS AND CONVECTION. CURRENTLY...VERY LITTLE CLOUD COVER IS
ASSOCIATED WITH THIS BOUNDARY. AT THIS TIME GUIDANCE VEERS WINDS
FROM SW TO NE OVERNIGHT...THEN BACKS THEM TO SW TODAY...AND ONLY
VEERS THEM NW TONIGHT. CONVECTIVE CHANCES ARE TOO LOW TO WARRANT A
MENTION IN THE TAF THIS AFTERNOON...AND LOW VFR CIGS WILL NOT BE
CARRIED WITHER.

ELSEWHERE...GUIDANCE FAVORS FOG AT DAYBREAK...BUT MAY BE  TOO
AGGRESSIVE. FOR NOW DAYBREAK MVFR VSBY AND CIGS WILL BE CARRIED AT
ALL SITES BUT KGMU. WINDS VEER FROM SW TO NE OVERNIGHT AS A COLD
FRONT APPROACHES FORM THE NE...BUT NEVER VEER NE AT ANY TAF SITES.
WINDS BACK TO SW TODAY...THEN VEER NW TONIGHT. THE PROXIMITY OF THIS
FRONT COULD SERVE AS A FOCUSING MECHANISM FOR CLOUDS AND CONVECTION
DURING THE DAY...BUT AT THIS TIME LITTLE CLOUDS COVER WAS NOTED WITH
THIS FEATURE. AFTERNOON CONVECTION WILL BE FEATURED AT KAVL ONLY...
WITH LOW VFR CIGS AND VSBY CARRIED WITH CONVECTION.

OUTLOOK...SCT AFTERNOON CONVECTION AND PATCHY EARLY MORNING FOG WILL
REMAIN IN THE FORECAST THROUGH THE WEEK. THERE WILL ALSO BE
INCREASING CHANCES FOR REMNANT ORGANIZED CONVECTION APPROACHING THE
AREA FROM THE NW DURING THE LATE NIGHT/EARLY MORNING HOURS.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-05Z
KCLT       HIGH  85%     HIGH  85%     HIGH 100%     HIGH 100%
KGSP       HIGH  87%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  98%     HIGH  96%     HIGH 100%     HIGH 100%
KHKY       HIGH  91%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH  91%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

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...JPT
NEAR TERM...JAT/JDL/PM
SHORT TERM...HG
LONG TERM...JPT
AVIATION...JAT






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