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Area Forecast Discussion

525
FXUS62 KGSP 240601
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
201 AM EDT THU APR 24 2014

.SYNOPSIS...
DRY HIGH PRESSURE...CENTERED NEAR THE GREAT LAKES...WILL CONTROL OUR
WEATHER THROUGH THURSDAY. A WEAK COLD FRONT WILL CROSS THE FORECAST
AREA ON FRIDAY...WITH A REINFORCING FRONT STALLING IN THE VICINITY
OF THE REGION OVER THE WEEKEND. A WET AND POSSIBLY STORMY PATTERN
WILL SET UP FOR EARLY NEXT WEEK...FOLLOWED BY COOLER WEATHER.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1245 AM...TEMPS/DEWPTS/WINDS ARE PRETTY MUCH ON TRACK. SO NO
CHANGES NEEDED EXCEPT TO UPDATE THE AVIATION GRIDS FOR THE 06Z TAFS.

AT 1030 PM EDT... VIRTUALLY NO CHANGES NEEDED IN LATE EVENING
UPDATE.  HIGH PRESSURE SYSTEM EXTENDING FROM CANADA SOUTHWARD INTO
THE SOUTHEASTERN STATES WILL BE THE PRIMARY FEATURE AFFECTING THE
WEATHER OVERNIGHT AND THURSDAY. WINDS CONTINUE... GENERALLY LESS
THAN 10 MPH... BUT WEAKENING TREND WILL PERSIST AS SURFACE-BASED
INVERSION DEVELOPS. AT 10 PM... NOAA/ESRL PROFILER AT MARION STILL
HAD FAIRLY DEEP LAYER... TO ABOUT 8000 FT... OF NORTHWEST WIND
AROUND 10 KT WHILE OLD FORT PROFILER AT THE FOOT OF THE BLUE RIDGE
ESCARPMENT DISPLAYED A VARIABLE WIND AT LESS THAN 10 MPH FROM THE
SURFACE TO ABOUT 4500 FEET. NEW NAM INDICATES SURFACE PRESSURE
GRADIENT RELAXES A BIT OVER WESTERN NORTH CAROLINA BY 2 AM... SO
EXPECT SPEEDS WILL DECREASE PER THE FORECAST.

PREVIOUS DISCUSSIONS...
AT 730 PM EDT... SATELLITE IMAGERY SHOWS CLOUD-FREE SKY CONTINUES
INTO THE EVENING ACROSS MUCH OF THE EASTERN U.S. CENTER OF HIGH
PRESSURE IS NEAR HUDSON BAY BUT THE SURFACE RIDGE EXTENDS SOUTHWARD
ALL THE WAY TO THE GULF COAST STATES. HIGH HAS SUPPRESSED MOISTURE
FAR TO OUR SOUTH AND UPPER LEVEL RIDGE IS OVER THE MISSISSIPPI
VALLEY SO CLEAR WEATHER WILL CONTINUE OVERNIGHT. AIR IS SO DRY THAT
FOG... EVEN IN MOUNTAIN VALLEYS... SHOULD NOT BE AN ISSUE. THURSDAY
MORNING LOW TEMPERATURES IN THE MID AND UPPER 30S IN THE MOUNTAIN
VALLEYS ARE SUFFICIENTLY COLD FOR FROST... BUT THE DRY AIR SHOULD
RESULT IN ONLY PATCHY FROST AS SUNRISE APPROACHES.

AT 445 PM EDT... HIGH PRESSURE CENTERED TO OUR NORTH AND UPPER LEVEL
RIDGE TO THE WEST CONTINUE THE FAIR WEATHER ACROSS THE REGION.
REMAINING GUSTINESS IN THE SURFACE WINDS WILL DIMINISH QUICKLY
AROUND SUNSET. ONLY CHANGES TO FORECAST AT THIS TIME TAKE INTO
ACCOUNT CURRENT TEMPERATURES AND DEWPOINTS.

AS OF 150 PM...WEAKENING PRESSURE GRADIENT HAS RESULTED IN MID TO
UPPER TEEN WIND GUSTS ACROSS THE MTNS AND NC FOOTHILLS/PIEDMONT THIS
AFTERNOON. LATEST OBSERVATIONS INDICATED A NOTICEABLE DROP IN RH
VALUES ACROSS THE REGION...ESPECIALLY ACROSS PIEDMONT AREAS. THE
FIRE DANGER STATEMENT CONTINUES TO LOOK WELL PLACED AND TIMED ACROSS
THE NC ZONES.

OVERNIGHT...DRY HIGH PRESSURE WILL RIDGE ACROSS THE WESTERN
CAROLINAS AS A COLD FRONT SLIDES ACROSS OK/TX. WINDS ARE FORECAST TO
REMAIN LIGHT FROM THE NE OR BECOME CALM DURING THE PRE DAWN HOURS.
THE LIMITED MIXING AND CLEAR/MOSTLY CLEAR SKY COVER WILL FAVOR
RADIATIONAL COOLING. HOWEVER...SOUTH H85 WINDS AROUND 15KTS AND LOW
AMPLITUDE RIDGING MAY PROVIDE WEAK LLVL WAA ACROSS THE SOUTHERN
APPALACHIANS. GIVEN THE WEAK WAA...I WILL INDICATE A SLIGHT INVERSE
LAPSE RATE IN THE MIN TEMPERATURE ACROSS THE MTNS. BLENDING OF THE
PREFERRED GUIDANCE SUPPORTS MIN TEMPERATURES BETWEEN 3 TO 6 DEGREES
BELOW NORMAL. I WILL INDICATE UPPER 30S ACROSS THE MTNS AND NC
FOOTHILLS...WITH LOW 40S ACROSS THE I-40 CORRIDOR...WITH MID TO
UPPER 40S ACROSS THE UPPER SAVANNAH RIVER VALLEY AND UPSTATE. PATCHY
FROST IS POSSIBLE WITHIN THE MTNS VALLEYS...BUT BELOW FROST ADVISORY
CRITERIA.

THURSDAY...THE COLD FRONT WILL SWEEP EAST ACROSS THE
ARKLATX...GRADUALLY INCREASING THE RETURN FLOW ACROSS THE FORECAST
AREA. DEWPOINTS ARE FORECAST TO RECOVER 5 TO 10 DEGREES FROM THIS
AFTERNOON. HIGH TEMPERATURES ARE FORECAST TO RANGE WITHIN 1 TO 2
DEGREES OF NORMAL...RESULTING IN RH VALUES IN THE 30S.
OVERALL...CONDITIONS SHOULD REMAIN DRY WITH MOSTLY SUNNY CONDITIONS.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
AS OF 240 PM WED...A RELATIVELY STRONG SHORT WAVE APPROACHES THE
AREA THU NITE AND CROSSES THE AREA FRI. THIS WAVE WILL PUSH A COLD
FRONT ACROSS THE AREA FRIDAY AS WELL. MOISTURE AND ISENTROPIC LIFT
INCREASE THU NITE...BRINGING CHC POP TO THE MTNS AND FOOTHILLS AFTER
MIDNIGHT. GOOD FORCING MOVES IN FRI MORNING WITH THE FRONT AND SHORT
WAVE...BRINGING LIKELY POP TO THE MTNS AND GOOD CHC POP TO THE I-40
CORRIDOR. FORCING AND DEEP MOISTURE IS A LITTLE LOWER OVER NE GA AND
THE WESTERN UPSTATE. THEREFORE...HAVE LIMITED POP TO 40 PERCENT OVER
ALL BUT THE MOUNTAIN PORTIONS. BEST CHC POP SHIFTS TO THE I-77
CORRIDOR FOR THE AFTERNOON AS THE FRONT MOVES INTO THAT AREA. THE
GFS STILL HAS MORE INSTABILITY THAN THE NAM...BUT ITS VALUES HAVE
DECREASED. WHILE THERE WILL BE SOME SHEAR GIVEN THE STRENGTH OF THE
SHORT WAVE AND COLD FRONT...IT GENERALLY REMAINS IN THE LIGHT RANGE.
THEREFORE...ALTHOUGH SCT THUNDERSTORMS WILL DEVELOP...SEVERE STORM
POTENTIAL IS LOW. QPF AMOUNTS ARE NOT EXPECTED TO BE EXCESSIVE
EITHER. TEMPS WILL BE AROUND 5 DEGREES ABOVE NORMAL.

PRECIP WILL QUICKLY TAPER OFF EARLY FRI EVENING AS THE FRONT MOVES
EAST OF THE AREA. A LOW AMPLITUDE UPPER TROF WILL CROSS THE AREA SAT
AS AN UPPER LOW MOVES FROM THE GREAT LAKES INTO NEW ENGLAND. AT THE
SFC...HIGH PRESSURE BUILDS IN BRIEFLY BEFORE A WEAK BACK DOOR COLD
FRONT APPROACHES FROM THE NORTH BY THE END OF THE DAY. THE RESULT
WILL BE DRY WX AND MOSTLY SUNNY SKIES. LOWS WILL RANGE FROM NEAR
NORMAL TO 5 DEGREES ABOVE NORMAL. HIGHS WILL BE 5 TO 10 DEGREES
ABOVE NORMAL.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 240 PM EDT WED...THE EXTENDED PART OF THE FORECAST STARTS WITH
A DEEP-LAYER SHORTWAVE RIDGE TRANSLATING ACROSS THE REGION. THIS
SHOULD BRING FAIR AND MILD WEATHER. HOWEVER...THE MODELS HAVE BEEN
TRADING OFF RUN TO RUN AS TO WHETHER A BACK DOOR COLD FRONT CROSSES
THE REGION...BRINGING WITH IT COOLER AND POTENTIALLY CLOUDY WEATHER
IN THE FORM OF COLD AIR DAMMING. FOR NOW I STAYED WITH THE WARMER
AND DRIER EC SOLUTION.

BY MONDAY PW/S BEGIN TO INCREASE ON THE GFS AND LLVL ISENTROPIC
UPGLIDE AND UPSLOPE FLOW DEVELOPS. THE ECMWF IS A LITTLE
SLOWER...THOUGH IT HAS BASICALLY THE SAME SOLUTION. AGAIN...THERE
ISN/T MUCH TO DISAGREE WITH CONCERNING THE WPC GRIDS AND I HAVE
MOSTLY CLOUDY SKIES AND A CHANCE OF SHOWERS. INSTABILITY WILL BE
LIMITED AND ONLY A SMALL CHANCE OF TSTMS IS EXPECTED. BY MONDAY
NIGHT AND TUESDAY THE GFS PW/S INCREASE TO ALMOST 1.75 INCHES AND
THERE IS A CONSIDERABLE INCREASE IN THE LLVL FLOW. WE SHOULD ALSO BE
UNDER STRONG UPPER DIVERGENCE AS A UPPER TROPOSPHERIC JET MAX SHIFTS
EASTWARD UNDER A BROAD UPPER LOW THAT WILL BE CENTERED OVER
MISSOURI. THE POTENTIAL EXISTS FOR HEAVY RAIN LATER MONDAY INTO
TUESDAY. THERE MAY ALSO BE A SEVERE THREAT...THOUGH THE MOIST
WORKED-OVER AIRMASS AND GENERALLY VEERED LLVL FLOW DOESN/T SEEM
CONDUCIVE TO THE HIGH END SEVERE THREAT THAT WILL AFFECT THE PLAINS
WITH THE SYSTEM OVER THE WEEKEND. OF COURSE IT IS STILL QUITE EARLY
TO GET TOO CUTE WITH THE CHANCES OF SEVERE WEATHER FOR THE MON/TUE
PART OF THE FORECAST.

CONFIDENCE IN THE DAY 7 PART OF THE FORECAST IS LOW AS THERE WILL BE
SEVERAL CHUNKS OF SHORT WAVE ENERGY EMBEDDED WITHIN THE BROAD UPPER
LOW THAT WILL SLOWLY CROSS INTO THE EASTERN CONUS. ALL THE MODELS
AGREE THAT THERE WILL BE CONSIDERABLE DOWNSTREAM BLOCKING...SO THE
TROUGH SHOULD DEFINITELY PARK OVER THE REGION FOR A FEW DAYS.
HOWEVER...DEPENDING ON THE TIMING AND HOW ADVECTIVE INDIVIDUAL SHORT
WAVES ARE...THERE MIGHT BE A CHANCE FOR SOME ORGANIZED SEVERE
WEATHER WITH THE COOLING HEIGHTS.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
KCLT AND ELSEWHERE...VFR CONDITIONS EXPECTED THRU THE PERIOD. A N-S
AXIS OF DRY HIGH PRES WILL SHIFT EAST OF THE AREA TODAY...CAUSING
THE WINDS TO VEER FROM NE OVERNIGHT TO SE BY MIDDAY. WINDS SHUD
REMAIN FAIRLY LIGHT...GENERALLY UNDER 10 KTS. OTHER THAN OCCASIONAL
FILAMENTS OF CIRRUS...IT SHUD BE SKC THRU THIS AFTN. A COLD FRONT
WILL ENTER THE OHIO/TENN VALLEY TONIGHT...WITH INCREASING MID AND
HIGH CLOUDS TOWARD THE END OF THE TAF PERIOD.

OUTLOOK...A COLD FRONT WITH POTENTIAL FOR SHOWERS/TSTMS IS EXPECTED
TO CROSS THE REGION FRIDAY. THEN DRY HIGH PRES RETURNS SATURDAY THRU
SUNDAY.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     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...DEO
NEAR TERM...ARK/LGL
SHORT TERM...RWH
LONG TERM...MCAVOY
AVIATION...ARK






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