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Area Forecast Discussion

875
FXUS62 KGSP 030246
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1046 PM EDT THU JUL 2 2015

.SYNOPSIS...
A BROAD UPPER LEVEL TROUGH WILL REMAIN OVER THE SOUTHEAST THROUGH
THE WEEKEND...STEERING A SERIES OF WEAK LOW PRESSURE SYSTEMS OVER
THE REGION. THESE SYSTEMS WILL INCREASE RAIN AND THUNDERSTORM
CHANCES EACH AFTERNOON AND EVENING. SLIGHT DRYING WILL OCCUR ON
MONDAY AND TUESDAY...BEFORE ANOTHER FRONT PUSHES THROUGH LATE NEXT
WEEK. HIGH TEMPERATURES WILL BE NEAR NORMAL THROUGH NEXT WEEK...WITH
LOWS JUST ABOVE NORMAL.

&&

.NEAR TERM /THROUGH FRIDAY/...
1030 PM EDT UPDATE...SOME LIGHT NON-THUNDER SHOWER ACTIVITY HAS
ENTERED INTO SOUTHWEST PORTIONS OF THE CWA.  SHOWERS SHOULD INCREASE
OUT WEST WITH SOME ISOLATED THUNDER OVER THE NEXT 6 HOURS...PER HRRR
GUIDANCE AND RADAR/OBSERVATIONAL TRENDS.  OTHER ASPECTS OF FORECAST ARE ON
TARGET.

800 PM EDT UPDATE...AREA IS MOSTLY CLEAR OF SHOWERS...EXCEPT FOR
EXTREME SOUTHEAST PARTS OF THE CWA WHERE SOME RESIDUAL LIGHT RAIN IS
POSSIBLE.  RADAR GUIDANCE SHOWS SOME THUNDERSHOWERS TO THE EAST AND
WEST OF THE CWA WHICH COULD EVENTUALLY DEVELOP INTO THE CWA LATER
TONIGHT.  WILL HOLD OFF ON INCREASED POPS UNTIL 10Z FOLLOWING HRRR
GUIDANCE.

515 PM EDT UPDATE...MOST SHOWERS HAVE EXITED THE AREA TO THE SOUTHEAST
WITH SOME RESIDUAL LIGHT RAIN.  MADE SUBSTANTIAL CHANGES TO THE NEAR
TERM PRECIP FORECAST TO ACCOUNT FOR THE ABSENCE OF PRECIP IN MOST
AREAS...NEGATIVE RADAR TRENDS...AND SUPPORT FROM THE HRRR TO KEEP
THE NEXT ROUND OF PRECIP OUT UNTIL MIDNIGHT.  ALSO UPDATED
TEMPERATURES DUE TO CONSIDERABLE RAIN COOLING IN SOME AREAS AND
EXTENSIVE CLOUD COVER HOLDING TEMPERATURES DOWN.

AS OF 245 PM EDT...AN OUTFLOW FROM EARLIER CONVECTION WORKING
SOUTHWARD OVER THE WESTERN AND SOUTHERN PART OF THE CWFA HAS
ENCOUNTERED INCREASED INSTABILITY...WITH 1500 TO 2000 J/KG OF SBCAPE
OVER THE UPSTATE AND NE GA THIS AFTN. POPS HAVE BEEN RATCHETED
ACROSS THE SRN THIRD OF THE FORECAST AREA FOR A FEW HOURS THIS
AFTERNOON...AND HAVE CONTINUED TO BACK AWAY FROM THE HIGHER POPS
PREVIOUSLY INDICATED BY THE MESOSCALE MODELS FOR CONVECTION COMING
OFF THE BLUE RIDGE INTO THE NC FOOTHILLS AND PIEDMONT. THIS IS
POSSIBLY JUST THE FIRST WAVE OF MANY...AS ADDITIONAL SHORTWAVES
EMBEDDED IN THE H5 TROUGH WILL CROSS THE FORECAST AREA LATER THIS
AFTERNOON AND EARLY THIS EVENING.

YET MORE VORTICITY LOBES WILL CROSS THE BASE OF THE SOUTHERN
APPALACHIANS LATER TONIGHT THROUGH FRIDAY AS THE TROUGH DEEPENS TO
THE WEST FROM THE LOWER OH VALLEY TO THE MS RIVER VALLEY. WESTERLY
850 MB FLOW WILL INCREASE TONIGHT THROUGH FRI ACROSS THE SRN TIER AS
THE 850 MB LOW CENTER DEEPENS SLIGHTLY OVER THE OH VALLEY. THE
FORECAST AREA WILL STAY SOLIDLY WARM SECTOR THROUGH THE NEAR TERM
PERIOD AS A SURFACE WAVE MOVES ALONG THE STALLED BOUNDARY FROM THE
LOWER OH VALLEY THROUGH THE CENTRAL APPALACHIANS. ANTICIPATE A
SMALLER THAN USUAL DIURNAL RANGE ON TEMPS WITH PLENTY OF
CLOUDS/DEBRIS...AND WILL NEED TO SHOTGUN HIGH CHANCE TO LOW END
LIKELY POPS FOR MUCH OF THE AREA BEYOND THE IMMEDIATE NEAR TERM
GIVEN THE MULTIPLE SHORTWAVES AND MOIST PROFILES. EXPECT GUSTY WINDS
WITH MIXING AGAIN ON FRI AFTN. HEAVY RAIN WILL POSE A LOCALIZED
HYDRO THREAT JUST ABOUT ANYWHERE THAT TRAINING OCCURS...WITH THE SW
MTNS STANDING THE BEST CHANCE OF FLOODING. CONFIDENCE REMAINS TOO
LOW FOR A FLASH FLOOD WATCH SINCE COVERAGE WILL BE HIGHEST IN THE
WESTERN MTNS BUT RATES WILL BE BETTER IN MORE UNSTABLE AREAS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 250 PM THURSDAY...UPPER TROUGH AXIS WILL REMAIN POSITIONED
WEST OF THE FORECAST AREA THROUGH THE WEEKEND...WITH UNSEASONABLY
HIGH PWATS (GENERALLY 1-2 STANDARD DEVIATIONS ABOVE CLIMO) THROUGH
THE PERIOD. A SERIES OF WEAK SHORT WAVE MOVING THROUGH THE TROUGH
AXIS WILL SUPPORT HIGHER-THAN-CLIMO POPS THROUGH THE PERIOD...WITH
AT LEAST GOOD CHANCES FOR CONVECTION PERSISTING INTO THE NOCTURNAL
HOURS. THIS WILL ESPECIALLY BE TRUE ON SAT NIGHT...AS THE MOST
SIGNIFICANT SHORT WAVE (POSSIBLY DEVELOPING INTO A CLOSED LOW) NEARS
THE AREA. HIGH CHANCE TO LIKELY POPS WILL BE CARRIED IN ALL AREAS...
MAINLY FROM SAT AFTERNOON THROUGH SUNDAY AFTERNOON. MOIST
THERMODYNAMIC PROFILES AND RATHER EXTENSIVE CLOUD COVER WILL LIMIT
CAPE THROUGH THE PERIOD...AND THE SEVERE THREAT SHOULD REMAIN HIGHLY
LOCALIZED THROUGH THE PERIOD. HOWEVER...WITH PWATS REMAINING
ELEVATED... THE THREAT FOR LOCALLY HEAVY AND POSSIBLY EXCESSIVE
RAINFALL WILL BE POSSIBLE THROUGH THE PERIOD. THIS THREAT IS
EXPECTED TO BE MOST PREVALENT ACROSS THE FAR WESTERN NC MTNS...WHERE
WESTERLY LOW LEVEL FLOW WILL SUPPORT UPSLOPE ENHANCEMENT TO COVERAGE
OF CONVECTION AND PRECIP RATES. ANTECEDENT CONDITION WILL PROBABLY
ALSO GRADUALLY DETERIORATE IN THOSE AREAS OVER THE NEXT 2-3 DAYS AS
WELL.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...THE MEDIUM RANGE BEGINS 00Z MONDAY WITH THE
AREA IN AN UPPER LEVEL SPLIT-FLOW REGIME. A QUASI-STATIONARY
BOUNDARY WILL BE LOCATED JUST TO THE SOUTH OF THE FORECAST
AREA...PROVIDING A FOCUS FOR DIURNALLY ENHANCED POPS THAT EXTENDS
ACROSS THE SOUTHERN APPALACHIANS. THE INFLUENCE OF THE BERMUDA HIGH
AND PERSISTENT SOUTHWESTERLY FLOW WILL KEEP DEEP LAYER MOISTURE
PLENTIFUL THROUGHOUT THE PERIOD...THOUGH THERE DOES APPEAR TO BE
SOME RELATIVE SLIGHT DRYING OF THE AIRMASS ON MONDAY AND TUESDAY.
DIURNAL POPS NEAR TO JUST ABOVE CLIMO WILL BE PRESENT BOTH DAYS. ON
WEDNESDAY...WEAK UPPER LEVEL TROUGHING WILL BEGIN TO BUILD BACK INTO
THE FORECAST AREA AS AN UPPER LOW AND ASSOCIATED FRONTAL BOUNDARY
TAKE SHAPE OVER THE SOUTHEAST...AND PWATS CLIMB BACK OVER 2 INCHES.
POPS ARE THEREFORE ABOVE CLIMO TOWARD THE END OF THE PERIOD...AND DO
NOT WANE MUCH OVERNIGHT. INSTABILITY DOES NOT APPEAR SPECTACULAR FOR
ANY DAY IN THE MEDIUM RANGE...BUT PLENTIFUL DEEP LAYER MOISTURE
THROUGHOUT THE ENTIRE FORECAST PERIOD WILL MEAN THAT 7-DAY QPF
TOTALS BEAR WATCHING.

DESPITE HEIGHT RISES THROUGHOUT THE MEDIUM RANGE...MOIST PROFILES
AND ASSOCIATED CLOUD COVER WILL KEEP MAX TEMPS HOVERING AROUND
CLIMO. MIN TEMPS WILL BE NEAR TO JUST ABOVE CLIMO.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
AT KCLT...SHOWER AND THUNDER ACTIVITY HAS MOVED SOUTHEASTWARD WELL
AWAY FROM THE AERODROME...LEAVING VFR CONDITIONS WITH A FEW CLOUDS
TO 4000 AND SCT TO BKN HIGH CLOUDS.  FOLLOWING LATEST RADAR TRENDS AND
HIGH-RES MODEL GUIDANCE...THE NEXT ROUND OF PRECIPITATION THAT MIGHT
AFFECT THE SITE WOULD BE AFTERNOON THUNDERSTORMS ON FRIDAY.

ELSEWHERE...SOME LIGHT RAIN EXISTS SOUTH OF KGSP...BUT AT THE MOMENT
NO PRECIPITATION IS AFFECTING ANY TAF SITES.  SOME AREAS OF SHOWERS
ARE POSSIBLE LATER TONIGHT AND EARLY TOMORROW MORNING FROM ANY
SHORTWAVE OR OTHER DYNAMICAL ACTIVITY FROM THE SOUTHWESTERLY FLOW
ALOFT.  HOWEVER...MAIN POSSIBILITY FOR SIGNIFICANT IMPACTS WOULD BE
LATE MORNING AND AFTERNOON THUNDERSTORMS ON FRIDAY.  FOG IS ALSO
POSSIBLE IN THE MORNING IN LOW-LYING MOUNTAINOUS AREAS DUE TO
CONTINUED MOIST AIR MASS.

OUTLOOK...A GRADUALLY WEAKENING UPPER TROUGH WILL SUPPORT MAINLY
AFTERNOON AND EVENING THUNDERSTORMS THROUGH EARLY NEXT WEEK.
RESTRICTIONS MAY OCCUR WITH PASSING STORMS...AND EACH MORNING OVER
RAIN SOAKED AREAS.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     HIGH  93%     HIGH  80%     HIGH 100%
KGSP       HIGH 100%     HIGH  83%     HIGH  84%     HIGH 100%
KAVL       HIGH 100%     MED   63%     MED   76%     HIGH 100%
KHKY       HIGH 100%     HIGH  97%     HIGH  84%     HIGH  97%
KGMU       HIGH  98%     HIGH  83%     HIGH  85%     HIGH 100%
KAND       HIGH  95%     HIGH  84%     HIGH  93%     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...LEV
NEAR TERM...HG/WJM
SHORT TERM...JDL
LONG TERM...LEV
AVIATION...HG/WJM



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