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Area Forecast Discussion

358
FXUS62 KGSP 291750
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
150 PM EDT SAT AUG 29 2015

.SYNOPSIS...
WEAK SURFACE HIGH PRESSURE WILL LINGER OVER THE REGION THROUGH THE
WEEKEND...BUT WITH MOISTURE GRADUALLY INCREASING FROM THE SOUTHWEST.
TROPICAL SYSTEM ERIKA IS EXPECTED TO MOVE SLOWLY NORTHWARD THROUGH
THE EASTERN GULF OF MEXICO ON MONDAY AND TUESDAY. THE FATE OF ERIKA
WILL BECOME MUCH MORE UNCERTAIN FROM MID WEEK ONWARD...BUT TROPICAL
MOISTURE COULD GRADUALLY REACH THE WESTERN CAROLINAS AND NORTHEAST
GEORGIA THROUGH THE UPCOMING WORK WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 145 PM EDT SATURDAY...CURRENT FCST REMAINS ON TRACK THEREFORE
ASIDE FOR MINOR TWEAKS TO TEMPS/SKY...NO OTHER CHANGES MADE/NEEDED
WITH THIS UPDATE.  FULL FCST DISCUSSION TO FOLLOW WITHIN THE HOUR.

PREVIOUS DISCUSSION...

AS OF 3 AM...THE CENTER OF WEAK SFC HIGH PRESSURE WILL REMAIN NORTH
OF THE REGION TODAY...SLIGHT RIDGING WILL LIKELY CONTINUE ACROSS
THE CAROLINAS AND NE GA. SFC WINDS ARE FORECAST TO REMAIN LIGHT FROM
THE EAST-NORTHEAST. LATEST WATER VAPOR IMAGES SHOW THE CENTER OF A
MID LEVEL LOW OVER THE MISSISSIPPI RIVER DELTA...WITH RIDGING OVER
THE SOUTHEAST CONUS. THE CIRCULATION AROUND THE LOW WILL RESULT IN
MOISTURE ACROSS THE FORECAST AREA TO INCREASE FROM THE TOP-DOWN
THROUGH TONIGHT. I EXPECT THAT CIRRUS AND CONTRAILS WILL BECOME
THICKER THROUGH THIS AFTERNOON...THE MID AND HIGH CLOUDS SHOULD
SWEEP NORTH ACROSS THE REGION TONIGHT. FORECAST SOUNDINGS INDICATE
THAT THE LOW LEVEL ENVIRONMENT WILL REMAIN RATHER DRY THROUGH
THIS AFTERNOON. THE COMBINATION OF DRY LOW LEVELS...A SIGNIFICANT
INVERSION AROUND 675 MB...MILD TEMPERATURES WILL RESULT IN LITTLE
TO NO CAPE TODAY. I WILL KEEP POPS LIMITED TO SINGLE DIGITS EAST
OF THE MTNS...AND SCHC ACROSS THE WESTERN MTNS. HIGH TEMPERATURES
ARE FORECAST TO RANGE FROM 2 TO 3 DEGREES BELOW NORMAL.

TONIGHT...THE MID LEVEL LOW IS FORECAST TO SLOW LIFT NORTH OVER
THE DEEP SOUTH...BUT REMAINING SOUTH OF I-20 THROUGH 12Z SUN. A
PLUME OF MOISTURE WILL LIKELY LIFT ACROSS THE SOUTHERN APPALACHIAN
REGION. IT APPEARS THAT A FEW SHOWERS WILL DEVELOP OVER THE EASTERN
UPSLOPE REGION FIRST...THEN INCREASE ACROSS THE WESTERN MTNS THROUGH
SUNRISE. THE GFS IS SEVERAL HOURS FASTER THAN THE NAM WITH THE
ARRIVAL OF MEASURABLE RAINFALL SUN MORNING. I WILL SIDE WITH THE
NAM SINCE MODELS HAVE GENERALLY BEEN TRENDING SLOWER WITH THE MID
LEVEL LOW. I WILL KEEP POPS LIMITED TO A CHC ACROSS THE WESTERN
TIER...AND SCHC WEST OF HWY 321. I WILL FORECAST LOW TEMPERATURES
FROM THE LOW 60S ACROSS THE MTNS TO NEAR 70 AROUND KAND.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 230 AM EDT SATURDAY...A 250 MB JETLET WILL MOVE NWD OVER THE
FORECAST AREA ON SUNDAY AS A MID/UPPER LEVEL SHORTWAVE PHASES BACK
INTO THE NRN STREAM FLOW AND LIFTS NE ACROSS THE SRN APPALACHIANS.
THIS IMPROVED FORCING WILL BE COINCIDENT WITH DEEPER MOISTURE
ARRIVING IN PROFILES FROM THE SW TO WARRANT SOLID CHANCE POPS FOR
SHOWERS IN ALL BUT THE NW NC PIEDMONT THROUGH SUNDAY. THE ASSOCIATED
CLOUDINESS WILL LIMIT INSTABILITY AND THE DIURNAL TEMPERATURE RANGE
ON SUNDAY...WITH SOME WEAK IN SITU WEDGING POSSIBLE IF SHOWERS
BECOME A BIT MORE WIDESPREAD. DESPITE THE CLOUDS...BRIEFLY STEEPER
LAPSE RATES ALOFT UNDER THE PASSING TROUGH WILL WARRANT AN ISOLD TO
SCT THUNDER MENTION FOR SUNDAY AFTN...ESPECIALLY IN SRN SECTIONS.

AN UPPER RIDGE WILL THEN BUILD OVER THE SOUTHEAST MONDAY THROUGH
MONDAY NIGHT AS THE SHORTWAVE DEPARTS TO THE NE AND THE LINGERING
SRN TIER TROUGH RETROGRADES TO E TX. TEMPERATURES SHOULD REBOUND
CLOSER TO CLIMO FOR MON...WITH DIURNAL ISOLD TO SCATTERED
SHOWERS/TSTMS EXPECTED WITH WEAK INSTABILITY BUT WITH DEVELOPING SE
UPSLOPE FLOW. PRECIPITATION CHANCES MAY BE SLOW TO WANE MONDAY NIGHT
IF ANY TROPICAL MOISTURE FROM ERIKA STARTS TO ENTER THE PICTURE.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 230 AM EDT SATURDAY...THE EVENTUAL TRACK OF ERIKA AND THE
ASSOCIATED MOISTURE WILL PROVIDE PLENTY OF UNCERTAINTY IN THE
CURRENT MEDIUM RANGE FORECAST. HOWEVER...THE SURROUNDING SYNOPTIC
FEATURES LOOK A LITTLE BETTER RESOLVED. THE UPPER LEVEL TROUGH AXIS
NEAR THE MS RIVER VALLEY WILL STRENGTHEN A 250 MB JETLET FROM THE
GULF COAST TO JUST WEST OF THE APPALACHIANS TUE THROUGH THU. THIS
UPPER LEVEL FEATURE MAY BECOME COINCIDENT WITH A LOW LEVEL 925 TO
850 MB RIDGE OF EQUIVALENT POTENTIAL TEMPERATURE STRETCHED THROUGH
THE PIEDMONT OF THE CAROLINAS. THERE IS SLOWLY GROWING CONCERN THAT
THIS MIGHT PROVIDE A FAVORABLE SETUP FOR A PREDECESSOR RAINFALL
EVENT...PRE...SOMEWHERE OVER THE REGION BY MID WEEK AHEAD OF THE
TROPICAL SYSTEM EXPECTED TO MOVE SLOWLY NORTHWARD THROUGH THE
EASTERN GULF OF MEXICO. ONE LIMITING FACTOR MAY BE THE LOW LEVEL
BLOCKING RIDGE OVER THE MID ATLANTIC WHICH COULD INHIBIT MOISTURE
TRANSPORT NORTHWARD. THE COMBINATION OF ANY PRE ALONG WITH E TO SE
UPSLOPE FLOW INTO THE HIGHER TERRAIN OF THE SOUTHERN APPALACHIANS
COULD CREATE THE POTENTIAL FOR HEAVY RAINFALL THROUGH THE PERIOD.
THIS MIGHT BE BENEFICIAL GIVEN THE CURRENT DROUGHT STATUS...BUT IT
COULD ALSO BECOME EXCESSIVE BY MID TO LATE WEEK.

GIVEN THE UNCERTAINTY...WILL SIMPLY FEATURE ABOVE CLIMO POPS FOR THE
TUE THROUGH FRI PERIOD AS THE ERIKA REMNANTS MEANDER NORTHWARD. WILL
GIVE THE POP TRENDS A SLIGHTLY DIURNAL CHARACTER WITH AN ISOLD TO
SCT AFTN THUNDER MENTION...BUT WILL KEEP SOME COVERAGE GOING THROUGH
THE OVERNIGHT HOURS. AND...WILL SHADE THE DIURNAL TEMPERATURE
CHANGES TO A SMALLER RANGE GIVEN THE POTENTIAL FOR MORE
CLOUDS/PRECIP. WILL HOLD OFF ON ANY HWO MENTION OF HEAVY RAINFALL
UNTIL THE TROPICAL MOISTURE/PRE POTENTIAL IS BETTER RESOLVED.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT...VFR THROUGH THE PERIOD.  UPPER LOW ROTATING OVER THE
NORTHCENTRAL GULF WILL SLOWLY MOVE INLAND THROUGH THIS TAF CYCLE AND
THUS ADVECT MOISTURE ATOP THE DEEP SOUTH ALL THE WHILE EDGING OUT
THE MID ATLANTIC SURFACE HIGH.  THUS...INITIALIZED TAF WITH LIGHT
ESE FLOW UNDER SCT MID AND BKN HIGH CLOUDS.  THESE CONDITIONS WILL
CONTINUE THROUGH THE AFTERNOON/EVENING BEFORE CALMING WINDS AND
BKN/OVC MID/HIGH CIGS PREVAIL THROUGH THE REMAINDER OF THE PERIOD.
MODELS DO INDICATE INCREASING SHRA ACTIVITY SLIDING NORTHWARD
BY DAYBREAK SUNDAY...HOWEVER SHOULD STAY SOUTHWEST OF KCLT FOR
THIS CYCLE.

ELSEWHERE...MUCH THE SAME AS KCLT ABOVE WITH VFR PREVAILING THIS
AFTERNOON/EVENING AMONGST INCREASING DEEP LAYER MOISTURE. IN
RESPONSE...ALL SITES HAVE MID/HIGH CLOUDS FEATURED THROUGH MORNING
WITH CIGS GRADUALLY DEVELOPING WITH TIME.  ONE CAVEAT IS THAT
GUIDANCE DID FAVOR LOW END MVFR FOG RESTRICTIONS IN THE FRENCH
BROAD VALLEY ON SUNDAY MORNING...THUS THE KAVL TAF FEATURES SUCH.
LASTLY...AS MENTIONED ABOVE...HIGHER RES GUIDANCE FAVORS SHRA MOVING
IN FROM THE SOUTH BEFORE/AROUND DAYBREAK.  OPTED TO MENTION VCSH AT
ALL SC SITES LATE IN THE PERIOD WITH ALL OTHER SITES REMAINING DRY.
WINDS WILL REMAIN ESE TODAY...CALMING OVERNIGHT...AND INCREASE
OUT OF THE SOUTH ON SUNDAY.

OUTLOOK...THE SOUTHEAST REGION IS FORECAST TO REMAIN UNDER A PLUME
OF GULF AND ATLANTIC MOISTURE THROUGH THE MIDDLE OF NEXT WEEK. IN
ADDITION...MOISTURE ASSOCIATED WITH THE REMNANTS OF ERIKA COULD
REACH THE SOUTHERN APPALACHIANS DURING THE MID WEEK. RESTRICTIONS
ARE POSSIBLE DURING PERIODS OF RAIN AND WITHIN THE MTN VALLEYS
AROUND DAWN.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH  94%     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  98%

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

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...HG
NEAR TERM...CDG/NED
SHORT TERM...HG
LONG TERM...HG
AVIATION...CDG



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