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Area Forecast Discussion

671
FXUS62 KGSP 261710
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
110 PM EDT SUN APR 26 2015

.SYNOPSIS...
COOL AND DRY HIGH PRESSURE RIDGES DOWN FROM NEAR THE GREAT
LAKES AND BE THE MAIN INFLUENCE IN OUR WEATHER THROUGH MOST
OF TUESDAY.  ANOTHER AREA OF LOW PRESSURE WILL MOVE EAST FROM
TEXAS IN MID WEEK GIVING OUR REGION A COOL RAIN.  A DRYING
TREND RETURNS FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
1715 UTC UPDATE...WINDS WERE UPDATED FORM A BLEND OF THE LATEST NAM
AND ADJMAV. SKY COVER WAS UPDATED FROM SATELLITE IMAGERY...AND POPS
AND QPF FROM RADAR TRENDS.

1545 UTC UPDATE...MAXIMUM TEMPERATURES WERE LOWERED IN THE COLD AIR
WEDGE NEAR KCLT...AND RAISED TO ITS SOUTH NEAR KGSP.

1430 UTC UPDATE...POPS WERE INCREASED SLIGHTLY IN THE NORTHERN NC
MOUNTAINS AND FOOTHILLS PER RADAR TRENDS.

1400 UTC UPDATE...WINDS WERE UPDATED FROM THE LATEST NAM AND GFS.
SKY COVER WAS ADJUSTED PER SATELLITE IMAGERY. POPS WERE ADJUSTED
BASED ON CURRENT TENDS AND EXPECTATIONS. ONLY MINOR CHANGES WERE
MADE TO TEMPERATURES AND DEW POINTS.

AS OF 650 AM...THE WEDGE BOUNDARY HAS SLIDE SW ALONG I-85 OVER THE
PAST THE COUPLE HOURS. THE PLACEMENT OF THE BOUNDARY WILL LIKELY
PLAY A KEY ROLE IN SFC CONVERGENCE AND CONVECTION EARLY THIS
AFTERNOON. THEREFORE...I WILL UPDATE THE FORECAST TO SHIFT CHC POPS
SW...DISPLACED FROM THE RECENT RUNS OF THE CAMS. OTHERWISE...I WILL
UPDATE SKY AND TEMPS TO ALIGN WITH THE LATEST OBSERVATIONS.

AS OF 330 AM...SATELLITE AND RADAR IMAGES CONTINUES TO SHOW THE OLD
MCS ASHING OUT ACROSS THE WESTERN CAROLINAS. LATEST RUN OF THE CAMS
INDICATE THE COVERAGE WILL SPREAD EAST...GRADUALLY FADING TO CHC TO
SCHC. IS WAS INTERESTING TO SEE A SPLITTING CELL ACROSS CHESTERFIELD
CO AT 730Z. AT THE SFC...THE WEDGE FRONT RUNS FROM THE NORTHERN TIP
OF LAKE WATEREE...WEST ACROSS THE GSP METRO AREA...NORTH ALONG THE
EAST FACING SLOPES ACROSS THE NC FOOTHILLS. NORTH OF THE
BOUNDARY...LOW CLOUDS AND FOG WILL PERSIST THROUGH SUNRISE. LOW
CLOUDS AND FOG WILL DISSIPATE FROM THE SOUTH TO NORTH DURING THE
EARLY DAYLIGHT HOURS. BY MID DAY...THE CENTER OF LOW PRESSURE IS
EXPECTED TO PASS ACROSS THE UPSTATE OF SC...TRACKING EAST. A WEAK
BACKDOOR COLD FRONT WILL SWEEP SOUTH ACROSS THE REGION DURING THE
AFTERNOON. AS THE LOW PASSES...THE ENVIRONMENT BETWEEN I-85 TO I-77
COULD SUPPORT SCT TSRA DURING THE MID TO LATE AFTERNOON...I WILL
FORECAST CHC POPS. HIGH TEMPERATURES ARE FORECAST TO RANGE FROM
AROUND 80 ACROSS THE UPPER SAVANNAH RIVER VALLEY TO THE MID 60S
ACROSS I-40 TO THE MTNS.

TONIGHT...IN THE WAKE OF THE COLD FRONT...HIGH PRESSURE WILL BUILD
ACROSS THE SOUTHERN APPALACHIAN REGION. CONDITIONS ACROSS THE REGION
SHOULD BECOME CLEAR TO MOSTLY CLEAR...WINDS BELOW 5 KTS...WITH
DEWPOINT DEPRESSION GREATER THAN 5 DEGREES. LOW TEMPERATURES SHOULD
FALL CLOSE TO NORMAL...FROM THE LOW 40S WITHIN THE MTN VALLEYS TO
LOW 50S ACROSS THE UPPER SAVANNAH RIVER VALLEY.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 AM SUNDAY...SHORT TERM BEGINS WITH LARGE UPPER CLOSED LOW
SPINNING OVER NEW ENGLAND AND SOUTHEAST CANADA...WITH A REINFORCING
SHORTWAVE PUSHING AROUND THE WESTERN PERIPHERY OF THE TROUGH AT THE
BEGINNING OF THE PERIOD. SURFACE HIGH PRESSURE CENTERED OVER SOUTH
CENTRAL CANADA WILL BE RIDGING INTO THE SOUTHEAST. EXPECT A CLEARING
TREND DURING THE DAY ON MONDAY IN THE WAKE OF THE DRY UPPER TROUGH
AXIS PUSHING THROUGH WITH HIGHS BELOW NORMAL UNDER WEAK DEEP LAYER
CAA. CONTINUED BELOW-NORMAL TEMPERATURES MONDAY NIGHT AND WILL HAVE
TO KEEP AN EYE ON LOWS AT THE HIGHER ELEVATIONS IN CASE FROST MIGHT
BE A CONCERN...ESPECIALLY AS WINDS DIE OFF TOWARD SUNRISE TUESDAY.
THE COOL TEMPERATURES CONTINUE ON TUESDAY EVEN WITH MIDLEVEL RIDGING
BEGINNING TO BUILD IN ACROSS THE AREA.

A CUTOFF LOW OVER THE SOUTHERN PLAINS WILL INDUCE CYCLOGENESIS
ACROSS THE NORTHERN GULF MONDAY NIGHT AND EARLY TUESDAY...SPREADING
MOISTURE INTO THE SOUTHEAST TUESDAY AFTERNOON AND EVENING. HAVE
CONTINUED TREND OF RAMPING UP POPS LATE IN THE DAY ON TUESDAY AS
ISENTROPIC UPGLIDE INCREASES ACROSS THE AREA. ECMWF IS BEGINNING TO
TREND A LITTLE FARTHER NORTH WITH THE SURFACE LOW...MORE INTO
SOUTHERN AND EVEN CENTRAL GEORGIA RATHER THAN REMAINING ALONG THE
FLORIDA PANHANDLE...WHICH MIGHT MEAN AN INCREASE IN QPF. OVERALL
MASS FIELDS NOT TOO DISSIMILAR BUT ENOUGH DIFFERENCES IN THE
DETAILS...ESPECIALLY TIMING AND PLACEMENT OF QPF...TO CONTINUE
BLANKETING THE AREA WITH HIGH CHANCE TO LOW LIKELY POPS AT BEST AS
WE TRANSITION INTO THE EXTENDED.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 315 AM SUNDAY...CHANCE TO LIKELY POPS /ESPECIALLY FOR SOUTHERN
ZONES/ BEGIN THE PERIOD AS THE AFOREMENTIONED SURFACE LOW WORKS ITS
WAY EAST ACROSS SOUTHERN GEORGIA. WITH WIDESPREAD CLOUDINESS AND
RAIN...NOT TO MENTION DECREASING THICKNESSES PLUS JUST BEING ON THE
COLD SIDE OF THE SURFACE LOW...WE CONTINUE TO ADVERTISE HIGHS ON
WEDNESDAY WELL BELOW SEASONAL NORMALS...IN SOME LOCATIONS 10 DEGREES
OR SO.

MODEL INCONSISTENCIES AND RUN-TO-RUN DISCONTINUITY CONTINUE WITH
THIS SYSTEM AS THE 00Z GUIDANCE HAS ONCE AGAIN SWITCHED...WITH THE
GFS EXITING THE PRECIP FROM THE AREA FASTER THAN THE ECMWF.
CONTINUED THE COMPROMISE TREND...PULLING BACK ON POPS DURING THE DAY
ON THURSDAY. ECMWF WANTS TO BRING ANOTHER SHORTWAVE AROUND THE BASE
OF THE ELONGATED TROUGH THURSDAY NIGHT INTO FRIDAY BUT HAVE NOT
REFLECTED THIS IN THE GRIDS AT THIS TIME...PREFERRING INSTEAD THE
DRIER SOLUTIONS...HOWEVER AS WE MOVE FORWARD THIS MAY NEED TO BE
REEVALUATED. WE SHOULD SEE A DRYING TREND INTO THE WEEKEND WITH
TEMPERATURES TRENDING MORE TOWARDS CLIMATOLOGY BUT CONFIDENCE IN ANY
ONE SOLUTION NOT PARTICULARLY HIGH AT THIS POINT.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
AT KCLT...THE COLD AIR WEDGE IS HOLDING FAST. GUIDANCE DOES SUPPORT
CIGS RISING TO MVFR THIS AFTERNOON AND LOW VFR THIS EVENING...BEFORE
COMPLETELY ERODING AFTER MIDNIGHT. MODEL VSBY IMPROVES TO VFR EVEN
EARLIER. NE WINDS WILL BACK TO NW BY DAYBREAK. LIGHT SHOWERS NEAR
THE BLUE RIDGE ARE HAVING TROUBLE SPREADING EAST...AND CONVECTIVE
CHANCES WILL BE BEST TO THE SOUTH WHERE BETTER HEATING WILL OCCUR.

ELSEWHERE...KHKY WILL FACE MUCH OF THE SAME RESTRICTION PROBLEMS
THAT KCLT DOES..WITH LOW CLOUDS SOW TO LIFT AND ERODE...BUT VSBY
IMPROVING PERHAPS A BIT MORE QUICKLY. SC SITES AND KAVL SHOULD
REMAIN VFR...ALTHOUGH KGSP IS AWFULLY CLOSE TO THE EDGE OF THE LOW
WEDGE CLOUDS. SW WINDS IN SC WILL VEER NNE AS THE FRONT MOVES
SOUTH THIS AFTERNOON...THEN BACK NW BY DAYBREAK. KAVL WINDS REMAIN
CHANNELED UP VALLEY FROM THE NW. CONVECTIVE CHANCES WILL BE BEST
IN SC...BUT CONFIDENCE IS TOO LOW FOR A MENTION IN THE TAFS.

OUTLOOK...DRY HIGH PRESSURE WILL BUILD IN THROUGH TUESDAY. ANOTHER
LOW PRESSURE SYSTEM MAY TRACK ACROSS THE DEEP SOUTH WEDNESDAY AND
THURSDAY.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       HIGH 100%     MED   69%     HIGH  83%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     MED   78%     HIGH  85%     HIGH 100%
KHKY       HIGH  83%     HIGH  93%     HIGH  83%     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...JAT/NED
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JAT



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