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Area Forecast Discussion

354
FXUS62 KGSP 221814
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
214 PM EDT TUE APR 22 2014

.SYNOPSIS...
A COLD FRONT WILL MOVE OFF THE CAROLINA COAST TONIGHT AS HIGH
PRESSURE CONTROLS OUR WEATHER THROUGH THURSDAY.  A WEAK COLD FRONT
CROSSES OUR AREA ON FRIDAY...WITH A REINFORCING FRONT STALLING TO
THE NORTH OF THE AREA OVER THE WEEKEND. COOLER WEATHER MAY ARRIVE
IN THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 2 PM...LATEST KGSP RADAR IMAGES INDICATED SEVERAL CLUSTERS OF
SHRA ACROSS THE MTNS AND FOOTHILLS...TRACKING EAST AROUND 25 MPH.
LATEST MESOSCALE ANALYSIS HAD AN AREA OF 500-1000 J/JG OF CAPE
ACROSS THE UPSTATE...DROPPING OFF TO 250 J/KG ACROSS KCLT.
CONVECTIVE ALLOWING MODELS INDICATE THAT CONVECTION SHOULD
STRENGTHEN AS IT MOVES ACROSS THE PIEDMONT LATER THIS AFTERNOON.

AS OF NOON...LATEST MESOSCALE ANALYSIS INDICATES THAT WEAK CAPE HAS
DEVELOPED ACROSS THE UPPER SAVANNAH RIVER VALLEY AND UPSTATE...WITH
SHALLOW CIN ACROSS THE MAJORITY OF THE NC ZONES. RECENT RADAR
INDICATED THAT SHRA WERE DRIFTING EAST ACROSS THE MTNS. I WILL
UPDATE THE FORECAST TO FINE TUNE POPS INTO THIS EVENING. IN
ADDITION...TEMPS UNDER LIMITED CLOUD COVER HAVE SURGED WELL ABOVE
THE FORECAST...I WILL UPDATE TO AGREE WITH OBS AND LATEST MOS.

AS OF 940 AM...SUNNY CONDITIONS EAST OF THE MTNS HAVE RESULTED IN
RAPID WARMING THIS MORNING. KGSP LATEST READING WAS 70 DEGREES. I
WILL ISSUE A QUICK UPDATE TO ADJUST SKY TO SATELLITE OBSERVATIONS. I
WILL ALSO UPDATE TEMPERATURE AND DEWPOINTS TO ALIGN WITH RECENT OBS
TRENDS. POPS APPEAR ON TRACK.

AS OF 645 AM...SHWRS ARE JUST ENTERING WESTERN GRAHAM COUNTY ON
SCHEDULE...ALTHO THEY ARE VERY LIGHT PER MRX RADAR. MID CLOUDS
AROUND 10000 FT ARE INCREASING IN COVERAGE ACRS THE MTNS AND
ADJACENT FOOTHILLS EARLIER THAN EXPECTED. THEY ARE STILL SPLOTCHY IN
NATURE ON IR SAT IMAGERY...SO NOT SURE HOW MUCH IMPACT THEY WILL
HAVE ON DAYTIME HEATING/MAX TEMPS AND RESULTANT SBCAPE THIS AFTN.
WITH PREVIOUS UPDATE I BLENDED IN CONSHORT TEMP GRIDS...WHICH
RATCHETED BACK MAX TEMPS ACRS THE WRN 2/3RDS OF THE CWFA FOR THIS
AFTN. CONFIDENCE IN ROBUST CONVECTION AND SEVERE THIS AFTN IS
DECREASING BASED ON THESE TRENDS.

AS OF 500 AM...FOR THE 0830 UTC UPDATE...I TWEAKED TEMP/DWPT TO
MATCH UP WITH LATEST OBS. THE RADAR MOSAIC SHOWS AN AREA OF SHOWERS
CROSSING CENTRAL TN AND NRN AL. THE LEADING EDGE LOOKS TO REACH THE
SMOKIES AROUND 7 AM. THE POPS LOOK ON TARGET...BUT IF THE COVERAGE
CONTINUES TO BE AS HIGH AS IT IS NOW...I MAY BUMP THEM UP A LITTLE
WITH NEXT UPDATE.

AS OF 245 AM...A FULL LATITUDINAL TROF WITH SEVERAL EMBEDDED VORT
MAXES WILL CROSS THE CWFA TODAY. ONE OF THE LEADING VORT MAXES IS
ALREADY CROSSING THE AREA EARLY THIS MORNING...WITH INCREASING
MID-HIGH CLOUDINESS. AT THE SFC...A COLD FRONT IS CURRENTLY ENTERING
THE OH VLY...AND WILL CROSS THE AREA THIS EVENING. DISORGANIZED
PRE-FRONTAL SHOWERS ACRS THE OH/TN VLYS SHUD START TO ENTER THE NC
MTNS RIGHT AROUND DAYBREAK THIS MORNING.

FOR TODAY...GUIDANCE SEEMS TO BE BACKING OFF POPS A TAD...WHICH
ISN/T TOO SURPRISING...AS LLVL FLOW VEERS TO WLY BEFORE THE FRONT
ARRIVES. THERE IS SOME Q-VECTOR CONVERGENCE AND UPR JET DIVERGENCE
AROUND 18Z ACRS WRN NC. BUT EVEN THAT IS NOT THAT IMPRESSIVE IN ANY
OF THE PROGS. BLENDING IN THE 00Z NAM/GFS...I ACTUALLY GET A
DECREASE IN POPS EAST OF THE MTNS...IN THE HIGH-END CHC TO LOW-END
LIKELY RANGE. TEMPS SHUD BE ABLE TO WARM INTO THE MID-UPR 70S.
HOWEVER...WITH LEADING SHORTWAVE ENERGY WORKING IN THIS
MORNING...MID LVL CLOUDINESS MAY HAMPER DIURNAL HEATING SOMEWHAT. AS
FOR SEVERE POTENTIAL...IT STILL DOES NOT LOOK GOOD. FCST SNDGS SHOW
MOIST MID LVLS WITH WEAK LAPSE RATES AND GENERALLY LESS THAN 25 KTS
OF 0-6KM BULK SHEAR. HIGH RES MODELS SHOW SORT OF SHOTGUN CONVECTIVE
COVERAGE WITH A FEW STRONGER CELLS...PRIMARILY ACRS THE NC PIEDMONT.
SO I THINK WE WILL SEE MAINLY SCATTERED TO NUMEROUS SHWRS WITH
SCATTERED TSTMS...A FEW OF WHICH MAY APPROACH SEVERE LIMITS IF WE
CAN MANAGE TO DESTABILIZE TO 1500-2000 J/KG OF SBCAPE (AS THE GFS
SHOWS). BUT THE GFS SEEMS TOO HIGH WITH SFC DWPTS ACRS MUCH OF THE
WARM SECTOR...SO MAY BE AN OUTLIER. THE NEW DAY ONE CONVECTIVE
OUTLOOK STILL HAS ONLY GENERAL THUNDER TODAY ACRS THE REGION. WILL
MENTION THUNDER THREAT IN THE HWO...BUT IF ANY MENTION OF
SEVERE...JUST THAT IT CANNOT BE RULED OUT.

TONIGHT...GUIDANCE IN GOOD AGREEMENT ON DRY AIR AND CAA WORKING INTO
THE AREA QUICKLY THIS EVENING. SO POPS PRETTY MUCH END BY 00Z THIS
EVENING...SAVE FOR A FEW SHWRS LINGERING ALONG THE TN/NC BORDER WITH
HELP FROM NW UPSLOPE FLOW. FLOW STRENGTHENS TO 40-50 KTS AT 850 MB
IN THE NC MTNS WITH A STRONG BUT LOW INVERSION...HELPING PRODUCE
STRONG CHANNELED VALLEY WINDS. RIGHT NOW...IT LOOKS LIKE WINDS SHUD
GENERALLY STAY SUB-ADVISORY LEVELS. TEMPS SHUD BE ABLE TO FALL INTO
THE UPR 30S TO LWR 40S IN THE MTNS AND MID-UPR 40S ACRS THE PIEDMONT
BEHIND THE FRONT.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 225 AM TUESDAY...DRY HIGH PRESSURE WILL BEGIN TO BUILD DOWN
OVER THE FORECAST AREA ON WEDNESDAY...WITH RESIDUAL BRISK NW FLOW
LINGERING THROUGH AT LEAST THE MORNING HOURS. THERE IS SOME
POTENTIAL FOR AN OROGRAPHICALLY INDUCED CIRRUS SHIELD TO FORM IN THE
MTN WAVE FLOW OVER WRN NC WED MORNING...BUT UPSTREAM MOISTURE
REMAINS A QUESTION MARK. OTHERWISE...EXPECT DRY CONDITIONS WED WITH
MAX TEMPS NEAR CLIMO IN THE SRN TIER AND ONE TO TWO CATEGORIES BELOW
NORMAL IN THE NRN TIER.

FLAT UPPER RIDGING WILL THEN BUILD IN FROM THE WEST LATE WED AND
LINGER THROUGH THU. SPOTTY 30S FOR OVERNIGHT LOWS WILL BE POSSIBLE
IN THE NC MTNS THU MORNING WITH GOOD RADIATION...BUT WITH TEMPS
PROBABLY A LITTLE TOO WARM FOR FROST. RETURN FLOW MOISTURE WILL
START TO SET UP FROM THE SW THU AFTN AND EVENING. THIS MIGHT
CONTRIBUTE A FEW MORE CLOUDS...BUT POPS STILL LOOK UNLIKELY. TEMPS
WILL HOVER NEAR CLIMATE NORMS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 100 PM EDT TUESDAY...THE EXTENDED RANGE PERIOD INITIALIZES
SATURDAY MORNING IN THE WAKE OF A PASSING FRONTAL BOUNDARY.  HIGH
PRESSURE DIVING SOUTHWARD FROM CENTRAL CANADA WILL SPREAD ACROSS THE
OHIO VALLEY WITH A REINFORCING BACK DOOR COLD FRONT PUSHING INTO THE
SOUTHERN APPALACHIANS SATURDAY EVENING.  FORECAST WILL REMAIN DRY
INTO LATE SUNDAY MORNING BEFORE POPS RAMP UP AHEAD OF AN APPROACHING
WARM FRONT WHICH WILL INTERACT WITH THE QUASI STATIONARY BACK DOOR
FRONT DRAPED ACROSS THE AREA.

THIS WARM FRONTAL INTRUSION WILL BE IN RESPONSE TO SURFACE
CYCLOGENESIS ACROSS THE CENTRAL PLAINS BEING DRIVEN BY AN EASTWARD
MIGRATING BROAD NEGATIVELY TILTED UPPER TROF.  MODEL DISCONTINUITY
REMAINS PREVALENT REGARDING THIS SYSTEM AND ITS IMPACTS ACROSS
NORTHEAST GA AND THE WESTERN CAROLINAS.  THE GFS SOLUTION HAS THE
ABOVE MENTIONED SURFACE RIDGE TRANSITIONING TO A BERMUDA TYPE HIGH
WITH A PROGRESSIVELY DEEPENING SURFACE LOW PASSING THROUGH THE OHIO
VALLEY.  THE ECMWF ON THE OTHER HAND SHIFTS THE ABOVE MENTIONED OHIO
VALLEY RIDGE OVER NEW ENGLAND SETTING UP A WEDGE CONFIGURATION ALONG
THE APPALACHIANS.  THE GFS SOLUTION FAVORS A MORE ROBUST AND DYNAMIC
EVENT WHILE THE ECMWF LEANS TOWARDS A LESS FAVORABLE THUNDERSTORM
ENVIRONMENT AS CAD LIKE REGIME INHIBITS WARM FRONTAL SURGE.
THUS...AT THIS RANGE DECIDED TO RAMP POPS UP TO SOLID CHANCE LEVELS
WITH MENTION OF A CHANCE OF THUNDER FOR MONDAY AND TUESDAY.
TEMPERATURES THROUGH THE PERIOD WILL GENERALLY REMAIN ABOVE NORMAL
THROUGH SUNDAY WITH SLIGHTLY COOLER TEMPERATURES POSSIBLE ON MONDAY
AND TUESDAY AS SKY COVER INCREASES ASSOCIATED WITH WARM FRONTAL
ACTIVATION AND POTENTIAL PRECIPIATION.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
KCLT...AT 2 PM...LATEST KGSP RADAR IMAGES INDICATED SEVERAL
CLUSTERS OF SHRA ACROSS THE MTNS AND FOOTHILLS...TRACKING EAST
AROUND 25 MPH. LATEST MESOSCALE ANALYSIS HAD AN AREA OF 500-1000
J/JG OF CAPE ACROSS THE UPSTATE...DROPPING OFF TO 250 J/KG ACROSS
KCLT. CONVECTIVE ALLOWING MODELS INDICATE THAT CONVECTION SHOULD
STRENGTHEN AS IT MOVES ACROSS THE PIEDMONT LATER THIS AFTERNOON. I
WILL CONTINUE TO HIGHLIGHT THE PERIOD FOR TSRA WITH A TEMPO FROM
19Z-22Z...WITH NW WIND GUSTS TO 20 KTS. BY 22Z...THE CLUSTER/BANDS
OF CONVECTION SHOULD MOVE EAST OF THE REGION...FOLLOWED WITH FROPA
BY 0Z. THE REMAINDER OF THE TAF PERIOD WILL FEATURE VEERING WINDS AND
VFR CONDITIONS. WINDS SHOULD BECOME NW BY 9Z.

ELSEWHERE...SHRA TO VCSH WILL IMPACT THE TERMINALS THROUGH LATE THIS
AFTERNOON. INSTABILITY HAS LIKELY PEAKED ACROSS THE
REGION...HOWEVER...KAND NE TO KGSP COULD SEE VCTS BETWEEN 20-22Z.
FROPA WILL LIKELY OCCUR DURING THE EARLY EVENING...FOLLOWED BE
VEERING WINDS. GUSTY NNW WINDS IS EXPECTED TO DEVELOP AT KAVL BY
8Z...REMAINING THROUGH THE REST OF THE TAF PERIOD. EAST OF THE
MTNS...WINDS WILL INCREASE FROM THE NNW TO AROUND 10 KTS BY
15Z...KHKY COULD SEE SOME MORNING MTN CIRRUS.

OUTLOOK...DRY HIGH PRES WILL REMAIN FOR THURSDAY. ANOTHER COLD FRONT
WITH POTENTIAL FOR SHOWERS/TSTMS IS THEN EXPECTED TO CROSS THE
REGION FRIDAY.

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 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...HG
NEAR TERM...ARK/NED
SHORT TERM...HG
LONG TERM...HG
AVIATION...NED






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