Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KGSP 150730
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
330 AM EDT MON SEP 15 2014

.SYNOPSIS...
COOL BUT UNSETTLED WEATHER WILL CONTINUE THROUGH TONIGHT...AS A
STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH BEFORE AN UPPER
DISTURBANCE PASSES THROUGH. A COLD FRONT WILL THEN CROSS THE AREA IN
ITS WAKE...USHERING IN SEASONABLY COOL AIR AND MOSTLY DRY WEATHER
LASTING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS WEAKENING HIGH PRESSURE RIDGE SLIDES OFF THE COAST TODAY
(ESSENTIALLY ENDING THE PERIOD OF NE FLOW)...AND THE FLOW ABOVE THE
SURFACE LAYER TURNS TO LIGHT WESTERLY...LOW CLOUDS SHOULD LIFT AND
POSSIBLY SCATTER AT TIMES LATER TODAY. THIS WILL ALLOW TEMPS TO
REBOUND TO 75-80 ACROSS MUCH OF THE AREA THIS AFTERNOON...WHICH IS
STILL A FEW DEGREES SHY OF CLIMO. THE ADDITIONAL HEATING SHOULD
ALLOW THE ATMOSPHERE TO DESTABILIZE MODESTLY THIS AFTERNOON.
COMBINED WITH PWATS THAT REMAIN QUITE JUICY FOR THE TIME OF
YEAR...ISLD TO WIDELY SCT CONVECTION SHOULD DEVELOP BY MID-AFTERNOON
ACROSS WESTERN AREAS...ESP ACROSS THE HIGH TERRAIN AND UPPER
SAVANNAH RIVER VALLEY...WHERE INSTABILITY SHOULD BE GREATEST.

THE SHORT TERM MODELS KICK A WEAK SHORT WAVE TROUGH...CURRENTLY SEEN
AS A SUBTLE FEATURE IN WV IMAGERY OVER NW TEXAS...OVER THE SOUTHEAST
LATER TODAY...WHICH SUPPORTS QUITE A BIT OF CONVECTIVE DEVELOPMENT
OVER THE TENN VALLEY/NORTH GA BY LATE AFTERNOON. THIS ACTIVITY
SHOULD MAKE A RUN TOWARD...AND/OR INITIATE NEW CONVECTION OVER OUR
AREA BY EVENING...AND THIS IS WHEN POPS REACH A NADIR. THE HIGHEST
POPS...GENERALLY 40-50 PERCENT WILL BE FAVORED OVER THE UPSTATE AND
NORTHEAST GEORGIA...WHICH SHOULD SEE THE MOST FAVORABLE
JUXTAPOSITION OF DEEP MOISTURE/INSTABILITY/FORCING. WHILE SHEAR WILL
BE SOMEWHAT RESPECTABLE FOR THE TIME OF YEAR...CURRENT INDICATIONS
ARE THAT PROFILES WILL BE TOO MOIST AND INSTABILITY TOO LIMITED TO
SUPPORT MUCH OF A SEVERE WEATHER THREAT. ADDITIONALLY...
UNIDIRECTIONAL WIND PROFILES SHOULD SUPPORT PROGRESSIVE CELL
MOVEMENT...SO EVEN THE HEAVY RAIN/FLASH FLOOD THREAT APPEARS TO BE
LOW.

COLD FRONT ASSOCIATED WITH POTENT SHORT WAVE TROUGH TRAVERSING THE
GREAT LAKES REGION IS EXPECTED TO ENTER THE CWA BY DAYBREAK...
SUPPORTING AT LEAST LOW POPS THROUGH THE OVERNIGHT. MIN TEMPS ARE
EXPECTED TO BE SLIGHTLY ABOVE CLIMO.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 300 AM MONDAY...UPPER PATTERN WILL GRADUALLY AMPLIFY OVER THE
CONUS THRU THE MIDWEEK EVENTUALLY LEADING TO DEEPER TROUGHING OVER
THE EAST. A WEAK AREA OF HIGH PRESSURE WILL MOVE EWD OUT OF THE
PLAINS TUE AND TUE NIGHT. A WEAK COLD FRONT AHEAD OF THIS HIGH WILL
WORK THROUGH OUR CWFA TUESDAY...WITH THE HIGH PRESSURE SLOWLY
SHIFTING ACRS THE MTNS BY WED AND PRODUCING WEDGELIKE EASTERLY FLOW
INTO THE AREA. MOISTURE IS NOT THAT IMPRESSIVE THROUGH THE COLUMN AT
ANY TIME DURING THE PERIOD...WITH INSTABILITY THE MAIN JUSTIFICATION
FOR POPS. THOUGH POOR MIDLEVEL LAPSE RATES ARE EXPECTED...THE
PERSISTENT CYCLONIC FLOW ALOFT IS SUGGESTED TO FORCE A LEE TROUGH
TUE AFTN...AND BRING EDDIES ACRS THE FA BOTH TUE AND WED NIGHTS.
CONTINUOUS LOW POPS WILL BE ADVERTISED WITH MINOR INCREASES WHEN
ENHANCED FORCING IS PRESENT. THE COOLER AIR WILL TAKE SOME TIME TO
FILTER IN...AND ESP WITH DOWNSLOPING TUE MAX TEMPS WILL RISE A TAD
ABOVE CLIMO. WED MAXES AND WED NIGHT MINS WILL BE A CATEGORY OR TWO
BELOW CLIMO WITHIN THE POST-FRONTAL AIRMASS.

IT SHOULD BE NOTED THAT THE NAM DEVELOPS MUCH MORE INSTABILITY TUE
AFTN THAN THE GFS BUT KEEPS SFC PARCELS SLIGHTLY CAPPED DUE TO THE
AFOREMENTIONED POOR LAPSE RATES ATOP THE MIXED LAYER. THOUGH ONLY
ISOLATED CELLS ARE EXPECTED TO BE ABLE TO FORM...0-6KM BULK SHEAR
VALUES WILL BE A BIT STRONGER THAN WHAT WE/VE SEEN LATELY. ACTIVITY
FORMING DURING PEAK HEATING MAY POSE A SMALL SEVERE RISK IF IT GROWS
TALL ENOUGH.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 230 AM MONDAY...AN INITIALLY SIMPLE WESTERN RIDGE/EASTERN
TROUGH PATTERN THURSDAY WILL BECOME MORE COMPLEX OVER THE WEEKEND
WITH REASONABLE AGREEMENT BETWEEN THE 15/00Z GFS AND 14/12Z EC AS TO
ITS EVOLUTION. THE ERN TROUGH PROGRESSES ENOUGH TO ALLOW REAL COLD
AIR DAMMING TO FORM BY FRI MRNG...REINFORCING SEASONABLY COOL TEMPS
FOR THE REGION AND SUPPORTING A DRY FCST THRU MOST OF THE WEEKEND.
WEAK UPPER RIDGING RETURNS TO THE SOUTHEAST SATURDAY AS THE PARENT
HIGH IS PUSHED OFFSHORE. THIS IN CONJUNCTION WITH LOW PRESSURE
MOVING ALONG THE CANADIAN BORDER INITIATES RETURN FLOW
SUNDAY...WEAKENING THE WEDGE AND ALLOWING A BRIEF WARMUP. THAT LOW
DOES THEN BRING ANOTHER COLD FRONT INTO OUR AREA TO START THE NEW
WEEK. GFS IS MORE BULLISH WITH THE FRONT AS IT DEVELOPS A SECONDARY
SFC LOW OVER THE MIDWEST IN RESPONSE TO A SHORTWAVE EMBEDDED IN THE
SYNOPTIC FLOW. THE 15/00Z EC JUST ARRIVED STILL FAVORING THE
PREVIOUS RUN/S TRACK OF THE CANADIAN LOW...BUT AMPLIFIES THE UPPER
TROUGH SUBSTANTIALLY. THIS BACKS UP A STRONGER FROPA FOR EARLY
MONDAY. EITHER WAY IT LOOKS LIKE EVEN COOLER WEATHER IS IN STORE
NEXT WEEK.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
AT KCLT...THE PRIMARY CONCERN SURROUNDS JUST HOW MUCH CIGS WILL
LOWER THIS MORNING. CONDITIONS ARE SOLIDLY MVFR AS OF 0530Z...BUT NE
FLOW JUST ABOVE THE SURFACE INDICATES SOME SLIGHTLY DRIER AIR IS
FILTERING INTO THE REGION. ON THE OTHER HAND...NEAR TERM MODEL
GUIDANCE IS IN AGREEMENT THAT THE FLOW WILL TURN TOWARD THE SW
TOWARD DAYBREAK...WHICH WOULD STOP ANY DRY AIR INFILTRATION AND
POSSIBLY ALLOW CIGS TO LOWER TO IFR. IN FACT...I THINK THERE/S
ENOUGH POTENTIAL FOR THIS TO INCLUDE A TEMPO BETWEEN 10Z AND 12Z.
SOME BR IN THE 5-6SM RANGE WILL ALSO BE POSSIBLE. OTHERWISE...CIGS
SHOULD LIFT TO VFR BY EARLY AFTERNOON...AND POSSIBLY SCATTER FROM
TIME TO TIME. AN UPPER AIR DISTURBANCE WILL BRING INCREASING
CHANCES FOR CONVECTION DURING THE EVENING...MAINLY IN THE FORM OF
SHRA. A PROB30 HAS BEE INTRODUCED TO ACCOUNT FOR THIS. LGT/VRBL
WINDS SHOULD BECOME LIGHT SW BY MID-AFTERNOON.

ELSEWHERE...OUR BEST PERFORMING GUIDANCE OVER THE PAST COUPLE OF
DAYS IS INSISTENT IN DEVELOPING LIFR (AT KAVL) AND IFR (ELSEWHERE)
CIGS WITHIN THE NEXT COUPLE OF HOURS...AND HAS PLENTY OF SUPPORT
FROM OTHER RELIABLE GUIDANCE. HOWEVER...CIGS HAVE ACTUALLY BEEN
SLOWLY LIFTING OVER THE PAST COUPLE OF HOURS. THERE IS ALSO
INDICATION THAT THE FLOW WILL VEER TOWARD THE W/SW ABOVE THE SURFACE
(ALBEIT REMAINING LIGHT) TOWARD DAYBREAK...RESULTING IN AN INCREASED
DOWNSLOPE COMPONENT WHICH WOULD BE A LIMITING FACTOR FOR CIGS
LOWERING MUCH FURTHER. NEVERTHELESS...WE ARE STARTING TO SEE PATCHY
FEW/SCT IFR CLOUDS SHOWING UP ON AREA METARS...SO TEMPOS FOR IFR
HAVE BEEN ADDED FOR AT LEAST A COUPLE OF HOURS THROUGH DAYBREAK.
KHKY SEES THE SHORTEST TEMPO (2 HOURS) DUE TO STRONGER EFFECTS FROM
DOWNSLOPING. MEANWHILE...KAVL IS ALREADY LIFR AND SHOULD REMAIN SO
THE REST OF THE NIGHT...ALTHOUGH WOULD NOT BE SURPRISED TO SEE THEM
VARY QUITE A BIT...ES ONCE THE W/SW FLOW BECOMES ESTABLISHED. AN
UPPER AIR DISTURBANCE WILL BRING INCREASING CHANCES FOR
CONVECTION TO WESTERN AREAS BY LATE AFTERNOON...CONTINUING THROUGH
THE END OF THE PERIOD. A PROB30 FOR TSRA HAS BEEN INTRODUCED TO
ACCOUNT FOR THIS.

OUTLOOK...SCT SHOWERS/THUNDERSTORMS WILL CONTINUE INTO EARLY TUE...
WHILE FLT RESTRICTIONS MAY DEVELOP AGAIN TUE MORNING IN LOW CLOUDS
AND/OR FOG. A RETURN TO MAINLY VFR CONDITIONS IS EXPECTED LATER TUE
INTO MIDWEEK OUTSIDE OF RESTRICTIONS WITH DIURNAL CONVECTION.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-07Z
KCLT       MED   75%     HIGH  87%     HIGH 100%     HIGH 100%
KGSP       MED   64%     HIGH  81%     HIGH  84%     HIGH 100%
KAVL       MED   75%     HIGH  80%     HIGH  90%     HIGH  85%
KHKY       MED   61%     MED   79%     HIGH  98%     HIGH  94%
KGMU       LOW   56%     HIGH  81%     HIGH  87%     HIGH 100%
KAND       HIGH  85%     HIGH  91%     HIGH  91%     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...WIMBERLEY
NEAR TERM...JDL
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.