Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 230550
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
150 AM EDT WED APR 23 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 TODAY/...
AS OF 145 AM...THE COLD FRONT LOOKS TO FINALLY CROSSED THE TENN
VALLEY...AND SHUD PUSH THRU THE MTNS OVERNIGHT. IN THE
MEANTIME...THERE IS ALREADY SOME DRY ADVECTION/MIXING AHEAD OF THE
FRONT TO LIMIT FOG DEVELOPMENT...BUT THERE IS STILL PATCHY FOG OUT
THERE. I UPDATED THE NEAR TERM GRIDS FOR THE 06Z TAFS...PERHAPS
BUMPING UP FOG COVERAGE/WORDING OVERNIGHT. OTHERWISE...NO
SIGNIFICANT CHANGES RESULTED FROM THIS UPDATE.

AS OF 1035 PM...THE COLD FRONT CONTINUES TO TAKE ITS TIME DROPPING
SOUTHEAST ACROSS THE TENN VALLEY. IN FACT...THE REAL PUSH OF SURFACE
DRY AIR IS REALLY JUST NOW BEGINNING ACROSS EAST TENN. IN ADVANCE OF
THIS AREA OF DRY AIR ADVECTION...THE AIR MASS IS QUITE MOIST LATE
THIS EVENING...WITH DEWPOINTS AS HIGH AS 60 ACROSS PORTIONS OF THE
PIEDMONT. MEANWHILE...WINDS HAVE BECOME LIGHT JUST ABOUT
EVERYWHERE...AND WITH MID/UPPER LEVEL DRIER AIR PUNCHING INTO THE
AREA...SOME POCKETS OF FOG HAVE BEGUN TO FORM. SINCE IT/S GOING TO
BE A FEW MORE HOURS BEFORE THE LOW LEVEL DRYING COMMENCES...WE HAVE
ADDED QUITE A BIT MORE FOG TO THE FORECAST SUITE...PRETTY MUCH
ENCOMPASSING THE ENTIRE FORECAST AREA WITH SOME AMOUNT OF RESTRICTED
VISIBILITY. FOG COULD BECOME DENSE IN A FEW AREAS...PARTICULARLY
SHELTERED MOUNTAIN VALLEYS. WE WOULD THEN EXPECT AN IMPROVEMENT IN
VISBY AFTER 06Z...SUCH THAT LITTLE FOG IS ANTICIPATED BY SUNRISE.
INCREASING COLD ADVECTION SHOULD ALLOW TEMPS TO COOL TO NEAR CLIMO
IN MOST AREAS BY SUNRISE.

AS OF 745 PM...POPS HAVE BEEN ALL BUT REMOVED FROM THE FORECAST FOR
THIS EVENING...AS THE MAIN AREA OF SHOWERS HAS SHIFTED EAST OF THE
FORECAST AREA. THE ACTUAL FRONT IS STILL PUSHING ITS WAY ACROSS THE
GREAT TN VALLEY/NORTH GEORGIA ATTM...ALONG WHICH REMAINS A DECENT
AREA OF LOW LEVEL CONVERGENCE AND SOME RESPECTABLE INSTABILITY.
HOWEVER...COVERAGE OF SHOWERS ALONG THE BOUNDARY IS UNINSPIRED TO
SAY THE LEAST. WILL NEVERTHELESS CARRY SOME TOKEN CHANCES ALONG THE
TENN BORDER...WHERE A BRIEF FLARE UP IN SHOWERS IS POSSIBLE AS THE
FRONT MOVES INTO THE SOUTHERN APPALACHIANS...AND RECEIVES SOME
ASSISTANCE FROM A NW UPSLOPE FLOW.

AS OF 245 PM...RECENT KGSP AND TCLT RADAR IMAGES INDICATED CLUSTERS
OF SHRA ACROSS THE MOUNTAINS AND FOOTHILLS...MOVING EAST BETWEEN 20
TO 25 MPH. THE SHOWERS WILL ENCOUNTER GREATER INSTABILITY ACROSS THE
PIEDMONT...BUT VALUES SHOULD RANGE BETWEEN 500-1000 J/KG. A FEW TSRA
MAY DEVELOP...BUT THE ENVIRONMENT WILL NOT SUPPORT SVR STORMS. THE
MAJORITY OF THE SHRA ARE TIMED TO MOVE EAST OF THE CWA BETWEEN
22-00Z...WITH A FEW UPSLOPE SHRA REMAINING NEAR THE TN LINE WELL
INTO THE EVENING. IN THE WAKE OF THE WEAK COLD FRONT...SKY COVER
WILL DECREASE STEADILY OVERNIGHT. GUSTY NW WINDS SHOULD RESULT IN
WEAK CAA ACROSS THE MTNS OVERNIGHT. A BLEND OF PREFERRED MOS
SUPPORTS MIN TEMPERATURES WITHIN A DEGREE OR TWO OF NORMAL.

ON WEDNESDAY...DRY CANADIAN SFC HIGH PRESSURE WILL BUILD ACROSS THE
SOUTHERN APPALACHIAN REGION. AS THE HIGH ARRIVES...GUSTY NW WINDS
ACROSS THE MTNS MAY YIELD A SMALL PATCH OF HIGH WAVE CLOUDS ACROSS
THE NC FOOTHILLS AROUND SUNRISE. OTHERWISE...SKY SHOULD REMAIN SUNNY
ACROSS THE REGION. HIGH TEMPERATURES ARE FORECAST TO RANGE FROM THE
U60S ACROSS THE MTNS TO MID 70S ACROSS THE UPPER SAVANNAH RIVER
VALLEY. THE SEASONABLE TEMPERATURE ABOVE DEWPOINTS IN THE 20S AND
30S SHOULD RESULT IN RH VALUES IN THE LOWER 20S.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
AS OF 240 PM TUESDAY...UPPER RIDGE BUILDS IN WED NITE AND THU AS SFC
HIGH PRESSURE NOSES IN FROM THE NORTH WED NITE THEN SLIDES OFF SHORE
THU. EXPECT LOWS WED NITE AS MUCH AS 5 DEGREES BELOW NORMAL AS GOOD
RADIATIONAL CONDITIONS DEVELOP. HAVE INCLUDED PATCHY FROST ACROSS
THE NC MTNS AND NRN FOOTHILLS WHERE TEMPS ARE COLD ENUF FOR FROST.
MOISTURE RETURN IN THE SLY FLOW AROUND THE DEPARTING HIGH PRESSURE
CENTER WILL LEAD TO INCREASING CLOUDINESS THU. HIGHS WILL END UP NEAR
TO SLIGHTLY ABOVE NORMAL.

A SERIES OF SHORT WAVES CROSS THE AREA IN THE FLAT TROF MOVING INTO
THE ERN CONUS LATE THU NITE AND FRI. GUIDANCE...IN GENERAL...HAS
INCREASED THE SPEED OF THIS SYSTEM AS IT MOVES EAST ACROSS THE AREA.
THEREFORE...BRING CHC POP INTO THE MTNS AND SLIGHT CHC ELSEWHERE
LATE THU NITE. STILL KEEP LIKELY POP LIMITED TO THE TN BORDER FRI
MORNING...BUT BRING GOOD CHC POP ACROSS THE CWFA DURING THAT TIME.
TAPER POP FROM WEST TO EAST DURING THE AFTERNOON...WITH ONLY A SMALL
PERIOD OF LINGERING SLIGHT CHC POP ACROSS THE I-77 CORRIDOR EARLY
FRI EVENING. SHEAR LOOKS BETTER WITH THIS SYSTEM...BUT STILL DOES
NOT REACH THE STRONG CATEGORY. OPS GUIDANCE SHOWS MODERATE
INSTABILITY POSSIBLE OVER THE ERN CWFA DURING THE AFTERNOON...BUT
ENSEMBLE MEAN SHOWS ONLY WEAK VALUES...EVEN IN MUCAPE. THEREFORE...
EXPECT TSRA TO DEVELOP...BUT ONLY A LOW CHC...AT BEST...FOR ANY
SEVERE STORMS. RIGHT NOW...PRECIP AMOUNTS DO NOT LOOK TO BE
EXCESSIVE EITHER. LOWS THU NITE 5 TO 10 DEGREES ABOVE NORMAL. HIGHS
FRI AROUND 5 DEGREES ABOVE NORMAL.

DRY HIGH PRESSURE BUILDS IN FRI NITE WITH LOWS AROUND 5 DEGREES
ABOVE NORMAL.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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 /06Z WEDNESDAY THROUGH SUNDAY/...
KCLT...ONLY A TRACE OF RAIN WAS REPORTED AT THE TERMINAL ASOS THIS
EVENING...SO CONFIDENCE ON GROUND FOG DEVELOPMENT IS LOW. THE DEWPT
DEPRESSION AT TIME OF 06Z TAF ISSUANCE WAS 2F...AND WINDS ARE LIGHT
WITH CLEAR SKIES. WITH THAT SAID...DRIER AIR IS WORKING IN ACRS THE
NC PIEDMONT...AND A COLD FRONT SHUD PUSH THRU BEFORE DAYBREAK. SO
WHILE FOG IS POSSIBLE...I THINK CHANCES ARE TOO LOW TO PUT IN THE
TAF. TRENDS WILL BE MONITORED CLOSELY...HOWEVER. OTHERWISE...IT SHUD
BE A QUIET TAF PERIOD...WITH CLEAR SKIES AND A LIGHT NW WIND THAT
MAY APPROACH 10 KTS THIS AFTN.

ELSEWHERE...BASED ON THE LIGHT RAIN THAT FELL YESTERDAY...ONLY KGSP
SEEMS TO HAVE THE RIGHT CONDITIONS FOR GROUND FOG AT THE TERMINAL.
THE OTHER SITES HAVE DEWPT DEPRESSIONS 4-10F...EXCEPT 2F AT KAVL.
HOWEVER...A COLD FRONT SHUD PUSH THRU OVERNIGHT...AND ADVECT DRY AIR
AND SOME MIXING...ESP AT KAVL WHERE CHANNELED VALLEY WINDS SHUD PICK
UP TO ABOUT 10 KTS WITH GUSTS BY DAYBREAK. KAVL WAS CALM AT TIME OF
TAF ISSUANCE...SO A BRIEF PERIOD OF FOG CANNOT BE RULED OUT...BUT
CONFIDENCE TOO LOW TO MENTION IN THE TAF. OTHERWISE...VFR CONDITIONS
ARE EXPECTED WITH NW WINDS.

OUTLOOK...DRY HIGH PRES WILL DOMINATE THRU THU. ANOTHER COLD FRONT
WITH POTENTIAL FOR SHOWERS/TSTMS IS THEN EXPECTED TO CROSS THE
REGION FRIDAY...DRYING OUT BY SATURDAY.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-05Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  94%     HIGH  91%     HIGH 100%     HIGH 100%
KAVL       MED   77%     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  94%     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...ARK/JDL/NED
SHORT TERM...RWH
LONG TERM...CDG
AVIATION...ARK






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