Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 130515
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
115 AM EDT SUN JUL 13 2014

.SYNOPSIS...
WEAK HIGH PRESSURE WILL LINGER OVER THE WESTERN CAROLINAS AND
NORTHEAST GEORGIA TODAY...BEFORE A FRONT APPROACHES. AN
UNSEASONABLY STRONG COLD FRONT WILL APPROACH THE AREA FROM THE
NORTHWEST ON MONDAY AND CROSS THE REGION TUESDAY. COOLER THAN NORMAL
TEMPERATURES WILL ARRIVE FROM MID TO LATE WEEK BEHIND THE FRONT.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...POPS WERE LOWERED PER RADAR TRENDS AND CLOUD
COVER FROM SATELLITE IMAGERY. WINDS WERE UPDATED FORM THE LATEST NAM
AND ADJMAV.

AS OF 10 PM...LATEST RADAR IMAGES INDICATE ONLY A COUPLE OF WEAK
SHOWERS ACROSS THE MTNS AND FOOTHILLS. I WILL UPDATE TO LOWER POPS
TO SCHC. FOG HAS STARTED TO FORM ACROSS THE EXTREME WESTERN NC MTN
VALLEYS...FORECAST APPEARS ON TRACK.

AS OF 740 PM...THE FORECAST TRENDS LOOK GOOD. I WILL UPDATE TO
ADJUST SKY AND TEMPERATURES TO OBSERVATIONS. CONDITIONS LOOK
FAVORABLE FOR MTN VALLEY FOG TONIGHT...A LITTLE LESS COVERAGE AND
DURATION THAN THIS MORNING. KCAE RADAR INDICATES THAT A SEA BREEZE
BOUNDARY WAS TRACKING STEADILY WEST. SOME PATCHY FOG IS POSSIBLE IN
THE WAKE OF THE BOUNDARY...GENERALLY ACROSS THE MIDLANDS.

AS 530 PM...THE CURRENT FORECAST REMAINS IN GREAT SHAPE. SCT
CONVECTION OVER THE MTNS HAS TRENDED WEAKER OVER THE PAST HOUR...BUT
COVERAGE HAS REMAINED NEARLY UNCHANGED. I WILL UPDATE THE FORECAST
TO ALIGN SKY WITH SATELLITE OBSERVATIONS AND TO TWEAK TEMPS.
OTHERWISE...CHANGES TO FORECAST WILL BE MINOR.

AT 245 PM EDT SATURDAY... CURRENT MESOANALYSIS INDICATES CAPES OVER
THE MOUNTAINS ARE AROUND 1500 J/KG AND GENERALLY LESS THAN 1000 J/KG
EAST OF THE MOUNTAINS. RAP FORECAST INTO THE EVENING SHOWS CAPE
PERSISTS FOR A WHILE IN THE FAR WESTERN ZONES... ALIGNED WITH THE
AXIS OF HIGH TERRAIN... BUT CAPE DECREASES SUBSTANTIALLY IN THE
EAST. AS HAS BEEN THE CASE DURING THE PAST COUPLE OF NIGHTS...
ISOLATED CONVECTIVE STORMS MIGHT CONTINUE WELL AFTER SUNSET. VERY
LIGHT WINDS THROUGH A DEEP LAYER COULD RESULT IN SLOWLY MOVING
THUNDERSTORMS AND THE POTENTIAL FOR LOCALLY EXCESSIVE RAINFALL.
OTHERWISE... PRIMARY FEATURE ALOFT AFFECTING OUR WEATHER THROUGH
SUNDAY IS A RIDGE EXTENDING FROM THE WEST COAST ACROSS THE SOUTHERN
STATES TO THE CAROLINAS. AT THE SURFACE... HIGH PRESSURE WITH A VERY
WEAK GRADIENT WILL COVER THE REGION. AS HEIGHTS FALL OVER THE
NORTHERN U.S. ON SUNDAY... THE EASTERN PERIPHERY OF THE UPPER LEVEL
RIDGE WILL WITHDRAW WESTWARD A BIT... BUT THROUGH TOMORROW THE RIDGE
IS GOING TO BE THE PRIMARY PLAYER IN CONTINUING THE CURRENT PERIOD
OF GENERALLY TRANQUIL WEATHER. THE AIR MASS OVER THE WESTERN ZONES
WILL REMAIN FAIRLY MOIST AND MODERATELY UNSTABLE THUS SUPPORTING
SCATTERED SHOWERS AND THUNDERSTORMS WHICH WILL BE MOST NUMEROUS OVER
THE HIGHER TERRAIN. CAPE VALUES EAST OF THE MOUNTAINS ON SUNDAY WILL
BE HELD AT BAY BY A RATHER WARM TEMPERATURE PROFILE. AN ISOLATED
SHOWER OR THUNDERSTORM IS POSSIBLE... BUT CUMULUS AND TOWERING
CUMULUS SHOULD DOMINATE THE SKY IN OUR PIEDMONT ZONES TOMORROW. LOWS
WILL BE AROUND 70 IN THE PIEDMONT AND IN THE 60S IN THE MOUNTAINS.
HIGHS ON SUNDAY WILL BE FAIRLY CLOSE TO NORMAL... PERHAPS A FEW
DEGREES ABOVE NORMAL AT A FEW LOCATIONS. HIGHS WILL BE AROUND 90
EAST OF THE MOUNTAINS AND IN THE LOWER AND MID 80S IN THE MOUNTAIN
VALLEYS.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
AS OF 230 PM EDT SATURDAY...THE SHORT RANGE PERIOD INITIALIZES
SUNDAY EVENING WITH A BROAD LONGWAVE UPPER TROF ROTATING ACROSS
SOUTHERN ONTARIO.  MEANWHILE...BERMUDA HIGH WILL CONTINUE TO ADVECT
WARM/MOIST AIR ACROSS THE SOUTHEAST...NORTHWARD INTO THE MID
ATLANTIC STATES.  EXPECTING ONGOING CONVECTION ACROSS THE HIGH
TERRAIN AT FORECAST INITIALIZATION DUE TO IMPROVED INSTABILITY AXIS
AND WEAK SOUTHERLY UPSLOPE FLOW.   CHANCE LEVEL POPS WILL BE
FEATURED INITIALLY ACROSS THE HIGH TERRAIN BEFORE TAPERING DOWN TO
SLIGHT CHANCE LEVELS BY DAYBREAK.  BY MONDAY MORNING...THE
FIRST...AND WEAKER OF TWO COLD FRONTAL BOUNDARIES WILL APPROACH THE
REGION FROM THE WEST.  ADJACENT WEAK UPPER IMPULSE COMBINED WITH
BOUNDARY INTRUSION WILL SPAWN CONVECTION ACROSS THE
MOUNTAINS/FOOTHILLS DURING THE AFTERNOON HOURS ON MONDAY.  DUE TO
THE SUSTAINED SOUTHERLY FLOW IN DAYS PAST...THE ATMOSPHERE WILL HAVE
RECOVERED ENOUGH TO YIELD A MODERATELY UNSTABLE WARM SECTOR AHEAD OF
THIS FRONT.  THUS...EXPECTING SHOWERS AND THUNDERSTORMS TO SPILL OUT
OF THE HIGH TERRAIN AND PROPAGATE EAST INTO THE PIEDMONT/FOOTHILLS
MONDAY EVENING.  AS SAID ABOVE...SUBSTANTIAL CAPE WILL BE PRESENT TO
SUPPORT SOME DEEPER UPDRAFTS LEADING TO A FEW STRONG/SEVERE
THUNDERSTORMS MONDAY AFTERNOON/EVENING...DESPITE WEAKER YET
IMPROVING SHEAR.  FORECAST WILL FEATURE LIKELY POPS ACROSS THE
MAJORITY OF THE MOUNTAIN/FOOTHILLS ZONES WHILE LOWER CHANCE POPS ARE
HIGHLIGHTED SOUTH EASTWARD ACROSS NORTHEAST GA AND THE NC/SC
PIEDMONTS.

TUESDAY MORNING THE ABOVE MENTIONED BOUNDARY WILL HAVE ESSENTIALLY
DISSIPATED AND BECOME STATIONARY ACROSS CENTRAL NC...SOUTHWARD
INTO THE MIDLANDS OF SC.  AT THE SAME TIME THE RATHER
DEEP/IMPRESSIVE UPPER LOW WILL ROTATE DOWN ACROSS THE GREAT LAKES
WHILE SURFACE CYCLOGENESIS OCCURS ALONG THE EASTERN SEABOARD.  THE
STRONG COLD FRONT WILL BE PUSHING THROUGH THE OHIO VALLEY BY EARLY
MORNING...EASTWARD INTO THE CENTRAL/SOUTHERN APPS BY MID/LATE
MORNING...THEN FINALLY FURTHER EAST INTO THE PIEDMONT REGIONS ON
TUESDAY AFTERNOON/EVENING.  EXPECTING THE ABOVE MENTIONED SURFACE
CYCLONE TO DEEPEN SLIGHTLY AND AID IN DEVELOPMENT OF A LEE SIDE
TROF ACROSS THE PIEDMONT/COASTAL PLAINS OF NC LATE IN THE
AFTERNOON.  THIS WEAK/DIFFUSE BOUNDARY COULD PROVIDE A FOCUS FOR
SURFACE CONVERGENCE AHEAD OF THE APPROACHING/STRONG COLD FRONT.
THERE WILL BE SUFFICIENT UPPER SUPPORT...SHEAR...AND BUOYANCY IN
PLACE TO SUPPORT ORGANIZED STRONG/SEVERE CONVECTION ACROSS THE
ENTIRE REGION ON TUESDAY.  THE FORECAST WILL FEATURE WIDESPREAD
LIKELY POPS FOR TUESDAY ENCOMPASSING THE ENTIRE REGION.  WILL
CONTINUE WITH SEVERE THUNDERSTORM POSSIBLE WORDING IN THE HWO FOR
BOTH MONDAY EVENING/OVERNIGHT...AND THROUGH THE DAY ON TUESDAY.
TEMPERATURES WILL BE ABOVE NORMAL ON MONDAY AS DEEP SOUTHERLY FLOW
PREVAILS AMONGST PARTLY CLOUDY SKIES WHILE MOSTLY CLOUDY SKIES
COMBINE WITH PRECIPITATION TO KEEP HIGHS A FEW DEGREES BELOW NORMAL
FOR TUESDAY.  BY WEDNESDAY MORNING...THE FRONT WILL BE EXITING TO
THE EAST ALLOWING FOR POPS TO TREND DOWN...ALONG WITH TEMPS.  LOWS
ON WEDNESDAY MORNING WILL REMAIN AT OR JUST BELOW NORMAL ACROSS THE
LOWER TERRAIN WHERE THE FROPA OCCURS LATER...WHILE THE HIGH TERRAIN
WILL SEE LOWS ON THE ORDER OF 5 DEGREES BELOW NORMAL.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 130 PM SAT...A BROAD TROUGH WILL BE IN PLACE ACROSS THE ERN
TWO THIRDS OF THE CONUS ON WED AS A DEEP LOW PRESSURE SYSTEM SPINS
OVER ERN CANADA AND THE NRN GREAT LAKES. DEEP LAYER DRYING IS
EXPECTED ON WEDNESDAY BEHIND THE SLOWLY DEPARTING/STALLING COLD
FRONT...WITH MAINLY NW FLOW ACROSS THE REGION. WEAK SFC HIGH PRES
WILL BUILD OVER FROM THE N...AND MAX TEMPS SHOULD DIP TO TWO
CATEGORIES BELOW NORMAL BY WED AFTN. AS THE WEAK HIGH SETTLES INTO
PLACE TO OUR N...LOW LEVEL EASTERLY FLOW COULD DEVELOP INTO THE SRN
APPALACHIANS BY THU. IT IS QUESTIONABLE HOW MUCH MOISTURE WILL
RETURN TO THE PROFILES...BUT SLIGHTLY IMPROVED BL RH COULD HELP
TRIGGER ISOLD TO SCT AFTN SHOWERS...ESPECIALLY IN AND NEAR THE MTNS.
MAX TEMPS LOOK TO BE A SOLID 5 TO 10 DEGREES BELOW NORMAL THU
AFTN...POSSIBLY MORE IF WE CLOUD UP QUICKER.

THOUGH SUBTLE MODEL DIFFERENCES EXIST BY LATE WEEK...THERE IS
REASONABLE CONSENSUS REGARDING SHORTWAVE ENERGY DIVING THROUGH THE
SRN PLAINS INTO THE BROAD TROUGH ON THU...AND THEN MOVING TO THE
BASE OF THE SRN APPALACHIANS BY FRI. THIS MAY BRING A WEAK SFC
REFLECTION AND ADDITIONAL MOISTURE BACK TO THE REGION...INTERACTING
WITH THE WEAK SFC HIGH TO THE NORTH AND POSSIBLY PROVIDING SOME
DEGREE OF COLD AIR DAMMING FRI INTO SAT. WILL KEEP MAXES WELL BELOW
NORMAL DURING THIS PERIOD...WITH MAINLY CHC POPS...HIGHEST NEAR THE
BLUE RIDGE.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
AT KCLT...VFR. SW WINDS WILL PERSIST...BECOMING GUSTY DURING THE
DAY. WINDS WILL STAY UP A BIT AFTER SUNSET AS THE PRESSURE GRADIENT
STARTS TO TIGHTEN AHEAD OF AN APPROACHING COLD FRONT. CONVECTIVE
CHANCES ARE QUITE LOW DUE TO WARM AIR ALOFT WHICH WILL LIMIT LIFT.
GUIDANCE DOES NOT FAVOR CIG OR VSBY RESTRICITONS...ALTHOUGH MODEL
TIME HEIGHTS DO SHOW SOME LOW LEVEL MOISTURE AROUND DAYBREAK.

KAVL...MODEL GUIDANCE FAVORS DAYBREAK RESTRICTIONS...AND PERSISTENCE
FROM YESTERDAY WILL BE USED. EXPECT LIFR TO VLIFR VSBY AND CIG
BEFORE DAWN...RETURNING TO VFR BY MID MORNING. SSW WINDS WILL BECOME
GUSTY DURING THE DAY...AND MAY STAY UP A BIT AFTER SUNSET AS THE
PRESSURE GRADIENT TIGHTENS AHEAD OF AN APPROACHING COLD FRONT.
ALTHOUGH CONVECTIVE CHANCES WILL BE GREATEST IN THE MOUNTAINS...THE
CHANCE AT KAVL WILL BE TOO LOW TO MENTION.

ELSEWHERE...VFR. SW WINDS WILL PERSIST...BECOMING GUSTY DURING THE
DAY...AND NOT DIMINSIHING AS MUCH AFTER SUNSET AS THE PRESSURE
GRADIENT TIGHTENS WITH THE APPROACH OF A COLD FRONT. CONVECTIVE
CHANCES WILL BE LIMITED BY WARM AIR ALOFT.

OUTLOOK...RESTRICTIONS IN THUNDERSTORMS ARE POSSIBLE MONDAY AND
TUESDAY. VFR WILL RETURN ON WEDNESDAY BEHIND A COLD FRONT.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-05Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   69%     MED   74%     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  94%     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...JAT/LGL/NED
SHORT TERM...CDG
LONG TERM...HG
AVIATION...JAT





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