Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 302357
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
757 PM EDT WED JUL 30 2014

.SYNOPSIS...
CANADIAN HIGH PRESSURE WILL BEGIN TO SLIDE EAST OF THE AREA AND
WEAKEN THROUGH FRIDAY. AS THE HIGH WEAKENS...MOISTURE WILL RETURN
FOR THE WEEKEND INCREASING THE CHANCES OF WIDESPREAD SHOWERS AND
THUNDERSTORMS. CONDITIONS RETURN TO THOSE MORE TYPICAL OF LATE
SUMMER BY THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
730 PM UPDATE...BIGGEST CHANGE FOR THE VERY NEAR TERM IS THE
ADDITION OF POPS OVER OUR SE BORDER ZONES. AN OUTFLOW BOUNDARY
REMAINING FROM THE MID-AFTERNOON CONVECTION NEAR COLUMBIA IS SLOWLY
PROCEEDING NORTHWARD THRU THE MIDLANDS....AND HAS KICKED OFF SEVERAL
ROUNDS OF ISOLATED...SLOW-MOVING SHOWERS. THE MOVEMENT IS SO SLOW
THAT I THINK ONLY THE SERN PORTIONS OF THE AFFECTED ZONES IN OUR
CWFA ARE CAPABLE OF SEEING ACTIVITY POP UP BEFORE DIURNAL
INSTABILITY WANES. SOME ELEVATED INSTABILITY MAY STILL BE PRESENT
AFTER SUNSET THOUGH...SO I KEPT THE ISOLD POP MENTION THRU 02Z.

OTHERWISE...THE LATEST GUIDANCE STILL SUGGESTS STRATUS OR STRATOCU
DEVELOPING AND MOVING INTO THE PIEDMONT FROM THE SOUTHEAST LATE
TONIGHT. ISENTROPIC LIFT FROM THE LIGHT SELY FLOW IS NOT VERY
IMPRESSIVE...BUT COULD BE SUFFICIENT FOR PATCHY CLOUDINESS. TRIMMED
BACK THE BLUE RIDGE POPS TO NOT BEGIN UNTIL AROUND DAYBREAK...AGAIN
DUE TO WEAK FLOW AND THE FACT THAT BETTER THERMAL ADVECTION DOESN/T
ARRIVE UNTIL LATER THAN EARLIER EXPECTED.

AS OF 215 PM...IN REGARD TO THE BIG PICTURE....SOME CHANGES ARE
ANTICIPATED TO GRADUALLY TAKE PLACE BY LATE THU. THE UPPER TROUGH
AXIS OVER THE EASTERN U.S. IS FORECAST BY THE MODELS TO BECOME
RE-ESTABLISHED TO THE WEST OF THE APPALACHIANS AS ENERGY FROM THE
CENTRAL ROCKIES DIVES SE. AT THE SAME...A STATIONARY FRONT NEAR THE
COAST WILL BEGIN TO MOVE SLOWLY WESTWARD AS A WARM FRONT. HENCE BY
LATE TONIGHT...BOUNDARY LAYER WINDS WILL BEGIN TO VEER TO THE E-SE
WHICH WILL ADVECT ATLANTIC MOISTURE INTO THE AREA AND PROVIDE WEEK
MECHANICAL LIFT ACROSS THE HIGHER TERRAIN. PLUS BY THU AFTERNOON...A
VORT MAX IS FORECAST TO APPROACH FROM THE SW AND SWING ACROSS THE
MOUNTAINS THU AFTERNOON. ALL THIS COMBINED WILL GIVE US AN
INCREASING CHANCE FOR SHOWERS ON THU....WITH THE BEST COVERAGE OVER
THE NC MOUNTAINS DURING THE AFTERNOON HOURS. WILL LIMIT POPS TO THE
CHANCE RANGE AT THIS TIME AS INSTABILITY APPEARS LIMITED WITH ONLY A
COUPLE HUNDRED JOULES OF CAPE EXPECTED. ONLY WIDELY SCATTERED
SHOWERS ARE EXPECTED OUTSIDE THE MOUNTAINS. WITH INCREASING CLOUDS
TONIGHT...MIN TEMPS SHOULD BE SEVERAL DEGREES HIGHER THAN LAST
NIGHT. CONSIDERABLE CLOUDINESS IS ANTICIPATED ON THU WHICH WILL
CONTINUE TO HOLD MAX TEMPS BELOW CLIMO.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
AS OF 220 PM...ON FRIDAY...MOISTURE ACROSS THE SOUTHEAST U.S. SHOULD
INCREASE SHARPLY AS ATLANTIC MOISTURE ADVECTS WEST AND MERGES WITH
MOISTURE ASSOCIATED WITH A FADING SOUTHERN PLAINS LOW. FORECAST
SOUNDINGS INDICATE THAT PW WILL INCREASE TO AROUND 1.75 INCHES BY
FRIDAY MORNING...WITH LCLS BELOW 2 KFT. NAM12 SHOWS ISENTROPIC LIFT
WILL STRENGTHEN BETWEEN 305K-315K FRI MORNING...PERSISTING THROUGH
THE AFTERNOON. LOW LEVEL LIFT WILL LIKELY BE AUGMENTED ALONG THE
EAST FACING SLOPES AS WINDS REMAIN FROM THE SOUTHEAST AROUND 20 KTS.
IN ADDITION...A BROAD AREA OF MID LEVEL Q-VECTOR CONVERGENCE WILL
REMAIN ACROSS THE SOUTHEAST...EAST OF AN AMPLIFYING L/W TROF CENTERED
ACROSS THE MISSISSIPPI RIVER VALLEY. THE COMBINATION OF THE DEEP
LIFT...ABUNDANT MOISTURE...AND WEAK INSTABILITY SHOULD SUPPORT
NUMEROUS SHOWERS AND THUNDERSTORMS ON FRIDAY... I WILL FORECAST
GENERALLY LIKELY POPS ALONG AND WEST OF I-85...HIGH CHC EAST. THE
LACK OF INSTABILITY ACROSS THE MTNS AND FOOTHILLS MAY SUPPORT ONLY
SHOWERS...THUNDERSTORMS APPEAR POSSIBLE ALONG AND EAST OF I-85.
PERIODS OF RAIN...ENE WINDS...AND THICK CLOUD COVER SHOULD LIMIT
DAYTIME HEATING...KEEPING HIGHS IN THE 70S ACROSS THE MTNS TO
WESTERN PIEDMONT.

ON SATURDAY...THE RIDGE OF SFC HIGH PRESSURE SHOULD TREND WEAKER
THROUGH THE DAY. HOWEVER...SHALLOW RIDGING IS EXPECTED TO LINGER
ALONG AND EAST OF THE HIGH TERRAIN. DEEP FORCING IS EXPECTED TO
CONTINUE ACROSS THE FORECAST AREA...AIDED BY THE APPROACH OF THE
AMPLIFYING MID LEVEL TROF. I WILL FORECAST A RANGE IN POPS...LIKELY
POPS ACROSS THE MTNS TO HIGH CHC EAST. LLVL WINDS ARE EXPECTED TO
VEER FROM THE SOUTHWEST...SUPPORTING TEMPERATURES 4 TO 6 DEGREES
WARMER THAN FRIDAY. FORECAST SOUNDINGS INDICATE WEAK INSTABILITY
ACROSS THE FORECAST AREA...SUPPORTING A MENTION OF THUNDERSTORMS FOR
ALL ZONES.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 200 PM WEDNESDAY...THE MEDIUM RANGE WILL START OUT WITH A
FAIRLY DEEP H5 TROF AXIS EXTENDING FROM THE GREAT LAKES SOUTH TO THE
LWR MS VLY AT 00Z SUNDAY. THE TROF WILL GRADUALLY WEAKEN/SHEAR OUT
EARLY NEXT WEEK...BUT SOME DEGREE OF TROFINESS WILL LINGER THRU
WEDNESDAY. A QUASI-STATIONARY FRONTAL ZONE WILL LINGER PARALLEL TO
THE SWLY UPR FLOW ALONG/JUST INLAND OF THE EAST COAST...KEEPING THE
CWFA IN A MOIST/UNSETTLED ENVIRONMENT INTO EARLY NEXT WEEK. THE
FRONT WILL WASH OUT BY WEDNESDAY...PER THE CONSENSUS OF THE MEDIUM
RANGE GUIDANCE.

SO BLENDING IN THE NEW GUIDANCE AND WPC GUIDANCE...I WILL FCST ABOVE
NORMAL POPS FOR SUNDAY AND MONDAY (HIGH-END CHC TO LIKELY)...AND
TAPERING SOMEWHAT TO SHOTGUN LOW-MID CHC FOR TUESDAY AND WEDNESDAY.
TEMPS WILL START OUT WITH BELOW NORMAL HIGHS (DUE TO
CLOUDS/PRECIP)...AND NEAR NORMAL LOWS THRU MONDAY...THEN AFTN HIGHS
WILL TREND TOWARD NORMAL BY WEDNESDAY WITH CONTINUED NEAR NORMAL
LOWS.

THE EXPECTED DECENT COVERAGE OF PRECIP OVER SEVERAL PERIODS LOOKS TO
BE MAINLY SUPPORTED BY PERSISTENT UPPER DIVERGENCE WITHIN RIGHT
ENTRANCE REGION OF A NEARLY STATIONARY JET STREAK ALONG THE
APPALACHIANS. HOWEVER...QG FORCING AND LLVL TRIGGERING WILL BE ONLY
MARGINALLY SUPPORTIVE...WITH THE BETTER MID LVL FORCING TO THE
NORTH...AND LLVL JET AND INSTBY TO THE EAST. SO CONFIDENCE IS LOW ON
ANY SEVERE WX OR HEAVY RAIN THREAT AT THIS TIME.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AT KCLT...ISOLD SHRA WILL CONTINUE SOUTH OF THE FIELD ON OUTFLOW
BOUNDARIES EARLY THIS EVENING...BUT CURRENT RATE OF PROPAGATION IS
NOT ENOUGH TO BRING IT NEAR THE FIELD BEFORE DIURNAL BUOYANCY IS
EXHAUSTED. GUIDANCE SOMEWHAT SPLIT ON STRATUS DEVELOPMENT TONIGHT IN
LIGHT BUT MOIST SELY LLVL FLOW. NAM AND ITS DERIVATIVES ARE MORE
AGGRESSIVE THAN THE GFS IN BRINGING IN THE STRATUS. HOWEVER THE FLOW
PATTERN LENDS CONFIDENCE TO THE NAM DEPICTION...THEREFORE I HAVE
KEPT A LOW VFR CIG AT KCLT BEGINNING AROUND DAYBREAK. FLOW ALOFT
CONTINUES TO BE MOIST AND WARM-ADVECTIVE THU...SO THE CIG IS
EXPECTED TO PERSIST THOUGH IT MAY LIFT A BIT. AFTER A MOSTLY CALM
NIGHT...WINDS SHOULD PICK UP FROM THE SE MID-MORNING.

ELSEWHERE...CIG FCST IS BASICALLY AS AT KCLT WITH MINOR DIFFERENCES
IN TIMING. ALL CIGS EXPECTED TO BOTTOM OUT AT VFR. SOME GUIDANCE
DEVELOPS WIDESPREAD MVFR FOG ACRS THE PIEDMONT WITH IFR IN THE MTN
VALLEYS. THIS SEEMS QUESTIONABLE WITH FAIRLY DRY CONDITIONS
CONTINUING AT THE SFC AND WITH CLOUDS INCREASING OVERHEAD. I
MAINTAINED THE MENTION IN THE VALLEYS AND AT KAVL. LIGHT SHOWERS
COULD DEVELOP AROUND DAYBREAK IN THE MTNS...WITH ISOLD SHOWERS
BECOMING POSSIBLE ACRS THE AREA BY THU AFTN. HOWEVER CHANCES ARE TOO
LOW FOR A MENTION AT ALL SITES. GENERALLY NLY SFC WINDS WILL VEER TO
E OR SE THU.

OUTLOOK...MOISTURE WILL CONTINUE TO INCREASE THROUGH THE
REMAINDER OF THE WORK WEEK AS A WARM FRONT APPROACHES FROM THE EAST
AND SOUTHEASTERLY FLOW CONTINUES. UNSETTLED WEATHER WITH ENHANCED
PRECIPITATION CHANCES ALONG WITH MORNING FOG/STRATUS ARE EXPECTED
THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-24Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH  95%     HIGH 100%
KAVL       HIGH 100%     HIGH  91%     HIGH  95%     HIGH  95%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH  95%     HIGH 100%
KAND       HIGH 100%     HIGH  98%     HIGH  94%     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...ARK
NEAR TERM...LG/WIMBERLEY
SHORT TERM...NED
LONG TERM...ARK
AVIATION...WIMBERLEY




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