Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 310224 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 1024 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/... 915 PM UPDATE...CIRRUS CONTINUE TO STREAM ACRS THE FA...COMING OUT OF THE SHORTWAVE OVER OKLAHOMA/ARKANSAS. REVISED SKY GRIDS TO BETTER REFLECT THE PRESENCE OF THESE CLOUDS...WHICH ARE LARGELY OPAQUE. SOME MIDLEVEL CLOUDS HAVE DEVELOPED BENEATH THEM AS WELL. LATEST EXPECTATION IS STILL FOR EVEN LOWER CLOUDS TO FORM OVERNIGHT...PER THE SELY FLOW PATTERN SEEN ON 00Z NAM AS WELL AS EARLIER MODELS. IN LIGHT OF THESE FACTS...AND NOTING SLIGHTLY WARMER TEMPS THAN PREV FCST AT THIS HR...I RAISED MIN TEMPS PERHAPS A DEGREE. SOME CLOUD COVER HAD ALREADY BEEN ANTICIPATED. AS FAR AS THE CONVECTION OVER THE MIDLANDS...IT WANED MORE OR LESS ON SCHEDULE...TAKING SOME TIME TO EXHAUST THE INSTABILITY. HOWEVER SOME LIGHT ACTIVITY CONTINUES TO FIRE WHERE THE BEST CONVERGENCE IS EVIDENTLY PRESENT JUST SOUTH OF CHARLOTTE. EXTENDED THE POP MENTION IN UNION NC A LITTLE LONGER. AS OF 730 PM...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 /03Z 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... 02-08Z 08-14Z 14-20Z 20-02Z KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100% KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100% KAVL HIGH 91% HIGH 88% HIGH 98% HIGH 90% KHKY HIGH 100% HIGH 86% 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...ARK NEAR TERM...LG/WIMBERLEY SHORT TERM...NED LONG TERM...ARK AVIATION...WIMBERLEY

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