Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 231504 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1104 AM EDT SAT JUL 23 2016 .SYNOPSIS... Broad deep layered high pressure will remain across the region through early next week, with a general weakness developing over the east coast on Monday. Moisture levels will gradually increase across the western Carolinas and northeast Georgia by the middle of next week as a weak cold front settles south into the area. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1045 AM EDT, isolated shower development is already starting in the SW mountains, and the latest HRRR runs have a good handle on this and also depict slightly better SHRA/TSRA coverage east of CLT this afternoon. Thus, the main two adjustments are slightly better chance PoPs in both of those areas for the afternoon hours and minor associated QPF adjustments. Temperatures look on track with the latest obs and sounding thicknesses so no adjustments will be needed with heat index capping out around 103 in the farther southern piedmont. Thermal profiles suggest 55 dbz core thresholds to 26+ kft for isolated severe convection today, with slightly lower values in any DCAPE regions that spike to 1100 to 1300 J/kg. Otherwise, Little change in the overall pattern is expected during the near term, as the forecast area will remain parked between the subtropical high centered over the Four Corners, and a weakness in the S.T. ridge off the southeast coast. While this pattern is not obviously supportive of substantial precip chances, it`s not entirely hostile to development of deep convection. The mid-level flow is expected to be more NE today, so it would stand to reason that any convection developing within lee trough and across the higher terrain would tend to drop south as opposed to SE, sparing much of the Piedmont of the solid scattered coverage that was observed yesterday. Convection should wind down this evening, with another warm overnight expected.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As 250 AM Saturday: On Sunday, the axis of the H5 ridge will build over the forecast area, increasing to 594 dm by the afternoon. At the sfc, little to no pressure gradient will exist across the western Carolinas and NE GA during the day. In fact, model guidance indicates that wind speeds are forecast to remain below 5 kts from the sfc up to H7. High thicknesses and good insolation should support high temperatures from around 90 degrees within the mtn valleys to upper 90s to around 100 across the I-85 corridor. Forecast soundings show the mixed layer deepening slightly above H8 during the heat of the afternoon. The mixing may lower sfc dewpoints from around 70 in the morning to the upper 60s during the afternoon. Heat Index values may peak between 101 to 106. In addition, forecast soundings indicate that llvl CIN will linger east of the mtns through most, if not all, of Sunday afternoon. Thermal profiles appear supportive of mtn ridge convection as early as mid day. Storms may propagate by developing along outflow boundaries. This process should support sct coverage across the mtns and isolated coverage east. Convection should ash out shortly after sunset, with debris gradually clearing into the late night hours. Low temperatures Sunday night are forecast to range for the 60s across the mtns to the low to mid 70s east. On Monday, a sfc front is forecast to slowly slide across the Ohio River Valley, with a lee trof across the foothills and Piedmont. light south winds should result in a one to two degree rise in afternoon dewpoint temperatures. As a result, llvl CIN appears weaker than Sunday across the foothills and Piedmont. NAM forecast soundings for KGSP indicates CAPE above 2500 J/kg and PW rising to 1.8 inches. Winds are forecast to remain less than 10 kts from the sfc to H4. I will time chc PoPs across the CWA by mid day, rising very quickly across the mtns around lunch, then spreading east across all of the Piedmont. A few areas may see high Heat Index values between 100 to 106 degrees during the mid to late afternoon. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 3 AM Saturday: Tuesday through Thursday, the center of the H5 ridge will shift over the Deep South. Models indicate that a series of weak mid level S/W will ripple across the forecast area. Each day, moderate instability and weak CIN will exist across the region during the afternoon and early evening. I will continue to indicate diurnal chc to ridge top likely PoPs each day, schc east. I would expect that PW values will remain above normal as a front becomes stationary to our north. Temperatures should range within a couple of degrees of normal, cooler than Sunday and Monday. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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At KCLT and elsewhere (except KAVL), VFR conditions are expected through the period at most terminals. Generally expect light S/SW winds to persist through the period. Isolated to scattered convection is expected to develop once again this afternoon, esp near the Upstate SC terminals and KHKY, and VCTS and/or PROB30s are advertised at these sites from late afternoon into the evening. Cannot at all rule out convection near KCLT, but coverage should be a bit more sparse in the Piedmont so will only feature VCSH at KCLT for now. At KAVL, scattered convection is expected to develop once again this afternoon, and VCTS is advertised beginning at 17Z, with PROB30s carried from late afternoon into the early evening. Another round of fog and/or low stratus is possible late tonight, but timing and magnitude of this is completely uncertain attm, and restrictions are limited to MVFR fog around daybreak. Outlook: Scattered/isolated afternoon and evening showers and thunderstorms will continue across the mountains/piedmont through early next week. Morning fog and low stratus will be possible each day in the mountain valleys and also in locations that receive heavy rainfall the preceding afternoon/evening. Confidence Table... 15-21Z 21-03Z 03-09Z 09-12Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 94% KAVL High 100% High 100% High 100% High 82% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 100% High 100% High 94% 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:
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&& .CLIMATE... RECORDS FOR 07-24 MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 96 1983 68 1985 71 1934 52 1966 1895 KCLT 100 1983 73 1938 78 2010 59 1947 1952 1883 KGSP 101 1952 70 1985 79 2010 59 1904 RECORDS FOR 07-25 MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 92 2010 68 2000 70 2012 51 1895 2005 2011 1987 2010 KCLT 101 2010 69 2000 79 2010 62 1947 KGSP 100 1995 72 2000 77 2010 57 1911 1890 && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...NED NEAR TERM...HG SHORT TERM...NED LONG TERM...NED AVIATION...HG CLIMATE...GSP is the U.S. government's official web portal to all federal, state and local government web resources and services.