Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 251454 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 954 AM EST Sat Feb 25 2017 .SYNOPSIS... A cold front will move off the Carolina coast late today as cool high pressure builds into our region from the west. Temperatures cool to near normal tonight through Sunday night, then warm up again during the first half of the week. A warm front lifts north through the area around midweek as a cold front approaches from the west bringing showers and storms. && .NEAR TERM /THROUGH TONIGHT/...
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As of 945 AM: Low pressure now over southern Ontario continues to drive a cold front across Appalachia. Winds are now NW and gusty across our mountain ASOS/AWOS sites. Along the front, some towering cu are evident from visible satellite as well as some light shower activity. This is expected to strengthen a bit as it moves into increasingly unstable air across western NC. For now per RAP prog profiles, it looks like the Upstate will not see lapse rates good enough to expect deep convection, though a shallow cu field should form. There remains a tiny chance that one of the NC cells could produce a damaging wind gust, particularly in the I-77 corridor, where a few hundred J/kg of SBCAPE are expected to meet the front around midday, as well as remarkable deep layer shear. The front will exit the area by early aftn. Beyond that a much drier/cooler airmass will advect into the region as quasizonal flow builds aloft and sfc high pressure moves in from the west. Thus skies will clear out late in the day, leading to optimal radiational cooling conditions and near normal overnight lows. Lastly, nwly veering winds will become quite gusty behind the front this afternoon, which combined with the possibility of little/no precip and low RH values, will support enhanced fire danger conditions across SC and possibly GA as well. Please refer to the Fire Weather section for details.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 305 AM Saturday, A low-amplitude/quasi-zonal upper air pattern will persist through the short term period, with gradually building heights anticipated across the East. The end of the weekend will be marked by dry and seasonably cool conditions, with high clouds expected to increase late Sunday into Sunday night, as a shearing vorticity max moves rapidly from the southern Great Plains to the Mid-Atlantic Sunday night through Monday. In response, moist isentropic lift will develop across the western Carolinas and northeast GA throughout Monday, with increasing clouds and precipitation chances expected, peaking by Monday evening. Some guidance sources are more bullish than others regarding the overall extent of the precip Monday into Monday night. Some models (e.g. the ECMWF) indicate a bit more in the way of surface wave development along the Carolina coast, which tends to disrupt the low flow across and shut off the upglide more quickly across our area. The upshot of this would be significant QPF confined to our western areas, with little to nothing across the eastern zones. With that in mind, pops range from 60-70 across western areas, to 40-50 along the I-77 corridor. Monday`s temps will be a bit tricky, depending upon how quickly precip arrives. As sufficient low level dry air should be in place to force establishment of in-situ cold air damming where precip falls. Nevertheless, with current data indicating that precip is likely to hold off until afternoon, will advertise maxes near to slightly above climo across the west, and about 5 degrees above normal across the NC Piedmont. Pops taper off gradually Monday evening. However, isentropic lift is expected to increase across the region once again by daybreak Tuesday, as large scale height falls overspread much of the western half of the Conus. Another round of precip is therefore possible by the very end of the period. Temps Monday night will be well above climo. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 155 AM EST Saturday: Low level SW flow at the 925mb level will persist Tuesday and Wednesday ahead of the approaching cold front. GFS 925mb wind speeds maximize on Wednesday with 30 to 45kts in the vicinity of I-85 from GA to NC. Moisture will be abundant with GFS Precipitable water around 1.4 along I-85 Wed afternoon. Instability is generally restricted to along and south of I-85 Tuesday PM, especially on the GFS where very low if any CAPE is north of the corridor. On Wed PM, CAPE of 400 to 600 from NE GA to CLT area along with the wind shear will give strong to severe storm concern. Of course, timing of frontal passage coincident with max daytime heating would make for the max circumstance with dynamics coming together. The 500mb trough crosses the western states early Tuesday with axis over the Plains States 12Z to 18Z Wed with low pressure forming in the eastern trough inflection point and moving NE across the Appalachians Wed evening. At least the models are in closer agreement as compared to 24HRs ago. GFS still the fastest model in taking the front across our area around midnight Wed while the EC has it passing a few hours later. After the front passes, there will be lingering moisture along the TN border with NW Flow combined with shortwave energy crossing just north of NC on Thursday and early Friday. Thickness values will be falling Wed night into Thursday and will be low enough for snow in the NC Mtns by late Thursday morning. The second shortwave could bring a brief NW Flow snow shower period around daybreak Friday for the central and northern NC Mtns. Temperatures are forecast to be 10 to 15 degrees above normal Tuesday and Wednesday then fall to near or slightly below normal behind the cold front for the second half of the week. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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At KCLT and Elsewhere: VFR and possibly MVFR over the next few hours along with a few SHRA invof cold front crossing the region. Deeper convective development may occur late morning further east along the I77 corridor region. Thus we do have a TSRA in TEMPO at KCLT for a few hours. Behind the front, TAFs go dry with low clouds SCTing out to high cirrus, then SKC for the remainder of the cycle. Swly winds will increase and veer nwly behind the front with gusts reaching upwards of 20-30kts at times today, before all winds weaken overnight. Outlook: A dry continental airmass will maintain VFR thru Sunday. Another wave approaches on Monday, once again increasing chances for precipitation/restrictions which may last into Tuesday. Confidence Table... 15-21Z 21-03Z 03-09Z 09-12Z KCLT High 96% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 86% High 100% High 100% High 100% KHKY High 93% High 100% 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: www.weather.gov/gsp/aviation
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&& .FIRE WEATHER... Gusty W/NW winds and much drier air will overspread the area in the wake of a cold front Today. Minimum RH of 25 to 30 percent is expected across much of the SC Upstate and Northeast GA, and may dip below 25 percent in some areas. Sustained winds will increase and veer nwly behind a departing cold front into the 15-20mph range with gusts nearing 30-35mph. These critical conditions could overlap for an hour or two this afternoon. Thus a fire danger statement has been issued for the all of northeast GA minus Rabun County, as well as all of Upstate SC starting at noon today, running through 6PM. && .GSP WATCHES/WARNINGS/ADVISORIES...
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GA...Fire Danger Statement until 6 PM EST this evening for GAZ017- 018-026-028-029. NC...None. SC...Fire Danger Statement until 6 PM EST this evening for SCZ001>014-019.
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&& $$ SYNOPSIS...DEO NEAR TERM...CDG/Wimberley SHORT TERM...JDL LONG TERM...DEO AVIATION...CDG/Wimberley FIRE WEATHER...CDG/JDL

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