Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 210307 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1007 PM EST Mon Jan 20 2020 .SYNOPSIS... Cold Canadian high pressure will bring below normal temperatures through the middle of the week. Temperatures gradually return to near normal late in the week. The next cold front approaches from the west on Friday bringing the potential for a wet start of the weekend. && .NEAR TERM /THROUGH TUESDAY/... At 1002 PM...Still seeing light returns on the KMRX radar and satellite imagery shows plenty of low clouds banked up against the higher terrain on the NC/TN border, so expect there is still some light snow or flurries falling on the TN border. The fcst was updated to account for this. Backwards trajectories aloft show a moisture source around Lake Huron, so there is some Great Lakes connection helping out. The low level flow being from the N to NNE is actually more favorable for the Smokies up to Madison County, and less so for the nrn mountains. As we get past midnight, though, the moisture source is cut off, so the activity should move more southwest down the chain as the flow goes more NNE. Not seeing any radar activity underneath the clouds that formed in the upper French Broad valley, and the new guidance has backed off, so we will cut back on the small area of low precip chances on the srn slopes. Temps were running ok, but the dewpt trend was a bit drier than fcst. Meanwhile...we continue to watch a small, dynamic, yet moisture-starved upper low swirling toward us on satellite imagery with much interest. Problem might be...just how moisture-starved with it really be? It is not hard to imagine a slightly better blob of moisture coming down across the southwest mountains, north GA, and western Upstate during the early morning hours to around daybreak, such that we are able to squeeze out some snow flurry activity. In fact, radar shows a small area of light returns that was moving down over the southeast corner of TN. Have amended the fcst to put that in during the early morning hours, but think it will be gone by daybreak. Otherwise...a cold evening is in store as high pressure works in from the NW...however winds will weaken somewhat and offset any significant wind chill issues overnight. Expect min temps in the teens across the mtn valleys and lower 20s outside the mtns. Another cold day is in store Tuesday yet with less wind as the pressure gradient loosens. The dense morning airmass will be hard to thermally modify with continued northerly flow...so expect max temps remaining about 10-15 degrees below normal. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 130 PM MLK Day: A sharp upper ridge will replace the departing shortwave trough early Wednesday. Surface high pressure will shift east, both features progressing as a deep trough is carved out across the Plains. Deep dry air will persist over the FA under an initially northeast flow, which veers to a more easterly direction by the end of the period Thursday evening. Moisture with the developing frontal system most likely will remain too far west of our area to warrant a mentionable PoP until later Thursday night. Temps will be 7 to 10 degrees below normal Wednesday morning, moderating a bit thereafter, but still a few degrees below normal. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 200 PM MLK Day: A cutoff upper low is progged to develop within a deep trough over the central US around the beginning of the medium range; the low appears likely to track through the lower Ohio Valley Friday and early Saturday. The GFS, which had depicted a slower progression of this system as it entered our area, has trended toward the Euro/Canadian camp, but remains the farthest north with its low track. Confidence in timing the return of precip to the FA has increased, as occluded front crosses the area Friday. With the arrival of warm air aloft, and the expectation that cold/dry air will be in place at the sfc from the midweek high pressure, there`s still potential for a wintry mix that morning, in the middle to higher elevations of the mtns along with the I-40 corridor of the northwest NC Piedmont. The main difference in the prog soundings between models is how much wet-bulbing occurs. For now the fcst reflects a warm nose cooling as the precip picks up, but still enough sfc warming by late morning to turn most areas back over to rain. Can`t rule out a brief in-situ wedge-like event for a portion of the area; model blend-derived temps are several degrees below climo on Friday as it is, but could go lower. Northwest flow on the back side of the system will induce upslope precip Saturday, which changes to almost all snow Saturday night. Depending on how long the moisture remains available--or how well the Great Lakes connection is--these showers could continue through Sunday. Mins are expected to remain a bit above normal next weekend, with maxes around normal. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: VFR through the period at all TAF sites. Wind will remain N to NE overnight and into Tuesday morning. The passage of an upper low will bring a mostly mid-level cloud deck across the region during the early morning hours on Tuesday, but the cloudiness should move off to the east during the mid to late morning hours. In its wake, only scattered high clouds with a few northerly wind gusts, from roughly 16Z onward. Outlook: VFR conditions persist through at least Thursday under deep and dry high pressure. The next chance for restrictions will not be until Friday when moisture returns ahead of the next weather system. Confidence Table... 03-09Z 09-15Z 15-21Z 21-00Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 100% High 100% 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 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 && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...PM/SBK SHORT TERM...08 LONG TERM...08 AVIATION...PM

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