Area Forecast Discussion
Issued by NWS Greer, SC

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184 FXUS62 KGSP 191055 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 655 AM EDT Fri Oct 19 2018 .SYNOPSIS... Cool high pressure will move off the east coast today as a cold front approaches from the west. A narrow band of showers crosses our region ahead of the front on Saturday. Much cooler and drier air arrives behind the front Saturday night through Sunday. The dry and cool air will linger into the early part of next week before the weather becomes more unsettled by late week. && .NEAR TERM /THROUGH TONIGHT/... As of 655 AM EDT Friday: Main update for the 12Z TAF issuance along with minor tweaks to temperatures to coincide with latest trends, as the rest of the near term forecast remains on track. Otherwise, with sfc high pressure overhead, quiet conditions prevail across the area this morning as light winds and nearly clear skies allow for ideal radiational cooling to take place. As a result, low cigs and patchy areas of fog have developed mainly across the mountain valleys and into portions of the northern foothills as well, and is expected to persist through daybreak. Temperatures have dropped 10 to 15 degrees from yesterday`s high temperatures, with latest obs depicting widespread low to upper 40s, into the 30s in some mountain locations where patchy frost is possible. Today, sfc high pressure will push offshore as latest guidance continues to prog an eastward propagating upper trough pushing through the Midwest later today/tonight. After a day of sunshine and high temperatures in the mid to upper 60s/near 70 degree, the return of WSW flow will allow for increasing moisture across the area. Thus, continue to anticipate the gradual infiltration of cloud cover tonight ahead of the next approaching system. With available forcing on the rise toward the end of the forecast period, isolated showers will be possible, initially along the TN/NC border and slowly expanding southeastward towards daybreak. With increased cloud cover, overnight low temperatures will be nearly 5 to 10 degrees warmer than this morning. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 245 PM EDT Friday: A strong short wave dives into the OH Valley Saturday creating height falls across our area. The short wave passes by to our north Saturday night dragging a trough axis across our area. At the surface, a cold front crosses the area Saturday. There is a narrow band of deep moisture ahead of the front the moves through rather quickly. The low level flow is also more westerly limiting the inflow. Still, forcing is rather strong, so have likely to high chance PoP across NC, falling to low chance or slight chance across the Upstate and NE GA Saturday morning. Precip chances drop of quickly during the afternoon as drier air moves in behind the quickly moving front. Very little in the way of instability, so thunder is not expected. The pattern favors NW flow precip Saturday night with CAA, strong NW winds, and lingering low level moisture. However, the moisture is not very deep, and the CAA while strong, is not very cold. The moisture also diminishes quickly after midnight. That said, the orographic lift could help the moisture briefly reach the snow growth zone, so snow showers could mix in across the higher elevations before ending. Winds could reach advisory level across the NC Mountains Saturday night, but any warning level gusts would be limited to locations above 5000 feet. Winds will be gusty outside of the mountains as well. That said, the Little TN Valley could be sheltered from the stronger winds. This would limit frost potential to those valleys with a freeze possible across the Northern Mountains and the higher elevations across the Central and Southern Mountains. High pressure and the colder air mass spreads across the area Sunday and Sunday night. Clear skies and light winds will allow for good radiational cooling conditions creating the threat of frost/freeze conditions across much of the area. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 345 AM EDT Friday: Weak short waves cross the area Monday night with low amplitude ridging moving in Tuesday through Thursday. The cold air mass over the area Monday moderates before a dry cold front moves through on Tuesday. Seasonal high pressure builds in behind the front Wednesday and Thursday. The guidance then shows a low pressure system moving east along the Gulf Coast Thursday. The GFS is weaker and farther south with the low while the ECMWF is stronger and farther north. As a result, the GFS is drier with much less precip over our area while the ECMWF has much more moisture and precip. Given the differences went with a model blend which has slightly chance PoP Wednesday night and low end chance for Thursday. Below normal temps Monday rise to just below normal for Tuesday and Wednesday then fall back below normal on Thursday. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Areas of low cigs and patchy fog continues to create IFR/LIFR at KHKY and KAVL this morning. Otherwise, VFR prevails at the other terminals with nearly clear skies and light winds. Expect flight restrictions at KHKY and KAVL to persist through daybreak, if not an hour after. After daybreak, expect conditions to improve to VFR at all sites with SE winds becoming SW ahead of the next approaching cold front. Have kept with the inherited trend of gradually increasing clouds late this afternoon/tonight as chances for VCSH/-SHRA begins late tonight across the TN/NC border, gradually expanding southeastward across the FA through the end of the valid TAF period. Outlook: A cold front passage Saturday will likely bring widespread rain with associated restrictions. Improving conditions are expected late Saturday into Sunday with breezy northwest winds behind the front. Confidence Table... 11-17Z 17-23Z 23-05Z 05-06Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL Med 69% 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...RWH NEAR TERM...SGL SHORT TERM...RWH LONG TERM...RWH AVIATION...SGL

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