Area Forecast Discussion
Issued by NWS Greer, SC

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589 FXUS62 KGSP 231054 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 654 AM EDT Fri Mar 23 2018 .SYNOPSIS... High pressure remains over the area today. The next low-pressure system arrives over the weekend with precipitation and well-below normal temperatures. The cold weather will persist through Monday as strong high pressure builds down the Appalachians. Temperatures rebound back above normal by Wednesday as moisture increases ahead of a cold front. && .NEAR TERM /THROUGH TONIGHT/... As of 345 AM EDT: A large area of dry high pressure will continue to slowly shift east across the region today under deep-layer northwesterly flow. A shortwave will round the ridge axis over the Plains later today into tonight, and will cause sfc cyclogenesis over the central High Plains. A warm front extending from this system toward the southeast will activate across Midwest to the TN Valley. Increasing mid and high clouds should start streaming in from the west atop the CWFA by late aftn or evening. But until then, skies should be mostly clear. Temps are starting out chilly, but should rebound by a category or two from yesterday`s readings. Dwpts are also on the increase, with weakening downslope flow. So min aftn RH doesn`t look as low as yesterday. Tonight, the 850 mb warm advection and frontogenesis start to ramp up over the CWFA due to the approaching warm front. Profiles gradually moisten up from the top down, with thicknesses supporting a mixed bag of sleet, snow and freezing rain when precip first breaks out overnight above 3500 ft. This looks to be mainly in the western and central mountains starting in the late evening or around midnight, then expanding across the rest of mountains overnight. QPF amounts look fairly light, generally less than a quarter inch. So any snow or ice accums should be light. The valleys will be tricky, as sfc-based warm layer may be too deep for anything but rain thru the night, but wet-bulb effects may lower temps more than guidance is showing. Elevations above 3500 ft may see an inch or two of snow by daybreak Saturday, mainly in the Northern Mountains. Min temps will be mid 30s to lower 40s for most of the area, except in the upper 20s to lower 30s above 3500 ft. && .SHORT TERM /SATURDAY THROUGH MONDAY/... As of 420 AM Friday: Very complicated and tricky forecast for the short range. Miller B type clipper system moves in from the NW with differing temps and thermal profiles depending on the model. Have issued a Winter Storm Watch for the northern NC mountains due to the potential for a significant mixed precip event. Amounts and p-types are much more uncertain across the rest of the NC mountains and the northern foothills and NW piedmont. Therefore, have kept those areas out of any winter products for now, but an advisory may be needed as the event nears. Just rain is expected across the rest of the area. Precip chances increase Saturday with the highest chances during the afternoon and evening. With strong cold air damming developing, temps fall to create the winter weather potential. A strong warm nose develops with cold air below it. The profiles suggest snow across the northern mountains Saturday morning then becoming rain mixed with sleet for the afternoon as the warm nose develops. Precip becomes freezing rain Saturday night over the northern mountains with the warm nose remaining in place and cold low level air moving in from the north. Sleet or snow will mix in across the I-40 corridor depending on the how the thermal profiles develop. Precip returns to mainly rain Sunday with warming then ends as a mixed bag across the mountains Sunday night. The highest QPF and any accums would be mainly Saturday afternoon through Sunday morning. Temps will be well below normal for all but the southern portions of the CWFA Saturday. Precip tapers off Monday. Highs will again be well below normal. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... As of 345 AM Friday: Looks like dry high pressure briefly builds in Tuesday before moisture returns ahead of a cold front Wednesday and Thursday. That said, there could be enough lingering moisture Tuesday for some light showers across the mountains. For now, have a dry forecast Tuesday with increasing PoP Wednesday and Thursday. Temps start our below normal Tuesday then rise above normal for Wednesday and Thursday. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... At CLT and elsewhere: VFR conditions expected today thru this evening. Dry high pressure still over the area today, but a warm front will approach from the west this aftn into this evening, and will bring increasing cirrus, then mid clouds by the end of the 06z TAF period. Precip is expected to breakout first in the mountains tonight, then start to spread east across the piedmont early Saturday morning. Winds will be westerly to northwesterly with low-end gusts possible beginning in the early afternoon. There are some gap winds producing occasional gusts at both KAVL and KGSP thru the morning. Then winds become lighter and turn out of the N or NE this evening. Outlook: Increasing precipitation chances and possible flight restrictions are possible this weekend with another approaching low pressure system. Cool and dry high pressure will try to build in from the north early next week. 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 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: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...Winter Storm Watch from Saturday morning through Sunday morning for NCZ033-049-050. SC...None. && $$ SYNOPSIS...RWH NEAR TERM...ARK SHORT TERM...RWH LONG TERM...RWH AVIATION...ARK is the U.S. government's official web portal to all federal, state and local government web resources and services.