Area Forecast Discussion
Issued by NWS Greer, SC

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234 FXUS62 KGSP 131930 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 230 PM EST Fri Dec 13 2019 .SYNOPSIS... A strong upper disturbance will cross the area tonight, bringing one last round of rain showers. Then high pressure gradually builds in Saturday through Sunday. Another wet cold front will traverse the area Monday into Tuesday followed by dry and cool Canadian high pressure building in Wednesday through Thursday. && .NEAR TERM /THROUGH SATURDAY/... As of 2:25 PM Friday: temps have warmed above freezing across the CWFA over the past couple of hours, thus we decided to cancel the Winter Wx Advisory a bit early. Widespread showers continue across most of the non-mountain zones with isolated showers over the mtns. Otherwise, broad upper trofing will continue to amplify over the Mississippi River Valley this evening and overnight. The upper trof will take on a more negative tilt as it approaches our fcst area tomorrow morning. The trof axis is expected to lift over our area tomorrow afternoon and just to our Northeast as the period ends late tomorrow. At the sfc, high pressure will continue to drift farther off the coast of Nova Scotia this evening. Low-lvl winds will remain NELY, outside of the mountains, as the wedge hangs on and moist upglide continues well into the evening. At the same time, a broad low pressure system will lift out of the NE Gulf of Mexico and move over the Carolina Coast later tonight and into tomorrow morning. The low will track up the mid-Atlantic Coast thru the day tomorrow, and move over Western New England tomorrow night. As it does, low-lvl winds will become SWLY and then WLY as the pressure gradient tightens and speeds pick up over the area. Currently don`t anticipate winds reaching Advisory levels, however elevations above 4000ft could see some 35 to 45 mph gusts tomorrow. In addition, solid-chance to likely PoPs will linger over the higher terrain thru tomorrow afternoon, due to the moist return flow from the backside of the above-mentioned departing low. Temps will change little tonight and thru tomorrow morning with lows just a few degrees cooler than today`s highs. With the wedge having dissipated and cloud cover diminishing, highs tomorrow are expected to climb a few degrees above climatology. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 230 PM EST Friday: Quasi-zonal flow will briefly set up across the CONUS, as one trough lifts NE out of New England, while another digs into the Pacific Coast. A modest air mass will build in across the region Saturday night thru Sunday, resulting clearing skies and near to slightly above normal temps. Whatever NW flow snow shower activity there may be lingering Saturday evening, should wrap up by daybreak Sunday. Only minor snow accums are expected. The western CONUS upper trough will progress into the Southern Plains Sunday night thru Monday, inducing cyclogenesis near the ArkLaTex region. The low pressure system will activate a warm front across the TN Valley and Carolinas, but will have little moisture to work with. Deep-layer SWLY flow will likely bring an increase in high clouds and possibly low stratus by daybreak Monday across portions of the forecast area. At the very least, strong LLVL WAA will keep temps about 8-10 deg above normal. Moisture begins to deepen enough in the SWLY flow for some upslope showers in the mountains during the aftn hours, but the eastern half of the forecast area is expected to be largely dry thru the day. Highs will be in the mid 50s to mid 60s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 230 PM EST Friday: A progress, positively tilted upper trough will cross the eastern CONUS Monday night thru Wednesday. The associated sfc low pressure system will track NE across the OH Valley to New England, dragging a trailing cold front thru the Southern Appalachians to the Carolina coast. The front looks like another anafront (like the one we had earlier this week). This means the bulk of the forcing and moisture is on the the cold side of the front. So instability will be lacking once again, and a brief changeover to snow in the highest peaks on the backside of the precip is expected. There is some disagreement on the exact timing of the front, with the GFS a little fast, and new EC coming in a little slower. But right now, it looks like the highest pops will be Monday night thru the first half of Tuesday. The front is a little faster-moving than the previous couple of fropas, and so QPF looks to be 1-2" across the SWLY upslope flow areas of western NC and the SC/GA mountains. But the rest of the area looks to get around 0.5". There is doubt on whether there will be any moisture left for snow at the tail-end of the precip Tuesday night, but if so, accums would be very light and confined to the highest elevations near the TN border. Temps start out well above normal Monday night just ahead of the front, but cool to near or slightly below normal by Wednesday morning with skies clearing out. The center of Canadian high pressure will settle over the forecast area Thursday, then shift slightly east to the Outer Banks on Friday. The last few runs of the GFS continue to be really fast with the next system, having a southern stream low pressure system cross the area late Friday into Saturday. But the last few runs of the EC have not shown this system at all, and keep dry high pressure in control of the Southeast. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... At KCLT and Elsewhere: conditions range from MVFR to LIFR as precip continues to move across the fcst area from the SW. I expect a mixture of MVFR to IFR to persist into the evening, with predominately IFR conditions settling in for the overnight and early morning tomorrow. Intermittent periods of LIFR will be possible at most sites beginning around midnight, if not just before. I used TEMPOs to reflect the most likely periods of LIFR for the overnight/early morning. Most sites should return to VFR, or at least MVFR, by late morning, however MVFR cigs will likely linger over KCLT and KAVL well into the afternoon. NLY to NELY winds will continue into the evening outside of the mountains and become light later tonight. They pick back up out of the SW tomorrow morning and remain SWLY to WLY thru the day. Winds at KAVL will favor a SELY to SLY direction thru the evening and become NWLY overnight. They will remain NWLY thru the remainder of the period. Outlook: Restrictions may continue well into Saturday as another trof of low pressure arrives from the west. Dry/VFR conditions will then return behind a cold front through Sunday and persist until the next front arrives Monday night or Tuesday. Confidence Table... 19-01Z 01-07Z 07-13Z 13-18Z KCLT High 86% Med 77% High 82% Med 71% KGSP High 86% Med 76% Med 68% Med 75% KAVL High 88% High 82% Med 73% Med 72% KHKY High 94% Med 77% Med 79% Med 79% KGMU High 80% Med 76% High 81% High 81% KAND Med 69% Med 70% Med 77% 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: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...ARK NEAR TERM...JPT SHORT TERM...ARK LONG TERM...ARK AVIATION...JPT

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