Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 201851 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 251 PM EDT Sat Apr 20 2019 .SYNOPSIS... An upper level low pressure center located near West Virginia will move slowly east through Monday. Expect a warming trend as as the upper low moves away from our area. Warm and dry high pressure will be in control of our weather for most of the week. Rain chances increase by the end of the week as a cold front moves into our area. && .NEAR TERM /THROUGH SUNDAY/... As of 240 PM...Closed upper low is now centered on the southern Appalachians, with an axis of vorticity oriented along the I-26 corridor. Along and ahead of this axis, a small amount of SBCAPE (probably 100 J/kg or less) widespread shower activity will continue, producing a few hundredths of an inch of rain by the end of the day. All areas at least potentially will see a few sprinkles. RAP profiles suggest the convective layer reaches up to icy temps. Thus a few stronger cells producing graupel and even maybe a little thunder can be expected in the area NE of I-26 until the end of diurnal heating. Clouds will become more sparse overnight. With less instability across the mtns, precip there has generally been stratiform and associated with a plume of deeper moisture near the core of the upper low. Rates are expected to increase this aftn as the moisture advects in; radar already indicates a band setting up across Knoxville and into the Smokies. Temps have already cooled enough to support light snow over the very high elevations, and snow levels appear to be around 4000 ft. However, warm ground seems to be limiting accumulations to the highest elevations (perhaps above 5500 ft) this aftn. The uptick in moisture will be fairly short-lived, with the low beginning to pull away to the NE this evening. Snow certainly will continue at the high elevations, and snow levels may even fall a bit, but potential for accumulation will diminish. Nonetheless it still appears 2 to 3 inches will be possible above 4000 ft, mostly in those areas where upsloping NW flow will continue to provide some enhancement tonight. With impacts in populated areas expected to be minimal, no advisory will be issued. Min temps will be mainly 4-6 degrees below climo tonight, and will dip into temperatures supportive of frost over portions of the southwest mountain zones. However, with breezy conditions continuing up there, frost looks unlikely, and the areas that freeze will be almost entirely in high elevations. We will forego frost/freeze headlines. The upper low will have moved northeast of the region by tomorrow, but near enough that it will still foster the development of congested cumulus in our eastern zones. However the convection will be too shallow to expect any precip to develop. With some cloud cover lingering, and cool northwesterly flow, temps will remain a few degrees below normal. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 120 PM EDT looks like we will see a return to warmer temperatures during the early part of the upcoming week. The old upper low will rotate off the Mid-Atlantic coast on Sunday night, allowing sfc high pressure to build in from the NW. The arrival of the high will provide us with one more cool morning on Monday, but the air mass should modify quickly as a flattening upper ridge builds in during the day. As a result, temperatures rebound another 5-10 degrees compared to Sunday. After a mild Monday night, the temps on Tuesday look even warmer...on the order of ten degrees above normal...with high pressure moving off the southeast coast. We could even have a few showers popping up along the ridgetops across the mtns of NC in the afternoon. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 2pm EDT Saturday: EC and GFS generally agree on low POPs through Wed. night as broad eastern upper ridge continues to hold sway. By Thursday morning, the GFS begins to wash-out the ridge and allows a weak frontal boundary into the mountains, giving some increase in rain chances at that time, which last through Saturday morning as front and upper southern-stream low advances into the region. EC, on the other hand, keeps the ridge stronger through Friday morning, with a more pronounced southern stream wave beginning to pop precip on Friday. Resulting blend will be some increase in shower possibilities beginning Thursday, and lasting through Saturday morning. Ridge will give above normal temps. until precipitation develops late in the forecast. Low temperatures are somewhat more uncertain due to differences of opinion in the amount of moisture retained under the ridge, and considerable differences in model indications of how much moisture advances ahead of the next system late in the week. Nonetheless, lows should be at or above seasonal normals throughout the forecast, keeping any frost out of the forecast. Winds should be fairly light under the ridge Wed. into Thurs., and may pickup as surface low begins to impact the region late in the forecast. GFS develops meager CAPE Thurs. - Fri., giving some chance for thunder with the late-period front; however, if the EC is correct with a stronger lower and an open Gulf, better instability and a chance for stronger storms could develop for Friday. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... At KCLT and elsewhere: An upper low skirting by the region will provide enhanced lapse rates and forcing, generating light showers across the Piedmont this afternoon. Some of these SHRA will bring MVFR cigs/vsby. Occasional brisk gusts could occur in their vicinity as well. the possibility of light nonconvective precip will persist acrs the mountains into tonight. Very high elevations will see light snowfall this aftn/evening, but most likely not reaching the valleys or KAVL. Clouds will become more sparse after sunset east of the mtns. While conditions will remain VFR thereafter, some congested cumulus may redevelop in the late morning tomorrow, albeit with near-zero chance of precip. Winds will remain SW and somewhat gusty this aftn, veering to NW overnight. Outlook: VFR conds are expected to prevail thru early next week. Confidence Table... 19-01Z 01-07Z 07-13Z 13-18Z KCLT High 97% High 100% High 100% High 100% KGSP High 95% High 100% High 100% High 100% KAVL High 85% High 84% Med 72% High 97% KHKY High 97% High 100% High 100% High 100% KGMU High 93% High 100% High 100% High 100% KAND High 87% 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...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...Wimberley SHORT TERM...PM LONG TERM...WJM AVIATION...Wimberley is the U.S. government's official web portal to all federal, state and local government web resources and services.