Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 180231 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 931 PM EST Tue Jan 17 2017 .SYNOPSIS... A weak cold front will approach the Carolinas from the west later this evening bringing increased chances for precipitation. A warm front will lift northward over the region on Thursday and Friday, bringing more rain to the southeast. A more significant low pressure system is expected to develop over the region on Sunday, bringing more unsettled weather to the area. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 930 PM EST Tuesday: Pre-frontal showers have moved east of the area. Showers associated with the front are moving in from the west. Still expect best precip chances will be across the mountains and the Upper Savannah River Valley with mainly slight chc elsewhere. Still expect patchy fog overnight with gusty winds across the mountains. Lows will be well above normal. Forecast only needed minor changes and looks generally on track. Otherwise, upper ridge over the Caribbean and Gulf remains over the area, but approaching front associated with upper low lifting toward the Great Lakes will help to push the ridge to the south somewhat briefly, though the high will pop back up behind the front tomorrow (so the shortwave is kind of like pushing down on a balloon). The downstream ridging will also be enhanced by a deep cutoff low lifting out of the Desert Southwest and into the Southern/Central Plains tomorrow, inducing surface low formation along the TX Gulf Coast (to impact us in the short term). There really isn`t much to this front and it certainly isn`t cold behind it, as is typically the case in the wake of CAD. Might see some precip with the frontal passage but most of that should be limited to the mountains, with really only slight chances elsewhere. While SPC does have portions of the SW mountains in a General Thunder area, CAPEs are nonexistent across the area (even MUCAPE) and have not reflected that in the grids. Front is just not dynamic enough for mechanical lift to result in thunder...at best just some showers but all pops pretty much gone within a couple of hours after sunrise. Wind swings around to the NW behind the front in the morning, and there should be enough moisture for another round of low clouds, but fog chances are greatly reduced with winds remaining 8-10kt through the period. Will see another night with lows warmer than seasonal highs, and then skies should clear and should see another day with well above-normal temperatures tomorrow with highs around 70 across most of the Piedmont (mid-upper 60s across NW Piedmont). Though cooler in the mountains, still far from what we would expect in January.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 230 PM EST Tuesday...The upper pattern will remain highly amplified and active across the Lower 48 thru the Short Term. An upper ridge will cross the Southeast Wednesday night thru Thursday, then a large upper low will lift out as a negatively tilted trough and cross the area on Friday. At the surface, a weak high will cross the area Thursday keeping it dry and mild, with lows in the upper 30s to upper 40s and highs in the 50s to lower 60s. Then a low pressure system associated with the upper wave will drag an occluded front thru the region late Thursday into Friday. The models have converged on the timing of highest PoPs to be mainly after midnight Thursday night to midday Friday. There will be some instability with the front, but a weak in-situ wedge will limit CAPE to mainly the mountains and southern piedmont. Shear will be adequate for organized storms, but the limited instability will keep severe threat low. Temps will remain above normal with lows in the 40s to lower 50s and highs in the 50s to upper 60s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 230 PM EST Tuesday: The medium range fcst period kicks off on Friday night amidst a brief period of shortwave ridging, while broad cyclonic flow continues to dominate the pattern out west. At the surface, weak high pressure will be in place beneath the aforementioned upper ridge axis across the Mid Atlantic states, while moderating southerly waa prevails across the Deep South. Pattern evolution through the medium range continues to be highlighted by the western upper trof and a rather robust closed low that develops through the day Saturday, all the while moving into the Southern Plains. In the meantime, an impulse of weak upper energy combined with moisture convergence along an old stalled frontal axis and an increasing unstable airmass will lead to robust convection along the I10 corridor region on Saturday. Guidance favors continuation of weak ridging across Northeast GA and the Western Carolinas, potentially providing focus for upglide forced stratiform rain Saturday afternoon, before the old frontal boundary lifts northward as a warm front yielding steepened lapse rates and thus improving instability promoting a transition to showers and perhaps isolated thunder for the overnight. Moving on to Sunday, the primary upper cyclone looks to be stacked atop a relatively newly formed surface low, centered around Texarkana by daybreak. Out ahead in the warm sector, showers and thunderstorms look increasingly likely along/near the Gulf Coast as moisture continues to stream in across the Southeast states amongst improving sswly H85 flow all ahead of a progressive cold front. As this entire complex slides east into the TN valley and Southern Appalachian region late in the day Sunday, copious amounts of moisture look to advect across the fcst area potentially fueling a threat of moderate/heavy rainfall given deep convection as well as upsloping along the southern/eastern escarpment. Given the strong swly llj that is progged to pass through ahead/along the front, strong/severe convection cannot be ruled out. The sfc front looks to advect east overnight into Monday morning, likely promoting continued light/moderate rainfall admist ongoing convection. Said front should clear the fcst area by around midday Monday, however pops will remain somewhat elevated into/through Monday evening across most of the region as the primary upper vort passes overhead, thus providing ample lift to support continued showers. The upper low will finally clear the region to the northeast on Tuesday morning as upper heights look to rise amidst a brief period of shortwave ridging to last through the remainder of the fcst period, therefore allowing pops to lower. Temperatures through the medium range will initialize well above normal on Saturday, cooling slightly, yet remaining above normal for Sunday/Monday and Tuesday amidst mostly cloudy skies and area showers. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
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At KCLT and Elsewhere: VFR to start at the TAF sites, but conditions deteriorate overnight with IFR or low MVFR cigs developing. MVFR VSBY also develops. SHRA most likely at KAVL and KHKY overnight but cannot be ruled out elsewhere. Conditions improve quickly after daybreak as a cold front moves through clearing out low level moisture. VFR is expected for the bulk of the day Wednesday. LLWS will continue at KCLT this evening and could develop at KAVL. SW winds ahead of the front become W to NW after FROPA. KAVL will see SW winds becoming gusty NNW. Outlook: Surface low pressure approaching from the southwest will bring chances for widespread precip to the area Thursday and Friday. Yet another cold front will bring chances of precip and restrictions on Sunday. Confidence Table... 02-08Z 08-14Z 14-20Z 20-00Z KCLT High 100% Med 77% High 100% High 100% KGSP High 97% Med 66% High 100% High 100% KAVL High 97% Med 69% High 100% High 100% KHKY High 100% Med 76% High 100% High 100% KGMU High 97% Low 50% High 100% High 100% KAND High 91% High 82% High 91% 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
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&& .CLIMATE... RECORDS FOR 01-18 MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 72 1933 20 1977 57 1943 0 1994 KCLT 71 1937 23 1893 62 1943 10 2003 KGSP 71 1928 30 1977 60 1943 5 1893 && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JPT NEAR TERM...RWH/TDP SHORT TERM...ARK LONG TERM...CDG AVIATION...RWH CLIMATE...

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