Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 252346 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 746 PM EDT Sun Sep 25 2016 .UPDATE... Issued at 746 PM EDT SUN SEP 25 2016 Forecast still on track so far this evening. Cloud cover will gradually overspread the area overnight, with 40 to 60 percent sky coverage expected by 12Z Monday. Patchy valley fog, dense at times, is also still on tap tonight, with near calm winds and mostly clear to partly cloudy skies expected. Ingested the latest obs into the hourly forecast grids to establish new trends. No other changes to the forecast were needed at this time. && .SHORT TERM...(This evening through Monday night) Issued at 327 PM EDT SUN SEP 25 2016 An upper level ridge remains in place across the Ohio River Valley today, but should start to break down overnight as an upper level wave and associated troughing move eastward into the upper Mississippi River Valley. The associated wave will strengthen into an upper level low across the Upper Great Lakes by tomorrow afternoon, with the deepening axis of the trough swinging across Kentucky throughout the day tomorrow as well. Models remain in good agreement through Monday night, with the closed low showing little forward momentum, but continuing to rotate and gain intensity throughout the night. This will keep lowering heights across the Ohio River Valley as well. This low will tap into the northern stream of the jet stream, with a strong pull of Canadian air expected to propagate southward and into the Ohio Valley. At the surface, a low pressure system is currently in place across southwest Ontario, coinciding with the upper level wave. This too will continue to push eastward and just north of Lake Superior overnight. A cold front is extending southward from this low, presently draped across WI, western Iowa, Missouri, and points to the southwest. A weak warm front is also extending from the low, currently draped across KY. This warm front is causing little impact to the ongoing weather pattern, however, with light winds and the upper level ridge still in place, abundant sunshine has boosted temps back into the mid and upper 80s once more this afternoon. Temperatures will quickly start to cool down this evening and into the overnight, with the cold front expected to make it into western KY by around midnight. Winds across eastern KY will begin picking up in speed slightly as they shift to a more S to SW direction during the overnight as well. This will begin pulling in some moisture in the form of clouds into the region, and then eventually precipitation just after daybreak tomorrow (Monday). Best precipitation chances will occur along the actual frontal boundary as it traverses eastern KY during the day tomorrow. Decent CAPE values according to the latest NAM12 soundings would promote some thunder potential with this system. While soundings do not favor hail potential, especially given the warm airmass in place leading into this event, some gusty winds and frequent lightning cannot be ruled out. That being said, once the cold front pushes through a location, winds will quickly shift to the Northeast and allow much cooler and drier air to begin filtering in. This, in addition to loss of daytime heating tomorrow evening, should quickly cut off best thunder potential across the CWA after 0Z. This is reflected in the quick loss of instability in the forecast soundings as well. Some rain showers may continue throughout the night in the far southeast due to upslope flow. It is during this time Monday night that we really start to tap into that strong pull of drier and colder Canadian air. This will result in clearing skies, aiding in the fall of overnight temps. While overnight lows are expected to be in the mid 60s tonight, overnight lows on Monday night will likely drop into the mid and upper 40s for much of the region. This pull of colder and drier air will continue into the mid and long term portion of the forecast as well as the upper level features show slow progression from this point forward. .LONG TERM...(Tuesday through Sunday) Issued at 327 PM EDT SUN SEP 25 2016 After agreement on a cool and dry start to the period, models continue showing disparity for the remainder of the period. A cold front will be well to our southeast on Tuesday, with dry air in place behind it for the local area. The upper level system which initially drives the cold front through will then become our main player. This large upper low will be moving south over the western Great Lakes Tuesday and Tuesday night, and into the Ohio Valley Wednesday. Although models do not agree on the evolution of this system, there are trends observed. The ECMWF is fairly consistent, but has shown a bit of a drift even further to the west as compared to 24 hours ago. Meanwhile, the GFS and its ensemble have made the larger shift, with a move toward the ECMWF solution. Instead of being progressive with the system, the GFS now also holds back a significant upper low (although, not as far west as the ECMWF). That being the case, will take the forecast more toward the ECMWf. This results in below normal temps and a potential for showers during the later part of the work week as the large, nearly cut-off upper low wobbles near KY. By the weekend, both the ECMWF and GFS have the low weakening considerably and lifting out to the NE-- albeit with different paths and timing. There is no return of low level warm air advection yet, but mid/upper levels warm with the jump in geopotential heights. This should lead to stabilization and an end to showers, and decreasing clouds. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) ISSUED AT 746 PM EDT SUN SEP 25 2016 High pressure will remain in control of our weather through Monday morning resulting in VFR conditions for most areas with light and variable winds. Skies will be mostly clear to partly cloudy for most of the night. Our far eastern counties may see BKN low level cloud cover 12Z Monday. Patchy valley fog will be around again towards dawn Monday, possibly affecting LOZ and SME with some MVFR BR for a couple of hours. A cold front will approach eastern KY by Monday afternoon. This could bring with it increasing chances of showers and thunderstorms for the remainder of the afternoon. Best potential should be after 18Z, so trended the TAFs towards these changing conditions, with MVFR conditions possible at SYM and SJS between 18 and 19Z Monday. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AR SHORT TERM...JMW LONG TERM...HAL AVIATION...AR is the U.S. government's official web portal to all federal, state and local government web resources and services.