Area Forecast Discussion
Issued by NWS Jackson, KY

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793 FXUS63 KJKL 200300 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1100 PM EDT Tue Sep 19 2017 .UPDATE... Issued at 1100 PM EDT TUE SEP 19 2017 Made several updates throughout the evening to better capture the radar trends for precip in the grids. Showers and thunderstorms made their way into the northern half of the CWA, and are continuing to fade out as we approach the 11pm hour. With the continued rain through the late evening, and expected clearing as we head into the overnight, conditions will be very conducive to fog in these locations. Meanwhile, other sites are already starting to drop to MVFR as we head into the overnight, with dense fog expected in most of the river valleys if not in some of the higher elevations as well. Based on this, as well as collaboration with LMK, decided to go ahead and issue a dense fog advisory through the morning commute. Also, updated the near term grids to make sure they were on track with the current observations. All grids have been published and sent to NDFD/web. A new forecast package was sent out to reflect changes to pops. A new HWO will also be sent out to reflect updates in thunder and fog. UPDATE Issued at 647 PM EDT TUE SEP 19 2017 Radar trends showed significant diminishment of ongoing convection across eastern Kentucky. However, all CAMS also pointed at isolated to scattered redevelopment across the Bluegrass early this evening, and then elsewhere across eastern Kentucky over the next few hours. Ended up reducing pops across much of eastern KY based on the latest radar trends, but as more convection began to pop up across the Bluegrass as the CAMS had predicted, ended up adding scattered pops back into portions of the northern CWA for much of the evening. So far a few more isolated showers have popped up, which is on par with isolated pops, but will continue to monitor in case pops/weather needs to be altered further. Also, given the expectation for fog overnight, went ahead and increased coverage of fog outside of just the river valleys, and added dense wording to the fog within the deeper/river valleys. Finally, made sure the near term grids were on track with the current conditions by loading in the latest observations. All change have been published and sent to NDFD/web. A new forecast package has also been sent out to reflect changes. This continues to carry a pre- first period, so will have to update again once showers/thunderstorms start diminishing late this evening. && .SHORT TERM...(This evening through Wednesday night) Issued at 435 PM EDT TUE SEP 19 2017 20z sfc analysis shows a bland sfc pattern in place over Kentucky while a mid level disturbance is passing through the Ohio Valley. This has activated the moist and humid air in place over the area to generate showers and a few thunderstorms that continue to move through eastern Kentucky this afternoon. The convection also brought plenty of clouds to the area limiting the sunshine by early afternoon. However, outside of any storm, temperatures had little trouble climbing into the low and mid 80s while dewpoints were in the mid 60s most places and winds light/variable. The models are in good agreement aloft with the longwave pattern through the short term portion of the forecast. However, some of the smaller scale, but important, features are handled just a little differently by each model. In general, though, they all depict the mini trough moving through the region tonight into Wednesday ahead of the ridge rebuilding from the southwest. The energy associated with the troughing feature will temporarily suppress heights and provide some impetus to any convection that manages to develop on Wednesday. Given the model agreement have favored a general blend updated with the latest guidance from the CAMS and higher resolution models. Sensible weather will feature convection dieing out this evening with some subsidence overnight clearing the clouds - probably leading to areas of dense fog developing in the river valleys, at the least, by dawn. The fog will burn off in the morning on Wednesday with isolated convection developing by afternoon - propelled by the energy aloft. Similar conditions as tonight will set up for Wednesday night with any convection fading out early in the evening followed by some clearing and then areas of fog developing - likely becoming locally dense in the river valleys again. The CONSShort and ShortBlend were used again as the starting point for all the grids. Did make some adjustments to the temperature ones each night based on terrain due to at least a small ridge to valley split setting up. As for PoPs, did again tweak them for the diurnal cycle peaking late in the afternoon and then diminishing after sunset on Wednesday. .LONG TERM...(Thursday through Tuesday) Issued at 349 PM EDT TUE SEP 19 2017 Models continue to display good agreement with a highly amplified long wave pattern developing across the CONUS into the weekend. Deep troughing will establish itself throughout the West. In the east, a seasonably strong ridge will build from the lower Mississippi Valley into New England. By early next week, the western trough and tropical activity in the western Atlantic pinches off the ridge, forcing the center to lift into the Great Lakes while the south end gradually dampens off. Sensible weather for eastern Kentucky remains uneventful and warm through most of the period. Thursday looks to be the only day when a few showers may threaten the area, before ridging becomes the dominant influence in our weather. Forecast soundings suggest enough surface based instability to warrant the mention of some thunder on Thursday. However, do question this after considering the rapid height rises taking place across the region through the day. For now, went ahead and included a slight chance of thunder, which actually helps to match up better with neighboring offices. After Thursday, the start of autumn looks to be dry and warm. Temperatures will run around 5 degrees above normal but will gradually drop closer to normal as heights slowly fall off with time. Highs will run in the mid 80s through the weekend, dropping off to the lower 80s by the end of the extended. Daily lows will start out rather warm as well, generally in the mid 60s but will drop closer into the lower 60s with time. Drier air settling into the area will allow for some cooler 50s in the valleys through the latter portion of the forecast. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) ISSUED AT 755 PM EDT TUE SEP 19 2017 Showers and thunderstorms are redeveloping across portions of the Bluegrass and will likely impact the northern most TAF sites over the next few hours. A few more isolated showers/thunderstorms cannot be ruled out over the next couple of hours as well, mainly for JKL/SYM/and SJS. If a site is impacted by one of these storms, expect a brief period of MVFR or lower CIGS and VIS. After the convection diminishes late this evening and into the overnight, skies may clear off again, leading to another night of likely valley fog. Indications are that the fog tonight could be a little worse than it was this morning with dewpoints running a tad higher. Kept with TEMPO groups to account for fog impacts at TAF sites, generally between 8 and 12Z. Forecast MVFR conditions, however, it is possible that rain that occurred today could result in periods of worst conditions. Will continue to update as needed. For will burn off by 14z with VFR conditions returning. Winds, outside of any storm, will be light and variable through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...GREIF LONG TERM...GEOGERIAN/RAY AVIATION...GREIF/JMW is the U.S. government's official web portal to all federal, state and local government web resources and services.