Area Forecast Discussion
Issued by NWS Jackson, KY

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791 FXUS63 KJKL 171215 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 815 AM EDT Thu Aug 17 2017 .UPDATE... Issued at 815 AM EDT THU AUG 17 2017 Did a quick update to drop the fog as it has been mostly light out there and is dissipating quickly. Also touched up the Sky, T, and Td grids per the latest obs and trends. The grids have been sent to the NDFD and web servers with an updated ZFP and HWO also issued to remove the fog. && .SHORT TERM...(Today through Friday) Issued at 420 AM EDT THU AUG 17 2017 07z sfc analysis shows a developing warm front lifting northeast through Kentucky. This is associated with a fairly strong area of low pressure over the Upper Midwest. A local area of higher pressure in the midst of these features has allowed for another night of partly to mostly clear skies resulting in a small ridge to valley temperature split as well as dense fog formation in the deeper river valleys. The high dewpoints are limiting the temperature fall this night with both not far from the low 70s most places, though valleys are in the upper 60s. Winds are light to calm with some patchy light fog outside of the valleys, as well. The models are in pretty good agreement aloft through the short term portion of the forecast. They all depict a fairly strong shortwave trough moving from the Upper Midwest into the Great Lakes. As this happens, height falls will pass through the Ohio Valley today along with some mid level energy riding through the base of the trough. The trough`s influence and its lower heights continue to press south into Kentucky on Friday as another cluster of shortwave energy/troughiness reinforces the main pattern. Given the decent model agreement will favor a general blend, though with a strong lean toward the higher resolution HRRR and NAM12 for weather details. Sensible weather will feature fog burning off by mid morning in the river valleys and elsewhere. Scattered showers and thunderstorms in the morning should develop and increase in coverage in the afternoon in the east as a lull sets up to the west ahead of the system`s cold front. This front goes through later in the evening and through the overnight with the best chances for showers and storms. Any storm during the afternoon and evening could become strong owing to good instability and favorable winds aloft. The main threat from these will be gusty and potentially damaging winds and SPC has outlined the northern portion of the CWA in a marginal risk for severe weather today. Have highlighted this in the HWO along with a mention of brief heavy rain supported by high PW air but limited by better storm motion than the past few days. The convection will end from northwest to southeast early Friday as the front departs. Drier air then spreads into the region providing relief by late afternoon from the high humidity of late. Once again the CONSShort was used as the starting point for the grids through the short term portion of the forecast with some adjustments to temperatures each night for terrain distinction. As for PoPs, mainly spread them out a bit further than initially populated for today and this evening as their remains some uncertainly to the timing and extent of the frontal convection. .LONG TERM...(Friday night through Wednesday) Issued at 250 AM EDT THU AUG 17 2017 The extended portion of the forecast begins Friday night with a continued active pattern in place. To start the period, an upper level shortwave ridge will be passing over the area as a mainly dry weekend will be on tap for eastern Kentucky. The one exception will be over northeastern KY when the eastern CONUS will continue to be under a lingering longwave trough. Thus another weak wave will follow in behind Friday`s exiting front providing a small chance of precip over the northern half of the forecast area for Saturday afternoon. High pressure will keep the area dry for Sunday. In fact, models suggest that the bubble will linger into Monday keeping the area dry another day, at least in far eastern Kentucky as the return flow will eek a bit of moisture into the I-75 corridor area. Still only a slight chance of precip is possible over the northern portion of the forecast area. By Tuesday morning, combined with return flow advecting ample moisture into the OH Valley and TN Valley, a strong cold front will move into the region creating a prolonged period of showers and thunderstorms Tuesday through Wednesday. The heavier activity will coincide with the max heat of the day on Tuesday as it seems PWATS will range between 1.75 and 1.90 during this period. Ample moisture in place during this prolonged period may be enough for a few minor flooding problems for early Tuesday through Wednesday afternoon. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) ISSUED AT 745 AM EDT THU AUG 17 2017 Cigs will gradually lower throughout the day ahead of an area of low pressure and its associated surface cold front approach from the west. Scattered showers and a stray thunderstorm will be possible throughout the area this morning and after a lull - by mid afternoon - SYM and SME can expected scattered to numerous showers and thunderstorms, as the front begins to move across the area. JKL, LOZ, and SJS should see their best convective threat toward evening. Look for the convection to move east during the evening. Will downplay the fog for tonight for now. Winds will be generally out of the southwest at 5 to 8 KTs during the day, otherwise light. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...GREIF LONG TERM...SHALLENBERGER AVIATION...GREIF

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