Area Forecast Discussion
Issued by NWS Jackson, KY

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246 FXUS63 KJKL 180744 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 344 AM EDT Wed Oct 18 2017 .SHORT TERM...
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(Today through Thursday) Issued at 344 AM EDT WED OCT 18 2017 Early this morning, rather zonal upper level pattern was in place across the Conus. An upper level ridge was centered southwest of the Baja of California and extended into Mexico and the southern Plains. Meanwhile, the shortwave upper ridge was moving through the Appalachians with a weak shortwave trough approaching from the west. At the surface, a ridge of high pressure was centered over the central Appalachians and was in control of the weather across East KY. A few high thin cirrus are passing overhead while fog has developed in the river valleys and near some of the area lakes and along some larger creeks. Temperatures were generally in the upper 30s to around 40 in the valleys with temperatures on ridges generally ranging through the 40s as of 7Z. The axis of the shortwave upper level ridge will move east of the area today as the weak shortwave trough moves into and across the OH Valley through tonight. At the same time, upper level ridging will begin to build across the western Gulf of Mexico and MS Valley with height rises over the lower OH Valley on Thursday. Also during this time frame, an upper low and associated surface low pressure system will be tracking well north of the area across Canada and the northern states. Locally, the axis of the surface ridge of high pressure will shift south of the area today resulting in light winds veering to average out of the south to southwest. With the upper level ridge building toward the end of the period, surface high pressure will become centered over the southern Appalachians, but remain in control of the weather into Thursday as well. The main forecast challenge during the period is overnight lows tonight and the extent to which mixing will lead to dewpoints dropping off this afternoon and on Thursday afternoon despite south to southwest low level flow. Temperatures will moderate further today with temperatures topping out near or just above the 70 degree mark in most locations. Weak low level flow today and on Thursday should limit the extent of mixing although have opted to undercut superblend dewpoints a few degrees in the afternoon leaning toward the lower MAV MOS values a bit. As for lows tonight, opted to go just above the coldest valley temperature compared to COOP MOS. With high pressure in place, ridgetop temperatures were warmed a few degrees from superblend guidance and lowered a few degrees in the valleys to account for the expected persistence of a nocturnal inversion and ridge/valley temperature split development. Some valley fog should again develop. .LONG TERM...(Thursday night through Tuesday) Issued at 250 AM EDT WED OCT 18 2017 Models in generally good agreement on maintaining the mid/upper level ridge across the area through the upcoming weekend. This will mean cool mornings and mild afternoons through the weekend. We will also continue to see low afternoon RH with dewpoints staying below guidance. 12z ECMWF becomes more amplified with the ridge late in the weekend as a sharp trough develops across the plains. GFS is much weaker with this feature, so amplification is much more scaled back. These differences translate into large amount of uncertainty heading into early next week regarding precipitation amounts. ECMWF is very wet with a much stronger system crossing the region, while the GFS is much weaker. Confidence is increasing we will see a decent chance of rain on Monday, just large variance in overall amounts. Thus, rain chances have been increased to categorical for Monday. The pattern will turn more active after a substantial cool down behind the early week system with several systems possible impacting us into the middle of next week. The ECMWF with the stronger system has a stronger push of cold air, but both models generally support it cooling down. Thus, while the pattern looks like it will shift to a cooler one, it also looks to be favoring a wetter one as well. Certainly with the colder pattern, we will become more susceptible to frost/freeze conditions as we through next week.
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&& .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) ISSUED AT 141 AM EDT WED OCT 18 2017 High pressure will remain in control of the weather through the TAF period. Mostly VFR conditions are expected to persist through the period, with the exception being in the river valleys and near larger creeks and lakes, where fog that has already developed or will be developing over the next few hours could become dense in some locations, especially between 8Z and 13Z. Some of the fog could advect into SME overnight with this less probable at the other TAF sites. The fog will lift and should dissipate between 13 and 14Z. Winds through the TAF period will remain light averaging out of the southeast to south. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...KAS AVIATION...JP

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