Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 170550 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 150 AM EDT Tue Oct 17 2017 .UPDATE... Issued at 147 AM EDT TUE OCT 17 2017 Hourly grids have been freshened up a bit to reflect the valley fog that has already developed per GOES 16 satellite imagery. Hourly temps and dewpoints were also freshened up based on recent observations and to be consistent with the fog already present. UPDATE Issued at 1020 PM EDT MON OCT 16 2017 Did a quick update to the grids to reflect the current obs and trends, otherwise the forecast is on track. These have been sent to the NDFD and web servers. UPDATE Issued at 750 PM EDT MON OCT 16 2017 23z sfc analysis shows high pressure building over the state. This is in the process of clearing out the lingering mid level clouds with winds now settling. Temperatures are running in the mid and upper 50s with dewpoints in the upper 30s to lower 40s. Look for clearing skies and light winds to support the development of an inversion overnight under good radiational cooling conditions to yield a decent ridge to valley temperature split later tonight. This will prompt valley temperatures to fall into the upper 30s by dawn with a few locations touching the mid 30s. Given the dewpoints and clear conditions we expect to see some patchy frost form in in the deeper valleys. However, most locations will experience fog development instead keeping the frost at bay. Locations along the rivers and near lakes will most likely see dense fog formation. An SPS is out for these concerns along with highlights in the HWO. Have updated the forecast to tweak some valley spot locations low temperatures and also sky cover per the latest satellite images. Also, modified the T and Td grids per the current obs/trends. These updated grids have been sent to the NDFD and web servers. && .SHORT TERM...(This evening through Tuesday night) Issued at 234 PM EDT MON OCT 16 2017 A sprawling area of surface high pressure from the southern plains into the OH valley will control our weather through Tuesday night. The forecast issue of the day is the frost possibility tonight and Tuesday night. Once the broken cloud deck currently over the area scatters out and winds diminish, tonight will be a good night for radiational cooling. However dewpoints are currently in the upper 30s to lower 40s, as are dewpoints well upstream over OH and IN. Based on latest guidance, blended data and upstream dewpoints it doesn`t appear dewpoints will be able to come down much more as we head into evening. Would really like to see lower dewpoints at this point, as it appears there may end up being more fog than frost especially where more rain occurred yesterday into last night. While there may be a few spots that see some very light frost, most of the area will not see any frost. After collaboration with neighboring offices have decided to not issue a frost advisory for any of our counties. Will issue a Special Weather Statement to cover isolated frost possibility and the locally dense fog possibility for tonight. Even as we head into Tuesday night, with another day of dry weather it still appears dewpoints will not be much lower than today, so only some patchy light frost will again be possible Tuesday night. .LONG TERM...(Wednesday through Monday) Issued at 304 PM EDT MON OCT 16 2017 The period will begin with an area of high pressure just to our east and weak trough aloft. This area of surface high pressure will meander near and just to the east of eastern Kentucky through Sunday, with upper level ridge building east by Thursday. The biggest issue through the period will be overnight lows and how this will be affected by afternoon mixing. Given this leaned toward the previous forecast which had the valley temperatures covered well, however, struggled to undercut the usually coldest COOP MOS guidance. Overall the period will be quite dry with afternoon MIN RH values on the 25 to 30 percent range through late week. The models become more convoluted moving toward day 7, with respect to approaching cold front and upper level features. The GFS brings the front through and leads to a couple of shots of showers along and near the front, and in contrast the ECMWF wants to close a upper low across the lower Mississippi River Valley which could cut some moisture off based on the 00Z solution. However, the latest 12Z ECMWF cutoff the low further west allowing more moisture to filter into the region. Given the large amounts of spread and less continuity will lean toward chance POPs given by the blended model data. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 145 AM EDT TUE OCT 17 2017 High pressure is in place across the OH Valley this morning. Some valley fog has already developed in East KY and this should become dense in a few valley locations during the next few hours. At this point, the TAF sites are expected to remain MVFR or better. The exceptions may be KSYM where fog is evident in the nearby Licking River Valley and possibly KSME. Guidance has generally trended toward less fog for both sites, however, so confidence was not high enough to go with IFR at this time. Valley fog will lift and dissipate by 14Z, with VFR conditions in all locations from then until the end of the period. Winds will be light and variable through the period with high pressure in place. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...SBH LONG TERM...DJ AVIATION...JP

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