Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 160555 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1255 AM EST Thu Nov 16 2017 .UPDATE... Issued at 1255 AM EST THU NOV 16 2017 We are seeing a line of light rain or drizzle moving across the region. This looks like possibly a weakening frontal boundary and should move through at a steady pace. Overall we have this handled with the patchy drizzle in the WX grids. Therefore, little changes needed this update, but did add some obs to gain a better trend in the forecast. UPDATE Issued at 1049 PM EST WED NOV 15 2017 Some light returns are noted on radar in the Bluegrass, with lowering cloud decks and visibilities. Have carried a few hours of drizzle as a short wave trough moves through the area. The latest satellite trends reveal clearing across western Kentucky. This will move into our northwest counties between 06 and 07z at its current pace, with clearing eventually working in to our far southeast by around 10z. Have adjusted the sky cover accordingly, while allowing for a little room for error, as clouds typically get hung up against the terrain. Temperatures are still running around 50 degrees for most locations, and this should continue until the cold front moves through the area. Lows ranging from the upper 30s in the northwest, to the lower 40s elsewhere, still look on target. Updates have been sent. UPDATE Issued at 749 PM EST WED NOV 15 2017 The bulk of the showers have exited off to the east, as dry slotting works in from the west. The surface cold front remains well off to our west and northwest, so would expect a temporary lull in the activity, until it moves through later tonight. Have allowed for more of a separation between the pre-frontal showers and light rain/drizzle to occur near or just behind the cold front. Updates have been sent. && .SHORT TERM...(This evening through Thursday night) Issued at 340 PM EST WED NOV 15 2017 A cold front is poised to shift southeast across the Ohio River and across portions of Kentucky late this afternoon, traversing eastern KY this evening and overnight. WPC shows this front exiting just SE of the state after 9Z. A line of precip is moving in ahead of this frontal boundary, in the form of rain. This precip line is currently making its way into the NW CWA and will continue to shift eastward across the CWA through the evening and first part of the overnight. Just behind the frontal passage, dry air will move in and cut off precip potential. This dry air will cut off the mid level moisture first, leaving llvl moisture trapped below a pretty steep inversion. As such, did include some patchy drizzle in on the backside of the precip as it is tapering off after 6Z. For Thursday, deamplified ridging moving across the south central conus, and a shortwave exiting NE of the Ohio Valley will result in rising heights across our region. An area of surface high pressure across the mid and upper Mississippi Valley at 1Z Thursday will shift eastward across the Ohio Valley and Kentucky Thursday and Thursday night. This dry westerly flow and rising heights will promote mostly clear skies but post frontal temperatures that are some 10 degrees below seasonal normal, in the upper 40s and low 50s. By thursday night, the location of the high will be passing almost directly overhead, subduing winds and making for ideal conditions for net radiational cooling. Ridge valley splits will be likely, especially in the east. Dropped the far east valleys down around 5 degrees from rest of the CWA, but wouldn`t be surprised if this spread ends up being even more. Rain tonight could provide enough lingering moisture to also promote fog, especially in theses cooler valleys. Did include patchy to areas of fog in the deeper valleys as well. .LONG TERM...(Friday through Wednesday) Issued at 359 PM EST WED NOV 15 2017 A rather progressive pattern is expected to continue into the long term period with mid and upper level as well as surface ridging shifting east of the area from Friday into Friday night while the next trough will begin to approach from the Plains. Individual shortwaves are expected to consolidate as the system approaches the MS Valley with the trough starting to become neutrally if not negatively tilted as it moves across the OH Valley and Great Lakes and into the northeast from Saturday into Saturday night. Height rises and shortwave ridging is expected to work into the area to end the weekend before moving east of the area later in the period. Model agreement decreases in the longwave details as with timing of individual shortwaves from late Monday through the end of the period. At the surface, high pressure will move east of the area with temperatures moderating on increasing southerly flow on Friday. The cold front will move into the area on Saturday afternoon, moving east of the area on Saturday night. The pressure gradient and winds aloft will increase with winds near 850 mb reaching near 50kt if not 55kt on Saturday. Winds will likely gust to 30 mph or more late Friday night on the higher exposed ridges above 2500 feet msl. Some of the momentum should mix down with some mixing ahead of the front and around or just prior to the arrival of a band of showers. 12Z GFS BUFKIT momentum transfer suggest potential for as much as 39KT gusts from JKL over to SJS and on into far northeast KY, but 12Z NAM remains generally 25kt or less. Have opted to go in the middle near the 30KT mark for wind gusts on Saturday and increased sustained winds a bit from Superblend more toward some of the statistical guidance. The degree of heating ahead of the front on Saturday and strength of warm advection will determine how high temperatures will max out ahead of the showers on Saturday. Some of the statistical guidance suggests values warmer than the superblend and current forecast which was a tad warmer than the superblend over the southeast. This system should bring a bit higher qpf than the current near term system with a quarter of an inch or so on average with some locally higher amounts. Colder 850 mb air will move into the area following this front and low level moisture possibly deep enough to reach -8C to -10C could linger late Saturday night or very early on Sunday across the VA border and far southeast KY. The higher ridges will probably cool off enough that if that occurs some snow could mix in with any possibly rain showers. 850 mb temperatures should bottom out in the -3C to -6C range at least around 12Z Sunday, with the past 6Z and 12Z GFS and 0Z ECMWF 850 temperatures colder than that. The bottom line is Sunday will be well below normal by 15 to 20 degree range. The MOS guidance was about 3 degrees warmer than superblend and opted to go about a degree warmer than the blended guidance for max T on Sunday and lower max for the highest terrain as well more in line with what the 850 mb temps support. Dry weather should prevail for most of Sunday through Tuesday with moderating temperatures. Uncertainty remains for the middle of next week, but opted for slight chance pops late Wednesday to give the latest GFS run some credit. It is certainly possible that Wednesday could remain dry. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 1241 PM EST WED NOV 15 2017 Most sites are beginning the TAF cycle with MVFR to IFR CIGs and even some VIS restrictions for fog/drizzle. The latest GOES-16 imagery is showing a good amount of clearing and drier air moving into portions of western and central Kentucky. Therefore, will taper the clouds off from northwest to southeast through the overnight into the dawn hours. Then we will see sites improve to VFR across the board to round out the period. Winds will remain light out of the southwest then veering west to northwest through the overnight into later today. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...JMW LONG TERM...JP AVIATION...DJ

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