Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 151832 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 132 PM EST Sun Jan 15 2017 .UPDATE... Issued at 120 PM EST SUN JAN 15 2017 Upstream radar trends continue to point to an increase in drizzle or shower activity as the afternoon progresses. This is also in line with many of the short term model runs. Some of the recent HRRR runs generally support that idea, but differ from run to run in coverage and QPF. The ongoing forecast that brings likely pops into the northern two thirds of the area later this afternoon and into the evening still seems reasonable and was not changed at this time. Some area of fog persist across the northern half or so of the area, with some of this dense at the higher ridge observing sites such as JKL and PBX. Webcams indicate similar conditions to that near Wolfe/Powell Co line along the Mtn Parkway. Some fine tuning of the ridgetop fog will be done based on the 1 PM obs. Otherwise, hourly temperature and dewpoint grids were freshened up based on recent observations. UPDATE Issued at 1025 AM EST SUN JAN 15 2017 Radar and some observations such as recent KSYM observations are indicating some light drizzle occurring across generally northern portions of the area. Fog dense on some ridges lingers. Meanwhile, an area of showers over Indiana and western KY are slowing approaching the area ahead of a shortwave moving into the Lower OH Valley. The hourly grids have been updated to include a slight chance or isolated drizzle across the northern locations and highest terrain near the VA border through early to mid afternoon along with some fog on the ridges. Meanwhile, the area of showers should move into the area, especially northern and central sections with scattered to numerous coverage by mid to late afternoon per recent NAM, GFS, and short term model runs such as HRRR. UPDATE Issued at 625 AM EST SUN JAN 15 2017 WSR-88D radar showing the earlier relatively higher returns have waned, but we are still seeing some drizzle is spots. Otherwise biggest issue will be the patchy dense fog in spots this hour. Updated grids to reflect latest obs and trends but otherwise forecast is on track. && .SHORT TERM...(Today through Monday) Issued at 332 AM EST SUN JAN 15 2017 Surface analysis shows area of high pressure centered to the NW this AM across IA/IL region and quasi stationary boundary is now across portions of the TN Valley. Based on the upper level data, would suspect the 925mb boundary still resides across the region and 850mb just to our north. That said, WSR-88D radar does indicate a line of shower/drizzle has developed across the center of the CWA and is near where the SPC mesoanalysis shows weak forcing at the 925mb level as mentioned above. This will progress south through the morning and kept as a drizzle mention given some areas are seeing light drizzle outside this line. Overall the HRRR/CONSSHORT seemed to be handling this idea and therefore nudged my POPs in that direction. Based on the obs this morning would think fog is more of the patchy dense variety and therefore kept that going through early morning before tapering through mid morning. The previously mentioned surface high pressure will progress east today with winds veering around to the NE by this afternoon. The 850mb front will remain north as mentioned before, as a mid level wave/PVA rides along the baroclinic zone. These two forcing mechanisms combined with saturated column will lead to decent chance of rain showers late this afternoon into this evening mainly north of the Mountain Parkway. While this is a decent shot of rain showers, the QPE will remain light with only a couple of hundredths of an inch expected. POPs will wane through the evening from west to east as better forcing pushes east. Given the moisture in place did opt to add patchy fog in for a good portion of the region through Monday morning. For Monday did keep slight POPs in the north and far NE, but this may have to be looked at further. The only fly in the ointment here will be the aforementioned quasi stationary will likely lift back north, and therefore could lead to slight POPs ahead of the eastward progressing cold front. Better POPs for the cold front will take place beyond this forecast period. .LONG TERM...(Monday night through Saturday) Issued at 434 AM EST SUN JAN 15 2017 Models start out in decent agreement, but soon go their separate ways concerning wx systems and precip potential. There is agreement that it will remain mild. It`s a question of how mild. For specifics, a low pressure system will be passing northeast over the middle of the CONUS Monday night. Its cold front will push into KY, with warm air advection ahead of it. This should keep temps nearly steady on Monday night. Showers along the front should be arriving from the northwest on Monday night, and lasting into Tuesday. This is when the first model differences start showing up. The ECMWF is more pronounced and faster with an upper level wave supporting the storm system, which allows the ECMWF to advance the cold front well to our southeast by Wednesday morning. Meanwhile, the GFS is weaker and slower with the upper level system, and still has the front near the KY/VA line early Wednesday. The NAM is in between. The result is a difference in precip/POP for early Wednesday, and a variation in Tuesday night/Wednesday morning low temps. The forecast is a compromise at this point. There is agreement for a period of dry weather from Wednesday afternoon into Thursday, even though upper level pattern differences continue to grow. The upper level differences affect the forecast again beginning late Thursday. The GFS has a shortwave trough dropping southeast out of Canada and phasing with the slower aforementioned upper level wave, morphing into one large trough over the northeast CONUS and Appalachians. This would bring cool temps and stratocu. The ECMWF does not phase the two systems and remains flatter with the flow over the northeast CONUS. Instead, the ECMWF becomes more amplified with a trough/upper low over the middle of the CONUS on Thursday. The resulting system pulls moisture back north, allowing for clouds to increase from top down on Thursday, and an area of showers moving through the JKL forecast area from SW to NE on Thursday night and Friday. The slower and weaker GFS takes this system by mainly to our south late Friday and Friday night. There is a large amount of uncertainty with this system, and have used low chance POPs Thursday night into Friday. Finally, by Saturday there is loose agreement for an upper level ridge to be positioned just to our east, supporting mild and dry conditions. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) ISSUED AT 130 PM EST SUN JAN 15 2017 Widespread IFR CIGS are currently being reported across the area with some stations such as JKL and SJS below airport minimums attm. A limited area near the TN and VA border including valley sites 1A6 and I35 are reporting MVFR. Some limited improvement but still IFR CIGS and or vis remaining is expected at all the TAF sites with some MVFR south of all sites through 0Z. However, a upper level wave will interact with the frontal zone lingering near the area to bring a renewed threat for rain showers and drizzle and this should maintain stratus build down across the area or result in these bases lowering by the overnight hours as the boundary begins to return back toward the area as a warm front. Thus IFR and possibly below airport min CIGS are again expected at the TAF sites during the 0Z to 15Z period. Improvement to MVFR may reach SME, LOZ, and JKL during the last 3 to 6 hours of the period. Light winds are expected through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...DJ LONG TERM...HAL AVIATION...JP

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