Area Forecast Discussion
Issued by NWS Jackson, KY

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754 FXUS63 KJKL 241902 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 302 PM EDT Wed May 24 2017 .UPDATE...
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Issued at 300 PM EDT WED MAY 24 2017 Updated the near term grids with the issuance of the tornado watch. Added severe wording to the wx grids and timed the storms via radar trends and latest from the HRRR. Also tweaked sky cover and the hourly T/Td based on obs and trends. These have been sent to the NDFD and web servers along with an updated set of ZFPs and HWO for the tor watch. UPDATE Issued at 1140 AM EDT WED MAY 24 2017 15z sfc analysis shows a seasonably deep, and stacked, low moving through the Tennessee Valley. The warm frontal structure with this is lifting northeast into eastern Kentucky with an associated cluster of showers and embedded thunderstorms. This first batch should go through relatively benign, but any `dry slotting` behind this initial band would open up the opportunity for increasing instability and the development on more organized and potentially severe storms given the favorable wind profile and cold pool aloft. We will monitor the situation through the early afternoon with a particular focus on clearing and thinning potential in the cloud cover. Temperatures currently are in the upper 50s to lower 60s with the rain and closer to the mid 60s outside of it with dewpoints nearly the same. Winds are light and variable away from any thunderstorm. Have updated the forecast to fine tune the PoPs, QPF, and wx through the afternoon per radar trends and the latest HRRR. Also, touched up the T and Td per the latest obs and trends. These have been sent to the NDFD and web servers along with an updated ZFP. UPDATE Issued at 644 AM EDT WED MAY 24 2017 The latest surface analysis shows that the deepening surface low near the TN/OH Valley will track NNE through the day. The HRRR suggest there will be multiple rounds of showers and thunderstorms, but differing solutions are offered up by other CAMs. Given will leave the POPs as is until better overall consistency and trends are seen. Based on the radar trends the lead shield of showers and thunderstorms will progress into the Lake Cumberland region by around 13Z and far east by 16Z. Severe risk concern is still in place owing seeing destabilization this afternoon.
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&& .SHORT TERM...(Today through Thursday) Issued at 410 AM EDT WED MAY 24 2017 Surface analysis shows an area of surface low pressure continues to deepen across Middle TN this morning. This as an upper level wave in the lower MS Valley based on WV SAT rides NE providing plenty of forcing for ascent across the TN and OH Valley. This will also drive the aforementioned surface low pressure NNE likely just NW of the CWA. This will probably drive a more occluded front across the region and lead to a solid chance of showers and thunderstorms from late morning into this afternoon. The low track certainly has our attention, as it would favor backed winds near the surface. The real issue at hand will be the large scale forcing could inhibit building any instability this afternoon with more debris clouds streaming into the region. However, despite the caveat if we do see clearing and subsequently more instability organized convection would be likely given ample shear, with effective values running in the 30 to 40-knot range. Also the low level backing mentioned above would combine with low LCLs and effective SRH approaching 200 m^2/s^2 leading to a isolated tornado risk. However, the main risks with any stronger storms that could get going would be damaging winds and large hail given the potential for rotating updrafts. The CAMs remain complicated and solutions continue to differ probably owing to the large scale ascent. The HRRR TLE does offer a shot of seeing severe hail, but the CIPS are lack luster when it comes to climo for this setup. Also given the deep moisture also can not rule out the potential for isolated instances of flash flooding. This upper level closed low will continue to wrap up today and deepen across the Ohio Valley. The low pressure will track north and this will lead to a lull in the precipitation this evening. Did not go no POPs tonight but would not be surprised if that is the case. However, this system will become vertically stacked across the Ohio Valley. This will send an area of PVA and low level convergence SE toward the region by dawn Thursday. An area of showers will accompany this area of lift and ride across the region on Thursday. Then surface pressure and height rises are left in the wake. Temperatures today will be dependent on clearing, but lower 70s will probably be the story. Did hedge below the blended guidance Thursday given the lowering 850mb temps and cloud cover. .LONG TERM...(Thursday night through Tuesday) Issued at 410 AM EDT WED MAY 24 2017 Wrap-around moisture on the backside of a departing upper low and surface low across the Ohio Valley will continue the threat for rain showers through Thursday evening, before a brief stint of ridging and subsidence filters into eastern Kentucky for the end of the week. This will bring some patchy fog to the valleys of eastern Kentucky, moreso in the Bluegrass and Lake Cumberland regions, Friday morning as clearing occurs earlier in the night. A ridge/valley temperature split should be in store as well as a dry Friday takes shape with seasonable temperatures in the mid-upper 70s. This reprieve from the wet weather will be short-lived as backing flow aloft takes shape downstream of an upper low rotating into Manitoba, along with attendant troughiness extending through the Great Plains into the Desert Southwest. A surface low pressure system will ride up the Ohio Valley as eastern Kentucky sits in the warm sector, bringing renewed chances of showers and thunderstorms through Memorial Day weekend. Numerous shortwave perturbations look to be entrenched in the prevailing southwest flow regime, leading to mid level cooling and large scale forcing for ascent. Eastward movement of this system into the Great Lakes late this weekend will bring a cold front through the Ohio Valley and toward eastern Kentucky later Sunday into Sunday night. While storms on Saturday should exhibit more of a discrete nature, increasing larger scale forcing later Sunday will likely lead to a linear storm mode. Therefore, the more widespread threat of any severe weather, most notably a damaging wind threat, would come later Sunday with this latter development. Still some details to be ironed out regarding southern extent of the greater upper level forcing along with the exact degree of destabilization that will materialize. Dry and somewhat cooler conditions should ensue for Memorial Day, prior to another round of showers and thunderstorms arriving Tuesday as another upper low swings into the upper Midwest and western Great Lakes on the heels of the weekend system. A subsequent cold frontal passage will further lower temperatures through the 70s as subsidence builds in for midweek. && .AVIATION...
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(For the 18Z TAFS through 18Z Thursday afternoon) ISSUED AT 230 PM EDT WED MAY 24 2017 It looks like multiple bands of convection will be crossing the area through the evening with thunderstorms possible at all the TAF sites. Initially the eastern ones will see storms with the west having a round between 19 and 22z. Some of these western ones may make it east into the JKL/SJS sites toward sunset, but uncertainty is high with the evolution and progression of this next band for the CWA. Following the convection later this evening, cigs will fall to MVFR or lower through the night with more scattered showers and less organized convective development. Outside of any storms winds will be light and variable.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...DJ LONG TERM...GUSEMAN AVIATION...GREIF

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