Area Forecast Discussion
Issued by NWS Jackson, KY

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996 FXUS63 KJKL 181840 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 240 PM EDT Mon Sep 18 2017 .UPDATE... Issued at 200 PM EDT MON SEP 18 2017 Did a quick update mainly to fine tune sky cover and adjust the near term T/Td grids per the latest obs and trends. These have been sent to the NDFD and web servers. UPDATE Issued at 1050 AM EDT MON SEP 18 2017 14z sfc analysis shows a relatively weak area of high pressure in place over eastern Kentucky. Once again, this did lead to a good night of radiational cooling which allowed areas of fog to form during the night becoming locally dense in the river valleys. The fog has just about dissipated now with mostly sunny skies in place. Some mid and lower level clouds are found to the west and drifting this way. The high res models are still indicating that a few showers or a storm could develop this afternoon in the western parts of the CWA so that part of the forecast appears to be on track. Currently, temperatures are running in the mid to upper 60s most places while dewpoints remain elevated in the low 60s and winds are light/variable. Updated the grids mainly to remove the fog, incorporate the latest obs and trends into the T and Td grids, and also to adjust the sky cover toward current conditions post fog lift out. The grids have been sent to the NDFD and web servers. An updated HWO and set of zones have been issued, as well. UPDATE Issued at 629 AM EDT MON SEP 18 2017 No update needed at this time with fog still ongoing in the valleys. Just made a few minor tweaks to temperatures to account for latest trends. && .SHORT TERM...(Today through Tuesday) Issued at 341 AM EDT MON SEP 18 2017 Areas of dense valley fog have developed this morning and much like the past few mornings, will continue past daybreak before burning off by 10 am. As for the rest of the day, mid/upper level ridging will remain in place today, keeping a rather stout cap in place. However, 00z models are showing a bit of a weakening in the cap in our southwest zones (near the I-75 corridor and west) this afternoon. This weakening could coincide with a few isolated showers this afternoon. Confidence is not high on this activity developing as overall forcing will be weak, but could be enough moisture pooling to allow for a few cells to pop up. Any activity will quickly fade away this evening. As skies clear out once more, another night of dense valley fog is anticipated with little change from the current night. Better rain chances will spread in on Tuesday as a mid level vort max crosses the Ohio river valley bringing some height falls. This should help to weaken the cap and provide some weak forcing allow for isolated to scattered showers and storms. No threat for any strong storms as wind shear will remain non-existent under the upper level ridge. .LONG TERM...(Tuesday night through Sunday) Issued at 341 AM EDT MON SEP 18 2017 There is decent model agreement with an amplifying long wave pattern. Deeper troughing establishes itself across the West, with renewed ridging across the Great Lakes and Ohio Valley regions, while the tropics remain active across the western Atlantic and into the Eastern Seaboard. Initially, the ridging in the East will be weaker, allowing for some passing short wave energy to allow for the small threat of mainly diurnally driven showers and a few thunderstorms. For eastern Kentucky, the highest overall POPs for the middle and end of the week look to occur on Wednesday. For Thursday and Friday, some slight chances will be possible along the far south and near the terrain, where enough moisture may pool to allow for a few afternoon and evening pop ups. This weekend, both the GFS and ECMWF show a building ridge across the Great Lakes and Ohio Valley regions. The ECMWF is a little stronger with the ridge, suppressing convection across the area, while the GFS is a bit weaker, allowing for a few storms along the terrain and west of I-75. Given the overall strength of the ridge and predominantly east and northeast flow in the lower atmosphere, will go with a dry forecast. Consequently, went a touch higher than the blended guidance for the highs. Temperatures throughout the period will average above normal, with highs in the low to mid 80s, and lows around 60. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) ISSUED AT 240 PM EDT MON SEP 18 2017 After a day and evening of VFR conditions, fog is expected again tonight, with developing commencing after 03z, but not likely impacting TAFS until after 06z. Fog should be similar to the past several nights and be confined mainly to the valleys, but still creep up into a couple of the airport sites for a time. Have used a tempo in a few of the TAFs for this concern. Light winds are expected through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...KAS LONG TERM...GEOGERIAN AVIATION...KAS/GREIF is the U.S. government's official web portal to all federal, state and local government web resources and services.