Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 261654 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1254 PM EDT Mon Sep 26 2016 .UPDATE... Issued at 1254 PM EDT MON SEP 26 2016 Updated the POPs and associated weather over the last couple of hours to better line up with earlier thinking. The main line of convection is weakening and starting to break down. Meanwhile, clouds are quickly developing and convection is starting to pop across eastern Ky over the last hour in the warm sector ahead of the front. Expect our northern counties to see coverage pops as the line continues to make its way eastward, but the rest of the CWA, especially the Southern portions, could see more scattered convection. With northwest winds, convection will also be more likely in the highest terrain along the VA border. That being said, with low clouds and cooler air moving in ahead of the initial line, instability is much weaker than originally anticipated. Kept in some isl to sct thunder, which may still be possible with some of the pop up activity starting to take place across eastern KY. However, initial line has weakened to the point that any further thunder activity may be unlikely. Also made sure the near term forecasts for temps, dew points, and winds were on par with current conditions by loading in the latest observations. All changes have been published and sent to NDFD/web. A new forecast package was sent out to reflect new weather wording. UPDATE Issued at 944 AM EDT MON SEP 26 2016 Continuing to monitor a line of showers and thunderstorms moving into the western and central portion of the state this morning. This line remains collocated with the frontal boundary location. However, of note, winds ahead of this line and ahead of the actual surface front are already shifting in direction. While much of the CWA is seeing light SW winds, winds are quickly switching to a more NE direction just along our western CWA border ahead of the line of precip. At first glance it was thought that the frontal boundary may be outrunning the precip, which would bring about the demise of the initial line but could cause some redevelopment across our CWA a little earlier than originally forecast. However, upon second glance it appears as though the frontal placement is in tact with the precip, but the wind shift could just be the result of an outflow of the line or perhaps a secondary weak trough axis. Either way, this will be something to watch as it will likely cause a weakening of the initial line as it continues to push eastward, especially considering low stratus is now outrunning the initial line as well. That being said, some redevelopment may occur ahead of the line, across our CWA where warmer temps and clearer skies still exist, but latest Hi-RES CAM models all support only scattered convection across our CWA throughout the day. And interestingly enough, most of them are also lining up with the thought of the initial line continuing to lose strength as it pushes eastward as well, showing the line continuing to shear out through 18Z and scattered convection popping up across eastern KY during this time. Will continue to monitor as we head through the next few hours in case any updates to POPs need to be made, but if this idea holds together, results of this line could be quite benign with some locations missing out on rain all together. A new forecast package was sent out with this update to remove morning fog wording. The latest observations for temps, dew points, and winds were also loaded into the near term forecast to make sure it was well on track with current conditions. All changes have been published and sent to NDFD/web. UPDATE Issued at 715 AM EDT MON SEP 26 2016 Another quick update to fine tune temps, dewpoints, and sky cover through the next few hours based on current obs and trends. These have been sent to the NDFD and web servers. && .SHORT TERM...(Today through Tuesday) Issued at 425 AM EDT MON SEP 26 2016 07z sfc analysis shows a well defined cold front moving into the western portions of the Ohio Valley. However, in the far eastern parts of Kentucky high pressure remains in control with mostly clear skies and light winds. As in the past few nights, this has allowed for a decent ridge to valley temperature difference. Specifically, readings vary from the low 70s on the ridges to the low and mid 60s in the more sheltered spots. Dewpoints, meanwhile, are in the low to mid 60s while the winds remain light. There are some mid level clouds around, but for the most part skies for eastern Kentucky are clear while lowering ceilings are approaching the state from the northwest. The front shows up well on radar, too. We can see the showers and thunderstorms rolling northeast along this boundary as they approach western Kentucky. Again in the east this night, river valley fog has started to form and some locally dense spots are anticipated through dawn but likely clearing out quicker this morning than the past few considering the inbound clouds and winds likely picking up sooner. The models continue to settle on a similar solution aloft. They all take the ridge, that has brought extended summer weather to the area for the better part of a week, east and flatten it out. The culprit for this pattern change is an impressive early fall season closed low/trough plowing into the Great Lakes this morning. This system brings strong height falls, a dynamic wind field, and ample mid level energy to the Ohio Valley today, initially brushing by Kentucky to the north. The best dynamics associated with this will pass by and through the JKL CWA between 18 and 21Z. Following this, heights will continue to fall as the parent upper low bottoms out, turns over on itself, and starts to head south down through the Great Lakes. Given the models` tandem movement to this more extreme solution will favor a blended starting point with emphasis on the latest NAM and HRRR for details. Confidence on the specifics is only average at best given the sense that the models are still in a state of flux working to resolve this closed low. Sensible weather will feature any river valley fog burning off quickly this morning with early sunshine giving way to increasing and thickening clouds from the northwest. A band of showers and thunderstorms are expected to enter northwest parts of the area by late morning, grow in coverage, and sweep through the rest of eastern Kentucky by late afternoon. Should enough instability build up ahead of the convective band a few of the storms could start to organize and become strong with wind gusts the main threat. Look for the timing of the front to keep the worst of the storms from developing until they get east of Kentucky, later this afternoon, but they will still need to be watched closely. The clouds and pcpn will keep temperatures in check today with much of the area not likely to get out of the 70s. Much cooler air arrives tonight in the wake of the front with some 40s anticipated by morning, especially in the higher terrain and more open areas. The valleys should hold up a bit better as the cooler air takes a bit longer to scour them out. Also, anticipate that northwest winds through the night and the cloud cover will keep fog to a minimum - for a change. A full fledged fall day will then unfold on Tuesday with partly sunny skies anticipated and a quite noticeable change to the air with temperatures only reaching the low to mid 70s for highs along with much lower humidities. Started with the CONSShort/ShortBlend for grid population into the evening and SuperBlend thereafter to 00z Wednesday. Made some substantial changes to the terrain derived edit areas and forecast points early this morning and tonight in the temperature grids to better reflect ridge and valley differences in a neutral pattern this morning and a cold air advection one tonight. As for PoPs - ramped them up for later this morning into the likely category through the afternoon and then dropped them quickly from west to east after 00z. This is a bit higher than MOS guidance matching up better with the MAV numbers rather than the MET. .LONG TERM...(Tuesday night through Sunday) Issued at 310 AM EDT MON SEP 26 2016 The models have come into better agreement regarding the upper low currently over the Upper Mississippi Valley. This low will become closed off and gradually drop southeast towards our area. At the start of the extended period, the low is progged to be over the Great Lakes states and then drop southward and be centered over Kentucky late Thursday. The low will then meander back into the Ohio Valley region on Friday before weakening and eventually lifting out of the area over the weekend. Models still struggle with the lows` exit over the weekend with the GFS taking the low up through New England while the ECMWF only lifts it into the Great Lakes. Given these differences, have opted to stay close to the CR Superblend solution which lifts the showers and thickest cloud cover north of the area on Sunday. In terms of sensible weather, it looks like showers and additional cloud cover will persist from Wednesday afternoon through Saturday as the upper low remains over the area. With the additional cloud cover, afternoon highs will be a bit cooler and overnight lows shouldn`t be as cold as yesterday`s forecast. The coolest days appear to be Thursday and Friday with highs only in the upper 60s. Overnight lows will generally remain in the upper 40s and low 50s through the period. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) ISSUED AT 725 AM EDT MON SEP 26 2016 High pressure is losing control of the weather through east Kentucky as a well defined cold front approaches from the northwest. Ahead of this, though, VFR conditions will exist for most areas through mid morning along with light and variable winds. Patchy valley fog will be around again towards dawn, possibly affecting LOZ and SME with some MVFR BR for an hour or two. The cold front will cross into eastern Kentucky by early afternoon. This will result in increasing chances of showers and thunderstorms for the remainder of the afternoon and into the early evening. Best potential is centered between 18 and 21Z and the TAFs reflect this, with MVFR vis and cig conditions possible at all TAF sites during this time frame and VCTS a concern for a couple hours either side. VFR conditions will then return quickly in the evening from west to east with the winds settling to light and variable. During the best chances for showers and storms, along and with the front, winds will shift from the southwest at 5 to 10 kts to the northwest at similar speeds. Some gusts to 15 and 20 kts can be expected for a few hours accompanying the pcpn, with higher gusts possible - associated with any storms. VFR conditions and light winds follow into Tuesday morning with fog less of an issue due to lingering clouds, a drier air mass, and light northwest winds. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...GREIF LONG TERM...JVM AVIATION...GREIF

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