Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 240552 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1252 AM EST Fri Feb 24 2017 .UPDATE... Issued at 1252 AM EST FRI FEB 24 2017 The IR SAT is showing a mix of high and low clouds moving across the CWA this hour. A band of low clouds at around 5 KFT is moving north across the central portions of the CWA, and actually played a role in modifying some of the cooler eastern valley locales. One example is Quicksand modified a couple of degrees as cloud deck moved across the site. This will make hourly temps difficult to nail down perfectly and will require some updates to obs and trends. Otherwise little needs to be updated at this time before new forecast package is released. UPDATE Issued at 1004 PM EST THU FEB 23 2017 Issued an update to the forecast to include the latest observations in the grids. Some of the deeper valleys across eastern Kentucky have begun to drop off this evening. The rest of the forecast seems to be on track. UPDATE Issued at 622 PM EST THU FEB 23 2017 Current conditions across the area continue to feature rather dry conditions in place as some 10 to 15 degree dew point depression are in place. As such with the best forcing to the north of the OH River, have pulled the showers from the forecast this evening and sent out a new ZFP along with freshened up grids with the latest observations. && .SHORT TERM...(This evening through Friday night) Issued at 400 PM EST THU FEB 23 2017 South-southwest flow aloft will keep our weather warm through the short term. Potent trough/low will plow into Great Lakes Region swinging a trough through the Commonwealth by late in the period. At the surface, high pressure is anchored over the Appalachians with a nearly stationary frontal boundary draped from roughly DTW southwest to STL. Low pressure currently taking shape over the central plains will march east-northeast along the boundary and into the Great Lakes by late Friday night. This feature will also pull a cold front eastward through the region, and into eastern Kentucky Friday night. This dynamic storm system could bring a round of severe weather to our forecast area Friday night. Main threat at this time appears to be winds, with hail being a secondary threat. Shear is quite strong with this system as well. Consequently could not rule out an isolated tornado. Gradient winds will increase across the area Friday ahead of the system, and from all appearances will become gusty. Main limiting factor to severe weather will be moisture as dew points struggle to climb to near 60 Friday into Friday night. Timing of the cold front is also not favorable for severe weather as it will not enter into our area until sometime just after midnight. Consequently any nocturnal inversion that develops will have to be scoured out, though surface gradient winds appear to be able to do just that, but generally only as the frontal boundary is approaching. Bulk shear is quite strong with this system as well, 40-60 kts, with the majority of the shear realized in the lowest 3 km. Thus the potential for bowing cells and line segments will be favored. Surface based instability to support this storm mode is not ideal but does appear to be sufficient, again mainly just ahead and with the frontal boundary itself. This has a distinctive QLCS flavor to it and considering the environment as a whole feel an isolated tornado can not be ruled out, though features of this type tend to be weaker than most and short lived. Strong gradient winds mixing down may have the potential for more damage should they occur. Low wet bulb temperatures and freezing levels mean hail is a possibility as well. .LONG TERM...(Saturday through Thursday) Issued at 400 PM EST THU FEB 23 2017 The long term portion of the forecast will be active, with several systems affecting the area. However there remains considerable uncertainty on the timing, track and strength of a series of short waves and associated surface lows and fronts that will affect the area next week. By 12Z Saturday the cold front which brings our severe weather threat Friday night will be east of the area, but some showers will linger across the area mainly during the morning. Gusty west winds will usher in cooler air on Saturday, with lows by Sunday morning expected to dip down into the mid to upper 20s. Surface high pressure will be over the area Sunday morning, but will shift to the east during the day. This result in dry weather Sunday with near normal afternoon temperatures in the upper 40s to lower 50s. The mean flow for the first half of next week will be southwesterly with a mean long wave trough axis centered over the western part of the country. This will result in warming temperatures with highs back in the 60s for Tuesday and Wednesday. The first in a series of short waves looks to affect the area from Sunday night into Monday, with rain shower chances increasing from Sunday night into Monday. If precipitation moves in quick enough Sunday night a few flakes of snow could mix with the rain before changing to all rain quickly by Monday morning. Tuesday still remains one of the least certain days of the forecast, with the GFS quickly moving out Monday`s system, while the ECMWF points to lingering rain chances for Tuesday. We will continue to follow the blended forecast for Tuesday which maintains rain chances but with probabilities generally lower than on Monday. There is better agreement that a stronger short wave, surface low and associated cold front will bring a better chance of showers and thunderstorms on Wednesday. In fact we will be be going with likely rain probabilities Wednesday. After the cold front passage cooler air will spread into the area Wednesday night and Thursday. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) ISSUED AT 1240 AM EST FRI FEB 24 2017 A mix of high and even a narrow band of lower clouds are moving across eastern KY at this late night hour. The good news is we are looking at VFR conditions for the TAF sites, with lowest band of clouds staying at or around to 5 KFT level. Now some of the valley locales have decoupled this evening and therefore some will see patchy fog. The other concern is a increasing LLJ, as 850MB winds increase ahead of strengthening surface and upper level system progresses east. Therefore kept the LLWS in the forecast starting around 08Z to 12Z timeframe. Places that will have to best chance of seeing the stronger jet will be Lake Cumberland and Bluegrass regions. This will mix out by around 14Z and by tomorrow afternoon we will see some of these stronger winds mix down leading to gusty conditions. Think again the better mixing will occur across the Lake Cumberland and Bluegrass regions where 25 to 30 mph gusts are possible. We are continuing to monitor the potential for strong to severe thunderstorms to round out the TAF period. Right now a line of storms is expected to move into areas west of a line from Sandy Hook, to Jackson, to Middlesboro at or around 04Z to 06Z. The main threat with any stronger storms would be for damaging wind gusts. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...RAY LONG TERM...SBH AVIATION...DJ

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