Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 211830 AAA AFDJKL Area Forecast Discussion...UPDATED National Weather Service Jackson KY 230 PM EDT SAT MAY 21 2016 .UPDATE... Issued at 145 PM EDT SAT MAY 21 2016 The showers have picked up a bit in coverage early this afternoon, particularly east, with even hints that some thunder could be not far off. Accordingly, did an update to address this in the grids and also to add in the latest ShortBlend T/Td/Winds with adjustments for current obs and trends. These updated grids have been sent to the NDFD and web servers. UPDATE Issued at 1110 AM EDT SAT MAY 21 2016 14z SFC analysis shows low pressure through eastern Kentucky and Ohio this morning. Plenty of low clouds and some light showers are found throughout the state. Though some clear pockets are noted in the latest visible satellite loop over the Cumberland Valley, it looks like plenty of clouds upstream will keep the skies mostly cloudy through the afternoon. Temperatures vary from near 60 north to the middle 60s in the south while dewpoints are generally in the upper 50s and lower 60s throughout the area. Winds are predominantly light across east Kentucky though some westerlies are moving into the area from the Bluegrass and south central Kentucky with speeds of 10 to 15 kts. The latest HRRR and NAM12 indicates scattered showers around through the afternoon, though focus is on a more consolidated and southward moving batch late in the day with the best chances for sustained showers and perhaps a stray thunderstorm. Have updated the forecast grids with these thoughts in mind and also tweaked temps/dewpoints per the latest ShortBlend guidance as well as the current obs/trends. These grids have been sent to the NDFD and web servers along with an update to the first period of the zones. UPDATE Issued at 725 AM EDT SAT MAY 21 2016 A few showers are starting to pop up across eastern KY early this morning, mainly across the higher terrain. A larger area of showers is located to our NE, across southern IN and OH. These will continue to propagate southward toward central and eastern KY, with more showers expected to pop up through the morning/early afternoon as we start heating up. Forecast seems to be in good shape so far this morning, though some minor adjustments may be needed to POP placement as the precip makes it closer to the CWA throughout the next few hours. All changes have && .SHORT TERM...(Today through Sunday) Issued at 358 AM EDT SAT MAY 21 2016 The center of surface low pressure continues to sit along the NE border of KY and Ohio/WV. Currently SE winds are pulling in drier air from the west and the north, leading to mostly dry conditions across the areas as of 730z. That being said, a few isolated showers do still exist, and there is enough lingering low level moisture that patchy fog and even some drizzle is ongoing across the CWA. During the day today, the low will make a slow shift to the east. This will allow winds to become more ENE (then eventually NE) and wrap-around moisture from the low will begin entering back into the CWA, especially in the afternoon as instability increases. Best QPF will be in the far eastern portion of the CWA. Latest NAM12 and GFS20 forecast soundings are pegging portions of the eastern CWA with decent instability in the afternoon, generally from KJKL and points eastward. 1500 to 2000 j/kg of CAPE will be possible between 18 and 21Z, with LI`s ranging from -4 to -6. Values will increase the farther east you go. Best instability matched up well with the highest pops, so ran weather to mention isolated thunder for numerous rain showers. Neighboring offices are also including thunder in their forecasts as well. Highs should remain quite cool, generally in the upper 60s. Loss of daytime heating this evening, as well as a growing distance to the center of the low, will quickly cut off instability/thunder chances after 0z Sunday. Pops will also dissipate and retreat to the east overnight. Skies will actually begin to clear from NW to SE as drier air begins to work into the region. A break in the weather may be short lived though as another weak upper level wave moves south across the CWA during the day tomorrow. This will promote enough moisture advection off of the Atlantic coast to increase cloud cover and introduce more isolated to sct pops during the afternoon, mainly in the far east. Temperatures will increase slightly from today, in the upper 60s to low 70s. There is a brief period of time, generally around 21Z, where locations expected to get sct showers may also hear a few rumbles of thunder, based on CAPEs briefly rising above 1500 j/kg and LI;s dropping back to -6 according to the GFS20. The problem is the NAM really doesn`t support this. Was on the fence as to whether or not to include in weather grids, and problem wouldn`t have, however both RLX and MRX did include it up to our border. Regardless, it will be a breif window of a few hours for development, and given the overall lack of moisture, there should be very little impacts. .LONG TERM...(Sunday night through Friday) Issued at 430 AM EDT SAT MAY 21 2016 The period is expected to begin with trough or closed upper level flow from the northeast into the Mid Atlantic states. Shortwave ridging is expected to extend from Mexico northeast into the MS Valley and western great lakes region. Meanwhile a trough should encompass much of the Western CONUS. At the sfc, an area of low pressure is expected to extend from the Great Lakes region south into the Lower OH Valley, TN Valley and Ms Valley regions. From Sunday night into Monday, heights across the area are expected to rise as the trough initially to the east of the area closes off and meanders off the Mid Atlantic coast and an upper level ridging builds further into the Great Lakes and OH Valley regions. The axis of the upper level ridge should move across the area by late Tuesday into Tuesday night. The ridge will become flattened with time as shortwaves move from the Western Conus across the Plains and toward the Great Lakes and eventually the Ohio Valley at midweek. The ridge building into the area should bring an end to convection at the start of the period, with gradually clearing skies. Valley fog could become a concern late Sunday night into early on Monday. With the ridge in place a ridge/valley temperature split will be favored on Sunday night and especially Monday night. Both nights many valley locations should drop into the mid to upper 40s while ridgetops mainly bottom out in the 50s. With the upper low and trough eventually moving further on off to the north and east, the axis of the ridge will have moved east of the area at midweek. This will set the stage for shortwaves to periodically move across the region and combine with increasing return flow of moisture for periodic chances for showers and thunderstorms. The region should remain in the warm sector through the middle to end of the week however, as ridging from the Gulf of Mexico to the Eastern Seaboard should keep a quasi stationary of slow moving sfc boundary from dropping any further south than the Great Lakes and Northeast states and the western and southwestern portion from moving east of the Plains states. Without a sfc boundary getting closer to the region to help organize and or concentrate convection, nothing more than a strong storm or two is anticipated through the period and rainfall is not expected to be heavy at any point. A return of above normal temperatures is favored by Tuesday with highs reaching near 80 if not the lower 80s in some locations by the end of the period. The 0Z GFS run and its associated GFS MOS guidance suggests some mid 80s are possible by Friday. However, those numbers are the warm end of guidance and stayed closer to the guidance blend at this time. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) ISSUED AT 230 PM EDT SAT MAY 21 2016 A center of low pressure is sitting just NE of the state and as this shifts slowly eastward this afternoon, wrap around moisture will pull showers and even some isolated thunder back into eastern KY into the evening. Cigs will vary between MVFR and times of VFR this afternoon but scattered showers will be around the FA during with lower vis and cigs possible should they go over any TAF site. Tonight, the low will continue to depart eastward, and drier air will begin filtering into the region. However, forecast soundings time heights suggest llvl moisture lingering across many of the northeast TAF sites during the overnight, likely resulting in lingering low clouds and fog development with lower VIS a potential overnight. The TAFs reflect this idea, though confidence is on the low side for any individual site`s forecast into Sunday morning. Skies should clear out more completely on Sunday, from southwest to northeast, with VFR conditions expected, except perhaps SJS where low clouds and the threat of a shower may linger. Winds will be from the west through the rest of the afternoon at 5 to 10 kts with occasional gusts to 15 kts, then light and variable this evening into Sunday morning. && .JKL Watches/Warnings/Advisories... None. && $$ UPDATE...GREIF SHORT TERM...JMW LONG TERM...JP AVIATION...GREIF is the U.S. government's official web portal to all federal, state and local government web resources and services.