Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210926 AFDJKL Area Forecast Discussion National Weather Service Jackson KY 526 AM EDT SAT MAY 21 2016 .SHORT TERM...
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(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.
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&& .AVIATION...(For the 06Z TAFS through 06Z Saturday night) ISSUED AT 158 AM EDT SAT MAY 21 2016 Very tough forecast tonight. Only a few light showers remain across the region, mainly affecting KJKL and possibly KSJS. Otherwise conditions varied greatly, with everything from lifr to vfr cigs chaotically distributed across the region. Each TAF site is also showing a great deal of variability as well. Tried to forecast for the overnight based on the most likely longest lived condition, which generally included lifr cigs at all TAF sites. Other than some steam fog at KJKL, expect this to be more of a low cig rather than a fog event overnight. Will continue to closely monitor overnight and update as needed, as there will likely be quite a bit of variability. Cigs will improve slightly during the day tomorrow, generally to mvfr, as another round of isl to sct showers move across the area in the afternoon. Uncertain at this time how these will impact the TAF sites, so left at VCSH. The system will begin moving east of the region tomorrow night. However lingering moisture will likely lead to some fog at the TAF sites and/or low cigs once more. Unfortunately confidence is low in this set up as well. && .JKL Watches/Warnings/Advisories... None. && $$ SHORT TERM...JMW LONG TERM...JP AVIATION...JMW

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