Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 202231 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 631 PM EDT Thu Apr 20 2017 .UPDATE... Issued at 631 PM EDT THU APR 20 2017 A broken line of showers and thunderstorms is attempting to make it in from central Kentucky. Most of this activity is diminishing as it is heading east, and all of the convection across eastern Kentucky has dried up, thanks to dew points in the lower to mid 50s, with a few upper 40 degree readings noted. As such, have delayed the POPs somewhat in the east and kept it dry until the cold front moves in closer later tonight. Skies have also thinned, and will allow for a bit of decoupling in the eastern valleys this evening. Updates have been sent. && .SHORT TERM...(This evening through Friday night) Issued at 428 PM EDT THU APR 20 2017 Ongoing isolated showers and thunderstorms are expected to continue to wain during the rest of the afternoon as we await an incoming cold front overnight. It is along and just ahead of this cold front that we will find our next best chances for precipitation across the CWA, including thunderstorm potential. Latest NAM12 forecast soundings are still showing soundings becoming saturated throughout the column after 6Z (first in the north and a few hours later in the south), giving good support for likely to numerous coverage. That being said, CAPE values aren`t looking that great, generally between 400 and 700 j/kg overnight, with very little llvl wind shear and moist upper levels that would deter any hail potential. As such, expect this to be more of a localized heavy rain event, with some good lightning based on the intensity of the rain...but otherwise not expecting much in the way of high winds (wind speeds aren`t very impressive aloft) or hail. Thunderstorms may intensify slightly during the first half of the day Friday across the southern CWA as the front continues southward through the state. As temps warm through the morning with southerly flow, this will help to boost CAPE values above 1000 j/kg, with LI`s falling to -4 across the central and southern CWA. Some low level wind shear will also be present with southerly winds near the surface and westerly flow in the mid and upper levels. All together, thunderstorms will likely be more prominent in coverage and strength tomorrow with some gusty winds and small hail not to be ruled out. However still think the main threat will be localized heavy rains and lightning. In the northern CWA the front will have already passed, so while showers and thunderstorms are still possible, they will likely be elevated in nature given more northerly flow moving in at the surface. By the latter half of the day, the front will have sagged just south of the state, where it will stall out through Friday night. This will keep enough moisture over the region to promote continued widespread precipitation. However, with northerly flow in the low levels on the north side of the front, we will not see much in the way of instability or thunderstorm potential. As such, have thunderstorms decreasing Friday evening, and kept out all mention of thunder from Friday night through Saturday morning. While temperatures should still reach the upper 60s to mid 70s during the day Friday despite cloud cover and precip in place, northerly winds behind the system will cool the airmass down substantially, dropping to the upper 40s to mid 50s for Saturday morning lows (coolest in the north). .LONG TERM...(Saturday through Thursday) Issued at 430 PM EDT THU APR 20 2017 The period will begin with a trough extending from Quebec southwest into the mid MS Valley and lower MO Valley region with riding extending from parts of the Eastern Pacific north into the Western Conus. At the surface, a wave of low pressure is expected to track along a boundary that will have stalled out to the south of the region during the near term period. This low will slowly track toward the Carolinas through Sunday evening while the southwestern end of the upper trough closes off into an upper level low and moves across the Lower OH Valley and into the TN Valley and southern Appalachians through the weekend. This upper low should meander into the Southeast and finally off the southeast coast for Monday into Tuesday. In its wake, an upper level ridge will build into the Southern Plains and lower OH Valley Sunday night into Monday. However, this ridge will dampen beyond Monday as a broad trough develops from the Western Conus into the Central Conus through midweek. Late in the period, a shortwave trough moving from the Plains into the Great Lakes should generally track northwest of the area with an associated surface boundary briefly approaching the OH Valley at midweek. However, another shortwave moving through the trough should lead to cyclogenesis to the Lee of the Rockies late in the period with the low tracking toward the mid MS Valley late in the period with the boundary returning north as a warm front. Unsettled weather should persist over the weekend, with a steadier rain or showers on Saturday as the shortwave approaches and surface low tracks to the south. Limited instability in the south could lead to isolated thunderstorms, but most locations should receive a good soaking rain from Saturday into Saturday evening. Shower chances will linger into the day on Sunday and possibly even Sunday evening mainly in the southeast as the upper low moves across the area. High pressure will bring drier weather and clearing skies by late Sunday night and persisting into Tuesday evening. With the shortwave passing northwest at midweek and the cold front dropping toward the OH Valley isolated convection will be possible on Tuesday night or early on Wednesday in the far north. At the next system nears late in the period, additional showers and thunderstorms will be possible. However, higher chances are possible after the period. High temperatures and average temperatures will be below normal over the weekend. However, with more sunshine and high pressure in place high temperatures should moderate to above normal levels by Tuesday through Thursday. The pattern from early to the middle of next week should support rather strong nocturnal inversions and valley low && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 220 PM EDT THU APR 20 2017 Isolated to scattered showers and thunderstorms continue to pop up across much of eastern KY, especially along the southern and eastern portions. Increased the cloud cover and winds in the TAFs based on latest trends, with gusts between 15 and 20 knots expected throughout the afternoon. Also introduced VCTS to all TAF sites for this afternoon given ongoing convection and expectations for it to continue expanding. Visibilities could be reduced briefly in the heaviest showers. Best thunder potential should taper off during the first part of the overnight as we lose afternoon heating. However, still tracking a cold front which will sink southward into our area overnight, and get hung up across the southeast portion of the state through the morning and to round out the forecast period. This will increase rain and thunderstorm chances starting late tonight, with rain and thunderstorms expected to continue through the remainder of the TAF period. CIGS should also decline due to the high amount of saturation, with MVFR expected late tonight and IFR or lower expected generally around 12Z or after. Still a little uncertain of how weather will affect visibilities at each TAF site, but do expect there will some variability depending on the intensity of rain showers. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GEOGERIAN SHORT TERM...JMW LONG TERM...JP AVIATION...JMW

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