Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210615 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 215 AM EDT Fri Apr 21 2017 .UPDATE...
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Issued at 215 AM EDT FRI APR 21 2017 Convection appears to be on the uptick as a cold frontal boundary continues to slide southeastward into the area. HRRR has been struggling on initializing accurately. Considering the general trends in the HRRR, ARW, and NMM, it would appear the greater threat for convection over the next several hours would be locations generally north of Hal Rogers, though showers and thunderstorms will be possible across the entire area. Made some slight adjustments to PoPs early on for thunderstorms that fired in our southern zones. Otherwise blended into inherited forecast. The remaining grids were in good shape, including T and Td only minor tweaks to the remaining grids. No update to the zones at this time. UPDATE Issued at 1047 PM EDT THU APR 20 2017 Only a few showers have popped up across eastern Kentucky thus far this evening. The general trend in the HRRR has been for less activity through first part of the overnight, before the cold front gets closer towards dawn. This seems reasonable given the current radar trends. As such, have delayed the better POPs later still. Temperatures have cooled into the mid 60s in the valleys, while broader valleys and ridges remain in the lower 70s. A modest ridge/valley split should continue over the next few hours, before thicker cloud cover moves in and mitigates the differences a bit more. Updates have been sent. 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.
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&& .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...
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(For the 06Z TAFS through 06Z Friday night) ISSUED AT 215 AM EDT FRI APR 21 2017 An approaching cold front will bring an uptick to shower and thunderstorm activity through the remainder of the overnight, generally from west-northwest to east-southeast. Flight conditions are expected to gradually deteriorate through dawn into solid MVFR territory. May see some improvements through the middle portion of the day as the boundary drifts further southward. Northern terminals such as SYM, SJS, and JKL may even see a break in activity for several hours. However, a wave of low pressure to the southwest will ride up into the region later tonight and bring widespread rain into the area, eventually dropping flight conditions into IFR or lower just beyond the end of the forecast period. Generally speaking weather late tonight into Saturday looks less than favorable for general aviation interests. Winds will be generally from the southwest around 10kts or less, with some gusts to about 15kts from time to time. Of course winds could be a bit stronger near any thunderstorms. Winds will veer out of the northwest behind the front as it drops through the area.
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&& .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ UPDATE...RAY SHORT TERM...JMW LONG TERM...JP AVIATION...RAY

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