Area Forecast Discussion
Issued by NWS Jackson, KY

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265 FXUS63 KJKL 260307 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1107 PM EDT Fri May 25 2018 .UPDATE... Issued at 1102 PM EDT FRI MAY 25 2018 Pops have been updated based on recent radar, satellite, and convective allowing model trends. This led to a bit higher pops in parts of Pike County and McCreary County over the next hour or so with a lull for a few hours overnight. However, several of the convective allowing models including the HRRR have showers and possibly a thunderstorm moving north into the TN and VA border counties prior to dawn as the upper level trough approaches. Some slight chance pops were added during that time frame in the south. Also, coverage of fog was adjusted to add more fog in Pike County down into Letcher County where heavier rain fell. UPDATE Issued at 840 PM EDT FRI MAY 25 2018 A few showers and even a thunderstorm near the TN and KY border linger as sunset approaches. This convection is largely diurnally driven and should wane over the next 1 to 2 hours. The overnight hours should generally be dry. With the upper trough working in, some of the convective allowing models indicate the potential for an isolated shower toward dawn in the southwest part of the area. We will continue to monitor trends on this. Otherwise, outside of showers, clouds will decrease and locations that picked up heavier rainfall from showers and thunderstorms today are expected to experience more widespread fog and it may become dense. Some of these locations include Whitley County near the I 75 corridor and portions of the Big Sandy region and portions of Letcher county. More widespread coverage of fog has been added overnight in these areas. Otherwise, fog development is anticipated in the valleys. && .SHORT TERM...(This evening through Saturday night) Issued at 405 PM EDT FRI MAY 25 2018 The afternoon surface analysis shows a weak boundary across the the Tennessee Valley and a surface high pressure off the North Carolina Coast. This high pressure is continuing pump more moisture into the region this afternoon, with dewpoints climbing into the mid 60s this afternoon. The latest radar data shows some showers and perhaps a isolated thunderstorm developing across the region. Interestingly, the lack of steering flow is leading to arcing outflow boundaries this afternoon and this could make convection more difficult to nail down through the early evening. Given this will keep thunder in isolated to scattered wording this afternoon and early evening. The CAMs have the mess of convective outflows and thunderstorm complexes across western Kentucky weakening this evening. Given this and the waning convection through the evening, and did lower POPs overall given the lack of steering flow from the west and loss of daytime heating. There could be some fog tonight in the river valleys or perhaps more so where rain has fallen this afternoon. This will have to be more fine tuned this evening. Temperature splits remain possible tonight, but they should be less overall given a little more cloud cover to contend with. An upper level trough across the Midwest will slowly spill weak height falls into the Ohio Valley Saturday. This in combination with strong low level lapse rates, modest mid level lapse rates, increased moisture and MUCAPE around 2000 J/kg should yield more numerous coverage in convection mainly in the afternoon on Saturday. Given the lack of larger scale forcing or surface features to work with this will be harder to nail down exact locations. The main threats will be heavy rain and frequent lightning given the lack of shear. By later in the afternoon, this maybe driven by convective outflows to a extent, but that will have to be evaluated as we get closer to that time. This convection may linger into the evening and perhaps some showers linger into the overnight. Did add some fog again for Saturday night, but again this is hard to nail down given the uncertainty on exactly where rain will fall. The temperatures splits will likely be more limited Saturday night as well given the additional cloud cover. .LONG TERM...(Sunday through Friday) Issued at 405 PM EDT FRI MAY 25 2018 A large but weak upper trough axis will extend from the Great Lakes to the Gulf of Mexico at the start of the period, with a strengthening tropical system (Alberto) over the northern Gulf. The northern extent of the trough will be progressive, while the flow around the tropical system becomes more closed as it deepens. This would shear the deep moisture regime originally over our area at start the period, shunting it southeastward, and allowing drier air aloft to advance southeastward over eastern KY. This would tend to keep precip more sparse, especially over the northwest part of the area. Meanwhile, the developing col in the geopotential heights over our area would lead to weak flow and rather featureless mid/upper levels, resulting in the movement and coverage of any precip becoming more limited from Sunday into Monday. As Alberto moves inland and weakens beginning Tuesday, we will come more under its influence and deep moisture should make a comeback. Along with this would come an increase in precip coverage. Aside from this generality, there is still a lot of uncertainty. The mid week forecast depends largely on the development and demise of Alberto, and models do not agree on the timing and track of the system in its waning stages. It`s still possible for it to track north, south, or over our area. Whatever the case, it should be to our east by Friday. However, without any real change in air mass, there still could be diurnal convection which pops up on Friday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 835 PM EDT FRI MAY 25 2018 Much of the first 6 hours of the period should feature VFR, outside of the few locations experiencing some initial showers and or an isolated thunderstorm with brief MVFR or IFR reductions. Otherwise, valley fog with mainly MVFR reductions and spotty IFR is expected to develop by 6Z to 8Z and generally not affect the TAF sites with the exception of SJS that received rain this evening. Reductions to at least MVFR by 3Z are anticipated there and some IFR fog is anticipated from about 6Z to 12Z. Convection is expected on Saturday, possibly before 15Z with chances lingering through the end of the period. Confidence in timing of onset and thunder on station at any one location was to low for more than prevailing VCTS during the second half of the period. Winds will average light and variable outside of any thunderstorms. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...DJ LONG TERM...HAL AVIATION...JP

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