Area Forecast Discussion
Issued by NWS Jackson, KY

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947 FXUS63 KJKL 240321 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1121 PM EDT Fri Mar 23 2018 .UPDATE...
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Issued at 1115 PM EDT FRI MAR 23 2018 Not many adjustments have been made so far as recent guidance does not support much in the way of change to the wintry precipitation event upcoming other than the slow down the increase in pops prior to 9Z. Temperatures in the higher terrain at Pike Co. Mesonet and Harlan County Mesonet were running colder than the previous forecast as were some of the eastern valleys where mid level clouds have yet to thicken up. Hourly temperatures and dewpoints were updated over the next few hours accordingly. UPDATE Issued at 850 PM EDT FRI MAR 23 2018 Hourly grids have been adjusted based on recent observations and trends for tonight. Clouds are gradually thickening and lowering from southwest to northeast. With some lower clouds having moved into parts of south central and middle TN. Some light rain has been reported as close as KGLW. A few of the eastern valley locations have experienced few if any mid level clouds so far and have dropped off to around the 40 degree mark. Taking a look at the upcoming event, not much in the way of changes appear to be needed at this time. Looking at 18Z and recent convective allowing models and making some slight adjustments to hourly temperatures storm totals generally remained very similar. Using smaller one hour time steps for snow to liquid ratios and these hourly temperatures which are a tad cooler int he north leads to a little less snow for upper end amounts in northern Fleming, Rowan, and Elliott counties. For locations from Estill to Letcher, this results in about half of an inch more snow for Saturday morning. At this time, no changes are planned for headlines, but each hourly run of HRRR will be evaluated for any any need for changes. A refreshed WSW product and SPS will be issued over the next couple of hours.
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&& .SHORT TERM...(This evening through Saturday night) Issued at 444 PM EDT FRI MAR 23 2018 Extremely complex forecast as low pressure moves out of the central plains and into the lower OH valley by Saturday evening. Precipitation type is an extreme challenge as model soundings in the north show some deep near freezing isothermal profiles, which may hold through much of the day on Saturday. If such soundings verify that could mean a very heavy wet clinging snow where even 3 or 4 inches may result in power outage problems. However, it also means that just a degree temperature difference can result in a very cold rain. With the trends of recent model runs, WPC guidance and collaboration with neighboring office have opted to go with a winter storm warning for our northern counties. Three to 5 inches of snow is forecast for the warning area, but a few isolated 6 or 7 inch amounts cannot be ruled out. South and east of the warning we continued the advisory, and also added a couple of counties to the advisory. There will be close to a 20 degree temperature spread from north to the southwest part of the area on Saturday. And further south some thunderstorms will be possible, mainly in the Cumberland basin. Latest indications are that rainfall will be spread out over a long enough time period that small stream flooding should not be an issue. WPC also has not placed any of the area in the excessive rainfall outlook. With that in mind have opted to not go with a flood watch, which we had been considering earlier today. However, a few points on the Cumberland river could reach flood stage sometime on Sunday. .LONG TERM...(Sunday through Friday) Issued at 111 PM EDT FRI MAR 23 2018 The long term portion of the forecast will feature a deepening upper level trough over the western U.S. early next week, with deep southwest flow becoming established across the OH and TN valleys. By the end of the week the trough will shift east, but with southwest flow across the eastern U.S. continuing. There is good model agreement with the overall upper air pattern though some differences are to be expected with individual short waves ejecting from the upper low that will be over the southwestern part of the United States through the first half of next week. With good model agreement with the overall pattern, the concern for the coming week will be the potential for heavy rain somewhere in the central to eastern U.S. with deep southwest flow becoming established. Current indications are that the heaviest rains will likely affect areas to our west early to mid week as a slow moving front moves into the MS Valley. The front will eventually move across our area during the second half of the week, but it is possible it will stall again at some point near us or just to our east. The greatest threat for heavy rains next week appears to be over western KY and TN. While this is outside our forecast area it is close enough that the coming week will need to be monitored closely. Considering the heaviest rain potential is still 5 days away or so, it is likely the forecast axis of heaviest rains will shift during the coming days. The southwest flow will also result in warming temperatures, with above normal temperatures expected from Tuesday through at least Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 835 PM EDT FRI MAR 23 2018 VFR conditions will prevail for the first 6 to 9 hours of the period, before deterioration to MVFR and then IFR for most locations after 14Z. The IFR should then persist through the end of the period as the lower levels saturate leading to low ceilings with falling precipitation. Low pressure will move from the central plains to the lower OH valley by Saturday evening. Clouds will thicken and lower tonight with low level clouds moving into the southwest part of the area during the next few hours and advancing northeast ahead of the approaching system. Precipitation should overspread the area between about 6Z and 13Z. Enough cold air will remain in place over the northern part of the forecast area that much of the precipitation will fall as snow or a rain and snow mix Saturday morning for JKL, SYM, and SJS. Further southwest just plain rain is expected. Some thunder will be possible generally after 17Z, mainly at SME and LOZ. && .JKL WATCHES/WARNINGS/ADVISORIES...
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Winter Storm Warning until 2 AM EDT Sunday for KYZ044-050>052- 060-104-106. Winter Weather Advisory until 2 AM EDT Sunday for KYZ059-107>110- 119-120.
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&& $$ UPDATE...JP SHORT TERM...SBH LONG TERM...SBH AVIATION...JP is the U.S. government's official web portal to all federal, state and local government web resources and services.