Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 091831 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 131 PM EST Sat Dec 9 2017 .UPDATE...
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Issued at 129 PM EST SAT DEC 9 2017 As of early afternoon, an eastern Conus and North American trough was in place with a western Conus ridge. A clipper system is moving through this trough with the surface low centered over southwest MI and the trailing cold front extending into western KY. Some light prefrontal returns have been moving east across the OH Valley and the Commonwealth and some of this scattered very light snow is likely starting to reach the ground across the westernmost counties. Meanwhile across the southeastern part of the area the mid and low level clouds have not yet arrived and temperatures are in the mid to upper 30s with some valleys near the 40 degree mark. The scattered mainly light snow showers should continue east this afternoon and then as cold air moves in aloft and along and just behind the cold front an increase in intensity and coverage of the snow showers is anticipated as it should take on more of a convective nature. This will be arriving later in the afternoon to the early evening and could be more impactful to travel with reduced visibilities and have a better chance of accumulating as temperatures drop toward sunset and after. This is mentioned in the HWO and an SPS and Graphical nowcast may also be needed later this afternoon. Hourly grids have been updated to time in snow shower chances from the west and to have pops peaking during the mid afternoon to early evening, when snow shower intensity should peak and have a more convective nature. UPDATE Issued at 630 AM EST SAT DEC 9 2017 The forecast is on track so far this morning. Mid and high level clouds will continue to stream across the area, before finally scattering out by mid morning. Snow showers should begin moving into the area from the west and northwest by early this afternoon. The latest obs were ingested into the forecast grids to establish new trends. No forecast update is planned for this morning.
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&& .SHORT TERM...(Today through Sunday) Issued at 300 AM EST SAT DEC 9 2017 Extensive cloud cover will continue to stream into the skies over eastern Kentucky through out the morning, as an area of low pressure moves across the southeastern CONUS and eventually up the east coast. The weather system of concern for our area for today and tonight is an area of low pressure that is currently spinning over the Great Lakes region. This fast moving system is forecast to move southward across the Ohio Valley and central Appalachian regions this afternoon through tonight. This little clipper system will bring scattered snow showers to eastern Kentucky today and early tonight. Even though surface temperatures may not always be at or below freezing today, there will be more than enough cold air in place above the surface to allow all snow or mostly snow to fall. Some light accumulations will be possible and will range from a dusting to four tenths of an inch. The highest snow fall totals will occur on the taller ridges along the Virginia border. Any snow accumulations will most likely be confined to grassy areas and elevated surfaces. The snow showers should taper off beginning late this afternoon, with snow flurries lingering once the snow showers exit the area this evening. The snow should finally be out of the area by early Sunday morning. Temperatures will not make it out of the 30s today and probably will not reach 40 for most locations on Sunday either. Another shot of very cold air is expected to hit the region tonight, which will allow temperatures to plummet into the upper teens and lower 20s by early Sunday morning. Extensive cloud cover will remain in place across the area through late tonight as well, before giving way to partly cloudy skies on Sunday. Winds will shift from the south to the west today, as the clipper system mentioned earlier moves quickly across the area. In fact, winds are forecast to increase to 10 to 15 mph sustained by mid morning and could gust to around 20 mph at times. .LONG TERM...(Sunday night through Friday) Issued at 330 AM EST SAT DEC 9 2017 The models are in generally good agreement aloft through the long term portion of the forecast as they all depict a dominant trough over the northeastern portion of the nation. However periodic shortwaves moving through this flow bring with them more model discrepancies at this smaller scale. The first of these waves will be exiting the area at the start of the extended portion of the forecast though another one will cut through Kentucky on its heels early Monday. A more potent impulse follows for later Monday as it targets the lower Ohio Valley. This takes place as the height anomaly over the Great Lakes deepens with the GFS and ECMWF quite similar and the GEM an outlier to the south and east. By late in the day Tuesday another stream of energy will pass over eastern Kentucky with a significant fall in the heights throughout the Ohio Valley into Wednesday morning. After that, the Great Lakes trough will shift east with heights rebounding over Kentucky into Thursday morning. However, the ECMWF does bring another wave to the area for Thursday but there is little support from the GFS or Canadian with this feature as the latter favor a slower and broader trough that will not come through the area until later that night. The differences here lowers confidence in any specific solution and leaves much uncertainty in the forecast specifics. This trough will shift east on Friday with heights again on the rebound - more substantially in the ECMWF than the GFS. Given the concerns with the smaller scale features throughout the extended portion of the forecast the blend was a reasonable starting point for most grids but caution was used for any specifics heavily influenced by solely one model. Sensible weather will feature a fairly cold period this upcoming week along with periodic chances for light snowfall - highly influenced by upslope flow and terrain enhancements in lieu of decent moisture content. For Monday night and Tuesday the JKL CWA will be targeted by these snow showers as a sfc low passes by well to the north and a cold front presses into the area early Tuesday with a reinforcing shot of arctic air and a prolonged period of upslope. However, with limited moisture available the QPF will be low for this time frame with just a series of dustings expected from the terrain affected snow showers. Following a very cold Wednesday morning, dry and quiet weather will follow through mid week before the next wave brings additional pcpn chances on Thursday into Friday with more upslope sfc winds prolonging the light snow shower chances in the wake of this latter system`s cold front. Made only minor adjustments to temperatures through the period mainly for terrain effects in the non CAA patterns of Sunday and Wednesday nights. Made more substantial adjustments to PoPs and snow chances through the week - beefing up the potential in our higher terrain Monday night into Tuesday and again Thursday into Friday. && .AVIATION...
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(For the 18Z TAFS through 18Z Sunday afternoon) ISSUED AT 105 PM EST SAT DEC 9 2017 Middle and low clouds continue to spread east in advance of a cold front with southwest or west southwest winds generally in the 10 to 15KT range with some gusts up near 20kt for most ridgetop and western locations. Some scattered very light snow is likely reaching the ground in the far west as well, but CIGS and VIS remain in the VFR range. CIGS should continue to lower as the cold front approaches consistent with upstream obs over central KY and coverage of snow showers should also increase during the first 6 hours of the period. Some at least brief MVFR to IFR VIS and MVFR CIGS are possible in this. Winds should shift to the west and northwest behind the front with gusts as high as 20 to 25kt with snow shower coverage diminishing from west to east from 0Z to 6Z. Northern and eastern locations will also experience a few hours of MVFR CIGS during that time. Clouds should begin to clear and CIGS improve by the 6Z to 12Z period, giving way to VFR for all locations by the last 6 hours of the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...AR LONG TERM...GREIF AVIATION...JP

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