Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 092345 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 645 PM EST Sat Dec 9 2017 .UPDATE...
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Issued at 645 PM EST SAT DEC 9 2017 The evening surface analysis shows a nearby cold front across eastern Kentucky, with the parent surface low located across the eastern Great Lakes region. In the upper levels, a trough axis extends from the Ohio Valley into the Gulf of Mexico. These features coupled with steep low level lapse rates and reasonable omega within the dendritic growth zone are driving the light to moderate snow bands we have seen this afternoon and evening. Much of the moderate snow has now moved into far eastern and southeastern Kentucky this hour, and the trends in the WSR-88D composite are indicating this will continue to become more scattered to isolated over the next few hours. This as the cold front continues to usher in colder and drier airmass across the Bluegrass State tonight. There does remain the concern of black ice, as colder air helps to freeze residual moisture to area roads and that has been highlighted in the latest SPS product. Otherwise more minor updated were needed to deal with latest trends in temps, dews, and winds.
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&& .SHORT TERM...(This evening through Sunday night) Issued at 408 PM EST SAT DEC 9 2017 As of mid afternoon, an upper level trough extended from eastern Canada south into the eastern Conus with an upper level ridge over the western Conus. The center of the sfc low of a clipper system is moving through the Great Lakes region with the associated cold front trailing south into Central KY while the associated mid level shortwave is approaching the region. The clipper system will track into the eastern Great Lakes this evening with the cold front moving across the area through early this evening. Snow showers and flurries are ongoing and should persist until after sunset as the colder airmass moves into the region and lapse rate rates remain rather robust. The escarpment in the Daniel Boone National Forest and the higher ridges of the southeast part of the area should be most favored for very light accumulations as winds become more of a favorable uslope direction. Temperatures are currently in the mid 30s across many areas of the eastern and southeastern sections of the area. With marginal ground temperatures, most locations should not receive more than a quarter to a half of an inch total from what has already fallen and what falls this evening. Elevations above 2000 feet may receive a bit more than these amounts. Temperatures will continue to fall and any light snow falling could initially melt on some untreated surfaces before possibly freezing or becoming slushy as additional snow showers pass resulting in slick or icy spots. An SPS has already been issued to handle this. The low level moisture will become shallower starting around 0Z or 1Z or 7 or 8 PM ESt in the western part of the area and then gradually become shallower from northwest to southeast. Enough low level moisture may linger long enough near the VA border so that flurries could linger until almost sunrise on Sunday. Low clouds should linger most of the night in many locations so ridgetops and far western locations with partial clearing will be coldest for overnight lows as coldest of the airmass moves through the area tonight. Mid level height rises will already have begun overnight behind the departing shortwave while surface high pressure begins to nose in from the Southern Plains. Mid level heights should rise further on Sunday with surface high pressure building across the Gulf States. Low level moisture and clouds is expected to diminish on Sunday morning, but additional shortwaves passing to the north should lead to bands of mid and high clouds on Sunday. This and a relatively cold airmass still in place will lead to continued cold temperatures. Dry weather will linger into Sunday night and with general mid level height rises and sfc high pressure centered to the southeast at least a moderate ridge/valley temperature split from the nocturnal inversion will be possible. COOP MOS guidance indicates this, but blended model guidance was more uniform. Opted to not go as low as the COOP MOS guidance just yet as the gradient could lead to some mixiness and although there will be periods of mostly clear skies, band of mid and high clouds aren anticipated and guidance has an increase in moisture around 850 mb and below so low clouds will also be possible. .LONG TERM...(Monday through Saturday) Issued at 230 PM EST SAT DEC 9 2017 The pattern will remain unchanged into next week with persistent upper level troughing over the eastern US with a series of weak clipper systems cross the great lakes and Ohio river valley. Models continue to advertise all of these clipper systems will struggle to bring much in the way of measurable liquid to eastern Kentucky. However, much like the system today, any of these systems may be capable of a quarter of an inch of snow. The first clipper system looks to come on through Monday night into Tuesday, with another one pegged for late Wednesday or Thursday. Temperatures will remain below normal through next week, although we could start to rebound a bit heading into next weekend. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) ISSUED AT 615 PM EST SAT DEC 9 2017 The period is beginning with a wide variety of restriction levels, as light to moderate snow showers move eastward across the region. The more robust showers continue to move off into the far east and the overall coverage of snow is lessening across central Kentucky. This will be the trend as drier air filters into the region behind the cold front tonight. Given the on going light snow have been most robust restrictions with VIS in the IFR range for most sites. The TAFs will come back to VFR through the evening into tonight as the drier air filters into the region and snow tappers off. The winds have been gusty this evening around 20 to 25 knots at times, but these will lessen through the night, but the winds will generally remain out of the west. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...JP LONG TERM...KAS AVIATION...DJ

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