Area Forecast Discussion
Issued by NWS Jackson, KY

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231 FXUS63 KJKL 230102 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 902 PM EDT Thu Mar 22 2018 .UPDATE...
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Issued at 845 PM EDT THU MAR 22 2018 Hourly temperatures have been freshened up based on observation trends. High pressure should bring mostly clear to partly cloudy skies tonight. MOS guidance points toward colder valley temperatures in the northeast and east compared to the previous forecast while LAMP guidance points toward ridgetop locations also a degree or two colder. At this time, have trended temperatures down a degree or two across the board with no other changes at this time. Lots of uncertainty remain with the system to affect the region late Friday night into Saturday especially with the thermal profile in the lowest few thousand feet. Model consensus is for the coldest profiles near 0C at the sfc and for several thousand feet aloft over Fleming, Rowan, and Elliott counties. The NAM has quicker warming aloft associated with the low level jet which would lead to melting and transfer of warmer air to the surface quicker. The GFS is colder, especially over northern Fleming County and this seems to be the most probable location for a couple of inches of accumulation. Whatever does fall will be battling rather warm ground and even limited solar insolation from late March sun should help inch temperatures above freezing in all locations by Saturday afternoon.
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&& .SHORT TERM...(This evening through Friday night) Issued at 340 PM EDT THU MAR 22 2018 19z sfc analysis shows high pressure building more effectively into eastern Kentucky. This is helping to settle the winds some after a time of gustiness following the breaking of the inversion early in the afternoon. Additionally, the high is helping to keep the cu to a minimum out there - mainly found in the far east. With ample sunshine temperatures have climbed into the low to mid 40s while dewpoints remain in the low to mid 20s. The latest satellite images shows the substantial erosion of any snow cover due to the warmer temps and late March sun. The models are in good agreement aloft through the short term portion of the forecast. They all depict full-latitude, strong ridging through the High Plains at the start of the period with Kentucky in the midst of fast northwest flow. This ridge does break down quickly as it attempts to come east but runs into a blocking closed low trough centered over New England. This will allow more Pacific energy and moisture to stream through the Upper Midwest and then down southeast into Kentucky for late Friday into Saturday morning. The core of this energy will be strong enough to buckle the ridge over the Central Plains Saturday morning - the NAM is strongest with this and actually starts to close off a mid level low while the other models maintain open waves. This all slides southeast into the JKL area on Saturday. Given the model agreement have favored general model blend with a strong lean toward the details from the higher resolution NAM12 and HRRR throughout the period. Sensible weather will feature high pressure moving over the state tonight and off to the east on Friday. Expect a ridge to valley temperature split to develop tonight with widespread frost through the area and some patchy fog along the river valleys. High clouds will slowly arrive on Friday from the west as a warm front starts to take shape to the southwest. This boundary lifts into eastern Kentucky later Friday night with ample moisture and lift to generate pcpn through the CWA as it moves from southwest to northeast with time. The cold air will be tough to shift out of the way in the northeast parts of the area along with wet bulbing likely to lower temps further at onset of the pcpn. Accordingly, expect the pcpn to move in as snow generally north and east of a line from Irvine to Whitesburg. Gradually this line will shift northeast through the night with a mix with and switch to rain anticipated for much of the area by 12z Saturday. Locations generally along and north of Interstate 64 will likely stay as snow and an inch or so of accumulation will be possible by sunrise Saturday. The snow will continue into the morning in our far northern areas - but likely remain below warning criteria due to low snow ratios. For that reason will keep Fleming and Rowan out of the Winter Storm Watches current in effect to the north and instead issue an SPS highlighting this concern in addition to mentions in the HWO. Started with the CONSShort and ShortBlend for the bulk of the grids in the short term portion of the forecast. Did make some significant adjustments to temperatures tonight for relative elevation differences - especially northeast. As for PoPs, beefed them up in the south quicker Friday night into Saturday morning closest to the NAM12 scenario. .LONG TERM...(Saturday through Thursday) Issued at 325 PM EDT THU MAR 22 2018 The extended will feature a period of colder weather and the potential for accumulating snowfall to start things off, before transitioning into a much warmer weather pattern that will feature chances of rain the first few days of the new work week. An area of low pressure is forecast to move southeastward and across the Ohio and eastern Tennessee valley regions Friday night into Saturday. Rain will quickly transition to a rain snow mix and then to all snow Friday night. The snow is expected to move across northern portions of eastern Kentucky through late Saturday morning, before change back over to all rain by the afternoon. Some accumulations of snow will be possible, but there is some uncertainty at this time as to how much snow we will see. The current pattern does suggest that the bulk of any accumulating snow would occur north of the Hal Rogers Parkway. As the area of low pressure moves across the area during the warmer part of the day on Saturday, it may even trigger a few thunderstorms from the Tennessee border northward to the Hal Rogers Parkway, where warmer temperatures and a bit of elevated instability may exist. The rain should finally begin to taper of late Saturday night, as the low pulls away to the southeast. We will likely see some snow mixing with the rain Saturday night as well, as colder air makes a weak southward push. Little if any accumulation is expected from this second batch of snow. Any remaining precipitation should move out of eastern Kentucky by early Saturday evening. Temperatures are expected to be below normal over the weekend as a trough of low pressure aloft keeps colder air in place over the region. Once this trough moves away, as a ridge of high pressure settles over the region. An area of low pressure will also be in play to during this time, and could bring a few rain showers to the western portions of our forecast area, but isolated to scattered at best on Monday and part of Tuesday. Better chances of rain will be in the offing Wednesday and Wednesday night, as a frontal boundary moves across the area. This boundary may even stall for a bit, bringing enhanced rain chances to eastern Kentucky. Southerly flow associated with this front, and the ridge that will temporarily set up across the area in the days before the front arrives, will also bring warm air from the Gulf of Mexico into the region. This will allow temperatures to warm into the upper 50s to perhaps 60 on Monday, and into the 60s the rest of the week. && .AVIATION...
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(For the 00Z TAFS through 00Z Friday evening) ISSUED AT 835 PM EDT THU MAR 22 2018 High pressure at the surface and northwest flow aloft is expected through the period. Some mid level clouds are expected in the northwest flow tonight with an increase in low and mid level moisture after 12Z leading to some thickening and lowering cloud bases ahead of a warm front. Some light rain could reach the Lake Cumberland region including near KSME by the end of the period. However, MVFR is expected to prevail throughout the period with light winds.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...GREIF LONG TERM...AR AVIATION...JP is the U.S. government's official web portal to all federal, state and local government web resources and services.