Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 082342 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 642 PM EST Fri Dec 8 2017 .UPDATE...
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Issued at 642 PM EST FRI DEC 8 2017 The evening surface analysis is showing a small influence from surface high nosing northward. Otherwise we remain stuck between two systems this evening. This keeps us mostly driven by the strong jet energy aloft and disturbance to the east that continue to render mid to upper level clouds across eastern Kentucky. This being to case did increase the overall cloud coverage for portions of the night. There remains some concern on weaker moisture making it into the far southeast tonight, however, the short term models are overdone based on current trends. These models have been most robust with the QPF and given this confidence remains low this evening for any snow. Therefore, did lower POPs and QPF in the southeast and this subsequently leads to lower snowfall potential. The cloud cover also leads to less confidence in the low temperatures tonight and did lean slightly higher based on that idea. Otherwise loaded the grids with latest obs and trends.
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&& .SHORT TERM...(This evening through Saturday night) Issued at 247 PM EST FRI DEC 8 2017 We have two weather systems we are monitoring this afternoon. The first one is pushing northeast across the southeastern states with a large plume of moisture extending across the southern Appalachians. The second system is diving southeastward across the far western great lakes. Presently, eastern Kentucky is sandwiched between these two systems, with nothing more than a bit of mid to high level cloud cover. This will change for a few folks tonight as moisture associated with the system to our south brushes the Kentucky counties bordering Virginia. RAP/HRRR have been wavering around with the northward extent of precipitation over the past 3 or 4 runs, but its looking more likely that some light snow will push into our counties bordering Virginia late this evening or overnight. RAP/HRRR/GFS all indicate about 0.05 to 0.10 inch of liquid equivalent tonight, which would support around an inch of snowfall with a snow ratio near 15:1. The highest totals will likely reside in the highest terrain, with drier air eating away at totals at lower elevations. For all other locations, expect skies to gradually clear overnight. The clearing skies and expected light winds will allow for temperatures to plummet tonight. Lows will fall well into the teens in many areas. The exception will be in the far southeast where precipitation and clouds keep temperatures in the 20s. Any snowfall will end around daybreak Saturday with a mostly sunny start expected. However, the second system will roll into eastern Kentucky from the northwest by midday or early afternoon. This will bring an increase in cloud cover and increased chances for snow showers. Low level lapse rates will steepen up quite a bit through the early evening hours, allowing for a few intense snow showers that could lay down a quick coating of snow. This is despite highs expected to reach into the mid 30s. We will likely see temperature falls within the snow showers. However, given the air temperatures near or above freezing, travel conditions should not be all that impacted. Expected liquid equivalent is only going to be a few hundredths of an inch for most, so this won`t support that much snow. Perhaps up to a half inch in favored westerly upslope regions. A few snow showers or flurries may linger into Saturday evening before coming to an end. Most of the moisture with this system will fall in the dendritic growth zone, so we could see some decent dendrites with the snow on Saturday. This could aid in some instances of reduced visibilities, impacting travel in the heavier snow showers. Temperatures Saturday night will drop back into the teens again with another strong push of cold air moving in behind the clipper system. .LONG TERM...(Sunday through Friday) Issued at 410 PM EST FRI DEC 8 2017 The long term period is expected to begin with a western Conus ridge and an eastern Conus/eastern North American trough. The axis of this trough is expected to have moved east of the area by the start of the period or shortly thereafter. At that point, surface high pressure is expected to be centered over the Southern Plains and southeastern states. The clipper system/shortwave that is expected to affect the region in the near term will have moved east of the area with another clipper system working through the Great Lakes at that point. Height rises are generally anticipated from Sunday into Monday with the eastern Conus trough becoming more broad in general and the airmass modifying. In fact, 850 mb temperature are expected to recover from near -9C or -10C to start the period to around 3C or so by Monday evening with southerly flow between high pressure departing to the south and east and the next clipper system dropping into the MS Valley on Monday. Like the previous clipper system, the one for Monday night through Tuesday is again expected to track north of the area a track typical of minimal wintry precipitation. The cold front associated with this system should move across the area on Monday night with a few snow showers and flurries with additional coverage of snow showers possible on west to northwest flow and increased instability due to solar insolation on Tuesday. At this point, isolated to scattered coverage of this is expected with any accumulations mainly above 2000 feet and limited to an inch or less as vertical motions should peak below the dendritic growth zone with limited moisture. The coldest of the airmass should move across the area on Tuesday night with 850 mb temperatures bottoming out near -15C. The period from late Tuesday night through Wednesday night appears to be in between clipper systems at this time, with cold high temperatures and a fair amount of mid and high level clouds. There is uncertainty regarding the track and timing of the last clipper system of the extended period which should arrive late Thursday or Thursday night with light precipitation chances lingering into Friday. What falls, if anything with this system should primarily be snow. After a cold start, highs should average 10 to 15 degrees below normal on Sunday. Clouds and some mixiness due to a moderate pressure gradient should keep temperatures from bottoming out on Sunday night. Highs should moderate to near normal levels for Monday. As colder air moves in, daytime highs may struggle to climb above the mid 30s on Tuesday in the cold advection pattern. With the heart of the cold airmass in place for much of the night on Tuesday night, widespread teens are expected for lows. The cold airmass will still be in place for Wednesday with many locations likely struggling to climb above freezing. Temperatures will likely moderate ahead of the the last clipper system of the long term period on Thursday to around 5 degrees below normal, with similar highs are expected on Friday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 622 PM EST FRI DEC 8 2017 We continue to see mid and upper level clouds from strong upper level jet and disturbances aloft. The good news is we remain VFR and this will be the story for the TAF sites through much of the period. There is a chance of seeing moisture sneak into our far southeast tonight which could lead to light snow. While this could lead to localized issues, the models are not handling this very well based on current observations leading to less confidence. Another upper level disturbance drops southeast Saturday afternoon, and we will see snow showers develop and move across the area. This could lead to localized drops in CIGs and VIS, but kept the TAF sites VCSH for now. Given some influence by nosing high pressure think the winds will remain calm tonight, and then winds will increase through the day Saturday out of the west at 10 knots with gusts of 15 to 20 knots. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...KAS LONG TERM...JP AVIATION...DJ

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