Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 082155 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 455 PM EST Thu Dec 8 2016 .SHORT TERM...
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(This evening through Friday night) Issued at 315 PM EST THU DEC 8 2016 Surface analysis reveals the strong Canadian high pressure remains parked across the central portion of the country and we remain in the middle across eastern KY. This has led to tighter isobars and consequently we have seen west to WNW flow with gusts 15 to 20 knots. Also we have seen some CU develop this afternoon given decent low level lapse rate and weak moisture at around the 850mb level. The better coverage of Stratocu is placed to our north and this will continue to spread SE through the evening and overnight. Model soundings would suggest we also manage to get some moisture into the dendritic growth zone and this will aid in the potential for some flurries. Also given the better cloud cover went really close to previous in trying to show overall higher numbers low temp wise in the east and lower values across the Bluegrass and Lake Cumberland region. Goes without saying that Black Mountain will likely be the big winner with lower teens. Friday the surface high pressure is expected to build east and this will ease the pressure gradient across the region. Also upper level winds will reduce overtime and lead to little influence from afternoon mixing. Cold air will be maximized early Friday as 850mb temps will be between -10 to -12C, and this will lead to one of the coldest afternoons of the season with most not making it above the freezing level. While 850mb temps begin to warm Friday night the surface high will crest across the region. This will lead to another night of teens and even lower teens for many including the valley spots. The only issue would be some mid level clouds and how they could lead to a slight dampening of temps. That said was not willing to go much lower than the lowest COOP MOS number which came in at 14 degrees. .LONG TERM...(Saturday through Thursday) Issued at 455 PM EST THU DEC 8 2016 The models are still in a state of discordance aloft through the bulk of the extended resulting in a lower confidence forecast for the overall period. Fast and near zonal flow will start out the extended on Saturday before the pattern starts to amplify over the High Plains on Sunday and the mid level energy rides east into the Ohio Valley. The core of this next system passes to the north, most amplified in the GFS, on Monday with more general fast zonal flow to follow. Attention then turns to a very deep low building over central Canada - most extreme in the GFS. This dominant low then progresses slowly south and east. The GFS, and to a lesser extent the ECMWF, bring a stream of energy through Kentucky and the Ohio Valley on Wednesday. The lowest heights remain over the area through Thursday in the GFS while the ECMWF`s heights rebound more quickly. Given the outlier solution from the GFS will favor a general model blend with a heavier lean toward the ECMWF, but this situation will need to be followed closely due to the potential of more southern interaction of the arctic jet stream mid week. Sensible weather will feature a dry and quiet start to the extended as high pressure slides over the region and heads east. This movement will allow for return flow from the southwest on Sunday moderating temperatures. Deep sfc low pressure then takes shape to our west and starts to come east on Sunday night and into Monday morning. With this, and a warm surge of air that night, rain showers are expected to spread over Kentucky by Monday morning. The cold front passes through during the day and temperatures are expected to fall in the afternoon. As such, a chilly evening and night are on tap for Monday night with some flurries or lingering snow showers possible - mainly in the upslope areas and places closer to the Ohio River - though the ECMWF would keep any ptype as liquid for the Cumberland Valley into the evening and overnight. The forecast gets a lot more complicated around mid week as the models diverge on the effects of the northern stream deep low and leading edge of arctic air. The GFS would shove the arctic boundary through around 12z Wednesday with a potential change over to mixed pcpn and then snow that morning - possible of significance. This solution has been discounted for now, though, in favor of the more benign ECMWF scenario. The latter forecasts moisture to seep north Tuesday night and Wednesday while the coldest air holds off to the northwest until later in the day and then the bulk of the pcpn departs quickly - owing to the sfc low moving to the Carolina Coast. Only that night would the air moving in from the west be cold enough for a mix or snow just about as the moisture exits to the east. Limited upslope flow with the ECMWF solution would also keep the post frontal snow shower activity to a minimum. Accordingly, the model differences keep confidence rather low for specifics during the latter part of the extended and for now have painted it more benign than the GFS extreme - but due to the potential this situation will need to be watched and tracked over subsequent forecast cycles. Made only minor temperature adjustments to the CR grid init mainly to allow for a nondiurnal curve Sunday night and Monday by using the CONSRaw. Also adjusted PoPs down on Tuesday given excessive influence from the unstable, of late, CMC forecast during this time frame.
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&& .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 1225 PM EST THU DEC 8 2016 Much of the lower deck from this morning has scattered out and now we are left with mostly high clouds across eastern KY. While we have returned to VFR this afternoon Vis Sat and Obs are showing a area of low MVFR building SE toward the region. These clouds will stream in through evening and overnight and some snow showers/flurries will also be possible. We have seen winds increase out of the west at around 7 to 10 knots this hour and would expect that to continue through the afternoon. Gusts will generally be around 15 to 20 knots. These winds are still expected to reduce through the evening. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...DJ LONG TERM...GREIF AVIATION...DJ

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