Area Forecast Discussion
Issued by NWS Jackson, KY

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366 FXUS63 KJKL 202130 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 430 PM EST Mon Feb 20 2017 .SHORT TERM...
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(This evening through Tuesday night) Issued at 430 PM EST MON FEB 20 2017 21z sfc analysis shows high pressure shifting off to the northeast with deep low pressure taking shape over the Norther Plains. The pressure gradient between these is tightening up to the west. Here in eastern Kentucky, the winds are starting to respond to the passage of the high by turning to the southeast and south - but still rather light. Ample sunshine through high clouds helped to propel temperatures into the upper 60s and lower 70s. Dewpoints decreased a bit during the middle part of the day with a range from the upper 30s to mid 40s for most places. The models are in good agreement aloft through the short term portion of the forecast. They all depict a strong ridge moving from Kentucky east to the Southeast Coast tonight while a full latitude trough splits apart with its southern extent closing off over the western Gulf Coast. To the north of this developing low, the northern portion will cross into the Great Lakes while some energy runs out ahead of its trough axis and passes over Kentucky into Tuesday morning. The main axis - though weakening aloft - will make it into the state later in the day and slowly pass that night along with some small height falls - more substantial in the ECMWF. Given the general model agreement will favor a blended solution for the larger scale while leaning toward the HRRR in the near term along with the ECMWF for weather details from Tuesday through Tuesday night. Sensible weather will feature a rather warm evening with a moderate ridge to valley temperature split developing under variable amounts of high clouds and an inversion. Good drying and mostly sunny skies today should limit the fog formation tonight to just the valleys ahead of thicker clouds moving in towards dawn. For Tuesday showers will push in from the southwest by mid afternoon with plenty of clouds and mild conditions continuing. The best rain chances will be later that night as a sfc low passes by to the south coupled with the weak energy aloft. This will make for another warm night with some places probably seeing soaking rains - depending on the interaction of the departing 300 mb jet north of the state and any divergence aloft that it generates over our area. For the most part the blended model solution looked decent, though the NAM seems to cut off the western extent of pcpn shield quicker than the ECMWF and GFS on Tuesday night but this seems to fast so have not backed off on the blended solution here. Again used the CONSShort and ShortBlend as the starting point for the grids through the short term portion of the forecast. Did make adjustments to temperatures tonight to account for a decent ridge to valley difference but readings should be similar Tuesday night with the rain. As for PoPs, did adjust them for late Tuesday into the night - translating the higher PoPs across the CWA more cleanly. .LONG TERM...(Wednesday through Monday) Issued at 330 PM EST MON FEB 20 2017 The extended forecast period begins on Monday with a deep closed upper low tracking northeast through the spine of the Appalachians. As this feature tracks northeast, blocking over the New England and Canadian Maritime region will hinder the exit of the back edge precip moving through eastern Kentucky. This slow exit followed with the approach of the colder air in behind on Monday night into Tuesday may lead to a brief mix of rain and snow on top of Black Mountain. In addition to this, models have been coming into more agreement of a prolonged heavy rainfall event coming to an end Monday evening into Monday night across eastern Kentucky. Some lingering minor flood problems may be possible, if not just some rivers running full. Both the Euro and GFS seem to have come to an agreement on this with the Euro being slightly wetter. Will keep this mention in the HWO. Heading into the midweek time frame, a brief period of ridging moves into the OH valley with a period of drying as southwest flow increases ahead of the next incoming cold front. High temps on Wednesday will climb into the upper 50s to low 60s with SW 10 to 20 knot winds bringing in an unseasonally warm airmass. In fact, models are suggesting an overall drying trend to the approaching front with the bulk of the moisture to the north over the Midwest and into Ohio. Little if any precip is expected with this feature. Passage of the front on Wednesday night will bring in a colder airmass to the region by Thursday with a possible prolonged upslope event taking shape for Thursday and Friday. At this point the pattern brings in a longwave trough across the eastern CONUS into the weekend. The northwest flow then brings a series of disturbances in an upslope scenario. At this point, while the models hint at temps being warm enough for rainfall during the day and snow showers overnight, an upslope event with the correct wind component would mean some convection and snowfall at warmer temps. For now, went with a general snowfall at 34 degrees and below due to the uncertainties in the models but this may need reevaluated. The general trend is cooler towards the end of the extended but models have backed off from the depth of the cold air. Due to this, will leave any mention of snow out of the HWO as none is expected to be impactful at this point.
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&& .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) ISSUED AT 1250 PM EST MON FEB 20 2017 VFR conditions will be the rule through the forecast period as nothing more than some high clouds stream overhead through midday Tuesday. East/southeast winds will remain light near or below 5 mph through today and tonight - switching to the south on Tuesday with a small increase in speed. Any fog tonight should be confined to the deeper valleys and not affect the TAF sites. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...GREIF LONG TERM...SHALLENBERGER AVIATION...GREIF

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