Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 240931 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 431 AM EST Fri Feb 24 2017 .SHORT TERM...
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(Today through Saturday) Issued at 340 AM EST FRI FEB 24 2017 Early morning surface analysis shows an area of surface low pressure continues to track NE out of the Central Plains into Missouri and a warm front is now well north across the Upper Ohio Valley region. WV imagery this morning showing plenty of upper level moisture streaming into the region and this is leading to scattered high clouds across eastern KY. Given these have only been high clouds and the valleys have decoupled leading to decent temp splits from some of the cooler valley locales. A mix of high clouds and possible some diurnally driven CU will remain the story through the day. LLJ will continue to move east in response to strengthening system to our west. This will begin to mix down as we move into the afternoon hours with gust of 25 to 30 possible across the Bluegrass and Lake Cumberland region. The other issue will be downsloping flow across the far east could also mix down drier air, with RH values in the mid 30s to lower 40s possible. This will have to be monitored today given the gusty winds, but it will help that the gustier winds will be west of the drier downsloped air. All the focus shifts to strengthening system to the west as we move into the late evening and overnight period. Models remain in good agreement with trailing cold front approaching from the west through the day. Initially convection will fire out ahead of the front and track across portions of the Midwest. Some of these will be single cell type storms, but as the system progresses east storm mode will become more multicell/QLCS. Given the strength of the cold front, lapse rates will remain steep through the evening and into the overnight. Also models, specifically CAMS, are in good agreement with the trailing cold front catching up to the initial convection possibly providing further lift as it moves into the region. One issue will be how much instability remains in place at that point given the time of day and year. However, if we are able to maintain this, the speed shear environment will be substantial through a deep layer and low level shear is rather impressive with some directional shear possible. This seem to be picked up well by the SHERBE (that deals with high shear low CAPE environments) with values near 1 or higher. Overall storm mode will remain more QLCS in nature and therefore the tornado threat will be very isolated. Think the better threat for tornado will exist further north across the Ohio Valley where more boundary interactions will take place. The main threat across eastern KY will be damaging winds given the storm mode and strong jet, and an outside threat of marginal hail given the airmass cooling aloft causing freezing levels to drop to near 10 KFT. In terms of grids, did opt to slow the progression of POPs to better align with the CAMs and also added enhanced wording for damaging winds given the greater threat. Behind this front will be progressively cooler temperatures from west to east early Saturday into Saturday afternoon. That said, higher terrain locations could hit the freezing mark by the end of the period. Given some wrap around moisture is possible did keep some sprinkles and perhaps flurries across the higher terrain into the afternoon. Given the high temperature will occur at midnight the temp curve will be quite unorthodox, and therefore leaned away from blended diurnally driven curve. .LONG TERM...(Saturday night through Thursday) Issued at 415 AM EST FRI FEB 24 2017 The period will begin with the mid and upper level shortwave trough and strong surface system that will affect the region during the near term period departing to the north and east. A broad through south of an upper level low in the vicinity of Hudson Bay is expected to extend through the Central Conus at the start of the period with rather zonal flow from the Plains east to the lower Ohio Valley for Sat night and into the day on Sunday. This will allow surface high pressure to build across the region on Saturday night before departing rather quickly east by Sunday night. A few sprinkles or flurries may linger into the start of the period with some uncertainty particularly across the northeast and east with timing of clearing on Sunday night. Also, the heart of the colder airmass will move across the area on Saturday night setting the stage for colder overnight lows compared to recent days. The position of the high appears most favorable for clearing and slightly colder overnight lows in the southwest part of the area. With the high moving across the area, a considerable amount of sunshine should lead to temperatures modeling into the upper 40s to around 50 on Sunday while dewpoints remain in the upper teens. Winds on Sunday will be light, but rh should fall to around 30 percent or below in some areas. Under the rather progressive pattern, several shortwaves should move east to start the week within this flow. One is expected to move through the northern Plains and approaching the Great Lakes on Sunday before moving into the St Lawrence Valley on Sunday night. Another more southern wave should move across the Rockies and emerge into the Plains on Sunday while a third shortwave is expected to move across the Four Corners region and into the southern Plains by late Sunday or Sunday night. The two more southern shortwaves should move into the lower OH and TN Valleys late Sunday night and into the day on Monday. An area of low pressure should develop over the Southern Plains on Sunday night in response to the more southern wave with an inverted trough developing east northeast into the Ohio Valley. Moisture returning with moistening from the top down could lead to some light precipitation possibly rain or snow initially from this very late Sunday night into the Bluegrass region and into early on Monday. As the atmosphere continues to moderate on southwest flow, any precipitation should quickly change to rain on Monday. Models have generally decreased qpf with this since 24 hours ago, likely factoring the initially very dry low levels. By the time the lower levels moisten it appears that the best forcing will be departing. Also over the weekend, another shortwave is expected to be dropping south and southwest into the Pacific Coast. This trough should rotate across the Western Conus through Monday night or Tuesday before moving across the Plains and into the Eastern Conus by Tuesday night or Wednesday. Models continue to vary with timing of this evolution with the GFS generally faster than the ECMWF. The period is expected to end with a trough across the eastern Conus. As the trough moves across the western Conus and nears the Plains, low pressure should organize over the Plains. This low should track northeast into the Great Lakes on Tuesday night or early on Wednesday. The associated warm front should lift across the TN Valley by Tuesday night with the cold front entering the Lower OH Valley late Tuesday night and then moving across the area at midweek. Much of the early to midweek period should be unsettled with chances for rain greatest Tuesday night into Wednesday. Uncertainty remains during this period with timing, but during the midweek period, showers and some thunderstorms appear likely though confidence in the Tuesday night versus Wednesday 12 hour periods is below average. For now opted to go with likely pops both periods or a little bit lower than the Superblend due to the timing uncertainties. After colder, but typical for late February lows on Saturday night and near to slightly below normal highs on Sunday, above normal temperatures should prevail through midweek. Behind the cold front at midweek, temperatures should return to closer to normal levels for early March.
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&& .AVIATION...(For the 06Z TAFS through 06Z Friday night) ISSUED AT 1240 AM EST FRI FEB 24 2017 A mix of high and even a narrow band of lower clouds are moving across eastern KY at this late night hour. The good news is we are looking at VFR conditions for the TAF sites, with lowest band of clouds staying at or around to 5 KFT level. Now some of the valley locales have decoupled this evening and therefore some will see patchy fog. The other concern is a increasing LLJ, as 850MB winds increase ahead of strengthening surface and upper level system progresses east. Therefore kept the LLWS in the forecast starting around 08Z to 12Z timeframe. Places that will have to best chance of seeing the stronger jet will be Lake Cumberland and Bluegrass regions. This will mix out by around 14Z and by tomorrow afternoon we will see some of these stronger winds mix down leading to gusty conditions. Think again the better mixing will occur across the Lake Cumberland and Bluegrass regions where 25 to 30 mph gusts are possible. We are continuing to monitor the potential for strong to severe thunderstorms to round out the TAF period. Right now a line of storms is expected to move into areas west of a line from Sandy Hook, to Jackson, to Middlesboro at or around 04Z to 06Z. The main threat with any stronger storms would be for damaging wind gusts. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...DJ LONG TERM...JP AVIATION...DJ is the U.S. government's official web portal to all federal, state and local government web resources and services.