Area Forecast Discussion
Issued by NWS Jackson, KY

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163 FXUS63 KJKL 221158 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 658 AM EST Wed Feb 22 2017 .UPDATE...
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Issued at 658 AM EST WED FEB 22 2017 Band of rain showers making slow progress to the south and east this morning. Still expecting the best coverage through the morning to be in southeast Kentucky as this shield of rain converges with showers streaming up from the south.
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&& .SHORT TERM...(Today through Thursday) Issued at 415 AM EST WED FEB 22 2017 Rain showers continue to drift east across eastern Kentucky this morning, owing to a multitude of upper level features. Northern stream energy is highlighted by an upper low across the Arctic, with trailing cyclonic flow through Canada into the western and northern U.S. A 300 mb jet streak, associated with a weakening upper low off the western shore of Hudson Bay, will push east/southeast this morning allowing for ascending motion in its right-entrance region. Lift will be further aided by remnant energy extending into the Ohio Valley, while a southern stream upper low digs into the northern Gulf of Mexico. Gulf moisture streaming north of this latter feature, along with diffluence aloft, will keep plenty of low clouds and rain showers in the offing through this morning and into a portion of this afternoon. Southeastern Kentucky will see the greatest rain chances from daybreak on due to being in closer proximity to the greatest northward streaming moisture and remaining forcing for ascent. This activity will be slow to push east as steering flow weakens with time, but drying should gradually take place this afternoon. Abundant moisture will allow low clouds to linger despite southeasterly downslope winds at the surface. Given this, cooler high temperatures will be in store today with readings generally in the low-mid 60s, with perhaps a few upper 60s in the Lake Cumberland region where clearing ensues earlier this afternoon. A dry period looks to be in place this evening and at least through early tonight, before a shortwave trough and attendant surface low traverse the Great Lakes later tonight. Height falls from this, combined with a developing warm front ahead of a surface low developing out of the lee of the Rockies in the central Great Plains, may spark isolated to scattered showers tonight and Thursday morning. Warm air advection and increasing instability will promote thunder chances by Thursday afternoon as southwest flow increases downstream of an upper trough spanning much of the western U.S. Shower/storm coverage looks to only warrant isolated/scattered mention at this time given the lack of a nearby surface boundary, but subtle impulses aloft along with an entrenched warm sector airmass will be enough to spark a few showers/storms as temperatures warm into the upper 60s to low 70s. .LONG TERM...(Thursday night through Tuesday) Issued at 415 AM EST WED FEB 22 2017 The period will be met with anomalously warm airmass hanging in, but a near normal airmass will soon be the story for the weekend. This as a longwave trough moves east and becomes cutoff across the Northern Plains by early Friday morning. A surface low that undergoes lee cyclogenesis will deepen, as upper low continues to take take on a negative tilt. Now this setup could lead to a double barrel surface low across the Great Lakes, but models are still trying to resolve the closed versus open upper low. Overall the models are in decent agreement with bringing a trailing cold front across the Bluegrass state. A line of Showers and thunderstorms will develop along and ahead of this boundary and some of the storms could be strong to severe. However less likely as you move toward the eastern side of the state. The biggest issue will be time of day with line of storms not making it into the region till around 03 to 06Z or later. The model soundings suggest the instability becomes more elevated and the low level inversion will be setup making it more difficult to mix down stronger winds aloft. However given the low CAPE and high shear environment the SHERBE does show values approaching 1 which is marginal and best values are further west along the western CWA border. Even with some of the negatives think a marginal risk for severe weather across the CWA is reasonable and the primary threat would be strong to severe wind gusts. The freezing levels are too high for such a low CAPE environment and would tend to lean away from any hail chances. These thoughts are also reasonably supported by some of the analog guidance such as CIPS and SPC MARS. Behind the front temperatures will crash and we will head toward normal temperatures for this time of year. The depth of the upper level trough will also lead to some complications with GFS rendering some wrap around moisture and ECMWF indicating more influence by eastward building surface high pressure. Given the low QPF and low support from other guidance leaned toward the dry model blend at this point. This high pressure quickly progresses east and the upper level pattern becomes a bit more flat in nature. We then see some weaker perturbations and PVA track through the flow leading to some smaller chances of precipitation by Monday. There are differences in the upper level patterns and this will consequently lead to divergence in the surface features. Right now best chances hold off till late in the period toward the Monday night to Tuesday time frame. There will likely be changes in the overall timing and evolution of this next synoptic system in subsequent guidance iterations. && .AVIATION...
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(For the 12Z TAFS through 12Z Thursday morning) ISSUED AT 658 AM EST WED FEB 22 2017 Ceilings have held in the VFR range through the night and early morning, except for a brief degrade to MVFR at SYM. Flow remaining out of the southeast, producing subsequent downsloping for eastern Kentucky, has proven hostile to low cloud development thus far. With rain continuing and further top-down saturation occurring, may still see some MVFR ceilings at all sites for a period this morning before VFR criteria prevail into this afternoon as rain comes to an end. A slim chance of showers may again develop later tonight, but not enough confidence in this to include mention at any terminal. Not expecting any sub-VFR ceilings tonight at this time given how conditions have played out overnight and this morning, but will have to monitor any developing showers and how much winds veer regarding potential MVFR possibilities.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GUSEMAN SHORT TERM...GUSEMAN LONG TERM...DJ AVIATION...GUSEMAN

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