Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 180604 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 104 AM EST Mon Dec 18 2017 .UPDATE...
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Issued at 104 AM EST MON DEC 18 2017 Given the fact we have seen lowering VIS at several sites and going outside have observed drizzle opted to introduce this back into the grids. Otherwise this will be minor update with most grids in good shape at this hour. UPDATE Issued at 1105 PM EST SUN DEC 17 2017 Radar trends indicate little if any drizzle is currently falling in eastern KY. However, some drizzle has been reported over the past few hours in parts of central KY. 0Z NAM guidance and to some extent the high resolution models indicate the low level moisture becoming a bit deeper during the 6Z to 12Z period and more supportive of some very light rain or drizzle. The low clouds and stratus build down fog and even patchy fog in the valleys are more certain and have lowered pops over the next few hours on average with increasing pops toward dawn as potential for drizzle increases toward dawn or after. UPDATE Issued at 815 PM EST SUN DEC 17 2017 Hourly pops, sky, temperatures and dewpoints have been updated based on recent observations. Clouds heights are still expected to decrease overnight with subsidence in the wake of the mid level wave that brought precipitation earlier today. Stratus build down to the ridgetop level if not lower should occur overnight. This and weak southwest flow from about 900 mb and below and a weak passing disturbance could still lead to some drizzle. Recent radar images generally just have what appears to be patchy drizzle across the 4 VA border counties and adjacent areas of far southern portions of counties just to the north. Overall, other than some adjustments for recent observation and radar trends, no substantial changes were made at this point. Although drizzle later on tonight is low confidence, confidence in the persistent low clouds and rather mild temperatures is high. Min T will be in the upper 30s and little drop in temperatures overnight from current readings.
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&& .SHORT TERM...(This evening through Monday night) Issued at 345 PM EST SUN DEC 17 2017 20z sfc analysis shows low pressure working into Kentucky with a weakening cold front spreading into our area. This is continuing to support light pcpn and a lowering cloud deck late this afternoon. Under the thick clouds temperatures are holding in the upper 30s to lower 40s most places while dewpoints are in the low to mid 30s. Winds are predominantly light and variable with the higher elevations and locations closer to the Bluegrass seeing southwest ones. They are light to the northwest with stronger ones at 10 to 20 kts above 2000 feet along with some gusts in the 30s. The models are in good agreement aloft through the majority of the short term portion of the forecast, though they diverge a bit late. They all depict fast and nearly zonal flow over the Ohio Valley tonight through Monday night. A dampening wave is currently departing the area with additional energy more concentrated well to the north of Kentucky on Monday. Meanwhile, a fairly deep and closed trough will be swinging through the Four Corners region tomorrow afternoon elongating as it heads into western Texas by Tuesday morning. At this point the models start to stray from each other with the NAM taking the core of the trough further north than the GFS and ECMWF. This difference continues through the day, Tuesday as the ECMWF digs its trough deepest and a bit quicker east than the others. Downstream, this will affect the amount of height rises over Kentucky with additional bits of energy slipping over the JKL CWA. Given the increasing model spread a general blend is preferred, though the higher resolution HRRR and NAM12 were leaned upon for wx details. Sensible weather will feature plenty of clouds through the short term as low level moisture will be tough to clear out. With lowering cigs tonight into Monday drizzle and pockets of light rain can be expected but very little in the way of QPF resulting. In addition the cloud cover will really tamp down the diurnal curve through the entire short term period of the forecast. With the falling cigs some may get low enough tonight for areas of ridgetop fog. Have included this in the grids, as well. Given the limited diurnal range did not deviate too far from the ShortBlend temperatures through the period. Did raise PoPs a notch during most of the short term to help define the drizzle threat. .LONG TERM...(Tuesday through Sunday) Issued at 250 PM EST SUN DEC 17 2017 The latest model data is suggesting that there will be two periods of active weather in the extended. The first will be from Tuesday afternoon through Wednesday evening, as an area of low pressure moves slowly across the Tennessee Valley. Scattered to numerous rain showers are expected for most of the area, as the weather system makes its way off to the east. The second period of active weather looks to be from Friday through early Saturday evening. It appears once again that temperatures will be warm enough to keep any precipitation in liquid form across the area. Both precipitation episodes should provide nothing more than a good soaking rain to eastern Kentucky. Temperatures through out the period are expected to be well above normal, with daily readings topping out in the 50s for most locations. There will be a few days where some spots will only make into the upper 40s, and other days where highs will be in the upper 50s. Nightly lows are forecast fall into the 30s and 40s, which would also be well above normal for this time of year. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) ISSUED AT 1246 AM EST MON DEC 18 2017 This period is met with a mix of MVFR and IFR conditions mainly because of lower CIGS. This low level moisture in combo with upper level jets will keep the potential for drizzle overnight into Monday. That said, several sites are showing signs of this with lowering VIS over the past few hours and here at JKL we are seeing drizzle this hour. This low level moisture will continue to promote IFR or lower CIGs through much of the TAF cycle and then some improvements are possible to round out the period to lower MVFR. The winds through the TAF cycle will remain light out of the south. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...GREIF LONG TERM...AR AVIATION...DJ

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