Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 220901 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 501 AM EDT Sun Apr 22 2018 .SHORT TERM...
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(Today through Monday) Issued at 440 AM EDT SUN APR 22 2018 Early this morning an axis of a shortwave mid and upper level ridge extended northwest into the OH Valley from off the southeast US Coast. Meanwhile a mid and upper level low was meandering in the vicinity of Wichita, KAS, Enid and Stillwater, OK vicinity. Convection was occurring to the east and southeast of the mid and upper level low center. The associated surface low was over Arkansas with a secondary surface low or wave near the TX and LA Gulf Coast area. A warm front extended across southern AR, southwestern MS to far southwest AL while the trialing wavy surface cold front extended from southwest AR down near the TX and LA border and into the Gulf of Mexico. Mainly high clouds and some mid level clouds have been moving across the region overnight. Mid level clouds are more numerous from southern IL and western KY into western and middle TN and south from there into the Gulf Coast states. East to northeast flow around surface high pressure centered to the northeast and east of the area was reinforcing dewpoints in the 20s for ridge and more open terrain areas though dewpoints are currently locally higher in decoupled valleys. The mid and upper level low is expected to track southeast to near Little Rock AR by sunset this evening and then move into southwestern TN around dawn on Monday and then meander to be centered northwest of Nashville by the end of the period. The axis of the mid and upper level ridge will move east of the region this afternoon and evening with the surface high departing to the north and east. Moisture should increase through the day today, more quickly at mid and upper levels than the lower levels. This will be especially true over the east and northeastern sections of the region where dewpoints are only expected to modify to the mid and upper 30s this afternoon. This combined with highs near 70 to the lower 70s should lead to min rh in the 20 to 30 percent range across northeast and southeast regions of the KDF if not the 20 to 25 percent range over portions of the Kentucky River and Big Sandy region. Locally, the pressure gradient is not expected to increase ahead of the mid and upper level low and surface system until this evening and tonight limiting fire weather concerns. Isentropic lift should lead to some showers encroaching on the Lake Cumberland region from the Cumberland Plateau and middle TN and central KY region by sunset. Moisture will continue to increase further tonight as the mid an upper level system get closer to the region. However, drier air to the north and east and even low level flow becoming downslope should slow this progression and areas nearer to the WV border will probably not experience anything more than sprinkles until after sunrise on Monday. The pressure gradient increases further on Monday and should be locally stronger over the higher terrain near the VA border. With this in mind opted to go considerably higher than than the blended model guidance for normal windier locations such as Black Mtn and the Flatwoods area of Pike County. In these locations sustained winds should reach into the 20 to 25 mph range with gusts as high as 35 to 40 mph. These winds will have a downslope component as well so although measurable rain should fall in most locations, though the downslope component should cut back on QPF several miles downstream of Pine and Black Mountains. Also, some limited insatiability will be present over the far southwestern portions of the area where MUCAPE should increase into the 250 to 500 j/kg range pending solar insolation. Model blend probabilties for thunder also get into the isolated to low end chance range here. Thus some thunder cannot be completely ruled out and regional ISC consensus was to include isolated thunder near the TN border out in the Lake Cumberland Region on Monday afternoon. .LONG TERM...(Monday night through Saturday) Issued at 350 AM EDT SUN APR 22 2018 The extended period will begin as a upper level closed low pressure system makes its way over the lower Ohio Valley, bringing increased chances of rain showers through mid-week. This will move to the northeast and out of the Commonwealth by Wednesday afternoon. The models are in good agreement for this first part of the long term forecast, but begin to deviate after Wednesday. As the split upper level flow merges Wednesday night into Thursday morning, a short wave looks to move through our area which could bring chances for showers as well. This will quickly exit eastern Kentucky, leaving most of Thursday dry. Models are still in quite a bit of disagreement with timing and intensity of a possible third system for Friday. The GFS is faster with this system, showing a neutral trough moving over the OH Valley with the potential for showers. The ECMWF shows a weak, positively tilted trough with little moisture associated with it. Will continue to monitor how this system develops for future updates. As for temperatures for the week, high temps will remain in the low to mid 60s for much of the week. The low temps will be in the low 50s until Wednesday night. Low temps Thursday night will decrease slightly to be in the low to mid 40s. This cooling trend looks to continue for Friday night, with temps right around 40. However, confidence is low due to model disagreement later in the forecast period.
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&& .AVIATION...(For the 06Z TAFS through 06Z Sunday night) ISSUED AT 235 AM EDT SUN APR 22 2018 Surface high pressure will gradually depart to the northeast of the area while the axis of upper level ridging should move northeast of the area after about 18Z. This will allow a low pressure system to approach with moisture gradually increasing, at mid and upper levels first followed by the lower levels by the last 6 hours of the period. Winds will generally be light through the period, though the pressure gradient will increase enough late for southeast winds nearing 10KT at LOZ and SME with even higher speeds above 2000 feet. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...CGAL AVIATION...JP

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