Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 190532 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 132 AM EDT Wed Apr 19 2017 .UPDATE...
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Issued at 132 AM EDT WED APR 19 2017 Some mid level dry air has worked into portions of the region and this has allowed the mid deck to erode in those locations. This is leading to temp splits and therefore updated temperatures to try and express that. Otherwise many of the CAMs are developing a 30 to 35 knot LLJ across Middle TN and south central KY and moving it NE through the overnight. This combined with a upper level wave will induce showers toward dawn and the alignment of the showers is really the question. The jet alignment would favor the Bluegrass coverage wise. This will be evaluated further with the package update. Otherwise the overall trends in the near term grids are on track. UPDATE Issued at 949 PM EDT TUE APR 18 2017 Some light rain showers are currently affecting locations generally along and west of I-75. Most of the higher resolution model guidance continues to support a gradual diminishment through midnight, before an approaching short wave trough initiates some additional lower topped convection from 09 to 12z. As such, will keep out the mention of thunder for the rest of the night, and fine-tune the uptick in POPs towards dawn. Some partial clearing is also working in from the northwest, which may continue to translate further southeast until the influence of the approaching short wave trough moves in later on tonight. As such, will play up the fog a bit more across the area. Low temperatures in the 55 to 60 degree range look on target, and will only make a few adjustments based on the latest trends in observations. UPDATE Issued at 751 PM EDT TUE APR 18 2017 A couple of areas of showers are currently moving across portions of eastern Kentucky. The remnant warm front has lifted off to the north, with dew points now recovering to the mid and upper 50s across the entire area. Have tried to fine tune the POPs over the next few hours, with better chances perhaps across portions of the Cumberland Valley, as some leftover shower activity pivots in from south central Kentucky. Expect a diminishment in areal coverage and intensity with the loss of heating over the next few hours. Thunder has once again stayed out of our area thus far, but will continue to hang onto slight chances over the next few hours.
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&& .SHORT TERM...(This evening through Wednesday night) Issued at 350 PM EDT TUE APR 18 2017 A shortwave trough was moving across portions of the Lower OH Valley this afternoon with an upper level ridge centered over the Caribbean and an upper level trough or weakness extending from the MS Valley into the western Gulf of Mexico. Another shortwave trough is moving across the Upper MS Valley region and nearing the Western Great Lakes. Meanwhile a shortwave trough was moving across the western Conus with a stronger trough nearing the Pacific coast. At present, isolated to scattered showers and a few thunderstorms are occurring across the OH Valley region and the TN Valley. The shortwave trough is expected to continue to move east and northeast across the OH Valley tonight and dampen as heights rise across the southeast Conus and lower MS Valley. At the same time, a weak warm front will continue to lift north across the area. This combination will lead to the threat for convection, mainly showers, into this evening and tonight. However, some thunder is also possible over the next few hours. The region will remain in the warm sector Wednesday and Wednesday night and well south of the stronger westerlies. Surface low pressure tracking across the Great Lakes should move into Quebec with the trailing cold front lays out east to west over the Southern Great Lakes on Wednesday. Further west, as a shortwave trough moves from the western Conus into the Plains, low pressure should develop and track toward the upper MS Valley and Great Lakes. A diurnal uptick in convection should occur during the day on Wednesday with small chances lingering into Wednesday night. Temperatures will remain mild, on the order of 5 to 10 degree above normal. .LONG TERM...(Thursday through Tuesday) Issued at 355 PM EDT TUE APR 18 2017 The extended portion of the forecast will feature a shortwave moving from the Upper Midwest into the Great Lakes Thursday, proceeding eastward into southeast Canada by Friday evening. This will lower heights across KY, but should stay confined enough to our north to keep more a zonal pattern across the state. This system will be followed up by another developing upper level low across the Central Plains Friday into Friday night. Models are in somewhat poor agreement about the placement of this upper level low during this time period, with the GFS being much farther south in the Southern Plains with its location. Regardless, expect it to keep tracking to the east through the weekend, as the Euro and GFS come into much better phase with one another again. It is poised to push across the mid Mississippi Valley and into the Ohio Valley late Saturday, where it will get held up through Sunday. It will finally push through eastern KY Sunday night into Monday, with more zonal flow taking hold to finish out the forecast period. At the surface, a low pressure system will be moving northeast in conjunction with the upper level shortwave, passing into the Upper Midwest and Upper Great Lakes during the day Thursday. A cold front will extend southeast from this low pressure system, traversing the Mississippi River Valley during this time. This will put much of Kentucky in a flow of warm moist air coming off the Gulf of Mexico ahead of the frontal system, with temperatures expected to reach at or just above 80 degrees in most locations. Such a flow will allow for isolated to scattered rain showers to be ongoing as we start out Thursday morning and into the day Thursday. However the better precipitation will be along the frontal boundary, which should impact eastern KY Thursday night into Friday. The front will connect to another low pressure system over the plains (in conjunction with the secondary closed low addressed above), and will wind up getting held up across Kentucky as it becomes elongated in a more west to east orientation during the day Friday. This will keep showers and chances for thunderstorms ongoing throughout the day (although instability is not very impressive, so more of a passing chance of rumbles, ending overnight). Temperatures will be much cooler due in part to the clouds and rain, generally in the 60s to low 70s. The frontal boundary will finally shift southward Friday night as the low pressure system over the South/Central Plains continues on its eastward track, reaching the Mid Mississippi Valley by Saturday, and crossing the Ohio Valley Saturday night into Sunday. The proximity to this low pressure system and the strong southerly flow off of the Gulf of Mexico will keep widespread rain chances and some isolated thunder across the entire state through the day Saturday, and continued rain (loss of daytime instability cutting off thunder chances) across eastern KY throughout Saturday night as well. Conditions will finally start improving on the backside of the system during the day Sunday, as drier northerly flow takes hold and the upper level low exits to the east. A drier airmass will move into the region, with temperatures expected to moderate back into the upper 60s to near 70 degrees for Monday and Tuesday under the zonal flow and more abundant sunshine. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) ISSUED AT 120 AM EDT WED APR 19 2017 The region is starting out VFR, and mid level dry air has actually cleared a good portion of the northern half of the eastern side of the state this hour. Still concerned about the MVFR potential in the north, as short term models actually leaning toward the better LLJ streaming into the Bluegrass. This could also be where the better POPs reside, but not ready to jump on that just yet. However, did bring showers into most of the region toward the early morning hours. Then by the late morning into afternoon hours we could see a few thunderstorms, but right now less confident on exact locations. Winds will remain light through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...JP LONG TERM...JMW AVIATION...DJ

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