Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 201040 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 640 AM EDT Thu Apr 20 2017 .UPDATE...
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Issued at 640 AM EDT THU APR 20 2017 WSR-88D radar showing some isolated showers are moving east along the TN/VA borders this morning. Otherwise a mix of clouds and even some areas of dense fog are the story this morning. Given the isolated showers added that to the grids and blended in the latest obs and trends.
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&& .SHORT TERM...(Today through Friday) Issued at 407 AM EDT THU APR 20 2017 Most spots have dried out this morning, however a fleeting shower is affecting portions of Pike County. Otherwise surface high pressure in the Carolinas is providing south to southwest flow across the region. Despite a weakly forced environment, a subtle wave and reasonable instability could be enough to kick off a isolated storm this afternoon. The best chances will be near the VA border where higher terrain could provide better lifting mechanism. Would think these would weak given the lack of shear in the lowest 6 KM to sustain better updrafts. Tonight we will be watching a more robust upper level wave eject out of the Northern Plains into the Great Lakes. At the surface, a low pressure will move across the southern Great Lakes and Northern Ohio Valley with attendant cold front extending into the Central Plains. This front will slowly slide SE and bring better chances of POPs into the region this evening into tonight. That said, a line of thunderstorms along and ahead of this boundary will move into the region. The timing is not the best instability wise, but a better shearing environment will advect into the region. Therefore, did keep thunder in the forecast through the night. Friday`s forecast is a bit more convoluted given the boundary becomes quasi stationary across the region, as the better upper level trough passes well to the north. The boundary will become another focus for convection on Friday, but the question is how much instability will be had given the potential cloud cover. Therefore, while effective shear values will approach 30 knots and convective temperatures of lower 70s will be reached the conditional instability could be the killer. The best chances of seeing a more robust storm will be in the far south and this is where SPC has placed a marginal risk. .LONG TERM...(Friday night through Wednesday) Issued at 400 AM EDT THU APR 20 2017 The models are in decent agreement with the long wave pattern aloft for the bulk of the extended. They all depict an amplifying trough moving into the Ohio and Tennessee Valleys to start the weekend with the GFS and ECMWF quite similar, but the Canadian is lagging. This trough slows and further deepens overhead on Sunday - most prominently in the latest ECMWF. However, it does appear to remain progressive enough to bring a rising height regime back into the area at the start of the new work week. While weak ridging sets up over Kentucky on Tuesday the northern stream will be active and may bring more troughing and energy into the Ohio Valley by evening - particularly seen in the ECMWF as the GFS is now out of step with its overseas cousin. Likewise, confidence falls for Wednesday as the ECMWF quickly presses a trough through Kentucky while the GFS holds on to ridging. With the agreement early - particularly among the GFS and ECMWF - will favor a blend having a good deal of confidence while further out as confidence flags a blend splits the difference effectively. Sensible weather will feature a wet and cool weekend as a nearly closed low descends over the region and slowly passes through. This will mean cloudy and wet conditions with a chance of thunder - mainly for our southern counties on Saturday. As the sfc low starts to pull away so will our thunder chances and better chances for measurable rain. There is a potential for showers to linger in the far east in Sunday night as the sfc low`s movement east is hampered by high pressure off shore. In time though, it will pull far enough away for drier conditions to prevail followed by more sunshine during the days ahead and temperatures back above normal. This will be the case through Tuesday before more uncertainty crops up as to whether a low passing through the Great Lakes will swing a cold front into Kentucky on Wednesday (ECMWF) or if sfc high pressure holds on for another day at least (GFS). For now have kept it dry, but confidence in this is lower than the rest of the forecast. Did make some adjustments to the temperatures each night with minor/spot specific ones early and then larger adjustments for Monday and Tuesday nights as ridge to valley splits should develop. With the PoPs, did not make many changes as the blend came in pretty good, but will caution that Wednesday may eventually need some PoPs if future model runs trend toward the ECMWF. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 120 AM EDT THU APR 20 2017 TAF sites are starting off the period VFR and should generally remain that way through the TAF period. The caveat will be the more valley sites could see fog, but right now will lean toward LOZ for MVFR VIS potential and leave out at other sites. Outside of TAF sites would think anywhere that saw convection and places that saw showers would have the chance of seeing fog through mid morning. While the convection this afternoon will be isolated in a weakly forced environment will mention VCTS for all the TAF sites. Winds will remain light out of the south to start the period, but deeper mixing into a modest LLJ could provide gusts of 15 to 20 knots through the afternoon. The better gusts would likely be in the Bluegrass and Lake Cumberland regions. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...DJ LONG TERM...GREIF AVIATION...DJ is the U.S. government's official web portal to all federal, state and local government web resources and services.