Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 201821 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 221 PM EDT Thu Apr 20 2017 .UPDATE... Issued at 211 PM EDT THU APR 20 2017 Have made several updates during the day to account for showers popping up across the region, first in the east, and now across the southern CWA. Some of these showers/storms are quite large in area, but overall are not much of a concern other than some locally heavy rainfall. Increased POPS to isolated in these areas through the late morning, and to scattered across much of the CWA throughout the CWA before the main line of showers and thunderstorms rolls through overnight with the cold frontal passage. Updates to the temps, dew points, and winds have also been made in the near term to make sure the latest observations were reflected. UPDATE 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. && .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 18Z TAFS through 18Z Friday afternoon) ISSUED AT 220 PM EDT THU APR 20 2017 Isolated to scattered showers and thunderstorms continue to pop up across much of eastern KY, especially along the southern and eastern portions. Increased the cloud cover and winds in the TAFs based on latest trends, with gusts between 15 and 20 knots expected throughout the afternoon. Also introduced VCTS to all TAF sites for this afternoon given ongoing convection and expectations for it to continue expanding. Visibilities could be reduced briefly in the heaviest showers. Best thunder potential should taper off during the first part of the overnight as we lose afternoon heating. However, still tracking a cold front which will sink southward into our area overnight, and get hung up across the southeast portion of the state through the morning and to round out the forecast period. This will increase rain and thunderstorm chances starting late tonight, with rain and thunderstorms expected to continue through the remainder of the TAF period. CIGS should also decline due to the high amount of saturation, with MVFR expected late tonight and IFR or lower expected generally around 12Z or after. Still a little uncertain of how weather will affect visibilities at each TAF site, but do expect there will some variability depending on the intensity of rain showers. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...DJ LONG TERM...GREIF AVIATION...JMW

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