Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 141603 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1203 PM EDT Mon Aug 14 2017 .UPDATE...
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Issued at 1203 PM EDT MON AUG 14 2017 Latest radar trends continue to support the idea of showers exiting the northern part of the forecast area early this afternoon with showers returning into the SW part of the area this afternoon. Satellite showing some breaks in the clouds over the southern part of the area, so with additional surface heating and destabilization could see some thunderstorms as well this afternoon. Have updated NDFD for latest trends. UPDATE Issued at 1001 AM EDT MON AUG 14 2017 Based on radar trends and latest short range guidance have updated NDFD. Showers will be most numerous in the north through the morning, with the best chance for showers shifting to the southwest and southern part of the forecast area this afternoon. This latest forecast thinking has been depicted in the NDFD. UPDATE Issued at 808 AM EDT MON AUG 14 2017 With the 06Z model run the NAM and GFS have come into better agreement for the 1st period, and have made minor updates to the forecast based on this. Unfortunately, the agreement falls apart overnight, with the NAM once again being inconsistent and showing convection with very heavy rain. The GFS has does not have the heavy rain and has been consistent, and it was relied on much more heavily for the forecast.
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&& .SHORT TERM...(Today through Tuesday) Issued at 458 AM EDT MON AUG 14 2017 A weak mid/upper level wave was approaching from the west southwest early this morning. Radar was showing precip expanding over south central KY in association with it, but with precip originating at mid levels, much of the initial returns on radar were probably still virga falling into drier air below. Will look for moistening to eventually allow for precip today. Models all show precip by day`s end, but there`s not good agreement on the details. With MOS guidance giving at least likely POPs, have gone with this over most of the area. However, it was a struggle as to how to depict the details in the required one hour increment grids. Weak instability also comes into play, and a slight chance of thunder was used early this evening. For tonight, have favored the GFS and ECMWF over the NAM. The NAM has been very inconsistent in recent days, with sporadic runs showing large amounts of precip at times (the latest one being the 06z 8-14 run for tonight). Will forecast a general decline in precip overnight. On Tuesday, diurnal destabilization may bring another increase in convective precip. However, it the convection would be fighting against an expected decline in deep moisture as the wave aloft pulls out to the east. That being the case, have only used low POPs. .LONG TERM...(Tuesday night through Sunday) Issued at 407 AM EDT MON AUG 14 2017 Upper level ridging will remain in place across the far SE conus through the extended portion of the forecast. With a deep upper level low across eastern Canada during much of the extended as well, Kentucky will find itself in a troughing pattern, though very deamplified due to the ridging to our south. Several waves are expected to traverse through this longwave pattern and move from west to east across the Commonwealth through the workweek bringing unsettled weather. Models start to diverge in solutions by the weekend, with the ECWMF developing a closed low over the Great Lakes and longwave troughing across the eastern Conus during the day Saturday, while the GFS is much weaker and slower in this development, not impacting the region until Sunday. By Monday they actually come back into agreement with a strengthening ridge building in across the state. At the surface, exiting high pressure to our east will allow for more southerly return flow to make its way into the region for Wednesday. This will interact with a weakening warm front just to our south to produce shower and thunderstorms chances throughout the day, mainly in the southern portion of the state. Meanwhile, a surface low will be located across the central plains and Upper Mississippi River Valley during the day Wednesday, moving northeast and into the Upper Great Lakes by Thursday. This will pull the above mentioned warm front farther northward and elongate it across the state from north to south through the day Thursday without much eastward progression as the parent low slows its movement. The low will pick back up the pace by Friday and continue farther NE, pulling the weakening warm front eastward across the rest of the state and JKL CWA. It still looks as though the warm front becomes a bit washed out by the time it makes it across our CWA, but should still provide good convective potential. A cold front will be close on the heels of the warm front, making it just NE of the Ohio River during the day Friday, and stalling out through the day Saturday. It will finally push southward across the state during the day Sunday, but with little impact. High pressure will take hold for the remainder of the extended as the stationary front remains just to our south. Overall, all this boils down to is unsettled weather through much of the extended, with near normal temperatures but humid conditions thanks to the southerly flow from the Gulf. Best chances for convection will be during the afternoon during peak heating/instability, and best coverage should be during the day Friday as the warm front shifts eastward across the region. The cold frontal passage on Sunday will be quite weak, with generally only isolated convection expected. However the boundary will remain close enough to our south to warrant isolated pops across the far SE for the daytime Monday as well. Otherwise much of the CWA should be clearing with high pressure taking hold. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) ISSUED AT 808 AM EDT MON AUG 14 2017 Showers were affecting much of the area at the start of the period, but were still not causing many restrictions. However, as precip continues and the air moistens, will expect the areas with the more persistent precip to drop to MVFR conditions for a while today. Shower coverage should diminish this afternoon, but with some heating and destabilization, a few thunderstorms could pop up late in the day and this evening-- mainly in the southern part of the area. By the end of the period, any showers should be sparse. The only caveat is that there is some model discrepancy for the upcoming night. The 06Z run of the NAM model shows very heavy rain for the southern part of the area, but it is not consistent with earlier runs. Have mostly discounted this, and relied more heavily on the more consistent GFS model which has decreasing showers. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...SBH SHORT TERM...HAL LONG TERM...JMW AVIATION...HAL

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