Area Forecast Discussion
Issued by NWS Jackson, KY

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570 FXUS63 KJKL 240421 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1121 PM EST Fri Feb 23 2018 .UPDATE... Issued at 1121 PM EST FRI FEB 23 2018 Late evening update to lower temps in the eastern valleys as we were meeting or just below advertised mins. Only dropped them a few degrees as incoming cloud cover should retard any serious drops through the remainder of the night. Still can not rule out a period of heavier rainfall through the morning hours Saturday due to aforementioned jet coupling and corresponding enhanced lift over portions of our area. But models are still undecided on exact amounts and location of potential heavier band. Thus was hesitant to make significant changes at this time. Averaging model QPF and it would appear there could be a half to three quarter inch swath of rainfall across some portion of our area through Saturday morning. For now passed on concerns to oncoming shift for reevaluation. UPDATE Issued at 833 PM EST FRI FEB 23 2018 Short wave disturbance will push across the area late tonight into early Saturday morning. Nose of an H850 LLJ, between 40 and 55 kts depending on what model you look at, will provide some convergence in the lower levels across a good part of our area towards sunrise. Area will also be near the right rear quadrant of a relatively weak but definite upper level jet streak. It appears that these two features may go through a short period of coupling, perhaps providing a bit more enhancement to our initial QPF forecasts across the south. At present there is some disagreement between the higher resolution convective allowing and synoptic models in the details of exactly where the core of more intense precipitation will occur. The 12Z ECMWF and 18Z GFS both show a relative max across our southwest of between three quarters and an inch of rainfall. The 18Z NAM is lighter, a bit slower, and further northwest with the heaviest rainfall. The HRRR has been waffling with the track of more intense rainfall. Will be watching trends in the HRRR/RAP and compare to the initial few hours of the 0Z run as they become available before deciding whether to increase QPF across our south with the late evening update. && .SHORT TERM...(This evening through Saturday night) Issued at 450 PM EST FRI FEB 23 2018 Record warmth occurred again today as a warm front lifted northward and sunshine broke through the clouds. It created enough instability for scattered showers to percolate this afternoon, along with a few isolated, sporadic lightning strikes. A few showers were ongoing at forecast issuance, but have been on the decline. Models depict the frontal boundary slowly sinking back south into our area this evening, with more showers developing. However, there is disagreement on the rainfall amounts and the axis of the precip. That being the case, confidence in forecast specifics is low for this evening, and nothing more than broadbrushed chance POPs were used. Both models show deep layer RH increasing overnight, and a greater potential for showers. MOS POPS are quite high for tonight as well. Taking this into account, have hit the POPs hardest toward dawn. Showers should last into the day on Saturday. The frontal boundary is expected to lift northward again on Saturday, and forecast soundings also show weak instability developing during the day. A slight chance of thunder is included in the forecast for Saturday. Barring training, rainfall amounts do not look overly impressive tonight and Saturday. If training occurs and localized amounts are heavier than forecast, some water problems can`t be ruled out. With a flood watch already in place, will leave run. However, the heaviest rain will probably occur on Saturday night. On Saturday night, a strong low pressure system tracking through the Midwest will bring a definitive cold frontal passage and a band of showers, and possibly thunderstorms. Brisk low level flow from the southwest will develop ahead of the front. If enough instability can develop to mix down environmental winds, severe weather can`t be ruled out. However the better chance is further west. The front and its showers will be progressive, so that once it passes overnight and early Sunday morning, our hydro concerns will end for a while. .LONG TERM...(Sunday through Friday) Issued at 323 PM EST FRI FEB 23 2018 A cold front will exit southeast Kentucky on Sunday, and rain chances will decrease as the day continues. While the 12Z GFS pushes the front far enough southeast Sunday night that rain chances would come to an end, the 12Z ECMWF shows another wave moving northeast along the front and thus keeping at least a slight chance of showers in the far southeast into Monday. Our standard blended model approach actually takes this into account and our forecast will push rain chances back north Sunday night, with slight rain chances lingering into Monday afternoon in the far southeast. Forecast rain amounts Sunday morning will mostly be less than 0.25 inch. Any rain from Sunday afternoon into Monday will be on the light side with amounts of 0.10 or less. Weak upper level ridging then builds into the area and a surface high slides across the OH valley, before moving to the east coast Tuesday night. This results in dry weather for Tuesday. Rain chances return by Wednesday as short wave energy moves northeast from a western U.S. trough. Rain chances then continue until another cold front moves through the area on Thursday. Dry weather will then return Friday, though a few showers may linger in the east to start the day. Temperatures will remain above normal with only a very slight cool down with the frontal passage on Sunday. Temperatures return to close to normal values with the passage of the late week cold front. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) ISSUED AT 833 PM EST FRI FEB 23 2018 Disturbance will move in from the southwest overnight. This feature is currently kicking off showers and a few thunderstorms across the Mid-South and stretching northeast into central portions of the Commonwealth. CIGS and VSBYS will drop as this activity lifts into our area during the predawn hours, or sometime after about 8-10Z. Until then can not rule out some isold to widely scattered activity just about anywhere across eastern Kentucky, though have seen a definitely downward trend in activity with sunset. Model guidance has not been real helpful but has trended more optimistic with MVFR CIGS versus previous IFR territory. Winds will be generally light and variable overnight around 4 kts on average but will increase from the southwest at about 10 kts through the day Saturday. && .JKL WATCHES/WARNINGS/ADVISORIES... Flood Watch through Sunday morning for KYZ044-050>052. && $$ UPDATE...RAY SHORT TERM...HAL LONG TERM...SBH AVIATION...RAY

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