Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 281604 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1204 PM EDT Fri Apr 28 2017 .UPDATE...
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Issued at 1204 PM EDT FRI APR 28 2017 The forecast has been updated to reflect the latest run of the HRRR model and the most recent severe outlook issued by the SPC for eastern Kentucky. The overall threat for severe weather has been extended further eastward and now includes almost all of eastern Kentucky in a slight risk for severe weather and a small portion of our western counties in an enhanced risk for severe weather. The general time frame for severe weather from roughly 6 pm this evening through 1 am tonight. Threats will include large hail, damaging wind gusts, and a few tornadoes. The hourly precipitation, sky cover, and weather type grids were updated to reflect the new model data and severe weather tags corresponding to the threats outlined in the SPC`s latest outlooks. Updated information regarding severe potential has also been placed on the JKL website for viewing. UPDATE Issued at 805 AM EDT FRI APR 28 2017 Continue to see significant differences in short term, high resolution model solutions this morning with a fairly consistent and stubborn HRRR being a general outlier when compared to the NAM/RAP/ARW/NMM. The ARW does lend a little support to the HRRR, but the NMM much less so. Interestingly the ECMWF lends some support to the HRRR as well. However, there continues to be what can best be described as a general disconnect between synoptic scale changes expected over the next 12 to 24 hours and the HRRR. The HRRR has waffled a bit but still wants to bring the main thrust of thunderstorm activity straight into the heart of the CWA late this afternoon and evening. Depending on the evolution of events over the next several hours, there could be some major alterations to PoPs and sensible weather. For now can only monitor and adjust the forecast as trends become more clearly defined. Did make some minor tweaks to the grids for the latest hourly trends. No update to the zone package at this time.
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&& .SHORT TERM...(Today through Saturday) Issued at 508 AM EDT FRI APR 28 2017 Models are in good agreement with general mid and upper level pattern through the period. Jet max will be digging into the Intermountain West resulting in the development of a cutoff low over the deep southwest by Saturday morning. This deepening western system will induce rising heights across the southeastern U.S. beginning as early as today with substantial height rises occurring across the region. At the surface, ridging aloft will drive a stalled out frontal boundary to our south quickly northward today. We expect this frontal zone will push north of the Ohio River Valley by this evening and become the focus of much more active weather for the next 24 hours. The Storm Prediction Center has focused on this baroclinic zone for the potential of widespread severe weather later today and tonight. Main forecast challenge for our area will be timing and location of the potential for severe weather this evening. Ridging aloft will help cap much of any activity across our area. Main questions causing the greatest amount of uncertainty is exact location of the surface boundary to our north and whether the cap over the area will be strong enough to limit convection across the region. At present thinking is that ridging will keep most of the activity across our area limited to the far north, generally along and north of I-64 and west of I-75. With the exception of the HRRR CAMs seem to support this line of thought. However, trends in the HRRR suggest the severe threat may extend further south than originally expected. Should the cap be weak enough, forecast soundings indicate more than enough instability and ample shear for the potential of severe thunderstorms with hail and damaging winds being the main threat. Strong shear in the lowest 1-3 km of the column allow for the potential of a few tornadoes as well. PWATs do not look impressively high. However, CAMs also suggest the potential of some training storms, would could increase the risk of some flooding. At this point, confidence in the described scenarios is quite low. In general there seems to be a disconnect in the strength of ridging developing across the region and the amount of convection being offered up by the CAMs. There is also considerable uncertainty in the location of the frontal boundary riding north today and where it eventually sets up. These factors will ultimately determine the location of greatest concern with respect to any severe weather this evening. Bottom line is to remain vigilant and aware of future updates in what may be a rapidly changing situation. .LONG TERM...(Saturday night through Thursday) Issued at 400 AM EDT FRI APR 28 2017 Eastern Kentucky will remain in the warm sector through Sunday with the unseasonable warmth continuing. Record highs on Sunday are a bit higher (88 for Jackson, and 89 for London) and will likely be approached, but may be hard to exceed those numbers. Regardless, another warm day with highs in the mid to upper 80s. Meanwhile, a low pressure system will become cut off over the western great lakes with an occluded front surging east across the Ohio river valley. Model guidance continues to slow down this front and now looks like it should pass through the area late Sunday night into Monday morning. Ahead of the front, winds could turn quite gusty Sunday night. As the band of showers pushes on through Monday morning we could see some gusty winds out of any showers as well. The weather should dry out Monday afternoon with much cooler conditions returning to the area to start the new month. Dry weather will last through Tuesday. Weather looks like it may turn more unsettled by the middle of next week as a shortwave trough ejects out into the region. While some uncertainty remains on the pattern, it does look like shower and thunderstorms chances are warranted from Wednesday through Thursday. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) ISSUED AT 805 AM EDT FRI APR 28 2017 Valley fog was prevalent this morning but had only temporary effects on area terminals. Expecting generally VFR conditions across the area through the period. However, there is considerable uncertainty in the forecast. A warm frontal boundary should lift to the north today and showers and thunderstorms are expected to develop along this feature. The main forecast challenge has been to determine the position of the boundary by the end of the day. Models have not been much help, even with trends. For now only have storms affecting SYM by late this afternoon. Winds will be light but pick up from the southwest through the day at about 10 kts, and could become gusty for a few hours during the late afternoon. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...AR SHORT TERM...RAY LONG TERM...KAS AVIATION...RAY

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