Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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943 FXUS63 KJKL 250615 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 215 AM EDT Wed Sep 25 2024 .KEY MESSAGES... - Repeated rounds of showers and thunderstorms through Wed night could result in heavy rain and isolated flooding. - The remnants of Helene is forecast to bring a widespread, soaking rain event later in the week. - Flash flooding could result form the remnant of Helene, but the potential may be limited by the quick movement of the system. - High temperatures will average near normal the rest of the week. && .UPDATE... Issued at 945 PM EDT TUE SEP 24 2024 All but a smattering of isolated showers have exited the JKL CWA as of 140z. Additional rounds of showers, along with some embedded thunder, can be expected for the overnight as disturbances stream northeastward ahead of a stalling cold front. The highest rain chances (50-80 PoP) will be across the two tiers of counties adjacent to Virginia. Rain chances will be lower (30-60 PoP) over counties further northwest. UPDATE Issued at 535 PM EDT TUE SEP 24 2024 Storms should hold together toward the US 23 corridor and the Severe Thunderstorm Watch 681 has been extended further east. && .SHORT TERM...(This evening through Wednesday night) Issued at 515 PM EDT TUE SEP 24 2024 Late this afternoon an upper level ridge was centered northeast of the FL peninsula with another ridge centered in the Great Basin vicinity. Meanwhile, an upper level trough extended from central Canada to the upper to mid MS Valley region to the Ozarks vicinity to TX. At the surface, an area of low pressure was tracking northwest of the Commonwealth near the southern end of Lake MI with a frontal zone trailing into western KY to Western TN to LA. Meanwhile, Helene continues to develop/strengthen in the Caribbean to the east of the Yucatan. Convection was ongoing across the region ahead of this system across the Lower OH and in the Appalachians. Recent mesoanalysis has inhibition remaining over northeast KY to the WV border with 1000 to 2000 J/kg MLCAPE across the remainder of the area. Shear is ample with effective in the 45 to 55KT range. Mid level lapse rates are analyzed at 5.5 to 6C/km with low level lapse rates of 7C/km or stronger in the southwest. This evening and tonight, the upper level trough is expected to remain in place west of the area with the southern end expected to begin closing off to an upper level low over the mid MS Valley vicinity. A shortwave trough is progged to pass northwest of eastern KY this evening. Meanwhile the sfc low should continue northeast into the Great Lakes through tonight and in Wed as the upper level trough axis remains west of the area and the upper level low meanders over the mid MS Valley vicinity. The trailing cold front should gradually move across western to central KY and then stall near or west of the area. At the same time, Helene should track into the northeast Gulf of Mexico. Convection should peak in coverage through around sunset. MLCAPE is progged in the 1000 to 1500 J/kg over the next couple hours with inhibition going away further to the east/northeast. Mid level lapse rates of 5.5 to not much more than 6C/km if that should linger into the evening as well while effective shear should remain in the 40 to 50KT range or so as well. Damaging wind gusts remain the primary threat with cells this evening though lower end severe hail could fall from any storms that rotates. A brief spinup tornado cannot be completely ruled out with an QLCS structure that may evolve. Instability should wane around or within an hour or two after sunset, but shower chances will linger overnight ahead of the boundary and with an upper level trough to the west of the area. The boundary will remain west of the are on Wed and into Wed night as well with the upper low west of the area and unsettled weather should continue. .LONG TERM...(Thursday through Tuesday) Issued at 435 PM EDT TUE SEP 24 2024 The period is expected to begin with an upper level low centered not far from the confluence of the OH and MS Rivers with an upper level ridge centered between Bermuda and Bahamas and extending north across parts of the western Atlantic with another upper level ridge centered in NM and extending north northeast to the Northern Plains/Upper MS valley to western Ontario. Meanwhile, Helene which should be a Major Hurricane as the period begins is expected to initially be centered over the eastern Gulf of Mexico. Meanwhile, a frontal zone should initially be in place from Quebec to the upper OH valley to the Commonwealth to AL to the northwestern Gulf of Mexico. The period is expected to initially be dominated by the upper level low as it interacts with Helene and Helene merges with it to begin the weekend. The upper level low center should drift south southwest to the Lower MS Valley Thu to Thu night and then meander to the mid MS Valley on Sat. After Helene tracks into the Conus, upper level ridging should build southwest into the eastern Gulf of Mexico and become centered nearer to the Bahamas while upper level ridging is progged to retrograde west to the Four Corners region/Southwest to upper MS Valley. The upper level low should continue to meander near the Lower OH Valley region to end the weekend before weakening to an open wave and merging with a shortwave trough crossing southern Canada to end the period. Helene will transport moisture into the Southern Appalachians and the Commonwealth with PW climbing from about 1.4 to 1.6 inch range early Thu to 1.9 to 2 inches on Thu night per 12Z LREF mean. PW in the 1.9 to 2 inch range per 12Z LREF mean should remain early on Friday before decreasing from the southeast on Friday to Friday night as the remnant low tracks across the Southern Appalachians and toward the Commonwealth/OH Valley. A widespread soaking rain should result across the region with the heaviest rain generally anticipated in the southwest/Cumberland River Basin in the southwest to near Black Mountain. The threat for the heaviest rain and perhaps flash flooding appears greatest from late Thu into Fri morning with WPC having a Marginal to Slight ERO during those timeframe. NBM deterministic wind speed and wind gust magnitudes as Helene nears the Southern Appalachians to OH Valley region appeared too low for the Thu to Sat. This is likely the result of the known low bias of NBM deterministic wind magnitudes when stronger systems work through an area. For those periods, the wind speed and wind gust magnitudes were trended 25 to 50 percent toward the 90th percentile magnitudes, especially for the higher terrain of 2000 feet and above. At this time, there appears to be a risk of wind gusts of 40 mph or stronger across the Log Mountains, the Flatwoods area of Pike County, and on Pine, Black, and Cumberland Mountain as areas immediately downwind for Thu night into Fri. Unsettled weather with chances for showers and storms at times will linger with the upper level low west of the area to end the weekend and to begin next week followed by this becoming an open wave to end the period. A cold front should also approach to end the period. Diurnal ranges should be limited with the approach of Helene and a lingering frontal zone across the area Thu to Fri with highs in the low to mid 70s and lows in the low to mid 60s. Highs should be near normal over the weekend before cooling a bit for Mon to Tue. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) ISSUED AT 615 AM EDT WED SEP 25 2024 Scattered showers and thunderstorms were ongoing at the start of the period, bringing localized sub-VFR conditions. Outside of the precipitation, conditions were mainly VFR. This scenario is expected to continue through the forecast. That being said, TAF sites may very well have restrictions at times, but nailing down timing is too difficult to explicitly state when, and including sub-VFR conditions would likely result in greatly over-forecasting poorer conditions. Hence, prevailing VFR is forecast, with the realization that there will likely be times of sub-VFR conditions. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GEERTSON SHORT TERM...JP LONG TERM...JP AVIATION...HAL