Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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021 FXUS63 KJKL 260330 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1130 PM EDT Wed Sep 25 2024 .KEY MESSAGES... - Showers and a few thunderstorms could result in heavy rain and isolated flooding through tonight. - The remnants of tropical system Helene are forecast to bring a widespread, soaking rain event later in the week. - Flash flooding could result from the remnants of Helene, but the potential may be limited by its quick movement. - Wind gusts of 40 to 60 mph are possible at times from Thu night to Fri as the remnants of Helene pass to the southwest. && .UPDATE... Issued at 1130 PM EDT WED SEP 25 2024 Showers continue late this evening, largely along the US-23 corridor and eastward. A few showers are also lifting northward into the Lake Cumberland area along the stalled frontal boundary. Still anticipate a resurgence in shower coverage and intensity from SSE to NNW between 6 and 9z as next surge of moisture/upper level energy approaches. UPDATE Issued at 800 PM EDT WED SEP 25 2024 No significant changes with this update. Refined overnight PoP forecast to reflect latest hi-res solutions -- expect showers to increase in coverage again, particularly after 6z. The soggiest conditions will be found over the southeastern half of the CWA. && .SHORT TERM...(This evening through Thursday night) Issued at 500 PM EDT WED SEP 25 2024 Late this afternoon, an upper level ridge extended from the western Atlantic northwest to the west of Bermuda toward the Canadian Maritimes while another upper level ridge centered over the Southern ROckies to northern Mexico area and extended to the northern Plains to central portions of Canada. An upper level low and trough were moving through the Hudson Bay to Ontario to Central Great Lakes area, while the southern end of this trough has closed off to an upper level low over the past 24 hours and was centered in the Lower OH Valley region. Meanwhile, Hurricane Helene continues to organize/strengthen in the eastern Gulf of Mexico to the west of Cuba. At the surface, an area of low pressure was centered north of the Great Lakes with a frontal zone extending into the Commonwealth to TN Valley to the Lower MS Valley to southern TX. Multiple weaker shortwaves moving around the upper level low are interacting with the boundary and lingering moisture with PW of 1.3 to 1.6 inches across the region. The highest PW and highest 100 mb mean mixing ratios are located across the Big Sandy region to northeast TN to the the Gulf coast states. Convection today has been most persistent across the Big Sandy region to the VA border. This evening and tonight, an initial shortwave trough associated with the ongoing convection will lift north early this evening, but another shortwave or two will move in quickly behind it later in the evening and during the overnight. These will rotate across the area as the upper level low meanders to near the confluence of the OH and MS Rivers. These will interact with moisture remaining across the region, PW generally 1.4 to 1.6 inches, and the boundary and result in continued rounds of convection during the evening and into tonight. At the same time, Helene will continue to the north and likely become a major hurricane. Thursday to Thursday night, the upper level low is expected to drop south to south of Memphis TN as upper level ridging builds north of the western Atlantic and a shortwave upper level ridge builds into the Great Lakes and the upper level ridge in the western Conus/Rockies retrogrades west. Helene should be drawn into the Souther Appalachian region as this occurs with the pressure gradient and winds aloft increasing as it does so on Thursday night. Precursor rainfall associated with the upper level low to the west and shortwaves rotating around it interacting with the boundary nearly stalled out near or just west of the area will lead to continued rounds of convection into Thursday, especially across the south and southwest portions of the area. Helene should begin to merge and interact with the boundary by the end of the period. PW should initially be 1.4 to 1.6 inches per 12Z HREF and then climb to 1.7 to 1.8 inches on Thursday afternoon. Further increases in PW to 1.9 to 2.1 inches should occur on Thursday night. More of a stratiform rainfall should develop and move into the are on Thursday night as Helene works into the southern Appalachians. This could be heavy in a few locations, but QPF has generally trended down for Thursday night with a track a bit more west/southwest of eastern KY. The increasing gradient should result in an increase in wind speeds and gusts in the more open terrain and locations above 2000 feet near the VA border on Thursday night. A High Wind Watch has been hoisted for Bell, Harlan, and Letcher counties starting at 11 PM on Thursday night and this runs into Friday. Some guidance suggests a possible increase in wind gusts to at least wind advisory criteria from US 25E to near London north along I-75 and points west late on Thursday night. The strongest wind gusts for most locations may hold off until Friday however. .LONG TERM...(Friday through Wednesday) Issued at 352 PM EDT WED SEP 25 2024 The forecast period begins with the area beginning to feel the impacts from the remnants of Helene. The hurricane is expected to make landfall on the Florida Panhandle Thursday evening and through the overnight hours quickly track north-northwestward toward the Commonwealth. By the start of the extended forecast window, the NHC has Tropical Storm Helene moving up the spine of the Appalachian Mountains but getting sheared apart by frictional forces from the mountains. The bulk of the remnants are expected to take a hard westerly turn to the northwest and fizzle out and get absorbed into a cut-off upper-level closed circulation. However, before that occurs, wind and rain will pound the entire CWA starting Thursday night and persisting through Saturday morning. Total QPF through the duration of Helene is expected to range from 1.00" to 1.50" along the eastern mountains to upwards of almost 2.00" to 3.00" along and west of the I-75 corridor. The easterly flow across the southeastern mountains will create a rain shadow effect for counties along the mountains and diminish overall QPF; however, the further away from the mountains; the less impact rain shadowing has on the QPF. Near high wind warning criteria winds are expected across the high terrain of the eastern mountains with sustained winds approaching 20 mph in the lower elevations are expected through Friday evening. Higher upper-level winds exist; however, with no widespread convection or mechanism to translate those winds to the surface, those winds will remain aloft. Through the evening Friday into Saturday, Helene will drift west-northwest toward western Kentucky and eventually be absorbed into a closed circulation that`s been largely stationary all week. After the merging of the closed circulation and the remnants of Helene takes place, the closed circulation will continue to aimlessly spin over the Commonwealth and keep persistent chances of showers and thunderstorms through the weekend. Models continue to remain in rather good agreement going into next week with the circulation getting picked up by the mean flow and ejecting out of the area by Monday morning but lingering PoP chances will exist through the end of the period as an upper-level trough, moving through southern Canada, drags a cold front through the region Tuesday afternoon which will then usher in cooler and drier weather for the middle of next week. Overall, the forecast period will be highlighted by multiple rounds showers and thunderstorms. The remnants of Helene will bring the best chances through Friday afternoon before the closed circulation keeps PoP through the middle of next week. Temperatures through the period will remain rather seasonal as highs are forecast to in the upper-60s to upper-70s. Overnight lows, will be warmer with the approach of Helene but with the approach of a cold front on Tuesday, cooler temperatures and fall-like weather will be in place for the end of the period. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) ISSUED AT 750 PM EDT WED SEP 25 2024 VFR conditions were reported at TAF issuance time. Anticipate conditions worsening to mainly MVFR from southeast to northwest overnight as the next round of showers move through the area. A rumble of thunder cannot be ruled out, but confidence in occurrence at a particular TAF site was too low to mention. MVFR or worse conditions can be expected during the day on Thursday. Winds will be light and variable. && .JKL WATCHES/WARNINGS/ADVISORIES... High Wind Watch from Thursday evening through Friday evening for KYZ087-088-118. && $$ UPDATE...GEERTSON SHORT TERM...JP LONG TERM...VORST AVIATION...GEERTSON