Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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507 FXUS63 KJKL 260920 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 520 AM EDT Thu Sep 26 2024 .KEY MESSAGES... - The remnants of tropical system Helene will bring a widespread, soaking rain event tonight into Friday. - Flash flooding could result from the remnants of Helene, but the overall potential may be limited by its quick movement. - Wind gusts of 40 to 60 mph are possible at times from late tonight through Friday as the remnants of Helene pass by the area. && .SHORT TERM...(Today through Friday) Issued at 520 AM EDT THU SEP 26 2024 08Z sfc analysis shows a weak pressure pattern over eastern Kentucky with a hint of an inverted trough ahead of a stalled frontal boundary to the west of the area. This boundary has been interacting with the high PW air in place over the area to keep showers and a stray thunderstorm on the scope through the night. Much of the convection is falling over grounds that have been soaked the last few days - especially Bell, Harlan, and Letcher counties. Plenty of clouds at various levels have kept temperatures and dewpoints fairly uniform through the area overnight - generally in the low to mid 60s. Amid light winds, areas of fog - locally dense along with some low stratus clouds have developed during the night, as well. Meanwhile, Hurricane Helene appears to be starting to undergo its rapid intensification process as it moves north through the eastern Gulf of Mexico. The models, and their individual ensemble suites, are in pretty good agreement aloft through the short term portion of the forecast despite a complicated forecast for this part of the Country. They all depict a 5h closed low seemingly stuck over western parts of the state with spokes of mid level energy rotating around - maintaining the convection for at least up in the east. To its south, the core of Helene is steadily approaching the Mainland U.S. It is this feature that will be the main focus for the weather over the next few days across eastern Kentucky. Helene looks to lift into the southern Appalachians and in a Fujiwhara manner rotate around the mid level low to our west later tonight into Friday. As a result, the core of Helene`s remnants push into the JKL CWA on Friday forming - and locking in place for a bit - a deeper 5h low over the region. There is enough general agreement among the models through the short term portion of the forecast, to favor the NBM as the starting point for the grids but with significant adjustments needed to the QPF, Winds, and PoPs from the CAMs through Friday evening. Sensible weather features a complicated and dynamic forecast on account of the remains of Helene tracking near and through eastern Kentucky. The strength of this system at landfall later today will have an effect on how well it can maintain its core of winds/rain into the southern Appalachians. East Kentucky will benefit from its easterly winds downsloping into the area and likely limiting the rainfall totals for much of the JKL CWA through Friday. However, much of the southeast is approaching saturation from the past three days of convection and the expectation of more rains today from the front to the west and the ongoing tropical fetch. High PW air and an increasingly tropical air mass will enhance the warm rain processes making for efficient rain producing showers. Expect limited thunder but that will likely not stop pockets of rain from reaching 2 to 3+ inches in a few hours for some places. On account of the expected rains and the antecedent soil conditions for the Cumberland Valley have gone ahead and hoisted a Flood Watch through Friday evening there. Could see the need for this to be extended west and north as the core of Helene`s path dictates later today and tonight. Look for the best rain chance to shift westward by Friday afternoon. Winds will be the other big concern from this event as the wind core of Helene will not have as much time to spread out and weaken as we typically see in these situations. Accordingly, anticipate - with significant support from the CAMs runs - strong winds and gusts over our higher terrain later tonight through Friday. A High Wind Watch remains in effect for our southeast higher terrain counties - above 2000 feet - for a potential of wind gusts in excess of 50 to 60 mph. Of heightened concern is the indicators in the CAMs that show drying from the east early Friday with a potential for the higher winds to mix down better in this environment in which case a wind advisory would probably be warranted for much of he area into Friday afternoon. Will keep watching this potential for possible additional headlines dealing with Helene. Otherwise, temperatures will be near normal for highs today and mild at night with warmer conditions in the east on Friday due to that drying and downsloping on tap. Any fog will likely be fleeting and associated with times of rain or any brief clearing of the lower clouds. The changes to the NBM starting point mainly consisted of increasing winds and winds gusts per the CAMs tonight and on Friday, as well as adding in more details from those higher resolution models for PoPs and QPF through Friday evening. .LONG TERM...(Friday night through Wednesday) Issued at 436 AM EDT THU SEP 26 2024 The remnants of Hurricane Helene is going to be the main story of the forecast heading into the extended. By 0Z Saturday the upper level low associated with Helene will have merged with the upper level low already in place across western KY. This merged mega system will remain nearly stationary during the first half of the day Saturday, before slowly moving eastward to the eastern half of the state Saturday night. The ECMWF is a bit slower with this progression, however, keeping the center of the low across western KY during this time. This sets the stage for model differences moving forward, with the ECMWF always being about 12 to 24 hours behind and displaced farther west than the GFS. This could lead to considerable differences in weather patterns across the Commonwealth, as one has the center of the low across the state (ECMWF) while the other (GFS) has moved well east of the state leaving us in NW flow. Furthermore, the GFS brings a shortwave through the Ohio Valley on Tuesday night into Wednesday morning, while the ECMWF starts to build ridging across the area. All this to say, held to the NBM after Saturday for sensible weather as a best guess between the two solutions. The swath of heavy rain that impacted us Friday will start to wrap north and eastward by Friday night, centering over western and central KY, with most models showing some drying taking place in the eastern CWA. This will persist through the first part of the day Saturday, until the system starts to make the above-mentioned shift eastward. Again, this is with the exception of the ECMWF which keeps the precip across the western and central portion of the state through the day Saturday and into Saturday night, keeping eastern KY dry. The NBM seems to be more in line with the GFS and NAM, spreading precip back into the eastern CWA by the second half of the day Saturday. Either way, QPF will have tapered off substantially by this point, with the best chances of totals around half an inch or so generally across the Bluegrass. The NBM has rain chances lessoning overnight with the loss of daytime heating/mixing, but ramps it back up across the eastern half of the state during the day Sunday. Interestingly, the same thing occurs on Monday, which seems more in line with the solution of the slower ECWMF, and a bit higher than the exiting GFS suggests. Will be interesting to see if these pops trend lower or remain likely depending on which solution the models continue to trend towards. After this point, the NBM continues to trend drier, with Wednesday likely being our first dry day in well over a week. Granted this isn`t exactly reflected in the models currently, especially with the GFS shortwave moving through, so expect that it could change as models hopefully come into better agreement over the coming days. One thing is for certain, the NW flow into the region through much of the period. This will likely peak by mid-week as part of the upper level jet dips down into the Commonwealth. As such, this northerly flow and presence of clouds plus precip will help to keep temperature at bay, with daytime highs generally in the low to mid 70s. By the end of the period, the clearing skies and lack of rainfall will help temperature to drop further overnight. Therefore, if the forecast holds, can`t rule out some temps in the upper 40s and low 50s for Tuesday night, and then down into the mid 40s by Wednesday night with another day of drying and clearing. The rest of the time clouds should keep us fairly insulated, with temperatures only bottoming out in the upper 50s and low 60s for lows. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 210 AM EDT THU SEP 26 2024 Variable aviation conditions were reported at TAF issuance time as areas of fog, low clouds, and a few showers are impacting the forecast area. Anticipate conditions to generally continue worsening to mainly MVFR visibility but IFR CIGs into dawn. 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 in showers, low clouds, and patchy fog. Winds will be light and variable away from any storms. && .JKL WATCHES/WARNINGS/ADVISORIES... Flood Watch through Friday evening for KYZ080-084>088-110-113- 115>118-120. High Wind Watch from this evening through Friday evening for KYZ087-088-118. && $$ SHORT TERM...GREIF LONG TERM...JMW AVIATION...GEERTSON/GREIF