Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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638 FXUS63 KJKL 271644 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1244 PM EDT Fri Sep 27 2024 .KEY MESSAGES... - The remnants of tropical system Helene will bring a widespread, soaking rain event today. - Flash flooding could result from the remnants of Helene, but the overall potential will be limited by its quick movement. - Wind gusts of generally 40 to 60 mph are expected at times today as the remnants of Helene pass. Locally higher wind gusts are possible. && .UPDATE... Issued at 1243 PM EDT FRI SEP 27 2024 Based on upstream observations and reports, we opted to add the counties that were in the wind advisory to the high wind warning as impacts of downed trees are likely to be realized. UPDATE Issued at 735 AM EDT FRI SEP 27 2024 No significant changes to this dynamic forecast with just the inclusion of the latest obs and trends for the T/Td/Sky/PoP grids. Meanwhile, the swirl of Helene continues to approach and the winds are definitely on the increase. The downslope rain shadow persists in the radar coverage but expect that to be overwhelmed during the next few hours. These minor adjustments have been sent to the NDFD and web servers with a freshening of the zones and SAFs. && .SHORT TERM...(Today through Saturday) Issued at 545 AM EDT FRI SEP 27 2024 09Z sfc analysis shows the quickly tightening pressure gradient approaching Kentucky as, still a hurricane, Helene lifts toward Kentucky. This system has spread copious amounts of rain over the area through the night helping to saturate the soils. It is also starting to push the higher winds into the this part of the state with the highest elevations affected first but some stronger gusts are starting to make it into the lower lands. Currently, under cloudy skies, temperatures and dewpoints are well mixed and uniform in the middle to upper 60s. Easterly winds are gusting to 30 mph on the higher observation sites with those values expected to climb towards dawn. The models, and their individual ensemble suites, remain in pretty good agreement aloft through the short term portion of the forecast despite a highly anomalous situation involving the landfalling hurricane intertwining with the persistent 5h low to the west of the area. This dance brings the remnant core of Helene to our doorstep just after sunrise with ample mid level energy wrapping around the reinvigorated upper low. This synoptic pattern will help to keep the system stronger than normal for these situations with all the attendant sensible weather concerns through the day, today. These concerns start to diminish this evening as the remnants transitions to extratropical and we deal with a deep 5h low meandering over the state generally holding to our west through Saturday. While the model spread is small for this situation, the NBM appears to be struggling in comparison to the higher resolution CAMs through the short term with respect to key details such as wind speeds, gusts, and rainfall. Adjustments were made to the forecast for these elements into Saturday. Sensible weather features a very active and concerning weather day across eastern Kentucky as the remnants of Helene lift through the area with high winds and excessive rains the primary threats. For the rain, bands of tropical moisture and efficient warm rain processes will wring out between 2 and 3 inches of rainfall with locally higher amounts through the early evening hours. For this reason, along with the antecedent rains of the past week, we have extended the flood watch for the almost the entire area - pushing the boundaries north on account of the last couple of the Helene rainbands modeled to pivot through that part of the area as it retrogrades to the west. Winds are the other big concern with definitive mid level drying arriving from the east by midday and likely prompting the high winds aloft to mix to the sfc for a time later this morning into the afternoon. Accordingly, in addition to the higher winds above 1500 and 2000 feet in the southeast this morning we look for winds in excess of 60 mph to reach the sfc on account of the drying and a building - again anomalous - easterly jet at 925 mb. The HREF and the individual CAMs show this threat clearly so we have upgraded the existing Wind Advisory for much of the area outside of the southeast to a High Wind Warning. Of greatest concerns will be the trees still flush with leaves and certain to be heavier as they are wet along with soaked soil around their rootballs leading to them being more easily toppled. Finally, pointing out the anomalous high wind direction for a third time, these trees probably have not been stressed from that direction too much through their life-cycle. The strong wind gusts will also be a threat to high profile vehicles - especially those on north to south oriented roads such as I-75. The winds should maximize in the Bluegrass and I-64 corridor from around noon through 4 pm before they gradually start to settle into the evening hours. Otherwise, temperatures will be warmer than normal in the east today, on account of the afternoon drying, and seasonable on Saturday though high dewpoints will keep the humidity up and make for another mild night. Patchy fog will be around through the day with the rain - and tonight with any temporary clearing. The stacked low overhead will then slowly move east on Saturday bringing high chances of showers back into the area along with more cloud-filled dreariness. The changes to the NBM starting point mainly consisted of again increasing winds and winds gusts per the CAMs today into tonight, as well as adding in more details from those higher resolution models for PoPs and QPF through the afternoon and again on Saturday. .LONG TERM...(Saturday night through Thursday) Issued at 327 AM EDT FRI SEP 27 2024 After the remnants of the Helene fujiwara with the mid-level low in parts of West Tennessee, it will become vertically stacked Friday night and this mid-level low will slowly meander eastward through early next week. This will keep the weather active with periods of showers and at times a few thunderstorms through Tuesday and there seems to be good agreement on this in the deterministic and ensemble outputs. The rain chances will generally peak in the afternoon hours each day. WPC does keep a small risk of flooding Sunday given the rainfall expected with the remnants of Helene, but this will be highly dependent on how the activity pans out today. There is good agreement in the ensembles and deterministic guidance on a northern stream trough axis pushing toward the Great Lakes and helping push the mid-level low and opening it up as it heads east. This northern stream trough will also usher a cold front eastward across the Ohio Valley. This will aid in bringing in a drier weather pattern and cooler morning starts eastern Kentucky by mid and late week. Given this opted to decrease valley lows closer to the tenth percentile of the NBM, with valleys dropping into the mid and upper 40s Wednesday and Thursday mornings. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) ISSUED AT 755 AM EDT FRI SEP 27 2024 Rain abounds with generally IFR conditions observed at TAF issuance time due to low clouds with winds peaking in the 25 to 30 kt range. A rumble of thunder remains possible through the afternoon, but confidence in it affecting any particular TAF site remains too low to mention. Winds will average from the east to northeast at 10 to 20 kts sustained, with gusts up to around 30 kts initially before picking up dramatically through the late morning hours. Winds will then ramp up to northeast as high as 20 to 30 kts sustained before beginning to trend to the southeast to end up with gusts in the 35 to 50 kts range through at least 22Z. LLWS will also be a threat for most of the day, with winds as high as 60 kts a thousand feet or so off the sfc blowing from the east to northeast initially - trending toward southeast after 18Z. Things settle for the latter part of the aviation period, as Helene`s influence wanes, but low clouds will likely remain in place for most locations. && .JKL WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 8 PM EDT this evening for KYZ044-050>052- 058>060-068-069-079-080-083>088-104-106>120. Flood Watch until 8 PM EDT this evening for KYZ050>052-058>060- 068-069-079-080-083>088-104-106>120. && $$ UPDATE...JP SHORT TERM...GREIF LONG TERM...DJ AVIATION...GREIF