049 FXUS63 KJKL 160335 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1135 PM EDT Sat Oct 15 2022 .UPDATE... Issued at 1135 PM EDT SAT OCT 15 2022 The current forecast remains on track so have mainly just added in the latest obs and trends for the T/Td/Sky grids. These updates have been sent to the NDFD and web servers along with a freshening of the zones and SAFs. UPDATE Issued at 840 PM EDT SAT OCT 15 2022 00Z sfc analysis shows a frontal boundary stalled over the southern portion of the CWA with a couple showers drifting east along the Tennessee border. Skies are mostly cloudy to the far southeast with a weak area of high pressure for our middle counties keeping the skies clearer there, but more clouds are inbound from the northwest. Expect these to limit the valley fog later tonight as well as helping to mix out the cooler sheltered spots after midnight. In the meantime, readings vary from the mid 50s in the eastern valleys to the the mid 60s on the ridges. Dewpoints have come up into the mid and upper 40s this evening, while the winds have decreased to generally 5 mph or less and became variable. For this update, have mainly added in the latest obs and trends for the T/Td/ Sky grids. These updates have been sent to the NDFD and web servers. && .SHORT TERM...(This evening through Sunday night) Issued at 442 PM EDT SAT OCT 15 2022 The large longwave troughing remains in place across much of the central and eastern Conus. The main low pressure system helping to drive this trough is over Ontario, with a secondary low rotating around it, currently across the Lower Great Lakes region. From this secondary low, a cold front has developed and is draped Southwestward. This cold front made its way across eastern KY during the morning and afternoon hours, and is now exiting east of the state. Most of the moisture associated with this system remains contained closer to the low and the northern extent of the cold front. Therefore, we really aren't seeing any precip across the CWA, as expected. The only way to know there is a front moving through is the strong mixing and breezy conditions that should begin to let up, and the decrease in dew points as drier air moves in behind the frontal passage. This front will then stall out just south and east of the state as we head into the evening, slowly dissipating throughout the overnight. Meanwhile, another offshoot low will develop in the upper level trough, rotating around the main low. This next low will also result in a cold front which is expected to drop SE towards the Ohio Valley during the overnight. With the weakening stationary boundary located just south of KY, and increasing SW flow ahead of this next frontal boundary, this will help to advect in moisture and also keep temperatures a bit more mild and uniform across the region as increasing clouds prevent best decoupling in the valleys. Unlike today's front, there will be enough moisture advection ahead of this next front to prompt precip potential. Pops will begin increasing in the early morning hours from the SW, quickly overspread and increasing across much of the CWA through the daytime hours. Models all show best pops across the southeastern portion of the CWA. Also, can't rule out enough lift and instability ahead of this front to prompt a few rumbles of thunder. However, with temperatures only topping out in the upper 60s, not expecting anything strong or severe. SPC also only has us in the general thunderstorm category, and only for the far SE portion of the state/CWA. Pops will exit east of the state throughout the evening and the first part of the overnight, as the front shifts the same direction. Again, strong NW flow in place, thanks to the upper level mega trough, will quickly usher in cooler and drier air. Clouds should generally clear out overnight, however can't rule out some lingering bkn to ovc skies in the far SE thanks to upslope flow. Overnight temperatures will be cooler, up to 10 degrees lower in some locations compared to tonight. However, it really depends on how quickly the cloud cover exits as to how far the temperatures will drop. .LONG TERM...(Monday through Saturday) Issued at 401 PM EDT SAT OCT 15 2022 Key Points: * Breezy and turning much colder on Monday * Air mass more typical of November/early December follows for Tuesday into Thursday * Daily record minimum highs and lows likely to be approached/broken at LOZ and JKL. * Growing season ending hard freeze certain during this timeframe. * Temperatures recover to slightly below normal by Friday and Saturday The 15/12z model guidance shows an anomalously deep low over/near Lake Michigan at the start of the period Monday morning. While models are in good agreement on the location is high, there are still several 10s of meters of spread on the depth of the low. This low will shift eastward to near/over the Ottawa Valley by 12z Tuesday while an embedded strong vorticity lobe drops across the Ohio Valley. Moderate to strong west to northwest 850 mb CAA will prevail through the first 24 hours of the period. GEPS/GEF/EPS show 850 mb temperatures falling to -6 to -8C by Tuesday morning. The strong CAA will be sensibly evident on Monday -- temperatures will peak in the 50s during the midday before holding steady or falling during the afternoon. Even the 925 mb temperatures will drop below 0C Monday night, indicating the likelihood for an advective freeze over the ridges and mountains. The arctic air mass is very dry thus causing dew points to fall off into the teens on Monday and likely remaining in the teens Monday night. The extreme dryness of the air mass is evident by model PWATs falling to around 0.15 inch or even lower with cloud-free skies for much of the night. There will still be a weak surface pressure gradient. However, any location which is sheltered from the weakening northwest flow will likely decouple and there will be plenty of room for temperatures to radiatively cool. In fact, the 10th to 25th percentile NBM minimum temperatures on Monday night range from the upper teens to lower 20s, a possibility in some of the more sheltered valleys. Anticipate mid to upper 20s in most locations and perhaps a few lower 30s in the warmest thermal belts. If any location somehow escapes a killing freeze on Monday night, there will be more opportunities on following nights. As winds turn more more northwesterly early Tuesday morning, much of the guidance shows the coldest 850 mb temperature coinciding with an uptick in the dew points, likely indicative of some Great Lakes moistening. (The temperature difference between the Lake Michigan and 850 mb will more than exceed the 13C difference needed to elicit a lake-effect response.) Moisture plumes sufficiently deep for notable lake-effect precipitation should remain off to our northeast over Ohio West Virginia and up into the Lake Erie snowbelt. However, for eastern Kentucky snow-lovers, there appears to be a low but non- zero potential for a few locations, mainly far east, to see a novelty flake or two. The 12z model suite time heights in the Canadian and ECWMF both hint at a pocket of RH exceeding 80% between 925 and 775 mb with the core of the coldest surge on Tuesday morning, along/just ahead of the potent vorticity lobe. Temperatures at the top of this layer appear marginally cold enough for ice crystals (-7 to -10C). There will also be some weak lifting both from the positive differential vorticity advection and northwesterly upslope flow. However, the lowest several hundred meters should still be quite dry, likely evaporating most hydrometeors that happen to fall. Even so, if the modeled low- level flow pattern materializes, a few stray flakes may slip through the near surface dry layer and be observed at ground level. The morning hours would be the favored time and the higher eastern ridges the favored location(due to a shallower dry layer at the surface) for a passing flake. The low-level flow may briefly become northerly enough for some of the Lake Michigan moisture plume to brush the Tug Fork of the Big Sandy later in the day as well, perhaps offering a second chance for a stray flake near the KY/WV border. Given nil impacts and low confidence, forewent any mention of flurries in the forecast grids. Otherwise, look for a cold and blustery day on Tuesday with plenty of clouds and some sun. It will be cold with highs only reaching into the 40s at lower elevations and remaining in the 30s above 2,500 feet. Once the 500H heights bottom out over the Commonwealth on Tuesday afternoon/evening, the upper low then shifts back northward toward the James Bay on Tuesday night to Wednesday night, allowing heights to gradually recover over the Ohio Valley. A shortwave trough rides around the retreating low and across the Ohio Valley on Thursday afternoon/night. It does appear that shortwave ridging returns, at least briefly thereafter, though model agreement deteriorates considerably on Friday and Saturday. At the surface, high pressure drops south from northern Canada to over the Lower Mississippi Valley through mid-week. While not cresting overhead, we will still be close enough to come under the high's influence on Tuesday night and more so for Wednesday and Wednesday night. Lows in the 20s are probable again for all locations which experience clear skies on Tuesday night. Lake-enhanced cloud cover may linger close to the WV border and keep temperatures closer to freezing. The 850 mb temperatures hold below 0C on Wednesday, only supporting highs in the upper 40s to lower 50s. This will set the stage for another widespread radiative freeze on Wednesday night with lows again falling into the 20s for all locations, except near 30 on the thermal belt ridges. On Thursday, the next upper level disturbance drops in from the northwest; but, with little moisture to work with, expect nothing more than increased cloud cover Thursday afternoon and night. The high pressure over the Lower Mississippi Valley lifts northeast and elongates along the Atlantic Seaboard on Friday and Saturday bringing a southwesterly return flow and moderating temperatures to the Commonwealth. Expect highs in the mid to upper 50s on Thursday, lower to mid 60s on Friday and mid to upper 60s on Saturday. Nighttime lows moderate into the mid 20s to mid 30s on Thursday night and in the 30s to lower 40s for Friday night. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) ISSUED AT 815 PM EDT SAT OCT 15 2022 Under variable cloud cover the earlier breezy conditions have settled with winds mostly variable at around 5 kts, now. Upper level clouds will increase ahead of an approaching cold front overnight. This front is set to pass through Kentucky during the day Sunday and as a result better shower chances will overspread the aviation forecast area from west to east, generally around 15Z at KSME and KLOZ. Overall, this will be a weak front and impacts from the showers will be minimal. Have held with no thunder chances at the TAF sites through 00Z Monday, though it cannot be ruled out in the afternoon for locations generally south and east of the terminals. Winds will become predominately southwest again during the day Sunday, but remain between 5 and 10 kts with gusts staying under 15 kts. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...JMW LONG TERM...GEERTSON AVIATION...JMW/GREIF