580 FXUS63 KJKL 072055 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 455 PM EDT Fri Oct 7 2022 .SHORT TERM...(This evening through Saturday night) Issued at 455 PM EDT FRI OCT 7 2022 Key Points: * Cool and dry air mass settles into the region tonight. * Widespread damaging frost and potentially killing freeze late Saturday night. 20Z sfc analysis shows the dry cold front just about exiting southeast Kentucky. This has brought a band of lower clouds, falling temperatures, and brisk northwest winds of 5 to 10 mph with gusts to between 15 and 20 mph to the area. Currently temperatures vary from the low 60s northwest to the low 70s in the southeast. Meanwhile, dewpoints range similarly from the mid 40s northwest to the mid 50s in the southeast right along the front. So far no sprinkles or light showers have shown up along the front so expect it to stay dry for our area as it departs. The models are in excellent agreement through the short term portion of the forecast. They all depict the large trough over the Great Lakes and points north swinging a sharpening node through the Ohio Valley tonight. This node pushes height falls through eastern Kentucky into Saturday morning with a weakening stream of mid level energy settling into the area for the first part of the weekend. By Saturday evening heights will rebound briefly as the node departs to the east, but the larger trough will continue to dominate into Sunday. The small model spread aloft through the short term supported using the NBM as the starting point for the grids with only some terrain based adjustments Saturday night and drier dewpoints for Saturday afternoon. Sensible weather will feature a cold night, post frontal, tonight, but mainly just a teaser compared to the very cold - near record - night that will occur Saturday night. The clouds will clear out earliest in the northwest with the winds settling there first, as well. This will set up radiational cooling in addition to the CAA allowing the valleys and open terrain for our western parts to have a good shot at picking up frost - accordingly a Frost Advisory is in effect for these locations. Further southeast, river valley fog will mitigate the frost in the coldest spots while slower to clear clouds and a stirring of the winds will likely limit the frost to patchy and just in the most sheltered valleys. Even drier air and little in the way of winds or cloud cover Saturday night will likely bring widespread frost to the area along with many valleys locations falling below freezing throughout eastern Kentucky. For this reason, a freeze watch is in effect into Sunday morning. Otherwise, Saturday proper will be on the cool and dry side with plenty of sunshine and low afternoon humidities. The main adjustments to the NBM grids were to add in more terrain effects for temperatures Saturday night and also drier dewpoints that afternoon. The PoPs continued to be near zero post frontal so did not need to make any adjustments as high pressure builds into eastern Kentucky through the short term. .LONG TERM...(Sunday through Friday) Issued at 358 PM EDT FRI OCT 7 2022 Key Points: * Widespread damaging frost and potentially killing freeze on Sunday morning. * Cool and dry air mass initially over the region moderates through mid-week. * Sharp cold front brings a next chance for wetting rainfall during the Wednesday night to Thursday night time-frame. The 07/12z model suite shows a high amplitude ridge-trough pattern over the continent. Deep troughing over the eastern CONUS will extend far south of its parent ~520 dam low centered near/over northern Labrador. Ridging prevails along the West Coast while a couple of embedded disturbances ride down the eastern side of the ridge. A potent ~528 dam low is riding across the Gulf of Alaska as is passes over the northern periphery of the western ridge. The regional surface analysis shows ~1027mb high pressure extending from the The Central Appalachians southwestward across the Commonwealth into the Lower Tennessee Valley. On Sunday - Tuesday, the Gulf of Alaska low will shift across the Canadian Arctic territories while sending an amplifying trough and preceding surface cold front dipping into the Northern Plains. Ahead of this, the trough over eastern portions of the continent will lift and be replaced by low-amplitude ridging extending from the Gulf of Mexico northward to the Hudson Bay. At the surface, high pressure will continue to linger over the Central Appalachians through Tuesday morning. This ridging aloft and and the surface will be rapidly be displaced off the East Coast on Wednesday and Thursday as the sharp and energetic upper-level trough and surface cold front plows across the Ohio Valley. There is still quite a bit of model spread as to the timing of the front as well as the intensity of the cold air to follow, but the 00z ensemble cluster analysis shows 68% of the ensemble members (mainly GEFS and EPS) favoring notable to significant negative 500-hPa height anomalies. The cold front will bring the only notable and much-needed chance for rainfall. The ECMWF ESAT shows PWATs recovering to 1 standardized anomaly above climo amidst southwesterly flow just ahead of the boundary. The progressive nature of the nature of the trough suggests a fast-moving cold front which likely precludes a soaking rainfall. With that said, the GEFS and EPS show a 70-90 and 80-100 percent probability of a wetting rainfall (0.10 inch or more), suggesting at least some limited relief from the increasingly dry soil and fuel moistures. The 12z deterministic ECMWF and GFS trended much more moist vs. the 00z suite - an encouraging trend. Instability appears limited with the boundary, a few hundred J/kg at best (enough for an isolated rumble), but shear will be more than ample. Opted to leave out thunder mention for now until timing is more certain. In sensible terms, look for a downright cold start Sunday morning with high pressure cresting overhead and very dry air aloft (PWATs will be around 0.25 inch or less). Temperatures at sunrise should be in the upper 20s to around 30 in many of the valleys and in the lower to mid 30s on the ridges. The daily record low temperature for October 9th at Jackson is 31F, set in 1989, while the daily record low at London is 30F, set in 1978 and tied in 2000. The record at Jackson is likely safe, but London's could be retied or possibly even broken. After that frosty cold start, look for a seasonably cool Sunday afternoon with highs in the 61 to 66 range. Other than these few degrees of temperature moderation, there won't be much change in the airmass, so another night of cold temperatures is in store for Sunday night into Monday morning. Widespread frost will be likely again for the valleys. Look for lows in the lower 30s valleys to mid and upper 30s on the ridges. Temperatures moderate a few degrees on both Monday and Tuesday while dew points creep up slightly each day. Look for highs to reach the mid 60s to lower 70s on Monday and well into the 70s on Tuesday. Nighttime lows will also moderate with mid 30s to mid 40s on Monday night and lower 40s to lower 50s on Tuesday night. Some patchy frost will again be possible on Monday night, mainly in the deeper Coalfield valleys. Clouds will increase on Wednesday ahead of the cold front and will yield to rain chances through the day on Thursday. Another shot of well below normal temperatures is likely by Friday. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) ISSUED AT 145 PM EDT FRI OCT 7 2022 VFR conditions will prevail through the period. A passing cold front is bringing scattered to broken lower end VFR clouds to the area from northwest to southeast in its wake. Clouds then diminish from northwest to southeast into this evening. South to southwest winds of around 5 kts will veer to the northwest and increase to 5 to 10 kts behind the boundary. Winds will then continue to veer to the north northwest by evening, generally dampening to around 5 kts under mostly clear skies and limited opportunity for just some light river valley fog. && .JKL WATCHES/WARNINGS/ADVISORIES... Frost Advisory from 2 AM to 10 AM EDT Saturday for KYZ044- 050>052-058>060-068-069-079-083-104-106-108-111. Freeze Watch from late Saturday night through Sunday morning for KYZ044-050>052-058>060-068-069-079-080-083>088-104-106>120. && $$ SHORT TERM...GREIF LONG TERM...GEERTSON AVIATION...GEOGERIAN/GREIF