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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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604 FXUS63 KJKL 181055 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 655 AM EDT Sun Aug 18 2024 .KEY MESSAGES... - Below normal temperatures are expected today through Wednesday behind a cold front passage today. - Showers and thunderstorms will remain possible today and Monday, especially in the afternoon and early evening, with a drying trend for Tuesday into Wednesday. && .UPDATE... Issued at 655 AM EDT SUN AUG 18 2024 Early morning update to the forecast to incorporate developing showers across our northern zones. Showers in northwest flow are beginning to kick off a little earlier than expected. In general, the probability of showers and thunderstorms will be increasing through the morning. Brought hourly temps in line with current surface observations as well. No other significant changes to the forecast package at this time. Updated zones and grids have been issued. && .SHORT TERM...(Today through Monday) Issued at 432 AM EDT SUN AUG 18 2024 Aloft, eastern Kentucky will be under a northwest flow regime through the period. Great Lakes mid/upper level low begins to fill and opens up into a trough as it begins to lift northeast out of the region. Short wave energy will be dropping into the base of the mean trough centered over the Midwest today. At the surface, a cold front is current poised to move through eastern Kentucky and is expected to be southeast of our forecast area by around mid-day. There is good model agreement with respect to this timing, both among operational models and CAMs. Sensible weather features the beginning of a cool spell with afternoon high temperatures some 5-10 degrees below our normal mid 80s. However, initially our area will have to deal with the threat of rain through the period, mainly in the afternoon and early evening during peak heating. If forecast soundings and profiles are correct, lapse rates are not great above the first ~4-5 kft of the boundary layer, but the column aloft is cold enough that any convection that does fire will have the opportunity to develop into thunderstorms, especially today. MLCAPES climb to between 750-1250 J/kg during peak heating this afternoon. Bulk shear is weak across the area today and Monday, on average less than 20kts. Also, by Monday afternoon, there is a mid level cap that begins to form as ridging begins to spread over the region. In general instability showers and thunderstorms can be expected during the afternoon hours over much of the forecast area today and mainly over our central and southeastern zones Monday. Convection is expected to unorganized and discrete. .LONG TERM...(Monday night through Saturday) Issued at 432 AM EDT SUN AUG 18 2024 This particular long term forecast package is defined by clearer skies and cooler temperatures than what we have witnessed here in Eastern Kentucky as of late. This drier and cooler air will advect into the region via northwesterly/northerly flow throughout the atmospheric column on the backside of the now-ejected upper level low pressure system that caused this weekend`s active weather. At the surface, a high pressure system will drop into the Great Lakes Region from Canada. Together, these features will work to instill a modified continental polar airmass over the forecast area. This notion is confirmed by modeled NOAA HYSPLIT back trajectories for next week, which suggest that this airmass originated in Northwestern Ontario/Saskatchewan. This particular piece of forecast guidance also suggests that the air will be subsiding (sinking) as it approaches the Ohio River Valley, which reaffirms the notion that this airmass will be dry. As such, skies should be mostly clear next week, although the potential for some Canadian wildfire smoke to advect into the air aloft will need to be monitored closely in the coming days. In short, fall-like sensible weather should settle into Eastern Kentucky on Monday night and stick around until Thursday, when the surface high shifts east and southerly return flow begins to slowly reintroduce warm, moist air into the column. Under clear skies, expect well-defined ridge-valley temperature splits and perhaps the formation of patchy valley fog on Monday, Tuesday, and Wednesday evenings. In low-lying areas, overnight lows could drop down into the upper 40s on Tuesday and Wednesday, whereas ridgetops will see MinTs in the lower 50s. Afternoon highs will be climatologically cooler than normal for this same time period, with temperatures staying in the 70s across the entire area on these dates. By Thursday, a warming trend will emerge, and afternoon highs will incrementally increase into the 80s and then perhaps the lower 90s in the Bluegrass by Saturday afternoon. Both low temperatures and dewpoints will recover into the 60s in this same time frame, and cloud coverage should subtly increase in response to these warmer temperatures. Precipitation chances, however, remain suppressed below 10 percent for the entirety of this week`s forecast. Thus, no hazardous weather is expected at this point for the Monday night to Saturday timeframe. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) ISSUED AT 228 AM EDT SUN AUG 18 2024 Showers and thunderstorms continue to wane across the area. Main forecast challenge will be residual moisture and the development of low stratus and at times fog. MOS guidance is generally optimistic, especially with VSBYS. However, LIFR to MVFR CIGS can not be ruled out at times. Regional satellite does show some patchy, transient low stratus going through cycles of developing and dissipation across the area. In addition, ensemble solutions show a fairly high probability (60-80%) of at least LIFR CIGS at times through 13-14Z. Ensemble mean VSBYS also drop to between 2-5 miles at times, especially across the north where there is a bit more clearing and thus a better chance for the development of patchy fog. Thus the potential for lower stratus, and at times some light fog will exist through the remainder of the overnight, or until the surface front clears the area. Currently the surface boundary is positioned roughly from KFGX to KFFT, to just south of KSDF. It will take from now until around 15Z for the surface front to move completely southeast of the forecast area. Winds will be light, around 5 kts from the west, but will veer out of the west-northwest through the day at 5-10 kts. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...RAY SHORT TERM...RAY LONG TERM...MARCUS AVIATION...RAY