492 FXUS63 KLMK 260655 AFDLMKArea Forecast Discussion National Weather Service Louisville KY 255 AM EDT Fri Sep 26 2025
.KEY MESSAGES...
* Areas of Dense Fog developing this morning, especially near bodies of water and recent heavy rainfall. Use caution for the morning commute.
* Mostly dry with warming temperatures expected this weekend.
* Uncertainty for next week, but the current forecast is for mostly dry and warm.
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.SHORT TERM /THROUGH TONIGHT/... Issued at 253 AM EDT Fri Sep 26 2025
Overall a much quieter night than the past several, however this quiet pattern will lend to a different forecast hazard through the pre-dawn hours into sunrise. Several obs have inconsistently bounced around between 1/4SM up to 5SM through the the first part of the overnight, however starting to see a bit more consistency in obs below 2 SM. In other words, conditions appear to be steadily deteriorating from a fog standpoint, especially near the river valleys. Current thinking is that we may end up needing a Dense Fog Advisory before the morning is over. Not quite there yet as we don`t have widespread 1/4SM on obs or on area webcams just yet. Thinking the most likely area will be in a half moon around the eastern/southern portions of the CWA. It is a pretty good type of setup for dense fog where you`ve had recent heavy rainfall, followed by a mostly cloudy day that limits mixing, then late clearing in time for good radiational cooling. We`ve checked all those boxes, and the only limiting factor has been some dry advection in from the NW. At the moment, this is why it feels likely we won`t need a headline up in those area. Will continue to monitor, and be quick to pull the trigger if obs continue to deteriorate.
Otherwise, look for a quiet day into tonight for all but our far SE Lake Cumberland region. Here, the upper trough axis closes off into a weak upper low, and may have enough lingering moisture/triggering for an isolated shower or storm around peak heating. Will continue to carry a 20 pop down there with everyone else dry. Highs today reach into the upper 70s to around 80. Lows tonight look to dip into the low and mid 50s for most, and will likely have another opportunity for at least some river valley fog, if not more.
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.LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 253 AM EDT Fri Sep 26 2025
Saturday - Monday...
Weak upper closed low will wobble/meander just south/southeast of our area through the weekend. Meanwhile, upper ridging will steadily build in from the central CONUS to the Mississippi River Valley, extending influence into our area. This feature will act to keep us dry and trend us increasingly warm. The one exception to dry will be a slight chance of a diurnal shower around the Lake Cumberland region either afternoon/evening. Highs on Saturday will trend slightly above normal to the upper 70s and low 80s, then values warm a bit more for Sunday and Monday more solidly into the low 80s. Look for pleasant overnight lows in the 55 to 60 degree range.
Tuesday - Thursday...
Confidence will remain low for now with respect to the early/mid week time frame thanks to some interesting tropical activity. Focus will be on a likely pair of tropical systems, one of which has a good shot to move into the Carolinas before heading toward the central Appalachians. This feature would interact with, and likely absorb, whatever is left of our weak upper low. The end result could be rain chances associated with the decaying former tropical cyclone, but too many scenarios and complexities associated with this pattern than to say much more than some low end rain chances. In addition, a tropical system approaching from the SE can sometimes encounter a downslope drying component with low level jetting perpendicular to the Appalachians. This dry effect, combined with an already dry upper ridge in place could gobble up a good amount of the moisture. For now, the forecast will remain optimistically dry (outside of 20% chances for our eastern CWA border) with highs in the upper 70s and low 80s.
Worth noting that another scenario is that the more western tropical system will interact, possibly a Fujiwara dance, with its eastern counterpart, and stay out to sea.
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.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 132 AM EDT Fri Sep 26 2025
Quiet night expected with mostly clear skies and light or calm winds. The big issue will be whether fog develops, and how dense it will become. Looking at afternoon crossover Ts for BWG/LEX/RGA, it would suggest that some pretty impactful (possibly dense) fog is likely in the pre-dawn hours through sunrise. As a result, hit the fog mention a little harder with this issuance.
Fog clears mid morning on Friday with mostly sunny skies and a light NNE wind taking hold. Looks like there could be a few cu around 5-6 k feet in the afternoon.
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.LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None.
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SHORT TERM...BJS LONG TERM...BJS AVIATION...BJS
NWS LMK Office Area Forecast Discussion