textproduct: Louisville

KEY MESSAGES

* Afternoon relative humidity values will drop into the 20 to 35 percent range each day through Friday, but light winds (generally less than 15 mph) should limit fire weather concerns.

* Remnants of Tropical Storm Isaias will bring widespread rainfall to the region over the weekend. While most areas will benefit from this rain given the ongoing drought, there is a low chance that localized rain amounts exceed 3 inches to result in flash flooding.

DISCUSSION

Issued at 123 PM EDT Wed Oct 7 2026

*** WARM AND DRY INTO SATURDAY ***

Early Wednesday afternoon, west-northwest flow aloft was present over the local area between a ridge across the Great Plains and upper level trough over the Great Lakes. Like yesterday, deep mixing will add a couple more degrees to surface temperatures for highs in the upper 70s (east) to low 80s (west), though it'll still feel mild for most - especially in the shade - as low relative humidity keeps apparent, or "feels like," temperatures a couple degrees below actual air temperatures.

A decaying cool front will sink south and wash out over southern Indiana tonight, while in its wake surface high pressure will shift east from the Midwest to the Appalachians tomorrow into Friday. This will result in gentle northeast winds which will keep the airmass dry and perhaps 1-2 degrees less warm during the day tomorrow. In addition, if we lose the wind overnight into Friday morning, rural low-lying areas may once again dip into the upper 30s or at least low 40s - though the probability of widespread frost is very low (less than 2%).

Meanwhile, tropical storm Isaias will be brewing over the Gulf, and on Friday it should start to lift northwards towards the coast as it merges with a cutoff low over Texas/Louisiana. In response, the local area will see strengthening easterly flow Friday into Saturday, by which time some guidance shows a notable downsloping effect in the pressure gradient field off of the Appalachians. While this would have a drying effect, the abundant tropical moisture accompanying Isaias' remnants may offset this - though perhaps not until late Saturday, sparking at least low concerns over fire weather early in the day. While confidence is much higher in daytime RH values of 20-30% (locally lower) on Friday, winds should be light enough (gusts generally less than 15 mph) to minimize any fire weather concerns despite minimum afternoon 10-hour fuel moistures of 7-9%. All the while, the continued dry and seasonably warm weather will result in expanding and worsening drought conditions.

*** TROPICAL REMNANTS TO BRING BENEFICIAL RAIN(?) BY SUNDAY ***

As what's left of Isaias lifts toward the local area, strong diffluence and synoptic lift in the right entrance region of the trough should lead to an expansive rain shield which models suggest will likely (80% chance) enter the local area sometime between early Saturday afternoon (LREF 10th percentile onset time) and around dawn Sunday morning (LREF 90th percentile onset time). The overnight Saturday night into Sunday morning timing (given by the LREF mean) of the heaviest bands of precipitation associated with the tropical remnants suggests diurnally-driven instability will be very low - limiting the risk for tornadoes. However, the screaming wind fields accompanying this system raise concerns about locally strong winds should any heavier showers/storms mix them down to the surface. In addition, the strong directional wind shear on the east side of the surface low - which the National Hurricane Center (NCH) suggests will track near or west of the local area - suggests that should its northward trek speed up, we'll have to watch southern Kentucky for brief spin ups as GFS soundings show strongly curved hodographs featuring 500-1000 m^2/s^2 0-3km SRH Saturday evening. Fortunately, the global models, whose resolution is too coarse to capture convective features, suggest gradient winds associated with this system are unlikely to be problematic with EPS (European ensemble) mean peak gusts around 20-30 mph Saturday night into Sunday; it wouldn't be surprising to see this increase, knowing how models struggle to resolve tropical systems, so we'll keep a close eye on it as we get closer to the weekend.

The main story with this system will be the rainfall, though amounts remain a source of considerable uncertainty with National Blend of Models (NBM) 25th-75th percentile 48-hour rainfall totals through 8am Monday morning ranging from roughly 0.75 to 2.25 inches across the local area. This means that, at any given location, the chance of total rain amounts falling either inside or outside of this range is 50% - that's a lot of spread. Given the antecedent dry conditions, RFC 6-hour Flash Flood Guidance (FFG) - or the minimum amount of rainfall required to induce flooding - is running 3.5-4.5 inches, which is around NBM's ensemble max for the whole event. This would indicate our flooding risk is low, though not negligible, since the global models comprising NBM won't resolve convective processes which could enhance rainfall rates; any flooding would likely be confined to a localized band of heavier rain - fueled by a 60-75 kt 850mb LLJ Saturday night.

AVIATION /18Z TAFS THROUGH 00Z FRIDAY/

Issued at 123 PM EDT Wed Oct 7 2026

VFR conditions will prevail throughout the forecast period. Southwest winds around 7-10 kt with a few gusts to 17 kt this afternoon will ease this evening and veer to a northeasterly direction tonight into Thursday morning.

LMK WATCHES/WARNINGS/ADVISORIES

KY...None. IN...None.