textproduct: Louisville

KEY MESSAGES

* Spotty showers continue through tonight, but severe weather is not expected.

* Heat and humidity begin to increase tomorrow, with temperatures near 90F and heat index values close to 100F.

* Max afternoon heat indices could be in the triple digits for some by early next week, but this remain conditional on any thunderstorm chances.

* A round or two of stronger thunderstorms is possible Sunday night and again Monday and/or Tuesday, however confidence remains low on the finer details.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 351 PM EDT Sat Jul 25 2026

Isolated light showers continue to pass over the area this afternoon due to weak isentropic lift over a stationary boundary to our southwest and a subtle upper level disturbance riding through the flow. An isolated to scattered shower chances will linger through the rest of the afternoon and into the evening hours, and perhaps a low end risk for a thunderstorm too. However, mostly cloudy skycover and the rainy conditions so far today has limited our heating and destabilization, so confidence in any thunderstorms for the rest of today remains low. Temps have been limited to the low 70s for a large portion of the area, though south-central KY has slightly better heating with upper 70s so far. Regardless, forecast temps have been knocked down a few degrees for the rest of today to match up with the current obs. A few isolated showers or a storm remain possible overnight as well, but certainly not a washout by any means. There will be lingering lower level moisture, resulting in a decent signal for low stratus and patchy dense fog across the area for the early morning hours.

Heat and humidity increase tomorrow as the upper ridge continues to build across the western US. Dry weather is expected tomorrow as we lack a trigger, with highs climbing into the upper 80s and lower 90s. Dewpoints start creeping back into the 70s, which will yield heat indices near 100 tomorrow afternoon. By Sunday night, there could be a convective cluster that develops over the Midwest, then dives southeast due to the NW steering flow and could impact our area Sunday night or early Monday morning. The 18z HRRR weakens this cluster Sunday night as low level stability elevates any overnight thunderstorms. However, additional waves may be possible into Monday.

LONG TERM /MONDAY THROUGH SATURDAY/

Issued at 351 PM EDT Sat Jul 25 2026

===== Monday - Tuesday ======

Forecast uncertainty is a concern for the first half of the upcoming week due to weak forcing and potential MCS activity, which is often handled poorly by deterministic guidance. Additionally, the temperature forecast for the time frame could be derailed if we do see thunderstorm activity, so there are multiple conditional forecast parameters at play for the beginning of the long term period.

Strong upper ridging will continue to have a tight hold over the western US, with downstream troughing across the eastern US, which places the Ohio Valley in deep NW flow aloft. A more amplified shortwave looks to pivot through the NW flow Monday and Tuesday, which will likely trigger some thunderstorm development across the Great Lakes and Upper Midwest region. However, due to the orientation of the steering flow aloft, will expect any thunderstorm complexes that develop will take a southeast dive into the lower Ohio Valley. There remains considerable uncertainty regarding if the forecast areas would even be impacted by these passing complexes, but SPC does include a Marginal and Slight risk for Monday across majority of the area. Both the GFS and ECMWF indicate a second MCS cluster moving in from the north late Monday morning, which would ultimately arrive before the peak of daytime heating and greatest destabilization. If that would happen to play out, it would most likely derail the temperature forecast for Monday afternoon, which currently has highs in the mid 90s and heat indices over 100F. If that MCS does not occur in our area, then there is high confidence that a Heat Advisory would be needed as we should see heat indices reach the 103-110F range.

Majority of the thunderstorm activity is expected remain to our north through this time frame due to the mean 700-300mb flow, though our north and northeast sections of the forecast area will be the most susceptible to being clipped by passing complexes. As mentioned in the previous discussion, we typically still like where SPC drew the outlook for Monday, but continue to advertise this being a conditional threat.

If we end up staying mostly dry for Monday and Tuesday, forecast temps could be in the mid 90s again for Tuesday, and possibly another day of Heat Advisory apparent temps. This is also conditional on how the thunderstorm chances play out.

===== Late Next Week =====

An upper shortwave looks to deepen into a low over the Northeast for Wednesday and into late next week, which will likely lead to pulling any substantial moisture off to the east and leaving us dry for Wednesday and Thursday. Temps also may decrease slightly back into the 80s for this time. There are signs that the upper ridge may finally begin to weaken by late next week, though we remain in general NW flow aloft all of next week.

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 139 PM EDT Sat Jul 25 2026

Scattered light showers will continue across the region, bringing brief and limited impacts to the terminals. We'll eventually see these light showers shift off to the east by tonight, but low stratus looks to blanket the region by tomorrow morning. Patchy dense fog will also be possible and could reduce vis for several hours tomorrow morning. We'll see gradual improvements to the forecast toward the end of the period.

LMK WATCHES/WARNINGS/ADVISORIES

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