textproduct: Louisville

KEY MESSAGES

* Strong to severe thunderstorms are likely on Tuesday. Damaging wind is the main threat, but large hail and tornadoes are also possible. Heat indices could reach 105 in parts of central Kentucky outside of storms Tuesday afternoon.

* Calm weather moves in with cooler than average highs for Wednesday through Friday this week.

SHORT TERM /THROUGH TONIGHT/

Issued at 356 AM EDT Mon Jul 20 2026

This morning is beginning with patchy fog and low stratus over south central Kentucky from all the moisture from yesterday's rain. Improvement should begin shortly after sunrise as we begin to warm, but it could take awhile for all areas to clear and see the sun.

An upper ridge with a closed upper high remain over the western United States. East of this high, the stronger northwest flow remains north of the Lower Ohio Valley before reaching an upper trough axis near the Atlantic Coast. Higher level winds actually drop south over us as anticyclonic winds turn to head back around the upper high. This is causing subsidence and mid-level stability. At the surface, a weak stationary front remains near south central Kentucky, but low level winds remain light.

This afternoon and evening, we could see a few isolated showers and thunderstorms as temperatures warm into the upper 80s to low 90s. Moisture remains high with precipitable water values between 1.5 to 2" throughout most of central Kentucky, but moisture drops lower north into Indiana, reducing shower chances. Severe weather isn't expected as updrafts will likely struggle with the mid-level inversion.

Tonight, expecting a quiet night as light southerly winds remain under mostly clear to partly cloudy skies. Temperatures are expected to drop into the low to mid 70s.

LONG TERM /TUESDAY THROUGH SUNDAY/

Issued at 356 AM EDT Mon Jul 20 2026

Tuesday, as the upper ridge begins to amplify north, up the West Coast into Canada, the upper trough begins to dive south over the Atlantic Coast states. A closed off low is expected to develop within the trough and move east across Ontario with a nearby surface low that will slide into Quebec. It will be this low that will drag a cold front under northwest flow that stretches from the Upper Plains, through the Midwest, and into the Ohio Valley. This cold front will bring a chance for severe weather as it brings forcing and winds energy into an area with warm temperatures and lots of moisture.

Yesterday while this system was in reach of the global models, shear at all levels and instability levels looked very concerning. Low level winds were very backed. It looked more concerning than today's data in the global models and CAMs. Instability remains high with MLCAPE values over 2,500 J/kg. MUCAPE could be over 3,500 J/kg. Deep layer shear has dropped some with 0-6 km values now near 30-40 knots, but directional shear isn't looking as good. Pooling moisture ahead of the front could push precipitable water values back above 2".

Most of the model guidance is having this system push through as a single line with a developed cold pool pushing the line out with straight-line winds being the main threat, or maybe two waves will push through with one pushing through early in the day as the system surges ahead and another line coming through close to the front later in the afternoon or evening. If supercells were able to develop ahead of the line, large 2+ inch hail and tornadoes would become more likely. Low level lapse rates are also more stable today than yesterday, dropping DCAPE values from over 1,200 J/kg to 800 J/kg. This could also make it harder to get all the wind energy to the ground, reducing confidence in 65+ knot winds. The uncertainty in storm mode and lack of a clear threat led SPC to pull the "Enhanced" farther east to only the Bluegrass region in our area.

Heat could also be a concern as highs currently are forecast to climb back into the upper 80s to low 90s. With dew points in the 70s, reaching the upper 70s along the western edge of the CWA, heat indices could reach to 105 in Ohio and surrounding counties. Depending on how early the expected system moves in. This could impact high temperatures.

Behind the front, surface high pressure will bring CAA and cooler temperatures with highs in the upper 70s to mid 80s through Friday before the high passes to the east and WAA returns, brining mid 80s to low 90s back for the weekend. Dry weather is expect through the end of the workweek with low-end rain chances returning around the weekend.

AVIATION /12Z TAFS THROUGH 18Z TUESDAY/

Issued at 701 AM EDT Mon Jul 20 2026

The low stratus and fogging over parts of the region will slowly begin improving as temperature begin to warm. Isolated showers and thunderstorm will remain possible during the rest of the day, but the chance of anything hitting a TAF site is so low, it was left out of area TAFs.

LMK WATCHES/WARNINGS/ADVISORIES

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