textproduct: Louisville

KEY MESSAGES

* Mainly dry weather continues today, with isolated to scattered showers and storms (20-40% coverage) returning to areas east of I- 65 on Wednesday.

* Better shower and storm chances, along with summer warmth and humidity, will return later this week, peaking at 40-60% Friday into Saturday.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 259 AM EDT Tue Aug 4 2026

This Morning through Tonight...

Early this morning, mostly clear skies are present across most of the area, with the exception of an area of 5k ft AGL clouds located along the KY/TN border. These clear skies have allowed temperatures to cool into the 60s and low 70s as of 06Z, with temps likely to fall a few more degrees before sunrise. There is a modest signal for patchy fog in the 0Z HREF, with 20-30% of the members showing sub-3 mile visibilities in area river valleys between now and sunrise. However, 10-15 knots of flow near the top of the boundary layer should keep enough mixing to prevent significant amounts of fog formation.

Today, a cutoff low will continue to meander over the southern Appalachians with shortwave ridging passing atop the low across the Midwest. Nearer to the surface, inverted troughing should develop along the west side of the Appalachians, serving as a focus for low- level moisture and scattered shower/storm chances. This inverted trough may drift far enough to the NW to bring a couple showers into our "foothills" counties (Cumberland up to Clark) later this afternoon; however, only about 5-15% coverage is expected and almost all will remain dry. Otherwise, increasing 1000-850 mb thicknesses should allow temps to rise by a couple degrees area-wide today, with highs generally in the 84-88 range.

Tonight, the cutoff low and inverted sfc trough are expected to continue to drift to the north. This will try to bring more moisture into the area, which could support better chances for patchy fog or a stray shower, mainly east of US 127. For most, another mostly clear and comfortable night is expected, with lows a bit milder, ranging from the mid 60s to around 70.

Wednesday and Wednesday Night...

Broader mid- and upper-level troughing will continue to move closer to the Ohio Valley on Wednesday, with the cutoff low to our southeast becoming less well defined. Higher sfc dewpoints and PWAT values should continue to creep to the north, increasing the chances for afternoon showers and thunderstorms. There will be a west-to- east gradient in instability Wednesday, with warmer 700 mb temperatures and lower sfc dewpoints west of I-65 limiting CAPE. 0Z HREF median SBCAPE ranges from less than 500 J/kg west of I-65 to 1000-1500 J/kg closer to the I-75 corridor. As a result, the best chances for any afternoon showers and storms should be across the eastern CWA on Wednesday. The 0Z hi-res guidance generally has fairly isolated coverage, likely due to the lack of a well-defined forcing mechanism, so PoPs were lowered to 20-40% coverage mainly east of I-65. 0-6 km shear less than 10 knots should cause any convective activity to be disorganized, single cell storms with limited impacts. Temperatures Wednesday should be near or slightly above persistence, with highs in the mid-to-upper 80s.

Showers/storms should dissipate quickly after sunset Wednesday evening, leading to another mostly dry night. While decaying showers/storms to the NW of the area will approach southern IN early Thursday morning, it should fizzle as it outruns better forcing and instability. Lows Thursday morning should range from the upper 60s to the low 70s.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 259 AM EDT Tue Aug 4 2026

Thursday through Saturday Night...

From Thursday through the first half of the weekend, the synoptic pattern should feature ridging across the western CONUS and off the east coast, with broad, flat troughing extending across the Midwest. This should allow a sfc cold front to approach our area from the northwest Thursday; however, it is currently not expected to move through the area as the upper trough will lack sufficient amplitude. Diurnal shower/storm chances should increase as we head later into the week and into the weekend, with LREF mean PWAT values rising to 1.75-1.9" and SBCAPE values rising to 1500-2000 J/kg. While this should be sufficient for at least isolated to scattered rain chances, some medium-range progs (e.g., 0Z ECMWF) depict a couple mid-level shortwaves passing across the region Friday into Saturday. If these shortwaves pass during peak heating, greater concentration of showers and storms would be expected, though confidence in timing is still fairly low.

It still doesn't look like the potential for strong to severe storms will be all that great, with LREF mean bulk shear values of 15-20 kt more supportive of garden-variety convection. As the previous discussion mentioned, deep warm cloud (>= 0C) depths and seasonably high PWATs could support a few instances of heavy rain/flash flooding Friday into Saturday, as highlighted by the WPC Excessive Rainfall Outlook. Temperatures during the late week/early weekend should be fairly seasonable, with highs ranging from the mid 80s to the low 90s.

Sunday into Early Next Week...

As the previous discussion outlined, much of the forecast for late in the weekend through early-to-mid next week will depend on the interplay between western US ridging and troughing over Hudson Bay. WPC 500 mb height clusters show that a more expansive ridge and more zonal flow aloft would support a generally warmer and drier pattern as we head into early next week. In contrast, a more amplified pattern would bring the storm track closer to the Ohio Valley early next week, leading to generally cooler and stormier conditions. At this time, the forecast tends toward the former solution, though we'll continue to monitor trends over coming days.

AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 111 AM EDT Tue Aug 4 2026

VFR conditions should continue through the current forecast period as high pressure sits just to the northeast of the region. There should be enough NE flow within the boundary layer later this morning to limit substantial VIS drops from fog; however, can't completely rule out brief MVFR VIS at some sites. Later today, expect light NE winds between 5-10 kt backing toward the north in the afternoon. A scattered cu field should also develop around 5k ft AGL.

LMK WATCHES/WARNINGS/ADVISORIES

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