textproduct: Louisville

KEY MESSAGES

* Patchy frost is expected again tonight, with a low (20%) chance of localized freezing conditions in a few low-lying, rural areas. To protect tender vegetation, cover or bring plants inside. * High confidence (near 100% chance) in dry weather all week. Ongoing drought conditions, most pronounced over southern Kentucky, will worsen in response.

* Mild, Fall-like weather will continue this week with warm afternoons (upper 60s to mid 70s) followed by crisp mornings (upper 30s to mid 40s).

DISCUSSION

Issued at 139 PM EDT Sun Oct 18 2026

*** PATCHY FROST AGAIN TONIGHT? ***

Early Sunday afternoon, high pressure was sprawled across the Mid- Atlantic and Ohio Valley, maintaining tranquil weather over the local area. Temperatures, in the low 60s at 130pm, will warm another 1-3 degrees before sinking like a rock tonight as clear skies and light-calm winds make for excellent radiational cooling. Taking this together with dewpoints in the upper 20s to mid 30s, we suspect low temperatures tomorrow morning - particularly in rural and valley locations - could end up on the low end of guidance. HREF probabilities for temperatures under 37 run 30-60% in valley locations especially near and east of the I-65 corridor, with a few splotches of localized 20+% probabilities for freezing temperatures in these areas as well. Given (1) the growing season hasn't officially ended yet and (2) the potential for lows to overachieve (be on the low end of the ensemble spectrum), we decided to issue a Frost Advisory for most of the area in coordination with neighboring offices. In addition, we added "patchy" frost to the forecast for much of the County Warning Area (CWA), and "areas" of it in the river valleys.

*** DRY AND MILD THIS WEEK ***

Tomorrow will be slightly warmer and drier as forecast soundings suggest we mix a bit deeper, to nearly 850mb (vs ~875-900mb today). Highs are slated to approach 70 across most of the area, which is near normal for October 19th. Like today, temperatures will drop quickly with the loss of incoming solar radiation ("insolation") after sunset, with lows Tuesday morning anywhere from the mid 30s in rural, low-lying areas to the low 40s in urban areas.

Tuesday and onward, we rinse and repeat as the large-scale weather pattern remains rather similar with weak ridging across the central US and a cutoff low aimlessly drifting in the western Atlantic. The one caveat might be a few mid-high clouds Tuesday into Wednesday as deterministic models show a weak shortwave drifting southeast through the region. Considering this feature will (1) rain out a lot of its (Pacific) moisture in the high terrain across the Great Basin and (2) dry via downsloping in the High Plains, we're not expecting any rain with it, but the clouds may keep us from radiating quite as much and consequently limit frost potential Tuesday night. In addition, they may keep us from mixing quite as deep on Tuesday. Still RH values are forecast to drop into the upper 20s to mid 30s each day through at least Tuesday, which would raise fire weather concerns if we had any wind; thankfully, winds should generally stay less than 10 mph given continued surface high pressure over the area.

The pattern becomes increasingly amplified late week into the weekend, as the central US ridge gets squeezed between a trough over the Northeast and another one lifting out of the Great Basin. This "omega block," with the upper ridge centered over the Mississippi Valley, will keep conditions dry and slightly warmer than normal right through the weekend. The only impact we can ascertain during this extended period would be worsening drought conditions due to this continued dry weather. Climatologically, normal would be just under 1 inch of rain per week during mid-late October, so we'd need to see at least that much (ideally more) to reverse the ongoing drought, which as of last week's USDM update was classified as D1 "moderate" across southern Kentucky and D0 "abnormally dry" across most of the remainder of the state.

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 139 PM EDT Sun Oct 18 2026

Easterly winds around 5-7 kt will go light and variable early tomorrow morning, while clear skies continue throughout the forecast period.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Frost Advisory from 1 AM EDT /midnight CDT/ to 9 AM EDT /8 AM CDT/ Monday for KYZ024-025-027>043-045>049-053>057- 062>067-074>078-081-082. IN...Frost Advisory from 1 AM EDT /midnight CDT/ to 9 AM EDT /8 AM CDT/ Monday for INZ076>079-083-084-089>092.