textproduct: Louisville

KEY MESSAGES

* Isolated light rain showers move in from the NW today. Sprinkles to very little rainfall amounts expected for areas mainly along the I-165 corridor.

* Well below normal temperatures today, with highs only in the upper 50s to low 60s. These temperatures will be around 15 degrees below normal.

* Areas of frost likely Sunday morning across most of southern Indiana and portions of central Kentucky. A frost headline will likely be needed for Sunday morning.

* Weather pattern is expected to become more active next week. Several systems will bring widespread showers and possible thunderstorms to the region Tuesday through late Wednesday.

UPDATE

Issued at 1201 PM EDT Sat May 2 2026

Latest NBM run came in a little cooler in the eastern forecast area, increasing confidence in at least frost conditions for a majority of our area late tonight/early Sunday. After collaborating with neighbors will go ahead with a frost advisory for most of the region. Just outside of that will hit on patchy to areas of frost potential. Updated products coming out now.

Also updated the grids trending towards the latest HRRR and RAP runs for pops. Now have "silent" thunder PoPs for Louisville with those values under 15%, but not zero. Seeing some stronger returns upstream over southern IL and they would be on a trajectory more for our SW zones this afternoon. Will have to watch for graupel potential in the stronger cores on radar.

Issued at 909 AM EDT Sat May 2 2026

Current radar imagery shows some light returns upstream of the I-65 corridor. Light rain was reported in the last hour at KHNB and KSDF, but with 10 mile visibilities, likely just sprinkles and nothing measurable. Upstream satellite imagery shows a few bubbles embedded within the mid deck perhaps trying to get taller. Looking at model soundings for this afternoon and with an upper trough moving right overhead, still looks like a few of those bubbles may get tall enough to product some rumbles of thunder and with cold air aloft maybe even graupel. Best chance for that thunder is right along the I-64 corridor and points south...which is obviously close to some bigger events today in Louisville. Will keep watch on radar and hi- res model trends through the morning and afternoon and update as needed.

Otherwise the morning Frost Advisory was allowed to expire. Will be looking at the forecast for later tonight on the need to issue another Advisory at some point later today.

SHORT TERM /THROUGH TONIGHT/

Issued at 345 AM EDT Sat May 2 2026

It is an unusually chilly start to the day, with KY Mesonet obs showing temps down into the upper 30s and low 40s so far this morning. Despite some upper level cloud cover, the CAA and nearly calm winds have allowed these sfc temps to be nearly 10-15 degrees below normal. Frost Advisory for the Bluegrass runs until 13z later this morning.

For today, a sharp upper trough axis will pivot across the Ohio Valley later this afternoon, resulting in an increase in cloud cover for the afternoon and evening hours. This upper level trough is already developing some light precip across central IL early this morning, evident by regional radar mosaic. These light showers are being supported by a mid-level vort max that will be stretching across the area today.

===== Very Light Precipitation Today =====

The CAMs have a good handle on seeing light radar returns move across the Wabash Valley this morning, with the best chance for light precip occurring generally along and west of the I-165 corridor (aka the Natcher Pkwy) through this morning and afternoon. We'll have a good amount of low level dry air in place across the area today, which will lead to primarily virga, though some very light precip may be possible. Will keep Louisville in a 10% chance for today, and still think that the low level dry air will win out over any light returns that could sneak a bit more east than the CAMs suggest.

Otherwise, hi-res soundings indicate that we will have quite steep low level lapse rates this afternoon, and perhaps some weak instability. Given how low the freezing layer will be today due to the cooler temps, we could see some graupel development if we get a strong enough cell/updraft. However, dewpoint depressions near the sfc will be nearly 20 degrees, which could be unfavorable for graupel survival to the sfc. Additionally, this dry low level layer will substantially limit overall expected precip, with the HREF 90th percentile only suggesting 0.02" for western Louisville, though up to 0.15" along the I-165 corridor. With all this said, generally expect isolated light rain showers or sprinkles today, with any activity winding down by late afternoon across south-central KY.

===== Breezy Afternoon Winds and Cooler Temperatures=====

Due to the steep low level lapse rates, we'll likely see our NNW sfc winds pick up by the afternoon. Could see wind gusts up to 20-25 mph for the afternoon. This will keep us in a stronger CAA regime, with temps today only in the upper 50s and low 60s. This translates to max temperatures around 15 degrees below normal for May 2. Winds ease by the evening, with clearing cloud cover as the upper trough axis shifts east. This will lead to a favorable night for frost development, which is discussed in the Long Term section below.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 345 AM EDT Sat May 2 2026

===== Sunday - Monday =====

Sfc high pressure will be settling into our area on Sunday, which will support a brief dry spell and continuation of below normal temps. Sunday morning will feature cold temps due to a lingering cold air mass from Saturday, but will be amplified from good radiational cooling by calm winds and clear skycover. We'll likely see temps down into the 30s area-wide, with high confidence in widespread frost development for at least east of I-65. There is a bit more uncertainty on the extent of frost potential across south- central KY, but still expect at least some patchy frost. The need for a Frost Advisory Sunday morning is pretty much a slam dunk for areas along and east of I-65, but will allow the current Frost Advisory to expire later this morning before making a decision on if the entire area will be placed in a headline for Sunday. We are dry on Sunday, with temperatures eventually reaching the mid-60s by the afternoon. Should have a good amount of sunshine, but could begin to see some increasing clouds from the north by the late afternoon.

We'll be underneath NW flow aloft, and by Sunday night we will have a quick-hitting shortwave move across the Ohio Valley. We'll be located in a WAA zone ahead of an associated frontal boundary, with increase moisture transport into the area due to a warm conveyor belt of low-level jetting. This will support overnight showers and storms for our area. Model soundings show little to no instability present, with meager low level lapse rates, though with a LLJ overhead, should have higher shear parameters. Can't rule out some overnight thunder, but severe prob is low.

The upper flow will gradually flatten out on Monday across our area, but will see a deepening upper low north of the Great Lakes that will be responsible for spinning off several vorticity wings into the Ohio Valley throughout the day. This will support additional precip chances mainly across our north throughout the day, with a marginal severe risk north of our area across central IN. We'll continue to have a WAA pattern in place, so our temps will warm back into the 70s by the afternoon.

===== Tuesday - Late Next Week =====

The upper flow will amplify by Tuesday as a western US trough pivots toward the central US, which will open us back up to a persistent southwest flow regime. This pattern favors a higher moisture fetch from the Gulf into the region, with guidance continuing to show a narrow moisture transport plume stretching from eastern Texas to the the Ohio River on Tuesday ahead of an advancing cold front. Showers and storms are expected to increase in coverage throughout Tuesday as a cold front approaches the Ohio Valley, with PoPs peaking by Tuesday night. Model soundings indicate little to no instability, but plenty of shear given a LLJ overhead and ample moisture. NSSL ML guidance shows a weak signal for severe probs on Tuesday, but a slightly stronger signal for Wednesday. The cold front is expected to pass through on Wednesday, which will provide more forcing in a saturated airmass. Soundings also suggest some instability could be present, with high shear parameters, but timing of the FROPA will determine likelihood of severe risk on Wednesday. For now, high precip chances will continue in the forecast for Tuesday through Thursday due to the cold front approach and eventual passage.

After the upper level trough axis moves through along with the surface front, a cooler/drier airmass will filter into the region for the end of the week. Current guidance suggests drier conditions for Thursday. However, weak waves in the upper level flow could result in additional showers by Friday.

AVIATION /18Z TAFS THROUGH 00Z MONDAY/

Issued at 114 PM EDT Sat May 2 2026

Upper level disturbance crossing the region this hour and bringing scattered rain showers with isolated embedded thunder to near the Wabash region. Not confident enough in thunder potential to put in the forecast, but have showers along the KHNB/KBWG corridor this afternoon. Northwest winds with occasional gusts will die down later this afternoon to light and variable as surface high pressure builds into the region. That high will scoot by quickly tonight and by early Sunday afternoon we will see a return southwesterly flow.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Frost Advisory from 3 AM EDT /2 AM CDT/ to 9 AM EDT /8 AM CDT/ Sunday for KYZ023>025-027>043-045>049-053>057-062>067- 074>078-081-082. IN...Frost Advisory from 3 AM EDT /2 AM CDT/ to 9 AM EDT /8 AM CDT/ Sunday for INZ076>079-084-089>092.