textproduct: Louisville

KEY MESSAGES

* Today through Tuesday, temperatures are expected to warm into the mid 80s to low 90s. Some daily max temperature records could be challenged. * This afternoon/evening, showers and/or thunderstorms arrive, especially for our northwestern counties. This is mainly a wind and hail threat.

* A line of strong to severe storms is expected to move through ahead of a cold front on Tuesday, possibly bringing strong winds and hail. The line will weaken as it moves east over the region.

* More active weather arrive later this week as multiple rounds of showers and scattered thunderstorms are possible going into Memorial Day weekend.

MESOSCALE

Issued at 1011 PM EDT Mon May 18 2026

Convection continues to slowly move eastward across southern Indiana this evening. We're watching a SW-NE oriented band of very heavy rainfall with some embedded thunderstorms that will train across portions of Meade, Harrison, Clark, and Floyd counties in southern Indiana over the next few hours.

Overall, atmosphere is marginally unstable with about 500-700 J/kg of MLCAPE and about 30-35kt of bulk shear. The ongoing convection resides within an enhanced PWAT plume with values 1.6-1.9 inches. With deep layer shear largely parallel to the synoptic scale ascent pattern, expect this convection to slowly move eastward with time while weakening. Latest CAM guidance suggests that this activity will diminish with time, likely in the 12-2 AM EDT time frame. Within this band, a solid 1.5-2.5 inches of rainfall is expected. Areas east of the band across far north-central KY have remained rain-free today, so this rainfall will be welcomed and with rates diminishing with time, good ground absorption will be possible, except in the urban areas.

Cold outflow from this convection has pushed southward and down toward the WK/BG Parkway corridor. Current expectations are fore this convection to mainly stay on the Indiana side of the Ohio River, though the southwest edge of the rainfall may make it into the Louisville metro region over the next 1-3 hours.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 241 PM EDT Mon May 18 2026

Current mesoanalysis shows 2000-2500 J/kg of uninhibited SBCAPE, about 20kts of deep layer shear, and steep lapse rates. Not seeing much agitated Cu over our CWA just yet, but just to the west, we have seen some initiation. Shear will slightly increase as the MCS approaches the CWA, which will help storms to become slightly more organized. Over the next few hours do expect some scattered strong to severe storms, with a wind and hail threat. The threat area will be small, over southern Indiana and just along the Ohio River. Most of the region will be spared of any storms. Additionally, PWATs near 1.8-2.0 inches and a slowly moving line of storms will allow for heavy rainfall. This line is also moving aprallel to the LLJ, which will allow for training. Due to this, there is also a risk for heavy rainfall to lead to some minor flooding issues over our far northwestern areas in southern Indiana.

As the sun sets, we will quickly lose instability. Showers and storms are expected to quickly dissipate. With broken sky cover and light southerly winds, not expecting a great radiational cooling night. Low temperatures will likely remain warm in the upper 60s and low 70s. This will be close to warm minimum records for May 18.

Ahead of an approaching cold front, WAA will continue to keep temperatures in the upper 80s and brushing 90. This will help SBCAPE to increase near 3000J/kg. Dew points will also creep into the upper 60s and low 70s. Though shear will remain low around 20kts. Pulse summertime thunderstorms will be possible in the afternoon prior to the cold front and association line of storms. When the cold front approaches, we are expecting a decaying line of storms to outrun the best forcing along the cold front. Wind and hail will be the main threat on Tuesday over the northwestern 2/3rd of the CWA. The cold front will begin to slow its progression southward Tuesday night, making it through most of the CWA by Wednesday morning.

LONG TERM /WEDNESDAY THROUGH MONDAY/

Issued at 241 PM EDT Mon May 18 2026

As the cold front slowly sags the the south on Wednesday, widespread showers and scattered thunderstorms are expected, especially for the southern half of our area. Rich moisture along the front will help fuel these showers and storms, with LREF PW values ranging from 1.4- 1.7" (>95th percentile climatologically). Instability to the south of the front will also help fuel these showers, with LREF mean SBCAPE around 750-1000 J/kg. The wind shear profile is very meager, so we don't currently expect severe weather at this stage. With the front moving through, temperatures will much closer to normal for this time of year, with highs in the mid-to-upper 70s north of the front in southern Indiana and northern Kentucky, and highs in the low 80s south of the front in south central Kentucky.

The front stalls out just south of our area by Thursday, but with some moisture still in place over our far southern counties chances for showers will be possible (35-50%). With northerly flow at the surface, temperatures across the region will be slightly cooler than Wednesday, with highs in the low-to-mid 70s.

Though an area of surface high pressure tries to build in over the Great Lakes and Ohio Valley regions Thursday, a broad upper level trough over the western CONUS pushes eastward and drives the high out of the area. Ahead of the trough axis, a series of shortwaves surges northeastward, lifting the frontal boundary northward Thursday night. Considerable southerly flow at the surface and aloft will allow deep moisture to surge back northward, helping set up a few decent periods of showers and some thunderstorms into Memorial Day weekend. The southerly flow will also allow temperatures to rise back up into the 80s by the weekend, but with dew points again in the mid 60s, it will also feel rather muggy outside. The more active pattern for rounds of showers is currently expected to last through the end of the forecast period, so a little bit of drought relief may finally be on the way.

AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 739 PM EDT Mon May 18 2026

A round of showers and thunderstorms are currently moving NE through southern IN causing gusty/strong winds. Rain chances to be out of HNB and SDF by 05z. A marginal signal for LLWS at HNB/SDF overnight (05-07z) as a LLJ scraps across southern IN. Winds will also take a shift to the SW by tomorrow. A mid level cloud deck will move in tomorrow bringing BKN/OVC100 to all sites. Ahead of a cold front, a line of showers and storms will move in tomorrow afternoon/evening. Wind gusts are expected to increase during this time with the potential for lower vis during periods of heavier rain.

LMK WATCHES/WARNINGS/ADVISORIES

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