textproduct: Louisville

KEY MESSAGES

* Heavy rainfall and strong thunderstorms are expected today into Saturday. Excessive rainfall may lead to flash flooding across portions of southern Indiana and north-central KY through tonight. A Flood Watch is in effect for areas along and north of the I-64 corridor through 8 AM EDT Saturday.

* There is a Slight Risk (Level 2 out of 5) for severe weather this afternoon and evening across southern Indiana and central Kentucky. The main severe weather hazards are localized damaging winds and a tornado or two.

* Summer heat and humidity will build across the region next work week, with triple digit heat indices likely (70-90% chance) west of I-65 on Monday and area-wide Tuesday through at least Friday. This will pose a risk for heat-related illness, especially among vulnerable populations.

SHORT TERM /THROUGH SATURDAY/

Issued at 330 AM EDT Fri Jun 26 2026

Numerous showers and scattered thunderstorms are ongoing over southern IN, west of I-65 early this morning. This is along and just south of an effective quasi-stationary boundary, which will fluctuate over the Lower OH Valley through the short term forecast period. A band of weak convection appears likely to continue evolving eastward near the I-64 corridor through sunrise as a 25 kt southwesterly LLJ noses northeast across the Mid-MS Valley and into the Lower OH Valley. The primary concern early this morning will be the potential for west-to-east training resulting in locally excessive rainfall/flooding.

Today into tonight, a mid-level shortwave trough is forecast to move east over the region. Persistent W/SW flow will advect anomalously moist air (2 in PW) over southern IN and central KY. The lower to mid-level flow will increase to 25-35 kts, enhancing moisture transport and lift ahead of the approaching wave. Some of the latest model runs indicate a convectively-generated MCV could also develop over the Lower OH Valley by the afternoon.

Convective evolution today into tonight is extremely complex. It appears at least three different waves of showers and storms are possible: 1) Scattered convection along and just north of the I-64 corridor early this morning, 2) a stronger band of thunderstorms pushing east across portions of southern IN and central KY this afternoon, and 3) additional thunderstorm clusters developing west to east (with training potential) across portions of southern IN and central KY this evening and overnight.

The second wave of convection during the afternoon and evening hours has the best chance at producing strong to severe storms. SW LLJ winds increasing to 25-30+ kts this afternoon will enhance low-level shear, especially if a MCV develops just north of the CWA and is deeper than anticipated. Moderate destabilization appears possible today to the south of the effective sfc boundary, which will be modulated by convective outflow. This appears likely to setup along or just north of I-64, with much of central KY likely to realize 1500 J/kg MLCAPE this afternoon. The CAPE profile is quite deep, and lapse rates are tempered by the unusually moist profile. Marginal deep-layer shear will also limit the overall severe weather potential. However, brief supercell structures and a low-end tornado risk are expected through the afternoon and evening hours, especially across southern IN and west-central KY where the STP peaks around 1.

Tonight, low pressure continues to shift ENE to eastern portions of the OH Valley and the LLJ/moisture transport axis orient more WSW- ENE along the boundary. This increases concern for training thunderstorms overnight, again across portions of southern IN and north-central KY. Because of this, the Flood Watch was expanded eastward along and north of the I-64 corridor. Rainfall amounts of 1 to 2 inches are likely, but HREF PMM QPF data suggest very localized rainfall amounts of 3 to 5 inches are possible in the watch area through 12Z Saturday. Localized significant flash flooding is possible within this zone.

The weak cold front finally makes some southward progress on Saturday as low pressure continues to drift over the Upper OH Valley. At least scattered showers and storms are likely across central and southern KY on Saturday, which should increase the risk for localized flooding further south across more of KY. Slow storm motions and training potential may necessitate a Flood Watch further south, but will hold off on that until forecast confidence increases in the mesoscale details.

Temperatures today will range from the mid 70s to low 80s north of I- 64, to the mid/upper 80s in south-central KY. Lows tonight will reach the upper 60s and lower 70s in most places.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Issued at 330 AM EDT Fri Jun 26 2026

Depending on how things evolve Saturday afternoon, a few thunderstorms may be ongoing at the start of the period (i.e., 8pm Saturday), with the highest chances (40-60%) from the HREF and REFS southeast of roughly US 62 - near our pesky, resident frontal boundary. This activity should gradually wane after sunset with the loss of diurnally-driven instability, however one more opportunity for convection will arrive early Sunday as a shortwave trough rides the periphery of an expanding ridge of high pressure centered off to our west. So far the RRFS has been advertising low coverage and intensity of associated convective activity, but with the ECMWF and GFS depicting 30-40 kt 0-6km bulk shear accompanying that shortwave coupled with increasing instability, this feature will bear watching for potentially organized showers and storms. Given uncertainty in coverage and timing, our forecast seems reasonable with 40-60% (highest west) precip chances early Sunday morning tapering to 20- 40% southeast of a Bowling Green to Lexington line by the afternoon.

Dry conditions should finally take hold by Monday as the aforementioned ridge expands into the region, setting the stage for a summer heatwave across northern Kentucky and southern Indiana. Both deterministic and ensemble guidance continue to offer high confidence in this heat and humidity, with the LREF mean bringing 500mb heights to 596-597 dam - the 99+ percentile of climatology - by the middle of the week. Temperatures each day will soar well into the 90s - possibly (30-40% chance) hitting 100 in urban areas (e.g., Bowling Green, Louisville, etc.) on Wednesday and Thursday - while dewpoints hover solidly in the 70s. The net result will be several days with afternoon heat indices in the triple digits (likely exceeding 105 one or more days), falling only into the mid to upper 70s overnight. Ensemble guidance begins to diverge heading into the weekend, making it unclear how long the steamy weather will stick around, but it's worth noting that the European ensemble system (EPS) mean maintains daily high temperatures in the 90s through next Sunday, July 5th; in addition, the Climate Prediction Center (CPC) depicts a 60-70% probability for above normal temperatures in days 8 to 14 (7/3 to 7/9).

AVIATION /12Z TAFS THROUGH 18Z SATURDAY/

Issued at 730 AM EDT Fri Jun 26 2026

SCT SHRA continue to spread east across the region this morning ahead of a line of showers and storms approaching from western KY. This line will bring SHRA and SCT TSRA to the terminals through the mid to late morning hours. Expect brief heavy rainfall, and localized gusty winds over 30 mph will also be possible for a short time. This round of convection may help suppress additional TSRA through a lot of the afternoon hours. Additional SCT TSRA will be possible this evening and overnight, which would all be capable of brief IFR conditions.

LMK WATCHES/WARNINGS/ADVISORIES

KY...Flood Watch through Saturday morning for KYZ030>043-049. IN...Flood Watch through Saturday morning for INZ076>079-083-084- 089>092.