textproduct: Grand Rapids

KEY MESSAGES

- Threat of strong to severe storms late tonight/Monday AM

- Heat wave begins Monday

DISCUSSION

Issued at 218 PM EDT Sun Jun 28 2026

- Threat of strong to severe storms late tonight/Monday AM

Several short range models, such as the HREF, Namnest, RRFS, and some runs of the HRRR show the development of an MCS over northeast Wisconsin tonight moving east and then moving south along the lake shore following the thickness gradient. MUCAPE increases to 1500 j/k toward 12z along the lake shore and shear values are progd near 40kts. So the potential exists for a few strong to severe storms late tonight and early Monday morning before the storms dissipate.

- Heat wave begins Monday

A building upper ridge over the Great Lakes will result in oppressive heat developing tomorrow and continue through most of the week. H8 temps increase from 18c Monday to 24c by Tuesday afternoon. High temperatures will be in the 90s through Friday. Highs around 100 are possible Wednesday and Thursday across the southeast cwa. Heat indices will top 105 in may locations thanks to dewpoints climbing into the 70s. Perhaps the worst part will be the lack of relief. Low temperatures during the week won't get below 75 in many locations.

As the week progresses, there will be short waves that ride up the western side of the ridge and try to flatten the ridge across northern Lower...most likely Thursday night. This may result in some convection over the cwa, so we'll keep an eye on that.

Throughout this upcoming heat wave, make sure to check on the elderly and ensure your pets have plenty of clean fresh water.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 130 PM EDT Sun Jun 28 2026

Satellite shows diurnal Cu development between 3-4kft which will last through the evening. Then we see cigs lower to around 5kft through the night as a system approaches from the west. The main potential impact, and source of uncertainty, is the potential for a thunderstorm complex to clip GRR/MKG late tonight or Monday morning. Short range model guidance is not in strong agreement on where or when exactly storms will track so have kept the PROB30s inherited from the previous forecaster. Outside of winds in thunderstorms, look for southeast winds to 10 knots today except for a westerly lake breeze at MKG. South to southeast winds are expected again Monday with gusts to 20 knots at MKG.

MARINE

Issued at 218 PM EDT Sun Jun 28 2026

South winds will increase tonight and continue through Monday and waves will respond by building to 3-5 ft. We've issued a small craft advisory and corresponding beach hazards statement from 06z tonight through Tuesday. Additionally, thunderstorms may spread south along the lake shore late tonight resulting in hazardous marine conditions.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement from late tonight through Tuesday evening for MIZ037-043-050-056. Extreme Heat Warning from 2 PM Monday to 8 PM EDT Thursday for MIZ037>040-043>046-050>052-056>059-064>067-071>074. MARINE...Small Craft Advisory from 2 AM Monday to 8 PM EDT Tuesday for LMZ846>849.