519 FXUS63 KGRR 290528 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 128 AM EDT Mon Jun 29 2026 .KEY MESSAGES... - Threat of strong to severe storms late tonight/Monday AM - Heat wave begins Monday && .UPDATE... Issued at 608 PM EDT Sun Jun 28 2026 Thunderstorms across central eastern Wisconsin have persisted past couple hours in an area of deep warm advection near and near the surface warm front. Added POPs for the western zones as convection moves southeast out of Wisconsin and across the Lake the next few hours. The FV3 seems to have a handle on the previous and current convection and was followed as it takes these storms east-southeast this evening. Wake low winds noted over southern Wisconsin and northern Illinois gusting over 40 mph. The are expected to weaken as they move southeast across Lake Michigan, but some squalls and brief gales are possible across the southern marine zones and we have issued a Marine Weather Statement. && .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 /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 128 AM EDT Mon Jun 29 2026 Weak showers with occasional thunderstorms over lower Michigan will move off over the next couple of hours. Still anticipating a decaying complex of thunderstorms to move toward MKG/GRR this morning with low chances for thunder at both terminals. Showers/storms are not expected to reach the southern and eastern terminal locations. Otherwise...breezy southerly winds this afternoon and early evening with gusts over 30kts possible. && .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 through Tuesday evening for MIZ037-043- 050-056. Extreme Heat Warning from 2 PM this afternoon to 8 PM EDT Thursday for MIZ037>040-043>046-050>052-056>059-064>067- 071>074. MARINE...Small Craft Advisory until 8 PM EDT Tuesday for LMZ846>849. && $$ UPDATE...Ostuno DISCUSSION...04 AVIATION...Maczko MARINE...04

NWS GRR Office Area Forecast Discussion