textproduct: Grand Rapids

KEY MESSAGES

- Thunderstorms expected this evening into Tonight

- Showers and storms Tuesday and Wednesday

- Slightly cooler than normal through the 7 day forecast

DISCUSSION

Issued at 356 AM EDT Sat Jun 13 2026

- Thunderstorms expected this evening into Tonight

The main focus of the 7 day forecast is on thunderstorms this afternoon and evening and whether or not we have a severe threat with these storms. The bottom line up front is there are small chances for severe, especially this evening. We are in a SPC marginal threat for severe weather today and agree with that assessment. Really there are quite a few factors going for convection today. Starting aloft, there is a 100 knot upper level jet overhead with some suggestion for a slight coupled jet structure. At the very least we look to be in a right front quad of a jet streak which will aid overall lift today. At 500mb we have 50 knots of flow, so the upper level variables one looks for are there. At 850mb we have around 30 knots of wind which is more than enough to aid convective development. In terms of low level moisture, +13C 850mb dew points are sufficient for storms as are the middle 60s dew points that are forecast. Deep layer shear is around 40 knots with MUCAPE values of 1,000 to 2,000 j/kg. So there really is a lot going for severe weather this evening. Machine learning models like Nadocast are also showing a threat for wind and hail over much of the area. If there was one slight negative its that the moisture through the depth of the atmosphere is a little bit down from what could be there today. PWATs are around 1.6 which could be higher in the month of June, but that is plenty to work with as well. We expect scattered showers and storms to slowly work southward with an advancing cold front this evening and overnight. Chances increase up along U.S. 10 around 22Z. Again, hail to around 1 inch or so and wind gusts to around 60 mph look to be the main threats.

- Showers and storms Tuesday and Wednesday

A deepening 500mb trough will be in place over much of the forecast period a mid level shortwave and associated surface cold front will move through during this time frame. Monday, and Thursday/Friday look mainly dry at this point.

- Slightly cooler than normal through the 7 day forecast

Given the troughing and potential for clouds and showers feel our highs will be near to slightly below normal. Highs will be comfortable in the 70s with lows dipping into the 50s.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 651 AM EDT Sat Jun 13 202

Limited aviation concerns today at the Southwest Lower Michigan TAF sites. There is one though and that is a gusty southwest of 15 to 25 knots that should occur much of the day. Skies will be clear to partly cloudy with clouds bases at or above 8,000 feet for the most part.

The focus this evening and tonight is on the threat of thunderstorms. We are expecting a broken line of showers and storms to work from northwest to southeast through the TAF sites starting at 23Z at MKG and ending at JXN around 10Z-12Z.

MARINE

Issued at 356 AM EDT Sat Jun 13 2026

Will leave the ongoing Beach Hazards Statement and Small Craft Advisory as is with this update. Considered bringing the headlines one zone further south to include Ottawa County beaches today, but in the end held off. Air temperatures will be higher than the water temperatures today, so the stability over the lake is a concern for how much wind is mixed down to the lake surface to build waves. Overall like the area we have selected for the Statement/Advisory. Expecting southwest winds of 15 to 25 knots north of Grand Haven where waves will build to 3 to 6 feet. Lighter winds and therefore smaller waves are expected from late tonight through the remainder of the weekend.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through late tonight for MIZ037-043-050. MARINE...Small Craft Advisory until 2 AM EDT Sunday for LMZ847>849.