textproduct: Grand Rapids

KEY MESSAGES

- Scattered Showers/Storms Press East Today

- Cooler and Breezy Sunday into Monday

- Midweek Rain Chances

DISCUSSION

Issued at 258 AM EDT Sat Aug 22 2026

- Scattered Showers/Storms Press East Today

Prefrontal scattered showers and thunderstorms have developed in a weakly sheared environment with MUCAPE values around 1000-1500 J/kg. This activity was best depicted by the 00z HRRR, though several of the CAMs have had at least somewhat of a clue. While many areas will completely avoid rain into the morning hours, small pockets of 0.25" or more are possible mainly near and west of US 131 where elevated instability is present. As the cold front moves into the region in the 12z-15z time frame, rain chances will press east with the front, and by 18z much if not all of the showers/storms will push east of US 127. One exception may be a few showers and storms that develop along the lakeshore after 21z underneath a post-frontal vort lobe that swings through the U.P. and WI, helping generate some precip over Lake Michigan given a somewhat more unstable boundary layer. NBM is not really picking up on this, but we may need to introduce POPs along the lakeshore for the evening hours depending on upstream convective trends this afternoon. - Cooler and Breezy Sunday into Monday

Anomalous upper troughing, as indicated by the 00z ECWMF's 500mb height anomalies of ~3 standard deviations below normal across the Great Lakes on Sunday, will assuredly cause cold air advection in the lower levels and also enhance surface wind speeds Sunday into Monday. Normal highs are in the low 80s, but we should max out around 70 to the low 70s on Sunday and maybe a touch warmer Monday. Wind gusts of 25 mph or greater are likely on Sunday, with gusts of 20 mph or greater likely on Monday.

- Midweek Rain Chances

Upper troughing returns in the Wednesday to Thursday time frame, with some weak upper jet divergence moving in. At the surface, a cold front is shown by model guidance to move through the Great Lakes. This system will not be tapping Gulf moisture, and the low and mid level winds don't look strong at this time. Still, there will be an opportunity for some scattered showers and storms with timing better pinned down as we get closer to this event.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 652 AM EDT Sat Aug 22 2026

A surface cold front will lead to a wind shift today (SW to NW) and also help push shower and thunderstorm activity east of the region with time. Have removed precipitation out of the MKG and GRR TAFs with this update as there is just a slight chance (10-20%) that a shower or thunderstorm could impact those terminals mainly through 15z or so. Otherwise, LAN and JXN would have the best shot at a shower or thunderstorm until about 18z before ending. Later this evening, especially closer to 00z, some high resolution model guidance shows a few scattered showers/storms trying to move in off Lake Michigan, possibly impacting MKG around or after 00z. Will keep an eye on trends.

MARINE

Issued at 258 AM EDT Sat Aug 22 2026

As a cold front moves through the region today, winds will turn NW after 12z with a good fetch over the lake. With cold air advection taking place today into Sunday, this will be a setup for hazardous winds and waves to small craft and also hazardous swim conditions especially south of Pentwater today and then all areas on Sunday. Small Craft Advisories and Beach Hazards Statements are in effect for all marine areas starting 8am today and lasting through Sunday evening. The north sides of piers will be especially dangerous, and piers may be swamped by waves. Sunday will likely feature the highest wave activity with 4 to 6 feet expected.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through Sunday evening for MIZ037-043- 050-056-064-071. MARINE...Small Craft Advisory until 11 PM EDT Sunday for LMZ844>849.