textproduct: Grand Rapids

KEY MESSAGES

- Breezy and Dry Today

- Some Showers Thursday Especially North of I-96

- Scattered Showers/Storms in the Area Friday into Saturday

DISCUSSION

Issued at 300 AM EDT Wed Jun 11 2025

- Breezy and Dry Today

Low level warm air advection overspreads the region today with a core of 30-35 kt winds aloft at 1k-2k ft that will mix down late morning into mid afternoon. Surface gusts over 30 mph are shown by a consensus blend of high resolution models. The windiest period will likely be 15z-20z before diminishing. Otherwise dry conditions and mostly sunny skies are forecast.

- Some Showers Thursday Especially North of I-96

By Thursday morning, a fairly significant 850mb thermal gradient develops over the region with a largely stationary frontal boundary looking to set up north of I-96 and especially toward US 10. Some upper jet divergence moves into this region but with very weak low level winds and almost no semblance of a LLJ to speak of. Elevated instability is present up against this boundary with MUCAPE values of 500-1000 J/kg. A narrow corridor for some showers and a few storms to develop will exist especially from I-96 to the north. This will be mainly during Thursday morning but a few pop up showers and thunderstorms could develop during Thursday afternoon. 00z model guidance is indicating low coverage at this time with many areas staying dry. Near US 10, highs may struggle to get into the 70s while elsewhere temperatures well into the 70s or low 80s are forecast.

- Scattered Showers/Storms in the Area Friday into Saturday

The trend on Friday is for the surface boundary to move north of most locations, keeping warm temperatures in play with highs for many areas likely getting into the 80s. However, just north of the boundary model guidance is showing highs in the 50s to low 60s. So, any slight southward shift in the surface boundary would lower temperatures by 20 to 30 degrees for our northern forecast area.

The main limiting factor in widespread showers/storms on Friday is the lack of any LLJ impacting the region. The best upper jet divergence sets up across northern WI, the UP, and northern Lower MI, while a much better LLJ impacts MN and WI. That said, with a boundary sitting over us and some moisture and instability, scattered showers and thunderstorms will likely develop at times. The surface boundary is currently favored to move south of the region Saturday evening into Sunday, taking the threat for rain with it. Until that occurs we have to continue including POPs in the forecast. The last few runs of the ECE have taken a hacksaw to rain amounts with probabilities for significant rain lowering for most areas. From Thursday into Saturday, the region north of M-46 has 60-80% probabilities for 0.50" or more and 20-40% probabilities for 1.00" or more. Dry conditions are forecast for Sunday with seasonable temperatures in the 70s.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 735 AM EDT Wed Jun 11 2025

Added a short period of LLWS at MKG through 14z, which has been in and out of model guidance since yesterday. This is due to higher shear in the lowest 2k ft before surface winds increase late morning. Otherwise, looking at wind gusts of 25-30 kts in the 15z-20z time frame, possibly lingering a bit longer. After winds diminish tonight, we could see some light fog development at the terminals as relative humidity values increase.

MARINE

Issued at 300 AM EDT Wed Jun 11 2025

Hazardous winds and waves for small craft will develop mainly north of South Haven today as southwesterly winds increase, leading to some 3 to 5 foot waves over the lake. These waves look to diminish after 20z or so. Little in the way of wave activity will occur late week as surface winds turn easterly or southeasterly.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement until 4 PM EDT this afternoon for MIZ037- 043-050-056-064. Air Quality Alert until midnight EDT tonight for MIZ050-056-057- 064-071. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LMZ845>849.