textproduct: Grand Rapids

KEY MESSAGES

- Showers and Storms Likely Tonight With A Few Severe Storms Possible

- Rainfall Chances Return Friday

DISCUSSION

Issued at 138 PM EDT Tue Aug 18 2026

- Showers and Storms Likely Tonight With A Few Severe Storms Possible

A cold front will traverse the region tonight, with instability sufficient for the development of showers and thunderstorms after approximately 7pm. Upstream VWP from KMPX shows a mid-level jet max that will progress into the area this evening supporting enhanced deep layer shear values. This will be in combination with moderate bouyancy with CAPE values over 1000 J/kg, highest closer to the lakeshore.

This poses the question of whether any storms will be severe. DCAPE/low-level lapse rates will be on the marginal side but, with strong shear/mid-level flow, sufficient for a cold-pool driven damaging wind threat. In addition, the long hodograph shape favors the potential for initially discrete storms to pose a hail risk. REFS and other CAMs indicate some UH swaths favoring potential supercell development matching this thinking. Hail risk will be favored northwest of a Muskegon to Cadillac line. The thinking is then storms will begin to cluster transitioning to mainly a wind risk. Storms look to clear the area by 1-2am.

- Rainfall Chances Return Friday

Surface ridging keeps things dry much of Wednesday and Thursday before unsettled conditions return Thursday night. Several shortwaves are then forecast to progress across the forecast area within a larger longwave troughing pattern. While as expected variability in small-scale details exist, a solid signal exists across ensemble and deterministic guidance for a closed low to develop across the Central Great Lakes by this weekend.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 128 PM EDT Tue Aug 18 2026

A cold front will move across the terminals tonight and there may be come convective development along/ahead of it this evening. We've included a prob group for this possibility. Otherwise, the southern terminals may see some IFR fog/cigs late tonight before improving conditions mid Wednesday morning.

MARINE

Issued at 138 PM EDT Tue Aug 18 2026

Have elected to maintain the ongoing Small Craft Advisory, but refrrain from adding a Beach Hazards Statement at this time. Forecast soundings indicate southwest flow increasing late afternoon into this evening ahead of a cold front. Scattered gusts to 25 knots are possible. However, short range model guidance favors winds being just low enough to keep waves generally in the 2-4 foot range. The caveat is thunderstorms are likely 6pm-12am tonight across the waters. Locally higher waves, large hail, and winds in excess of 34 knots are possible in any thunderstorms.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 5 PM this afternoon to 11 PM EDT this evening for LMZ846>849.