textproduct: Grand Rapids

KEY MESSAGES

- Showers and Storms Once Again Today with Severe Potential

- Period of Dry Weather This Weekend into Early Next Week

- Less Humid Air This Weekend

DISCUSSION

Issued at 350 AM EDT Fri Sep 4 2026

- Showers and Storms Once Again Today with Severe Potential

Showers and thunderstorms continue to fill in to our west over Lake Michigan and Wisconsin. This convection is occurring on the nose of the low level jet which is aiding in low level theta-e advection into the storms. The low level jet is forecast, which was discussed in yesterday afternoon's AFD, to fold over to the east and be aimed into Southwest Lower Michigan much of the morning. Consistency with this feature has been good, which is something we have not seen of late in the models given somewhat nebulous forcing which is common in the late summer. Deep layer shear is expected to be around 40 knots this morning with MUCAPE values in the 1,000 to 2,000 j/kg range. The parameter space is robust even at this early hour which is evidenced by nearly 2 inch hail in the middle of the night to the west of the lake in Wisconsin.

We expect rounds of storms to move through Southwest Lower Michigan this morning between 4am and noon. The initial activity is crossing the lake now and given the surge of low level moisture via the low level jet severe weather is possible any time during that window. Its possible some activity may persist slightly past midday in our south and east towards JXN and LAN, but the afternoon should trend drier with time. Wind looks to be the main severe threat with gusts to 60+ mph possible. Severe hail cannot be ruled out either.

Heavy rain and localized flooding remain possible today given PWATs near 2.00 inches and the threat of training thunderstorms. Amounts of 0.50 to 1.00 inches of rain will be likely, but swaths of 1.50 to 3.00 inches are quite possible as well. Short term flooding potential will be monitored this morning.

Some redevelopment of showers and storms in the far southwest CWA towards South Haven will be possible this evening.

- Period of Dry Weather This Weekend into Early Next Week

A period of dry weather is expected this weekend into early next week as ridging will be in control of the area weather. High confidence in dry weather this period given consensus in the ensembles of both the GFS and ECMWF.

- Less Humid Air This Weekend

After what has been a period of very humid air it will be noticeably less humid this weekend. Dew points are in middle 60s to around 70 this morning. Dew points in the 50s this weekend will feel quite pleasant in comparison.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 209 AM EDT Fri Sep 4 2026

Another night of patchy fog in place at 06z, some of which is locally dense with visibilities around 1/2 mile. We may see some MVFR fog at the TAF sites early this morning but in large part the lower ceilings and visibilities associated with fog should remain over Central Lower Michigan.

The bigger threat to aviation interests will be thunderstorms. Storms have been working this way through Wisconsin overnight and we expect that trend to continue. Showers and thunderstorms should move into the area between 07z and 10z and continue into the daylight hours of Friday morning. By 16z to 18z the storms should be moving off to the south and east of the area. MVFR conditions as the storms move through are likely with IFR and lower certainly possible. Very heavy rain rates are possible which will affect visibility as well as the potential for stronger winds (in excess of 40 knots) and hail (to around 1" in diameter).

VFR weather will return this afternoon in the wake of the morning thunderstorm activity. Bottom line...we are looking at active weather at the TAF sites especially between 08z and 16z.

MARINE

Issued at 350 AM EDT Fri Sep 4 2026

The quiet period (lower waves and winds) continues on the Big Lake today and into the weekend. Overall, the pattern continues with a slack gradient today which transitions into surface high pressure this weekend. Winds should for the most part be in the 5 to 15 knot range. Winds may be slightly stronger on Saturday, but the flow will be off shore. Waves should be 2 feet or less today through the weekend.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.