textproduct: Grand Rapids

KEY MESSAGES

- Showers/Storms Through Late Afternoon, Then Overnight/Friday AM

- Likely Dry Friday Afternoon; Scattered Storms Possible Late

DISCUSSION

Issued at 231 PM EDT Thu Sep 3 2026

- Showers/Storms Through Late Afternoon, Then Overnight/Friday AM

Through the end of the afternoon, the most concentrated areas for stronger convection will be near/north of I-96 and east of US 131 where scattered damaging wind gusts and large hail will be possible. In this region, effective shear values of 40-45 kts are present along with SBCAPE of 2000-3000 J/kg. Surface vorticity enhancements along any outflow boundaries could also aid in a rotational component to stronger thunderstorms with a tornado not out of the question especially across central and south central Lower MI. There is a CAM signal for some swaths of convective wind gusts exceeding 60 mph east of US 131 into late afternoon or early evening before ending.

Redevelopment of overnight storms is quite likely. This round of storms will be fueled by an increasing LLJ (30-40 kts) over Wisconsin that will move our direction, intersecting a largely stationary boundary over the region. Model sim refs are indicating a few possible outcomes including a QLCS or elongated/training convective event, the latter being more concerning in terms of an urban and poor drainage flood risk. Areas that would be most susceptible to localized flooding overnight and into Friday morning would be along US 10 (where 1"-2" occurred today) as well as the greater Lansing area where several rounds of thunderstorms have occurred. HREF 6 hr PMM rainfall indicates 1"-2" especially near and west of US 131, though max 6 hr QPF from the membership indicates areas of 2"-3" or slightly more. Placement is not certain at this time, and could shift east. In terms of a QLCS risk, there is some signal for this to occur in the 09z-13z Friday time frame. Nam3km and HRRR soundings ahead of this potential feature indicate 400-500 J/kg of CIN, likely indicating strong winds will not mix down to the surface. Hail and heavy downpours/localized flooding would be more likely threats.

- Likely Dry Friday Afternoon; Scattered Storms Possible Late

The surface boundary in place today looks to slide south toward I-94 and the MI/IN border by late Friday. Subsidence in the wake of morning rain on Friday will likely inhibit convective development Friday afternoon outside of an isolated pop up shower or storm that could occur on any residual outflow boundaries that remain in place during daytime heating. Predictability of these is low. Best indications are scattered showers and thunderstorms could develop late afternoon/evening and into Friday night near and south of a Grand Rapids to Lansing line after sufficient daytime heating. A HRRR sounding near Lansing around 21z indicates quite a bit of DCAPE at 1200 J/kg with fairly substantial 0-3 km shear of 35 kts. An isolated severe thunderstorm cannot be ruled out near and south of GRR to LAN with damaging wind gusts the primary hazard.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 640 PM EDT Thu Sep 3 2026

Ealrier storms have left the area with VFR conditions at all terminals. After 06z tonight, MVFR and lower fog/cigs is likely to develop at all terminals thanks to ample rainfall earlier today. Then, a cluster of showers and thunderstorms tracks across the terminals between 08z-15z with IFR and lower conditons in any thunderstorms. Conditions then improve to VFR mid to late morning. Light and variable winds increase from the southest at 3-8 knots Friday morning, increasing from the west in the afternoon to 5-10 knots.

MARINE

Issued at 231 PM EDT Thu Sep 3 2026

Winds and waves should stay below hazardous levels for mariners through the weekend. Mariners should stay abreast of thunderstorm potential from this afternoon into Friday night and have plans to seek safe harbor when necessary.

GRR WATCHES/WARNINGS/ADVISORIES

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