textproduct: Grand Rapids

KEY MESSAGES

- Storms possible today across Southern Lower Michigan

- Less confidence in storms on Wednesday

- Drier weather settles in for the latter half of work week

DISCUSSION

Issued at 343 AM EDT Tue Aug 11 2026

- Storms possible today across Southern Lower Michigan

The focus today is on the warm front to our south which stretches from portions of Iowa into Indiana. A low level jet max at 850mb will work eastward down the warm front this morning which should bring continued development to convection near and north of the front off to our west. A marked increase is convective coverage has been noted in the past 1-2 hours from the MI/IN border region through Southern Wisconsin to far Southeast South Dakota. All of this activity is working eastward with the mid level flow towards Southern Lake Michigan. MUCAPE values are significant even at this hour with the RAP indicating 2000-5000 j/kg. Given a low level jet forcing the activity and a large reservoir of instability the activity will no doubt continue/expand. Agree with both the SPC day 1 outlook and machine learning guidance like NadoCast indicating the far southwest corner of the state stand the best chance at severe weather today. Areas to the south and west of Grand Rapids will be the area of concern between 14Z and 21Z. Winds looks to be the main threat.

- Less confidence in storms on Wednesday

Wednesday we will remain under zonal upper flow with what looks to be convectively driven vorticity maxima working through the area, at least in the GFS. The SPC day 2 outlook shows general thunder to marginal risk levels across the forecast area. We seem to lack a trigger on Wednesday with no major shortwave aloft, no low level jet to speak of aimed at the region and a surface warm front that will likely remain situated in Illinois and Indiana. Given MUCAPE values in excess of 2,000 j/kg we have thunder in the forecast.

- Drier weather settles in for the latter half of work week

Surface high pressure gradually builds in and takes over our weather for Thursday and Friday. BUFKIT overviews look dry for the most part from Wednesday night through Friday night. High temperatures actually trend back into the 70s from Friday into Saturday.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 211 AM EDT Tue Aug 11 2026

Varied aviation conditions are in place to begin the TAF period at 06Z. Conditions range from VFR to LIFR with fog and stratus. These varied conditions will remain the case through daybreak around 11Z with a gradual downward trend and expansion of the fog and stratus, especially for the I-94 TAF sites. The fog and stratus will lift in the 12Z to 15Z time frame.

The next focus will be thunderstorms that may potentially sweep through the southwest corner of the state after 15Z. These storms are at present forming out over South Dakota and Nebraska. The storms will move/develop eastward along a warm front situated from Iowa to Indiana. Near and north of the front storms will sweep east most likely impacting AZO and BTL, although all TAF sites could be impacted if the complex comes a bit further north in its eastward push. We will be watching the 15Z to 21Z time frame as the sweet spot when storms have the potential to move through. MVFR and IFR conditions are possible with this activity.

MARINE

Issued at 343 AM EDT Tue Aug 11 2026

A typical mid summer weather pattern will be in place the next few days, meaning light winds due a slack pressure gradient. This type of regime is common in August when we often see light winds, sunshine and some of our warmest water temperatures. Current water temperatures at the buoys...Michigan City 79, Cook/Bridgman 74, South Haven 73.

As far as winds and waves go we will see winds of 15 knots or less generally which will produce a limited wave field of 2 feet or less the next few days. The main exception is that winds and waves could be higher in and near thunderstorms. There is a signal in the high resolution models indicating storms sweeping the southern portion of the lake, near and south of Holland between 15Z and 21Z. Waves may briefly be higher down in that zone if storms sweep the lake.

GRR WATCHES/WARNINGS/ADVISORIES

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