textproduct: Grand Rapids

KEY MESSAGES

- Dry though Saturday

- Showers and Thunderstorms Saturday Night into Next Week

DISCUSSION

Issued at 254 PM EDT Thu Aug 27 2026

- Dry though Saturday

We were originally a bit concerned about persistent low cloudiness lasting into this afternoon due to local observed and forecast soundings indicating a deep and nearly saturated surface layer. However, formidable late August insolation is winning the day growing an even deeper mixed boundary layer. Recent cloud erosion over our central forecast area was impressively quick. This presumed lower tropospheric subsidence continues to be well sampled by GOES-E Lower Level Water Vapor (Channel 10) imagery. Moreover, we saw slightly divergent surface flow per area observations earlier today and that may have been an additional mesoscale downward response in the wake of a subtle low level, low amplitude gravity wave that appears to have worked southeastward through the flow while creating local upticks and downticks in the depth and coverage of stratocumulus observed this morning across much of Lower MI.

As noted before, there are some model solutions, such as outlier REFS members, that pop up isolated showers generally along and southeast of a Lansing to Battle Creek line this afternoon. This is a low probability outcome (around 10 percent). Thunderstorms look especially unlikely due to expected strengthening of the subsidence inversion that will keep conditional instability confined well beneath the ice production layer.

Friday and Saturday still look dry with rather sharp upper shortwave ridging upstream over the northern Plains and Upper Mississippi Valley. Negative differential vorticity advection aloft downstream of this feature and over the western Great Lakes will promote continued deep tropospheric subsidence and surface pressure ridging.

- Showers and thunderstorms Saturday night into next week

Our greatest risk for significant weather beyond Saturday looks to be Sunday night when there could be locally heavy rainfall. The exact corridor in which this occurs remains in question. The upper ridge will gradually deamplify while surface high pressure exits east of the area. A plume of anomalously large PWAT (90+ percentile) will approach from the west and overspread most of Lower MI by Sunday evening. By Sunday night, medium range ensemble mean guidance develops a seasonably strong low-level jet (30+ knots at 850 mb and ~90 percentile) over the Midwest that should be aimed towards Lower MI. This sets up a concern for locally heavy rainfall; accordingly, WPC does put our area in a Marginal risk for excessive rainfall from 12Z Sunday through at least 12Z Tuesday.

Predictability really suffers after the expected round of precipitation Sunday night into Monday as substantial convective augmentation of the synoptic flow will be possible. The best guess right now is continued unsettled conditions with episodic rainfall through Wednesday. In general terms, there does seem to be a trend towards the reestablishment of upstream upper ridging starting Wednesday night that will return subsidence and reduce PWAT magnitudes to more seasonal levels.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 724 PM EDT Thu Aug 27 2026

Diurnal Cu continue to slide east and should dissipate shortly after sunset. Clear skies then take over overnight with light winds. Patchy MVFR fog is possible, best chance at JXN, BTL, and LAN, but strong winds just off the deck keep probabilities around 30% so will maintain 6SM for the favored window of 09-13z for now. Where any fog develops, brief periods of MVFR cigs are possible similar to Thursday morning as diurnal Cu forms and lifts through the day. Expect winds to increase from the west Friday afternoon, shifting from the mainly southeast flow in the morning.

MARINE

Issued at 254 PM EDT Thu Aug 27 2026

Winds and waves continue to come down with current observations of waves around one to two feet. Northwest winds will continue a steady decline this evening and overnight with an associated slow reduction in wave heights. Winds become more easterly into Friday morning. The lake breeze will develop Friday afternoon with waves heights around a foot or less.

Our next chance for Small Craft Advisory and High Swim Risk conditions moves in Saturday and continues through at least Sunday due to stronger southwest winds causing waves to build. Our next chance for thunderstorms moves in Saturday night and continues into next week.

GRR WATCHES/WARNINGS/ADVISORIES

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