textproduct: Grand Rapids

KEY MESSAGES

- Chance of Severe Weather and Flooding in Southern Michigan

- Quieter Late Week Then Rain and Storms Possible Sunday

DISCUSSION

Issued at 401 AM EDT Wed Jun 17 2026

- Chance of Severe Weather and Flooding in Southern Michigan

Anomalously deep low pressure cyclone for June, featuring two pressure minima at or below 990 mb over Minnesota and southern Lake Michigan, associated with a developing coupled upper-level jet structure supporting significant upper-level divergence, will provide dynamic weather to the Midwest today. A several hour period of rain and thunderstorms between early-mid afternoon and late evening will bring threats of strong winds and flooding.

Ahead of the low, a 60 to 70 knot 850 mb jet nosing into southern lower Michigan late in the day will help supply moisture for a large area of moderate to heavy rain. Initially rain-cooled air at the surface over Lower Michigan will keep much of the severe and tornado threat over Illinois and Indiana. However there are signs of a weaker warm frontal boundary advecting into southwest lower Michigan under destabilizing midlevels during the evening. Vertical wind shear in the low and mid levels will become extreme for a time this evening especially in southern Michigan between 5 and 9 PM, including sfc-1 km shear values around 50 knots in the vicinity of an anticipated convective complex embedded within the rain.

While surface parcels may not be outright convectively unstable in the vicinity and north of I-94 this evening, a strong to severe wind threat may still manifest in portions of the area. Some runs of the HRRR and other HREF member models develop narrow bands of wake-low enhanced southeast winds at times on the northwest edge of the precipitation shield. Additionally, some runs of the HRRR are producing small scale signatures of Gravity Wave Associated Convection (GWAC) within one of the cells in southern Michigan amid the complex, which if this does indeed occur, may entail an increased hail threat despite meager elevated instability, and a temporary wind direction reversal from southeast to northwest as the stable air in the lower levels is lifted and dropped.

As far as precipitation, broadly 1 to 2 inches of rain is supported in the larger mesoscale picture. However, depending on the evolution of the smaller mesoscale convective features, a narrower swath of 2 to 4, perhaps isolated 5 inches of rain may fall in several hours. This is shown in the HREF's local probability matched mean QPF. A flood watch has been issued to cover this threat of flooding particularly for low-lying and urban areas.

- Quieter Late Week Then Rain and Storms Possible Sunday

Thursday and Friday look cool and breezy with just very light and scattered rain showers possible at times through Saturday. The next shortwave trough ejecting from the western CONUS may develop another surface low over the Plains to Midwest late in the weekend. Depending on the track, another batch of heavy rain could move in later on Sunday. There is still a wide distribution of QPF amid the ensembles due to differences in the low's track, so confidence in heavy rain or thunderstorms is not high for now.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 707 AM EDT Wed Jun 17 2026

Associated with a strong low pressure system for June, rain is expected to move in from the west between 16 and 19 Z, gradually becoming heavier with worsening visibility and ceilings between 19 and 21 Z. Enough instability for thunderstorms embedded within the rain will likely be present starting between 20 and 22 Z, persisting for a few hours, then followed by a few more hours of prob30 thunderstorms as the predominant rain ends and showers become the mode. LLWS and gusty surface winds over 30 knots are possible during the hours of most intense rainfall.

MARINE

Issued at 452 AM EDT Wed Jun 17 2026

Small craft advisory is in effect beginning this afternoon as southeast winds strengthen with gusts to 30 knots under rain and thunderstorms through this evening. Gale force wind gusts from the southeast could occur in the vicinity of some showers/storms as indicated by high resolution models. Tonight into Thursday, west winds will build hazardous waves, and a beach hazard statement will be needed.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Flood Watch from 4 PM EDT this afternoon through late tonight for MIZ064>067-071>074. MARINE...Small Craft Advisory from 2 PM this afternoon to 4 PM EDT Thursday for LMZ844>849.