textproduct: Grand Rapids

KEY MESSAGES

- Storms Tonight

- Upper Troughing Continues through next week

DISCUSSION

Issued at 258 PM EDT Mon Jul 20 2026

- Storms Tonight

A vigorous upper shortwave trough is phasing with troughing over eastern Canada, while a deepening surface low north of Lake Superior drives a cold front into a moist and unstable airmass across Wisconsin. The convective allowing models show a line of storms initiating in that area this afternoon then moving southeast across Lake Michigan and into western Lower Michigan this evening. They also show a general weakening trend as instability decreases this evening, although shear profiles remain impressive.

The main threat appears to be downburst winds associated with bowing line segments along with isolated large hail in the strongest, most persistent updrafts. The threat should be ending Tuesday morning as the cold front pushes through.

- Upper Troughing Continues through next week

The heat and humidity of last week looks to be gone for a while with all the long range models showing a persistent pattern of ridging across the SW CONUS and troughing across the NE CONUS. This will keep the Great Lakes region in a northwest flow regime for the next week at least, with occasional cold front passages that could focus convection. The next one appears to be next weekend. Overall, a cooler and drier than normal weather regime for the rest of the month is expected.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 153 PM EDT Mon Jul 20 2026

A few areas of MVFR smoke visibility remain but gradual improvement has been occurring. Otherwise, cloud bases are expected to be at or above 4,000 feet this afternoon with southwest winds. Thunderstorms from Wisconsin are expected to cross Lake Michigan into Western Lower Michigan late this evening. Models differ on how far east the storms will extend into Lower Michigan tonight. For now, will continue prob30 thunderstorms especially between 01 and 08 Z. Heavy rain with IFR visibility, and stronger wind gusts over 35 knots or LLWS are favored to be associated with storms if they do occur.

MARINE

Issued at 258 PM EDT Mon Jul 20 2026

SCA continues through Wednesday evening. We may need a Gale Warning for strong north winds Tuesday night as the pressure gradient tightens between the departing low and the advancing high. Conditions will quickly improve on Thursday as the high builds in.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Air Quality Alert until midnight EDT tonight for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. Beach Hazards Statement through Wednesday evening for MIZ037-043- 050-056-064-071. MARINE...Small Craft Advisory until 11 PM EDT Wednesday for LMZ844>849.