textproduct: Grand Rapids

KEY MESSAGES

- Thunderstorms Tonight With Damaging Winds Possible

- Dry and Cooler Mid to Late Week

DISCUSSION

Issued at 237 AM EDT Mon Jul 20 2026

- Thunderstorms Tonight With Damaging Winds Possible

Primary concern with this forecast package is for the potential of severe thunderstorms tonight. A cold front looks to trigger storms across the upper midwest this afternoon which progresses eastward Monday evening. Questions remain as to the strength of any convection, with timing favored to be late this evening into the early overnight hours.

Evaluation of forecast profiles suggests the potential for an MCS on the nose of a 40 kt LLJ, with strong low-level and deep layer shear. This lends itself to a primary threat of damaging winds, with large hail in any discrete convection given steep mid-level lapse rates. Instability looks to be sufficient as well (albeit waning with eastward extent), so even with uncertainties as to convective strength, the environment warrants the Slight (Level 2/5) risk in place across most of the CWA. The threat ends Tuesday morning as the cold front exits the CWA.

- Dry and Cooler Mid to Late Week

Tuesday through late week will feature a relatively stable pattern with persistent upper-level troughing and surface ridging across the area. Combined with the dry airmass, dry conditons are favored at this point. Look for highs in the 70s mid-week climbing back into the low 80s by the weekend.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 104 AM EDT Mon Jul 20 2026

Smoke continues to support MVFR conditions at AZO/MKG and IFR at GRR. Given persistence forecast from previous days, espect conditions to remain the same through the night if not deteriorate slightly near daybreak. Mixing then increases favoring VFR conditions at all terminals beginning mid to late morning. A line of storms potentially arrives from the west after 00z Tuesday, however existence of timing and storms remains uncertain. Given this have elected to go PROB30 at GRR/MKG to start and can re- evauate with future packages. Gusty winds from the south to around 20 knots are expected today, with locally higher winds and MFVR and lower conditions possible in any storms tonight.

MARINE

Issued at 237 AM EDT Mon Jul 20 2026

Winds and waves increase this morning ahead of a cold front with 3-6 foot waves building by this afternoon. Winds veer northwesterly Tuesday behind a cold front with waves to 5-8 feet. Winds of 20-30 knots are expected with a 40% chance of gale force gusts Tuesday evening. Hazardous winds and waves continue into Wednesday evening. Will hoist a Small Craft Advisory and Beach Hazards Statement for this multi day hazardous wind and wave event. In addition, thunderstorms, the strongest of which may have winds in excess of 34 knots, are possible this evening across the nearshore and open waters.

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 from 11 AM EDT this morning through Wednesday evening for MIZ037-043-050-056-064-071. MARINE...Small Craft Advisory from 11 AM this morning to 11 PM EDT Wednesday for LMZ844>849.