textproduct: Grand Rapids

KEY MESSAGES

- Scattered showers/thunderstorms late Friday into Saturday

- Cooler and comfortable Sun-Tue then midweek rain chance

DISCUSSION

Issued at 204 PM EDT Thu Aug 20 2026

- Scattered showers/thunderstorms late Friday into Saturday

Increasing low-level moisture returns Friday in a weak warm-air advection zone, ahead of a cold front that is expected to pass through with a deepening upper-level trough Friday night into Saturday morning. Models generally have CAPE values around 500-1500 J/kg with about 20 knots of deep layer shear. Scattered showers and thunderstorms may develop from late in the day Friday and through the night into part of the day Saturday. Severe weather potential appears low at this time, though isolated and temporary intersections of better low-level shear and CAPE can't be ruled out. Average QPF is approximately 0.1 to 0.25 inches, but realistically rain totals could be more hit-or-miss, with isolated spots of over an inch possible.

- Cooler and comfortable Sun-Tue then midweek rain chance

Ensemble agreement in the general pattern from the weekend into mid next week is fairly good, with troughing over the Great Lakes evolving into a cutoff low over northeastern parts of the region. This would likely put Lower Michigan into a northwest flow of somewhat cooler and drier, more comfortable air Sunday and Monday. There is a slight chance of daytime showers popping up inland on Sunday during peak heating underneath the upper-level trough. Somewhat warmer and more moist air then returns Tuesday ahead of the next cold front with a chance of showers/storms from late Tue into Wed.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 634 PM EDT Thu Aug 20 2026

Scattered diurnal Cu will diminish over the next 1-2 hours with mainly high clouds overnight. High clouds will thicken into Friday as a warm front approaches the area. There is a low (10-20 percent) chance of MVFR fog at AZO, BTL, JXN, late tonight. Light and variable winds overnight increase to 7-12 knots from the southwest Friday. After 18z, scattered showers and isolated thunderstorms are possible at all terminals, best chance at LAN/JXN. Given low confidence in terminal impacts have introduced the risk with a PROB30 for showers and kept thunder out of the TAF at this time.

MARINE

Issued at 204 PM EDT Thu Aug 20 2026

Low waves and low swim risk through early Friday morning. Southwest winds increase on Friday 10-15 knots gusting to 20-25 knots, particularly north of Whitehall, where a small craft advisory and beach hazards statement may be needed for the afternoon. Then behind a cold front and amid northwest flow of cooler air during Saturday and Sunday, hazardous waves and currents are likely for swimmers and small craft.

GRR WATCHES/WARNINGS/ADVISORIES

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