textproduct: Grand Rapids

KEY MESSAGES

- Thunderstorms Friday and Saturday, Severe Possible

- Lingering Showers and Thunderstorms Sunday, Mainly East

- Dry Monday and Tuesday, Rain and Storms Wednesday

DISCUSSION

Issued at 327 PM EDT Thu Jul 10 2025

- Thunderstorms Friday and Saturday, Severe Possible

Overall there is uncertainty in the exact timing of rain and thunderstorms due to differences in the overall pattern features. However confidence is higher for showers and storms to move into western Michigan early Friday morning from the remnant MCV over western Wisconsin. This feature will cause thunderstorms to redevelop overnight and move through the area Friday morning. Some stronger storms are possible, but overall not expecting anything severe with the morning round.

The morning convection looks to clear by the late morning/early afternoon. Depending on how quickly storms clear will impact our chance for afternoon thunderstorms which could be severe. At time time the main window would be during the late afternoon and evening hours. Mean HREF SBCAPE values are in the 1000-2000 J/kg range during the afternoon mainly sough of I-96. 0-3 km storm relative helicity values during that time are in the 100-200 m2/s2 range. Therefore there is enough spin in the atmosphere for stronger storms producing hail, gusty winds, and perhaps a tornado. This will be a higher concern with any remnant boundaries in the area from the morning round of thunderstorms. This matches up with the updated SPC outlook for Friday. Thunderstorms will also produce heavy rainfall with precipitable water values approaching 2 inches. Rainfall rates around an inch per hour are possible. Areas that see thunderstorms track repeatedly overhead could see higher rainfall amounts of 2 or more inches. This could lead to minor flooding especially in urban areas. Friday night thunderstorms will gradually diminish as we lose our daytime instability.

Saturday a shortwave trough moves through the area bringing with it another round of rain and thunderstorms for the afternoon and evening. NBM 25th-75th percentile SBCAPE values range from 2000-3500 J/kg across much of the area, shear isn't that great but with that amount of instability it won't take much for a storm to become severe.

- Lingering Showers and Thunderstorms Sunday, Mainly East

Another shortwave through moves through Sunday which could spark additional showers and thunderstorms during the day. Highest chances are south and east of Grand Rapids but we'll need to monitor for a westward trend. Overall not expecting the day to be a complete washout, but something to keep an eye on for those with any outdoor plans.

- Dry Monday and Tuesday, Potential for Rain and Storms Wednesday

High pressure builds in for the beginning of next week with highs in the 80s to low 90s and lows in the 60s to around 70. Wednesday into Thursday a deeper, more organized trough looks to move through the region. With the hot, moist environment it looks like another good set up for thunderstorms.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 744 PM EDT Thu Jul 10 2025

Weakening showers and thunderstorms from upstream will arrive after 08-09z tonight and cross the terminals through the morning hours. Occasional reductions to MVFR conditions are likely in heavier showers, particularly for MKG and GRR. Limited instability will preclude thunder chances with this package. Forecast soundings suggest a few hours of MVFR conditions behind the showers at MKG. Afternoon conditions are somewhat uncertain at this point as it will be highly dependent on how conditions settle after the morning period. It is likely that in the afternoon and/or evening a period of showers and thunderstorms will develop across lower Michigan. Short range model guidance varies highly as to how this evolves with storm arrival times ranging from mid afternoon to after the TAF window. Given that evening guidance will have a better handle on ongoing storms than the previous guidance, will leave thunder out for now for the afternoon. Whenever storms develop, the strongest will be capable of IFR and lower conditions and gusty winds.

MARINE

Issued at 327 PM EDT Thu Jul 10 2025

Short range models presently favor winds and waves remaining below levels hazardous to small craft and beachgoers through the weekend. However a low (around 20 percent) chance of hazardous winds and waves exists later Friday into Saturday associated with a frontal boundary crossing the area. The other marine concern is that several rounds of showers and thunderstorms are likely through the weekend beginning early Friday. Locally higher winds and waves are possible in any storms, particularly later Friday and again on Saturday. Mariners and beachgoers should monitor the forecast this weekend.

GRR WATCHES/WARNINGS/ADVISORIES

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