textproduct: Grand Rapids

KEY MESSAGES

- Rain and Thunderstorms This Afternoon into Tuesday

- Hot Wednesday

- Storms Wednesday night through Thursday night, severe possible

- Dry Friday, thunderstorm chances return for the weekend

DISCUSSION

Issued at 254 PM EDT Mon Jun 8 2026

- Rain and Thunderstorms This Afternoon into Tuesday

No real changes to previous thinking. We are now at a short enough forecast projection time to fully utilize the CAMs for assessing the heavy rain threat. Starting with the SPC HREF, LPMM/PMM QPF guidances advertises localized splotches of 2+ inches tonight into early Tuesday. This looks plausible given that we are looking at anomalously high precipitable water, nearly 13000 ft warm cloud depths, and almost stationary Mesoscale Beta Element (MBE) vectors, indicative of the potential for boundaries to synergize with convection in a way that keeps precipitation slow-moving. All of this being said, the individual CAM solutions point towards only scattered and progressive storms that would reduce the threat for heavy rain. That, when combined with relatively dry antecedent conditions, reduces the threat for flooding somewhat; however, rainfall rates could still be quite significant. Even half an hour of intense rainfall like this could be enough for localized flooding, especially across extensively paved areas.

For Tuesday, convection will eventually depart to the east and as noted previously, thunderstorms could redevelop in the afternoon/evening timeframe around US-127 during peak diurnal destabilization. Suboptimal thermodynamics and kinematics will likely keep this convection sub-severe.

Additional thunderstorms may develop with the warm front late Tuesday night into Wednesday morning, otherwise chances hold off until Wednesday night.

- Hot Wednesday

Wednesday looks to be the hottest day of the week with apparent temperatures reaching or exceeding 100F farther south towards I-94. Highs around 90F and dewpoints in the low to mid 70s are rather unusual for this time of year, so people will likely be unaccustomed to these type of conditions. The area will likely remain under partly cloudy skies until Wednesday night when the next round of thunderstorms enters the area.

- Storms Wednesday night through Thursday night, severe possible

An advancing upper level trough will bring increasingly southwest and slightly difluent flow to the area Wednesday through Thursday. This will provide ample synoptic forcing for multiple rounds of thunderstorms. Precipitable water (PWAT) values will remain anomalously high, approaching two inches, meaning that very efficient rainfall can be expected with quick accumulations even for the more rapidly moving storms.

As noted previously, we expect mainly remnant convection from WI Wednesday night. Downstream conditional instability over Lower MI will be quite strong with MUCAPE at or above 3000 J/kg. This suggests an outflow-dominant MCS will be the most likely storm mode, yet one still with the potential to create expansive damaging wind gusts.

After a pause in precipitation for the first part of Thursday, dynamic forcing for the Thursday night round of storms will be particularly strong with cyclonic breaking of the upper wave across the area in the 06-12Z Friday timeframe. Although this does coincide with maximal diurnal stabilization, it's highly plausible that an MCS with an already established cold pool will be upstream and poised to move into the forecast area. Furthermore, the shear and instability parameter spaces look better balanced compared to Wednesday night. This means probabilities are better for greater organization, intensity, and longevity with this particular system with the main threat being damaging winds.

- Dry Friday, thunderstorm chances return for the weekend

Dry air moves in behind the thunderstorms Thursday night bringing a break in the rainfall along with cooler temperatures. Rain chances return for the weekend with an upper level trough in the vicinity. The best chances (30 to 50 percent) continue to be Saturday night into Sunday as was also noted previously. This consistency in model guidance helps confidence a little, but predictability is simply not great at this time range after a succession of other precipitation events. So, be prepared for a possibly ever-changing weekend forecast.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 212 AM EDT Tue Jun 9 2026

2 main concerns the next 24 hours...the potential for low ceilings and threat of thunderstorms. Low ceilings are expected to develop and/or spread into the area over the course of the remainder of the night and into the morning hours of Tuesday. Ceilings will likely dip to IFR at most TAF sites during the 09z to 16z time frame. We expect improving ceilings during the afternoon on Tuesday as the low ceilings lift/spread northward.

As for thunderstorms, there are two distinct time frames, one is the rest of tonight and the other is this afternoon. For the remainder of the night the storms should be scattered and on the weak side. This afternoon, stronger storms are anticipated. KAZO, KBTL, KLAN and KJXN will be most affected. Storm chances are highest at these TAF sites from 18Z to 23Z.

MARINE

Issued at 254 PM EDT Mon Jun 8 2026

Waves are expected to remain 2 feet or less through Wednesday morning as winds remain light. Southeast winds are expected through tonight before shifting to the southwest behind the low. Rain and thunderstorms are expected late this afternoon into Tuesday. Expect low visibilities within any thunderstorms as they will be capable of heavy rainfall. The increased dew points over the cold waters of Lake Michigan may also pose a threat for fog as well. We'll need to monitor conditions in case a Marine Dense Fog Advisory is needed.

Winds and waves then pick up Wednesday afternoon into Thursday. South to southwest winds gusting to around 25 knots will cause waves to build to 3 to 6 feet especially for areas north of Holland and around the Sable Points.

GRR WATCHES/WARNINGS/ADVISORIES

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