textproduct: Grand Rapids

KEY MESSAGES

- Round of storms expected overnight

- Another round of storms late Saturday night/Sunday morning

- Stronger storms expected both Monday and Tuesday

DISCUSSION

Issued at 310 PM EDT Fri May 15 2026

- Round of storms expected overnight

Strong to severe thunderstorms are expected to erupt this afternoon and evening across Western Iowa. These storms will roll east and push out over Lake Michigan in a weakening state after 200am. A round of likely sub severe storms will move into Western Lower Michigan off the lake around 400am. The storms will sweep east and out of our area including the Highway 127 corridor by 800am or 900am. Some light rain will linger into the day on Saturday ending from west to east in the afternoon. Wind will be the main threat overnight with wind gusts to 45mph or so possible over the lakeshore counties. Could envision needing a few Special Marine Warnings or Special Weather Statements.

- Another round of storms late Saturday night/Sunday morning

After the showers and storms press off to the south and east on Saturday an effective boundary will be located in that direction. A warm front will push northward into and through the area late tonight and on Sunday. While the low level jet is on the weaker side during this time frame the moisture surge is not trivial. Expecting showers and storms as the warm front pushes northward through the area. Models are not bullish at all on precipitation, so this time frame is lower confidence.

- Stronger storms expected both Monday and Tuesday

Better chances for severe weather exist on both Monday and Tuesday. Monday's event looks to occur during the afternoon and/or evening associated with a strong low level jet (LLJ) and what appears to be a MCV from upstream convection. It is early to be nailing down timing of such a feature, but the 35-45 knot LLJ and moisture surge of +15C dew points point towards a higher threat. SPC agrees with a day 4 slight risk.

There may be a break in the convective activity Monday night into Tuesday morning, but the LLJ remains strong leading one to believe storms may continue through the night. Another round of storms is likely then on Tuesday ahead of the main cold frontal passage during the afternoon and evening. The front is strong with a healthy dew point gradient across it. Lift from the front alone will be enough to drive convection some that could be strong. as Monday and Tuesday get closer we will better fine tune threats.

PWAT values increase to around 1.75 inches especially on Monday and Tuesday which will make heavy rain a distinct possibility. The good news is rivers have receded significantly from last months rainfall so we have room in the rivers for absorb rises. Expecting heavier swaths, but forecast rainfall amounts are mainly in the 0.50 to 1.25 inch range. Localized short term flooding is possible in spots given PWAT values that are off the charts for this time of year.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1223 AM EDT Sat May 16 2026

Regional radar shows thunderstorms over Wisconsin moving east at 40kts. This places the storms over the lake around 430-500 am...pretty much in line with recent CAM trends. Storms will then move across the cwa and exit around 12z. The rest of the period looks to be dry.

As the LLJ moves across the terminals early this morning, some LLWS is possible from 08z-14z or so. Cigs may briefly fall to MVFR as the precipitation moves through, then rise back to VFR by late morning.

MARINE

Issued at 310 PM EDT Fri May 15 2026

A Small Craft Advisory is in effect through 500am Saturday as strong south winds will continue into tonight. Winds along the lakeshore at this time are gusting towards 30 knots. We expect winds and waves to settle some overnight with waves falling below 4 feet by daybreak. A more slack gradient will set up for Saturday into Sunday. So for the weekend better conditions are expected, although there will be rounds of thunderstorms.

FIRE WEATHER

Issued at 310 PM EDT Fri May 15 2026

After coordinating with the Michigan DNR, we will not issue a Fire Weather Watch for Saturday across Central Lower Michigan. First, it appears criteria may be close but not fully met. It will be warm with highs in the 80s, winds look to potentially be just shy of criteria in the 10-20 mph range and RH will be just above criteria as well dipping into the lower 30s percent. Secondly and more importantly, the DNR is mainly worried about the jackpine forest of Northern Lower Michigan based on conditions they monitor. An increased fire danger is expected across much of the area on Saturday with Central Michigan being the closest to criteria. Fully met criteria will occur north of our area.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory until 5 AM EDT early this morning for LMZ846>849.