textproduct: Grand Rapids

KEY MESSAGES

- Thunderstorms Move in Monday Night through Tuesday Night

- Rain Chances Return Late Week into Weekend

DISCUSSION

Issued at 251 PM EDT Sat Mar 28 2026

- Thunderstorms Move in Monday Night through Tuesday Night

After dry and mild days in store Sunday into Monday, there are two main periods of concern for thunderstorm potential, the first being late Monday night into Tuesday morning (SPC Day 3 Marginal Risk) and then again later Tuesday afternoon into early Tuesday night. For the first period, a classic nocturnal elevated storm setup will likely take shape across WI/MI late Monday night, possibly as early as midnight and then lasting into early Tuesday morning. As has been discussed, a robust and ideally oriented LLJ straight off the Gulf will advect in low level moisture at 50 to 60 kts and converge over a warm front draped across central Lower MI. Sufficient CAPE above 850mb on the order of 1000-1500 J/kg will support hail potential (also supported by mid level lapse rates of 7- 8 C/km). The 12z RRFS shows a plausible scenario with some elevated convection moving through during the 12am-8am Tuesday timeframe. One thing to watch will be whether any residual mixed layer instability remains in place. The RRFS and GFS indicate there may in fact be a few hundred J/kg of MLCAPE remaining but MLCIN could also be a hindrance. While hail will be the main threat, some wind damage can't be ruled out if MLCAPE lingers given such strong wind fields in place just off the surface.

Depending on when morning convection exits and to what extent our region destabilizes, organized convection may develop along and ahead of a strong cold front slated to move through Tuesday evening into Tuesday night. Given strong low and mid level jets, severe weather may occur with even modest mixing. NCAR's AI-based NWP Convective Hazards Forecasts continue to favor a threat for severe weather across Lower MI should this scenario materialize, with some AI models showing rather concerning severe probabilities in our region. This will have to be fine tuned over the next couple of days as the setup and threat become clearer. Outside of thunderstorms, Tuesday looks like a fairly windy day with some 30-40 mph gusts possible.

- Rain Chances Return Late Week into Weekend

Ensemble guidance is favoring a break in precipitation on Wednesday but with increasing odds for rain moving back in as early as Thursday. GEFS/ECE mean 500 mb heights and vorticity indicate a shortwave in SW flow moving our direction by Thursday. In spite of chilly temperatures in the 40s, this anticipated shortwave will help draw up higher PWAT values into the region. A chance for showers will return to the forecast and can't rule out a period of a wintry mix (less likely at this point). A more potent shortwave may arrive by next weekend bringing the risk for more rain and thunderstorms.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 724 PM EDT Sat Mar 28 2026

No changes to the forecast. High pressure overhead will advect sct-bkn mid/high clouds across the terminals through the period.

MARINE

Issued at 251 PM EDT Sat Mar 28 2026

Another SCA will be in place starting 5pm this evening from Whitehall to the north and then adding Holland to the north starting at 10pm this evening. This occurs as S/SW winds over the lake increase and hence wave activity will also be increasing. Waves look to decrease late Sunday afternoon into the evening.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory until 5 PM EDT Sunday for LMZ846-847. Small Craft Advisory until 5 PM EDT Sunday for LMZ848-849.