textproduct: Grand Rapids

KEY MESSAGES

- Cool and dry today

- Warming trend midweek, chance of a thunderstorm Tuesday evening and Friday

DISCUSSION

Issued at 313 AM EDT Mon Apr 20 2026

- Cool and dry today

Lingering cold air mass underneath high pressure today will keep temperatures about 10 degrees below normal. Dew points will stay rather dry in the teens and 20s, and relative humidity should drop toward about 30 percent.

- Warming trend midweek, chance of a thunderstorm Tuesday evening and Friday

High pressure moving away and increasing southwesterly low-level flow on Tuesday will bring a quick return of milder and less dry air. There is a slight chance of a sprinkle Tuesday morning as midlevel moisture precipitates into dry air, for now not mentioning in the forecast. Then have a chance of showers and slight chance thunderstorm near I-94 Tuesday evening. Southwesterly flow with higher moisture around 800 mb may support the development of elevated showers or thunderstorm cells while cooler temperatures and modestly steep lapse rates are present 700-500 mb. Not all models develop convection near I-94, but some including the HRRR and experimental MPAS core models do. If a relatively robust cell develops late in the day while mixed lower levels are present underneath, locally gusty winds would be possible.

Ensembles continue to favor Thursday as the warmest day of the week with highs well into the 70s. Instability should return to some degree, and a weak cold front extending from a Northern Plains occluded low should move through Michigan on Friday, bringing a chance of showers and thunderstorms.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 102 PM EDT Mon Apr 20 2026

High confidence in VFR through the TAF period as high pressure and a dry ambient airmass drive the forecast. FEW to SCT mid and high clouds are expected over the next 24 hours, with enough wind to mitigate any fog concerns. The only impactful weather is a period of LLWS developing late tonight into Tuesday morning as a 40 kt LLJ moves overhead. Winds increase to around 15 knots with gusts to 20-25 knots from the southwest after daybreak Tuesday.

MARINE

Issued at 313 AM EDT Mon Apr 20 2026

Light winds and low waves this morning in the nearshore waters. Increasing south winds particularly north of Whitehall late in the day will tend to build waves. A small craft advisory will likely be needed there starting after sunset today. Small craft advisory conditions are likely along the whole shoreline Tuesday morning.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 8 PM this evening to 5 PM EDT Tuesday for LMZ844>849.