textproduct: Grand Rapids

KEY MESSAGES

- Warmer with increasing chances of showers/storms into next week

- Strong to severe storms possible Monday

- Cooler mid to late week

DISCUSSION

Issued at 316 AM EDT Fri May 15 2026

- Warmer with increasing chances of showers/storms into next week

Radar imagery shows light showers moving across eastern WI toward the cwa. There has been a slow decay of these showers as they encounter much drier air as seen on 00z soundings. We don't expect much more than a mid deck and a few sprinkles as they move across the cwa this morning. By afternoon, we'll see the clouds thin with increasing amounts of sunshine which will help to boost temperatures into the lower 70s.

The next chance for rain comes after midnight tonight as convective development along a weak trough over Wisconsin moves east in quasi zonal flow aloft. HRRR max reflectivity and RRFS-EMC both indicate showers/storms over Lake MI around 08z and exiting the cwa Saturday morning around 12z. Mid level lapse rates climb to around 7c/km south of I-96 and that would be where we'd likely see any stronger storms tonight. Later Saturday afternoon, H8 temperatures around 14c will translate to close to 80 at the surface. More storms are expected along a warm front across northern Indiana Saturday afternoon. Some of those storms could be strong to severe but CAMs indicate they will likely remain south of the cwa.

Sunday will be mostly precipitation free, but warm and humid with highs in the 80s and dewpoints climbing into the mid 60s.

- Strong to severe storms possible Monday

As upper ridging drifts east Sunday night, an upper trough and surface low will advance eastward toward the Great Lakes. This is the time that moisture transport vectors increase significantly. NCAR medium range AI convective progs continue to suggest the possibility of severe storms Monday as the approaching upper trough collides with a moist and unstable airmass. Shear values increase to 45-50 kts Monday afternoon south of I-96 and SBCAPE increases to 2000+ j/kg. The severe threat could last into Tuesday as the cold front will still be west of the cwa. We'll definitely keep an eye on this.

- Cooler mid to late week

The cold front is currently progd to move across the cwa Tuesday afternoon, after which cooler air will begin to move back across the cwa. Highs Wednesday and Thursday will be in the 60s before climbing back to around 70 by Friday.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 624 AM EDT Fri May 15 2026

Clouds have overspread the terminals as the remnants of showers to the west dissipate and move across the state. We'll see these clouds thin out later this morning. The next chance for showers/storms is late tonight after 08z. Models are suggesting storms develop in Wisconsin tonight and move across the southern portion of Lower MI after 06z.

MARINE

Issued at 316 AM EDT Fri May 15 2026

A small craft advisory remains in effect north of Holland through tonight. The pressure gradient will tighten as the high drifts east and low pressure approaches from the west. Waves 3 to 5 feet are expected in the advisory area.

Another small craft advisory may be needed Sunday night as another low approaches from the west. 146

FIRE WEATHER

Issued at 316 AM EDT Fri May 15 2026

Low dewpoints and increase afternoon temperatures are beginning to result in elevated fire danger across the region. Fuels are drying out and latest fire danger readings are high to very high across the southern cwa and moderate over the north. South winds will gust to 25 mph today but also bring in some moisture from the south. Minimum relative humidities around 35 percent will be located in the northeast cwa early afternoon before the higher dewpoints arrive and push relative humidity values upward.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory until 5 AM EDT Saturday for LMZ846>849.