textproduct: Grand Rapids

KEY MESSAGES

- Chance for Isolated Thunderstorms This afternoon and evening

- Foggy and chances for light rainfall through the south to end the work week

- Precipitation Chances This Weekend

DISCUSSION

Issued at 234 PM EDT Wed Aug 12 2026

- Chance for Isolated Thunderstorms This afternoon and evening

Low stratocu continues to remain through the southern tier of Michigan with light southerly winds. Severe weather through Indiana continues to track to the south east with any outflow moving northward running into a wall of stability. That stability will stifle any convection this afternoon and evening through southern Michigan. The sole caveat will be convection from boundary interactions. Currently there is three different outflow boundaries moving in different directions that are set to intersect through southwest MI. There are some CAMS that suggest that some convection could form. SFC based CAPE is around 1000 J/KG along the I 94 corridor. However, there is upwards of 200 J/KG of CIN. So while it is possible that convection could form through the south and will need to be watched, the stable air could preclude storm development.

The better chance will be as a speed max moves from the east to southeast across central lower MI. Lapse rates in the tri city area are 6 to 7 C/km through the mid levels. Couple that with MU CAPE around 1400 J/KG and PWATS of 1.43 inches and you have a decent environment for storm development. There is some cu development through central and norther lower. However, a large cirrus shield should limit daytime heating, though Max temps along the US 10 corridor could get into the mid 80s. Latest CAMS continue to suggest the potential for isolated storms to be possible after 20Z. DCAPES are in the 800 to 900 J/KG range so Damaging winds are the main concern. Any shower and storm chances will dwindle through the evening hours,

- Foggy and chances for light rainfall through the south to end the work week

Any rainfall and convection will add to the moisture throughout the lower levels through southern Michigan. Calm winds, a stable air mass and moist lower levels is a great recipe for another round of fog through Thursday morning. Expect areas of fog to develop overnight. Fog could be denser than this morning's but will hold off on any advisories for now. Another upper level trough will drop down from the west tomorrow. The track of that trough is trending towards this week's previous systems. They are trending towards IN south into Ohio. The only precipitation could be on the fringes along the I 94 corridor. Only light rain is expected with a low chance for any thunder.

- Precipitation Chances This Weekend

The next chance for widespread precipitation will be Saturday night and Sunday as the pattern shifts and the zonal flow shifts northward bringing a mid level shortwave propagates over high pressure building into the Great Plains. That short wave will bring decent surge of moisture Sunday. There is some question on timing an position of the mid level trough. However there should be good thickness advection with MUCAPE values in excess of 2000 J/KG. So there is the persistent trend for the potential for stronger storms. Mid to long range models also continue to show a 35 to 40 kt 850mb jet through Lower Michigan Sunday morning. This will aid storm development Sunday.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 745 PM EDT Wed Aug 12 2026

MVFR ceilings persist early this evening along the I-94 corridor, including AZO/BTL/JXN. As discussed previously, these clouds have indeed been slower to erode during the day. Even though these clouds may ultimately break up for a brief period this evening, this set up will likely exacerbate the development of IFR fog and vsbys again tonight in all areas, given elevated dew points, recent rainfall, and light winds.

The low clouds and fog area-wide /IFR conditions/ will dissipate roughly 12-13Z, with a few CU/SC and thickening mid/upper clouds thereafter /VFR/.

Winds will remain light and variable throughout the TAF period, with the exception of an onshore lake breeze at MKG after 18Z.

MARINE

Issued at 247 PM EDT Wed Aug 12 2026

Not expecting much winds and waves over the next few days. The main concerns will be the potential for marine fog and any thunderstorms moving from the west in the afternoons. Fog will remain a threat over the water until drier dew points move into the region. That does not really happen this week so the threat of fog will continue through the rest of the week.

GRR WATCHES/WARNINGS/ADVISORIES

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