Saint Johns, MI Weather

Key Messages

- Mild and dry weather with morning fog through the weekend

- Cooler temperatures and modest rain chances return next week

Discussion

Issued at 209 PM EDT Thu Oct 22 2026

- Mild and dry weather with morning fog through the weekend

Our extended stretch of pleasant fall weather continues for a few more days, thanks to a building ridge of high pressure and the return of southerly low level flow. Before we get to the next few days though, there is yet another potential for overnight and early morning fog in several areas tonight, with perhaps a slight increase in coverage as well. Light northeasterly winds are expected to carry increased low level moisture into the area this evening, and this should boost the potential for fog as radiative cooling commences under clear nighttime skies. High resolution model guidance (RRFS to be specific) continues to produce a convincing signal for fog locally, and when combined with the pattern and repeated fog development over the past few days, another round is expected tonight, likely with an increase in coverage.

From tomorrow through Sunday, the aforementioned upper ridge will continue to steadily build overhead, while a deep low pressure system across the Canadian Prairie drives southerly low level winds. This will produce consecutive days of well above average temperatures across lower Michigan (roughly 8-12 degrees above seasonal averages), equating to highs in the mid 60s to near 70s. Meanwhile, precipitation chances remain near zero throughout the weekend.

- Cooler temperatures and modest rain chances return next week

Between Sunday night and Monday afternoon, a weak back-door cold front will sink into lower Michigan as a shortwave passes well to our north. This will drive a steady cooling trend that will persist through mid-week, bringing temperatures back to near seasonal averages (highs in the upper 50s to low 60s / lows in the mod 30s to low 40s). Confidence in the temperature forecast is a bit lower overall on Monday, owing to ensemble member variation in the timing of the cold front and trailing cold air advection. This uncertainty is highlighted by increasing temperature forecast spreads on Monday in particular, with decreasing spreads Tuesday onward as a low-variance high pressure pattern becomes established.

Aviation

Issued at 702 PM EDT Thu Oct 22 2026

VFR conditions this evening deteriorate Friday morning as LIFR fog is favored to develop, potentially as low as 1/4SM at times. Best chance for dense fog is LAN/JXN where prevailing flow suggests moisture enhancement off of Lake Huron/Saginaw Bay/Lake Erie. Model guidance tends to underestimate fog intensity in these scenarios so have maintained the inherited forecast there. Some question of how far AZO/BTL/GRR deteriorate depending on inland penetration of moisture so observational trends will need to be monitored into the overnight hours. MKG is also not favored to see restrictions at this time given forecast high pressure placement, but that may change if wind direction does. Any fog that develops is forecast to mix out mid to late Friday morning.

Marine

Issued at 209 PM EDT Thu Oct 22 2026

Light winds and very low wave heights of 1 foot or less persist through tonight. Sustained south-southeast winds increase to near 10 kt tomorrow, and to 15 to 20 kt tomorrow, causing wave heights to increase to between 2 to 3 feet by Saturday afternoon, mainly north of Whitehall. These conditions largely continue through Sunday, but a cold front will bring a quick transition to northerly winds with similar speeds by Monday.