Marine Weather and Tide Forecast for St. James, MI

DISCUSSION
Issued at 103 PM EDT Wed Jun 17 2026

Pattern Synopsis/Forecast: Closed upper-level low pressure continues to spin just south of Hudson Bay this afternoon -- likely to remain in a similar position into the start of the weekend before ejecting east. Longwave troughing evident across the eastern two-thirds of NOAM with an embedded shortwave pinwheeling around closed upper low to our north into the western Great Lakes this afternoon. This aiding in impressively deep (for mid-June) surface low development on the nose of 130+ kt jet streak that extends from British Columbia southeastward through the northern Plains into the mid-MS Valley. As has been noted for several days, the strength of this system is noteworthy as sub-700 mb heights and MSLP remain progged to be lower/deeper than any comparison from the '79-'09 CFSR climatology for a multi-week period centered on June 18th.

Low pressure departs east on Thursday, although lingering wrap around moisture and mid-level perturbation(s) likely to yield a fall- like day across much of the forecast area. Beyond Thursday, broad troughing likely to persist across the Great Lakes through at least the upcoming weekend with at least slightly below normal temperatures expected to continue.

Forecast Details: Increasing/thickening clouds across northern MI early this afternoon with initial rain chances expected to build into the southwestern reaches of the forecast area in the next few hours. Current confidence is for rain to spread farther northeastward across much of northern lower by 22-00z, and into the eastern U.P. during the mid-evening hours. Latest trends favor steadiest rain falling over portions of northern lower before exiting east through the overnight hours. Highest probabilities exist in northern lower for 0.40 - 0.75" of QPF. Low probabilities (<30%) for 1"+, with those probs maximized near the M-55 corridor where likelihood of some embedded convection is highest. While strong to severe storms are not the expectation, elevated instability upwards of 500 J/kg is favored near and south of M-55 this evening. Hail would be the primary threat if any organized storms can manifest. Wind not so much of a concern given there should be a strong inversion in place, but that said, strong jet dynamics/jet coupling nearby may aid in introducing the potential for gravity waves, which would indicate a locally damaging wind threat despite that inversion.

Thursday shaping up to a be a fall-like day with some wrap around isolated to scattered lingering showers, lots of clouds, breezy west- northwest winds all leading to below normal daytime temperatures.
Slowly moderating temperatures expected heading into the weekend along with generally drier conditions (although some low shower chances do exist at times over the weekend). High temperatures favored to remain a few degrees below normal through at least early next week.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
Issued at 740 PM EDT Wed Jun 17 2026

Rain continues to overspread northern MI. Vsbys and cigs will continue to lower tonight, with IFR to LIFR at all sites for part of the overnight into Thursday morning. A stray TSRA is possible, especially as you head further south (MBL/TVC with the best chance). Conditions improve heading to Thursday midday and afternoon. Easterly breeze increase for a time tonight, with breezier nw winds kicking in Thursday.

APX WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...Small Craft Advisory until 8 PM EDT Thursday for LHZ348-349.