Marine Weather and Tide Forecast for Grand Beach, MI

DISCUSSION
Issued at 220 PM EDT Tue May 13 2025

Upper low center over the western TN Valley will finally get a push north into the OH Valley and southern Great Lakes tonight into Wednesday in response to a deep upper trough edging east toward the Rockies. This system will continue to generate isolated to scattered showers and storms (mainly diurnal) thanks to a moist column through much of the troposphere and just enough diurnal heating, with the greatest coverage likely focused near small scale vort lobes rotating around the upper low. Overall weak dynamics, flow and instability precludes a severe wx risk with lightning, brief downpours and cold air funnels possible with heavier showers each afternoon.

The Rockies upper low will eject into the northern Plains and Upper Midwest Thursday into Thursday night with an associated strong sfc low emerging over MN by Friday morning per latest guidance. A leading warm front and low level theta-e ridge advect into the local area on Thursday with warm temps (near records) and a conditional severe risk Thursday night. Progged shear/instability profiles check the box for potential deep/severe convection, however, delayed forcing and what looks to be a very warm EML base may keep a lid on organized convection along an incoming pre-frontal trough or convective outflow.

Height falls eventually slide east through the Great Lakes Friday into Saturday with the upcoming weekend trending cooler, dry and breezy in response to the suppression. Could see another frontal wave drive a convective complex through the region Friday PM in this transition, though the bulk of guidance continues to favor areas off the south for more organized convection chances. Thursday night's activity, or lack thereof, will dictate the timing/track of Friday's potential convective system.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
Issued at 138 PM EDT Tue May 13 2025

Modest heating and at least some instability is allowing for a slow increase in coverage of showers which have already impacted KFWA. Cigs/vsbys will be rather variable through 00Z, but should reside mainly in the MVFR range outside of any convection. For the time being have removed the tempo group for thunder as confidence in duration and coverage isn't quite high enough to warrant a 4 hour period. Some lightning is noted upstream (SE of the site) that could maybe signal a small period of thunder later. Will amend if needed. At KSBN, some showers will be nearby, but confidence on coverage and impacts there is even lower. Have kept with a pop30 this afternoon and will see how the coverage evolves. Higher end MVFR cigs are likely to stick around with any showers bringing a shot for brief IFR cigs.

Any convection should quickly wind down after 00Z. Given the moist atmosphere, will need to watch for stratus deck to lower overnight with IFR cigs at 1 or both sites. Will fine tune in later forecasts.

IWX WATCHES/WARNINGS/ADVISORIES
IN...None.
OH...None.
MI...None.
MARINE...None.