Marine Weather and Tide Forecast for Plymouth, MI

AVIATION

MVFR ceilings are vacating to northern Ohio as drier low level air is drawn into the area. Upstream observations show ceilings ranging from 5-7kft which will expand over the region through the rest of the night. Scattering in cloud coverage also expected towards the early morning hours as drier air becomes more established. That said, some VFR diurnal cloud still possible by late Thursday morning. Modest NNW with peak gusts near 20kts hold for much of the day Thursday before high pressure builds overhead supporting light and variable flow by Thursday night.

D21/DTW Convection... No thunderstorms are in the forecast today through Thursday.

DTW THRESHOLD PROBABILITIES

* High for ceiling 5000 ft or less tonight, low by Thursday morning.

PREV DISCUSSION
Issued at 414 PM EDT Wed May 13 2026

DISCUSSION...

Resident occluded low remains anchored just east of Georgian Bay, maintaining cyclonic flow aloft into the overnight hours. A dense stratocumulus field has engulfed the lower peninsula today, but shower activity has been minimal given shallow saturation and instability depths. Light reflectivity returns have been sampled per KDTX and CASET radars over portions of The Thumb region as a lobe of CVA passes overhead. Only a brief detection of rainfall was reported at KBAX indicating mostly virga through the near-term. For the rest of today, expect a slight expansion in virga and light shower coverage over The Thumb after low-level flow veers from WNW to NNW this evening. Low-end potential exists for light activity to expand further inland/downwind of the Lake Huron shoreline late evening and early tonight. Current gustiness in the 25-30 mph range will linger into the early overnight hours as a surface-based mixed layer persists while 30 knot LLJ flow extends down to 2 kft AGL. By mid- May standards, much chillier tonight with temperatures dropping into the lower 40s. Should the existing cloud deck clear out more aggressively, a few locations could drop below 40F by sunrise, especially for areas west of US-23 where anticyclonic flow approaches sooner. Patchy frost will be possible west of US-23.

A synoptic pattern shift gets underway on Thursday as geopotential heights rise with inbound longwave ridging. At the surface, high pressure builds in, but becomes more diffuse as it extends from The Gulf up to Hudson Bay. Dry conditions are likely since the mature low ejects southeastward across the eastern Great Lakes and drier continental Canadian air filters in through the mid and upper levels. Seasonably cool again Thursday with temperatures in the lower 60s, capped by marine-layer modified NNE flow given cool Lake Huron waters. Winds trend toward calm and eventually flip southerly Friday which marks the start of a warming trend.

The ridge axis gets sheared out on Friday, in part due to a higher amplitude trough feature of Pacific origin moving into Manitoba. The wave starts to fill in mid-morning as it drifts toward western Ontario. Its cyclonic flow field appears expansive, with favorable low-level dynamics to quickly ramp-up warm advection. 850 mb temperatures jump from the single digits (Celsius) into the teens by Friday night. Initial phase of moistening over Lower Michigan occurs Friday afternoon, but will be insufficient for a precipitation response. More substantial ThetaE advection arrives Saturday evening, but it will generally be confined to the lower troposphere. Forecast soundings indicate a weak capping inversion could prevent surface- based parcels, but elevated instability could promote a nocturnal response. Potential exists for a decaying MCS to move in on Saturday with additional convective activity dependent on the progress of a frontal boundary from the Ontario low. An unusually hot and increasingly unstable airmass resides for much weekend with highs into the 80s amidst a growing reservoir of potential instability.

MARINE...

Low pressure is now over Georgian Bay, with just isolated shower coverage showing up over Lake Huron. Winds have organized out of the northwest with gusts of 25 to 30 knots spanning all marine areas.
Elevated wave plume has started to clip the nearshore in the northwest flow regime, with wave heights of 4 to 6 feet peaking overnight. Gradual departure of the low into Ontario will relax the pressure gradient and allow wind speeds to subside Thursday, with all ongoing Small Craft Advisories set to expire by Thursday afternoon. Transition to breezy southerly flow expected Friday as the high departs and low pressure center slides across Ontario.
Trough axis extending from the parent low into CONUS gets pinched off as it moves overhead this weekend, resulting in an unsettled and uncertain precipitation pattern for the weekend-early next week.

DTX WATCHES/WARNINGS/ADVISORIES
MI...None.
Lake Huron...Small Craft Advisory until 10 AM EDT Thursday for LHZ421.

Small Craft Advisory until 4 PM EDT Thursday for LHZ441>443.

Lake St Clair...None.
Michigan waters of Lake Erie...None.