Marine Weather and Tide Forecast for Port Sanilac, MI

AVIATION

A ridge of high pressure in place gradually gives way as low pressure from the Plains begins to work into the southern Great Lakes. A feed of dry Canadian air maintains VFR conditions while high cloud steadily thickens and lowers through the day. The tightening pressure gradient results in easterly wind becoming gusty to around 20 to 25 kt. An arc of light rain moves in from the southwest late in the day, reaching the terminal corridor around or after sunset and continuing into the overnight period. Deeper saturation brings ceilings down to MVFR after midnight, then to IFR in the Metro area Wednesday morning as the center of low pressure arrives just to the south.

For DTW/D21 Convection...No thunderstorms through tonight.

THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less after 00z after midnight and through Wednesday.

PREV DISCUSSION
Issued at 324 AM EDT Tue May 20 2025

DISCUSSION...

The upper low churning over the northern plains will undergo considerable shearing over the next 24 to 36 hours. Additional mid level troughing and convectively induced vorticity maxima will in turn advance across the Ohio Valley late today through tonight.
There will be a strengthening axis of mid level deformation between these waves and the high amplitude ridging across the eastern and northern Great Lakes. The majority of model solutions drive this mid level frontal forcing into SW Lower Mi this afternoon, then across Se Mi late this afternoon and this evening, eventually into the Saginaw Valley/thumb region toward Wed morning. The mid level forcing will warrant high pops tonight. Considering the proximity to the mid level ridging and greater depth of low level dry air, the rain chances will remain lower in the thumb region tonight. The easterly gradient will increase during the course of the day, maintaining some degree of influence off the lakes. This and a thickening high cloud canopy will limit diurnal heating, supporting highs from the mid 50s to low 60s.

An elongated mid level low is forecast to evolve across the nrn Ohio Valley and eastern Great Lakes region Wednesday. There are variations among the model ensemble members as to the extent of interaction between this developing low and another upper low rotating into the northern Great Lakes from the James Bay region.
The main point of interest will be to what degree if any mid level deformation is enhanced across central and southern Lower Mi. There is at least enough support among the ensemble members to carry high probabilities for rain. Model soundings also indicate ample low level moistening. So even if the mid level forcing is a little on the lean side, low level moist cyclonic flow should support areas of drizzle.
Sfc cyclogenesis across the eastern lakes will result in a strengthening northeasterly wind off Lake Huron. This and the ample low clouds will result in a very chilly late May day Wednesday with forecast afternoon highs only in the low to mid 50s.

The aforementioned upper low over the northern Great Lakes is forecast to expand southward Thursday before advancing to New England by Saturday. This will maintain seasonally cool conditions across the region into the start of the weekend before rebounding heights offer a potential warming trend toward the end of the forecast period.

MARINE...

A low pressure system will cross the Midwest today before getting deflected into the northern Ohio Valley and eastern Great Lakes by Wednesday. This brings periods of rain and stronger winds for the central Great Lakes. New Small Craft Advisories have been issued for all the nearshore zones Tuesday morning through Wednesday morning.
Gusts should easily climb into the upper 20 knot range along the coastal areas by Tuesday afternoon with occasional wave heights in excess of 5 feet for most areas. Modest pressure gradient maintains 15-20 knot prevailing winds through Wednesday as the center of the system moves into the eastern Great Lakes by Wednesday night. The system will be slow to fully exit which keeps additional opportunities for Small Craft Advisory extensions into the late week time-frame.

HYDROLOGY...

An elevated front will bring the widely scattered to numerous rain showers from south to north late today and tonight. Shower coverage will expand north through Wednesday morning and afternoon. There is reasonably high confidence that total rainfall from this afternoon through Wednesday evening will be between a quarter and a half inch.
Chances for rain totals exceeding a half an inch are generally below 30 percent. The rain will occur over roughly a 24 to 36 hour period, so flooding is not expected.

DTX WATCHES/WARNINGS/ADVISORIES
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT Thursday for LHZ421-422.

Small Craft Advisory from 10 AM this morning to 10 PM EDT Thursday for LHZ441>443.

Lake St Clair...Small Craft Advisory from 10 AM this morning to 10 AM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM this morning to 10 AM EDT Wednesday for LEZ444.