Marine Weather and Tide Forecast for Bay City, MI

AVIATION

Mid to late afternoon storms across SE Mi continue to exit into Lake Huron and Ontario as attention is turned upstream for this evening.
Activity over IN/IL represent a few extra hours shower/storm support in SE Mi, mainly from PTK southward across the DTW corridor. The standard wide range of flight conditions in briefly heavy rain transitions to a more persistent MVFR ceiling toward FNT and mbS.
These clouds attempt to fill in toward the south while loosely confined by the southward progress of the diffuse trough that trails the northern Great Lakes surface low moving into Ontario by sunrise.
This boundary moves back northward as new low pressure develops in the upper Midwest followed by scattered to broken VFR ceiling and reinforcement of heat and humidity into Lower Mi for Wed afternoon.
The air mass supports a stray late day thunderstorm however the bulk of new storm activity is projected for later Wednesday evening.

D21/DTW Convection...The time window for scattered thunderstorms is extended a few more hours until closer to midnight tonight.
Thunderstorms end after midnight and are not expected to redevelop through mid afternoon Wednesday.

DTW THRESHOLD PROBABILITIES

* Moderate for ceiling aob 5000 feet tonight and Wednesday.

* Moderate for thunderstorms from 00Z to 04Z this evening.

PREV DISCUSSION
Issued at 354 PM EDT Tue Jun 9 2026

DISCUSSION...

Active midday period arose as a persistent cyclonic swirl developed at the lead edge of a lower atmosphere kinematic surge. Backed flow and enhanced helicity in a buoyant near surface environment were enough to bring a heightened potential for tornadic circulations.
Model data suggests the convergence maximum associated with this troughing signal will carry northward out into Lake Huron late this afternoon.

With the establishment of a deeper boundary layer and greater unidirectional flow, forecast reasoning for the remainder of the day was provided in earlier discussions and remains valid. The main concern for the late afternoon and evening will be the potential for isolated flooding from heavy downpours and isolated strong to severe wind gusts from wet microbursts.

Upper level ridging is shown to amplify again locally over the central Great Lakes Wednesday with a good amount of convectively modulated moisture/saturation contained within the rising heights.
The net result is a very warm and humid airmass expected with low predictability with regards to convective timing and coverage.
Clouds are a tough forecast in a moist environment, however NAM RH progs and probabilistic NBM gives low probs for greater than 50% of total cloud coverage 10am to 6pm Wednesday. With dewpoints reaching the lower 70s and highs reaching +90 degrees there is high confidence in Wet Bulb Globe temperatures (accounting for June sun effects) exceeding 88 degrees. Decided to go ahead an issue a Heat Advisory for Wednesday between Noon and 8pm EDT.

Proximity and approach of upper level troughing will bring the potential for upstream convection to make a run at Southeast Michigan at various times late Wednesday. Challenging to pin down favored time windows as hires signal suggests multiple opportunities for thunderstorms all the while Southeast Michigan will be in a low shear environment. As a result, MCS activity will have the potential to weaken rapidly at approach both Wednesday evening and/or possibly again late Wednesday night. Timing of the convection will likely determine the potential for severe weather because a subset of solutions exist that instability will be elevated for any late Wednesday night thunderstorms. It is also after the 6Z Thursday timeframe that heaviest rainfall potential may occur. Not anticipating much mesocyclone threat Wednesday which limits severe weather type to large hail to 1 inch and/or damaging wind gusts to 60 mph. Southeast Michigan is designated as a Marginal risk for severe weather.

A good anticyclonic vorticity advection signal exists early Thursday in a favorable zone for subsidence downstream of the approaching upper level PV maximum. The subsidence is expected to result in a good amount of clearing with NBM probabilities showing 0-50% of greater than 50% cloud cover. Expectations are for a quick recovery of the hot and humid conditions with heat indices rising into the 90 to 100 degree range. A Heat Advisory will likely be needed again Thursday for at least a portion of Southeast Michigan.

A strong absolute vorticity center is forecasted to lift into the Straits region Thursday evening driving the main jet core and cold front into Lower Michigan Thursday evening/night. It appears that deep layer shear will increase immediately in advance of the cold front with 0- 6km bulk shear values climbing between 30-50 knots. A probable solution is that convection will organize over portions of Iowa and Illinois before advancing eastward along a forward propagating cold pool. A few solutions, including 12km NAM, GEM, and RRFS suggests a linear mode MCS system tracking towards lower Michigan around 3z Friday. The latest Swody3 has Southeast Michigan designated as a Slight Risk for severe weather.

Zonal flow pattern aloft will develop over the Great Lakes region bringing more seasonable conditions to Southeast Michigan Friday and the start of the weekend. Latest indications suggests a secondary cold front impinging southward sometime Sunday.

MARINE...

Weak low pressure over northern Lower MI tracks into Lake Huron this evening. Scattered showers and thunderstorms will continue to spread across the local area as high humidity surges in. This humidity will cause marine fog to develop over the cool open waters of Lake Huron tonight, and a Dense Fog Advisory may be needed. Southeast wind around 10 kt will veer around to westerly as the low passes through overnight into Wednesday morning. A warm and unstable air mass will then take residence Wednesday and Thursday, bringing additional chances for showers and thunderstorms as several disturbances move through. Severe storms will be possible, mainly Wednesday night and again Thursday night. Prevailing wind will be out of the west and southwest with potential for gusts upwards of 20 kt at times, especially over the shallower, warmer waters of Saginaw Bay, western Lake Erie, and Lake St. Clair. A cold front passes through the region Thursday night and brings a brief period of drier conditions.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory from noon to 8 PM EDT Wednesday for MIZ069-070-075- 076-082-083.

Lake Huron...None.

Lake St Clair...None.

Michigan waters of Lake Erie...None.