Marine Weather and Tide Forecast for South Monroe, MI

AVIATION

Shallow cold advection in the wake of a cold front will bring a lowering inversion and a likelihood for MVFR stratus tonight. There does remain a potential for IFR cigs with some chance at reduced visibilities in light br, however, forecast soundings have trended more optimistic. Confidence is low on fog with a lack of clearing.
MVFR conditions at daybreak are expected to transition to VFR ceilings for Saturday afternoon.

DTW THRESHOLD PROBABILITIES

* High for ceiling at or below 5000 ft tonight.

PREV DISCUSSION
Issued at 338 PM EDT Fri Apr 25 2025

DISCUSSION...

A pair of longwave troughs will impact the region the rest of today through tonight. The first trough of note is a weaker southern stream trough with very little jet support, but several weak shortwave embedded within it. The stronger trough is lagging a bit to the west dropping into the Midwest this afternoon before strengthening and becoming more closed off while passing over Lake Huron Saturday afternoon.

The leading southern stream trough complex will lift through SE MI this afternoon/evening bringing the chance showers and thunderstorms to the area. We were able to clear out most of the clouds for a good chunk of the day helping to destabilize the boundary layer a bit. In addition, a stalled frontal boundary lifted north of the state line from and is draped along the I69 corridor which allowed mid 70s to surge northward through the region with dewpoints into the mid 50s.
deeper moisture will lift north over the next few hours as low pressure tries to come together along the front with dewpoints rising into the low 60s. In addition, PWATs are expected to rise to around 1.25 inches so moisture will be ample for storm/shower development and heavy rain. CAPE values per SPC Meso Analysis has already climbed to around 1500 J/kg south of M59 and 1000 up to Port Huron. Low level lapse rates will become strong but mid level lapse rates are weak, as is overall shear profile. Without stronger upper level or low level jet support, shear will struggle to help organize storms. You have to get up to around 20kft to get winds over 30 knots. Models are advertising a brief window this evening where the low level convergence of the surface front and the deformation of the surface low come together over the Irish Hills helping to enhance the storms coverage and intensity before the low peals off to the east pulling the cluster of storms eastward through St Clair, Macomb, and Wayne Counties. Main threat with these storms will be heavy rainfall with storm motions around 20 knots and slow movement to the cluster as it pivots around the low so we remain in a Marginal Risk of excessive rainfall from the WPC. Gusts look to largely remain in the 40-50 mph range but can't rule out a stray gust to 60 mph. Trough pushes east of the region between 00-03Z which will end the threat of storms.

Second northern stream trough then pushes through the region tonight into Saturday. A cold front will push through Saturday morning with pretty good cold advection behind it with 850mb temps down to -3C behind it. Northerly cold flow through the day will help limit max Ts to the 50s. Model soundings mix up to around 4kft which will tap into winds of 25-30 knots so should be a gusty afternoon. Precip on the trailing trough may stay north of the area during the day, but could also brush southward into the Thumb producing light rain. Will lean dry with this forecast with high pressure actively building across the Great Lakes.

High pressure then holds across the region Sunday and Monday with a warming trend back into the 60s Sunday and 70s Monday as ridging amplifies over the eastern conus. Attention in the long term remains on Tuesday as the next cold front sweeps through the region presenting the next chance of strong to severe storms.

MARINE...

A low pressure system lifts through Lower Michigan today offering opportunities for showers and thunderstorms this afternoon and evening within the system's warm sector. Localized higher winds and waves are possible with any isolated strong to severe storms that move through. Relatively light non-convective winds back with time before strengthening from northern Lake Huron down to the southern waterways, tied to the progression of the system's cold front tonight. Cold advection and northwest flow promote an uptick in gradient winds, into the 15 to 20 knot range early Saturday which results in increased wave action along the southern Huron nearshores. As such, the Small Craft Advisory will remain in place.
It has been expanded to include Inner Saginaw Bay given sufficiently steep low-level lapse rates mixing down 25-30 knot winds from between 2-4 kft AWL. The surface low then spins into the eastern Great Lakes Saturday while the back edge of the system lingers over the Huron basin. It will take some time for the gradient to relax as high pressure builds in, eventually leading to weaker and more variable winds. A much more potent low pressure system organizes out west Monday into Tuesday featuring a pre-frontal warm sector with gusty winds, followed by a strong cold front. Expect a period of thunderstorms and gusts in excess of 30 knots.

HYDROLOGY...

Increasing daytime instability and surface low pressure arriving this afternoon will support showers and scattered thunderstorms, as PW values rise aoa 1.25 inches. Increased coverage of shower and storm potential will be possible into the evening hours. Although basin average rainfall is generally expected to be a half an inch or less, slower storm motions along with the potential for heavy downpours will bring the highly localized rainfall totals of 1.0- 1.50 inches or higher in a short period. Highly localized flooding in low-lying and/or flood prone locations will be possible.

DTX WATCHES/WARNINGS/ADVISORIES
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT Saturday for LHZ421-441.

Small Craft Advisory until 10 PM EDT Saturday for LHZ422-442-443.

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