Marine Weather and Tide Forecast for Mackinac Island, MI

SHORT TERM /THROUGH SUNDAY/
Issued at 241 PM EST Sat Dec 7 2024

Pattern Synopsis: Split flow pattern persists across North America, with the northern stream being the only branch of interest through the short term of the forecast. A clipper system starts the period moving across northern Lake Superior and Ontario. This system quickly passes off to the east tonight, with short wave upper-level ridging building across the western Great Lakes for most of the day on Sunday. This ridging is largely due to the amplification of the upper-level flow due to a strong wave diving southeast out of the Gulf of Alaska at the start of the period.

Forecast Details: Precipitation impacts of the clipper system will quickly come to an end across most of the area this evening where they have not already done so. Snow is still falling across eastern Upper Michigan and the immediate Straits area at the Tip of the Mitt. Further south, precipitation has ended and clouds have thinned to a large degree. Relatively mild southwesterly flow (for December)
will swing around to the northwest tonight as the clipper moves off to the east. Do not expect much, if any, lake effect precipitation in the cooler air behind the clipper. While forecast soundings saturate beneath the developing subsidence inversion tonight, the moisture depth is shallow (below 3k feet) and too warm for any ice crystals. Can't rule out a little drizzle or flurries, but little impact is anticipated. Quiet weather is expected for Sunday as weak upper/surface ridging push across the area. Precipitation with the next system will be approaching by very late in the period, but this should hold off until Sunday night.

Temperatures won't fall too much tonight given lingering cloud cover and weak cold advection behind the clipper. Most locations should bottom out around 30 degrees. Temperatures climb back above freezing on Sunday, with locations near Saginaw Bay topping out near 40.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
Issued at 241 PM EST Sat Dec 7 2024

Upper level ridging will continue over over Great Lakes region Sunday night into Monday morning. Low level warm air advection continues to work its way over northern MI. It will meet up with northeasterly winds and higher surface pressure over Canada, which could keep eastern upper cooler aloft as a precip shield moves in from the west later Sunday evening. A surface low over far northwest WI will move a warm front towards northern lower MI and provide this precipitation shield over eastern upper and near the tip of the mitt. Precipitation here will likely start as snow late Sunday night. Surface winds will be breezy overnight for northern MI. Most model soundings show temperatures near freezing for northern lower with the warm sector aloft reaching above freezing. It also takes most of early Monday morning (1 AM thru 7 AM) to saturate above that. Accounting for little fluctuations in actual temperature and moisture profiles across northern lower, mixed precipitation will likely exist Sunday night into Monday morning with mostly drizzle southeast of M-72, rain for lower elevation places north, and freezing rain/drizzle for higher terrain areas of northern lower where surface temperatures can remain near freezing. Higher snow pack in higher terrain locations will also aid in keeping surface temps on the colder side of 32F. Thoughts on measurable precipitation is that it will still be lower. Any freezing rain will likely only produce ice accumulations of < 0.02 inches. Later Monday morning the surface low moves over Lk Superior and takes the moisture with it. Mixing heights rise and clouds will start to scatter out. Surface temperatures will increase to above freezing (high 30Fs into low 40Fs).

Northwest flow will be restored Tuesday, leading to colder air returning. Lake effect snow will return Tuesday morning as an upper level low over the central Rockies merges with a Clipper system over the Great Lakes area. Widespread snow returns due to this mid week with colder temperatures through the end of the work week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 1251 PM EST Sat Dec 7 2024

Snow moving out of the area where it has not already done so.
Expect a period of VFR conditions at all TAFs sites aside from KCIU. MVFR CIGs will spread back across the area later tonight.
Gusty southwest to west winds will diminish and trend northwest tonight.

APX WATCHES/WARNINGS/ADVISORIES
MI...Winter Weather Advisory until 5 PM EST this afternoon for MIZ086>088-095-096.
MARINE...Small Craft Advisory until 7 AM EST Sunday for LHZ345>349.
Small Craft Advisory until 7 AM EST Sunday for LMZ323-341-342- 344>346.
Small Craft Advisory from 10 PM this evening to 10 AM EST Sunday for LSZ321.