Marine Weather and Tide Forecast for Munising, MI

DISCUSSION
Issued at 321 PM EDT Sat Apr 18 2026

Afternoon GOES water vapor imagery and RAP analysis indicate a deep trough pressing into the Great Lakes from Central Canada and the Northern Plains. This is sandwiched between two mid level ridges over the west and east coasts. Beneath it the ~980mb low over Hudson Bay continues departing northward with high pressure building to the west and south of the UP. CAA, the tight pressure gradient, and pressure rises is yielding breezy west to northwest winds and much colder temps in the upper 20s to low 40s, coldest in the Keweenaw.
Gusts up to 20-25 mph (30-40 mph in the Keeweenaw and near Lake Superior) will gradually taper off into tonight. An embedded shortwave enhanced by Lake Superior attempts to squeeze out some isolated light snow showers in the east, however limited moisture would suggest flurries would be the more likely solution with no impacts (if anything precipitates at all). Dry air and a colder than normal airmass yield lows by Sunday moring in the 20s.

850mb temps reach -14C to -16C Sunday morning, starting a marginal push for LES. This is expected to be low on snow accumulation given the limiting dry air. Up to 1 inch is possible in the east (15-30% chance). Temps once again will be below normal on Sunday, only peaking in the 30s to low 40s. Expect even colder temps Sunday night as high pressure takes hold over the western Great Lakes, winds become light and skies clear out. This favorable set up will bring lows into the teens to low 20s; would not be surprised to see a few spots dip into the single digits interior west (25% chance). The mostly dry and cold period through the weekend will limit flooding over portions of the UP into early next weekend. Thus the Flood Watch was allowed to expire. However, river flooding concerns will persist with continuing runoff.

This high pressure moves east over the Great Lakes early next week while the mid level ridge moves out over the Plains. Temps return near normal on Monday as a result of the increasing southerly flow with highs in the 40s. A mid level trough tracking across far Northern Ontario brings a weakening surface low across Hudson Bay.
This in turn sends a cold front across the UP on Tuesday. Limited moisture leaves the forecast dry. As the mid level ridge moves over the Great Lakes mid to late week, a trough swings over the west CONUS into the Rockies. Persistent southerly flow brings above normal temps back, with highs in the 50s and 60s; some low to mid 70s interior west on Thursday. Lows return to the 40s and 50s. This once again accelerates snowmelt on lingering snowpack. Another low pressure develops over the Northern Plains Wednesday night into Thursday as a result of the mid level trough. Confidence in the low's track falls apart into this weekend, however chances for showers and storms return already on Thursday ahead of a warm front (15-30%). Better chances (50-75%) hold off until the cold front on Friday. There is a 30-40% chance for 0.5 inches of rain.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
Issued at 223 PM EDT Sat Apr 18 2026

Lingering MVFR cigs at CMX will improve to VFR by this evening, while IWD and SAW are already at VFR. VFR will then be the prevailing flight category through the end of the TAF period. So, main threat this issuance will be the strong west winds that are continuing to gust up to 40 kts at CMX and 25 kts at IWD and SAW.

MARINE
Issued at 348 PM EDT Sat Apr 18 2026

Westerly gales slowly diminish through early tonight; maintained Gale Warnings as is. Resulting significant wave heights this afternoon are between 6-12 ft, highest over the far east. Cold air advection keeps winds between 20-30 kts through Sunday morning over the west half and Sunday evening over the east as winds shift northwest. Passing high pressure settles winds below 20 kts lakewide for Sunday night and most of Monday. In turn waves settle below 4 ft over the west by early Sunday afternoon and by early Monday morning in the east.

A cold front moving through early on Tuesday results in an increase in southerly winds ahead of it. Winds of 20-30 kts are expected, but gale chances remain low and only over the east (20-50% chance of 35 kts). In the wake of the cold front, winds once again fall below 20 kts for the middle of the week. The next shot at 20-30 kt winds starts on Thursday and persists into the weekend as a low pressure over the Northern Plains moves near the Great Lakes.

MQT WATCHES/WARNINGS/ADVISORIES
Upper Michigan...
None.
Lake Superior...
Gale Warning until 8 PM EDT /7 PM CDT/ this evening for LSZ241>243-245>248-250-251-263-265-267.

Gale Warning until midnight EDT tonight for LSZ244-264-266.

Lake Michigan...
None.