Marine Weather and Tide Forecast for Copper Harbor, MI

DISCUSSION
Issued at 350 PM EDT Wed Apr 15 2026

Anomalous midlevel ridging exists over the eastern third of the CONUS, while a deep, compact trough is over the Pacific Northwest.
Between these features, a compact shortwave trough is shifting northeastward across the central Plains. At lower levels, a diffuse boundary runs from low pressure near Omaha to another low in northern Lower Michigan. An area of convection is developing along this boundary in the central Plains, which should move northeastward into this evening. Most of this activity will remain south of the area, although a few showers in the stratiform portion of the convective complex could brush the southeast half overnight, with no impactful precipitation amounts expected. Weak high pressure over Lake Superior is resulting in onshore flow, keeping northern areas cool. Meanwhile, some of the low clouds have cleared out over the interior west, which has allowed temps to spike to 55-60F. Tonight, guidance suggests fog redevelops, with highest confidence in areas where dewpoint depressions remain low this afternoon. A Dense Fog Advisory has been issued from 10 pm EDT this evening through 10 am EDT Thursday for the MQT County Warning Area.

Thursday, there is better confidence in earlier low clouds clearing in roughly the western half, with shortwave ridging building in. As the airmass remains anomalously warm (850 mb temps around 10C or +1 to +2 sigma), unseasonable warmth will occur where clouds clear and deeper mixing happens, with a high chance of temps in the 70s and a low chance of approaching 80 in some spots. Meanwhile in the east, clouds hanging on longer and potential for onshore flow will keep things significantly cooler, with areas along the lakeshore likely remaining below 50F.

Friday, ridging builds ahead of the Pac NW trough shifting across the northern Plains. A strong capping inversion should keep things dry until the front arrives and crosses the UP from west to east roughly 00-06Z Sat. Another very warm day is expected in the west half, while it will be a bit cooler with flow off Lake Michigan in the east half. GFS/NAM indicate elevated instability approaching 1000 J/kg with strong deep layer shear, so a few stronger storms resulting in hail and gusty winds cannot be ruled out. Anomalous moisture with PWATs of 1-1.25 inches will be in place, but the quick movement of the trough is expected to limit QPF to 0.25-0.75" in most areas. However, potential for a wave to develop along the front would prolong rainfall a bit, which could result in higher precip amounts (20-30% chance of exceeding an inch in southern locations).

A sharply colder airmass will move in for the weekend with temperatures back below normal. Some light snow is possible Saturday morning but is not expected to be impactful.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
Issued at 205 PM EDT Wed Apr 15 2026

Fog and low ceilings will continue to be the main aviation concern across the region over the next day with generally light winds and ample moisture from snowmelt present. For the rest of the evening, we will see MVFR to IFR conditions at all terminals. After sunset, dense fog will develop and conditions will deteriorate back to LIFR.
It is anticipated (greater than 80% chance) that the visiblity will be below airport minimums at all three terminals during the overnight and early morning hours. After sunrise Thursday morning, conditions will improve and the fog will thin out, with conditions expected to improve to MVFR by the afternoon.

MARINE
Issued at 350 PM EDT Wed Apr 15 2026

Light, stable flow is expected through Thursday with a weak pressure gradient over the area. Areas of dense fog continue through at least tonight into Thursday morning.

Southerly winds will develop and increase on Friday ahead of a deepening low pressure, with a 30-50% chance for brief gales over the eastern lake Friday evening. With stable southerly flow, the highest winds will be observed on high observing platforms. This low will push through over the weekend bringing a cold front and the potential for northwesterly gales (around 50% chance Saturday into Sunday).

HYDROLOGY
Issued at 350 PM EDT Wed Apr 15 2026

NOHRSC analysis showed the the snowpack had eroded over much of the southern and far western U.P. Over the north and east several inches to over a foot of SWE remained, greatest in the higher terrain.
Snowmelt will continue through the week and accelerate late in the week as a warm, moist airmass moves into the U.P. An area of showers and thunderstorms will move through late Friday into Friday night with 0.25-0.75 inches expected for most areas, and a 20-30% of exceeding an inch in the southern UP. Colder weather is expected for Saturday night and Sunday which should slow the melt of any remaining snow.

Waters remain high in the southern UP where recent heavy rains and snowmelt contributed to flooding of low-lying areas and some rivers.
Rivers will continue to rise in portions of the northern UP due to continued snowmelt and additional rainfall. A Flood Watch remains in effect through Thursday night for all but the far western UP, and may be extended through Friday night.

MQT WATCHES/WARNINGS/ADVISORIES
Upper Michigan...
Flood Watch through late Thursday night for MIZ001-003>007- 010>014-084-085.

Dense Fog Advisory from 10 PM EDT /9 PM CDT/ this evening to 10 AM EDT /9 AM CDT/ Thursday for MIZ001>007-009>014-084- 085.

Lake Superior...
Dense Fog Advisory until 11 AM EDT /10 AM CDT/ Thursday for LSZ240>251-263>267.

Lake Michigan...
Dense Fog Advisory until 11 AM EDT Thursday for LMZ221-248-250.