Marine Weather and Tide Forecast for Copper Harbor, MI

DISCUSSION
Issued at 350 PM EDT Tue Apr 14 2026

This afternoon an expansive area of low clouds was over the U.P.
with upslope flow bringing fog into the Keweenaw. Winds had turned southerly bringing warmer, moist air northwards into northern WI, approaching the far western U.P. Between the mess of low, mid and upper level clouds there were a few breaks starting and wouldn't be surprised for locations closer to the MI/WI state line to see some sunshine this afternoon. Temperatures were in the 40s to low 50s across the U.P. but still expecting the south and west to rise into the 60s by late afternoon or early evening. The warmest air was over central and southern WI where a warm front was stalled. Fog and drizzle this morning had diminished with the exception of the Keweenaw. Rivers were still slowly rising over the central and eastern U.P. but a trend downwards was starting in the far west where much of the snowpack has eroded. Though most of the snowpack was also gone in the south-central heavy rainfall over the last several days continued to cause flooding.

The warm front will move very little through Wednesday with the U.P.
remaining on the cooler side of the boundary. The biggest impacts to the weather through tomorrow will continue to be warmer temperatures and higher dew points leading to increased snowmelt, with potential flooding of river, small streams, creeks and low lying areas. With the low level moisture and weak flow expect that fog, dense at times, will become widespread tonight along with drizzle as the saturated layer reaches upwards of 3 kft. There will be elevated instability over the area and a few showers, possibly a thunderstorm far south, could get kicked off as a shortwave and upper level jet move across the region tonight. However, the better dynamics will be further south in WI so not expecting strong or severe thunderstorms tonight. Rainfall amounts should generally be light with any showers that do form.

Wednesday will start out foggy with drizzle but expect conditions to improve through the day, we could even see a rare appearance of the sun over the central and west during the afternoon. Much like today temperatures will vary greatly across the U.P, with low 40s in the far north to the low 60s south. A few showers are possible in the afternoon as a shortwave approaches the area. The chance for showers will increase Wednesday night, especially over the south and east as the shortwave passes through the area. Precip amounts look to be less than a quarter of an inch though cant rule out locally higher amounts should thunderstorms form in the south and east.

A warmer stretch is expected for Thursday into Friday as a deep trough moves into the western U.S. Easterly winds will develop on Thursday, becoming southerly by Friday. This will bring the potential for some of the warmest temperatures thus far this spring, reaching into the 70s over the west (90% chance for temperatures over 70). The strengthening southerly winds, warm temperatures and higher dew points will accelerate the melting of the snowpack further with continued flooding concerns.

More uncertainly exists for the weekend as the low pressure moves east along or north of Lake Superior. Slower solutions keep warmer air in the U.P. well into Saturday while faster solutions would bring a front through and much cooler temperatures by Saturday morning. Another round of rain and thunderstorms is likely to accompany the front. Behind the front it will be much cooler with snow showers possible Saturday night into Sunday. Some guidance still suggests a wet snowfall for the western U.P. NBM probabilities for 2" or more of wet snow in the west are around 20-40% Saturday night into Sunday. Stay tuned.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
Issued at 157 PM EDT Tue Apr 14 2026

While SAW and IWD start the 18Z TAF period out with low end MVFR cigs and VFR vis, CMX will continue to observe upslope LIFR to IFR fog and low cigs. All sites are expected to deteriorate to VLIFR tonight as widespread dense fog sets up over the region courtesy of ample low level moisture with weak flow.

MARINE
Issued at 350 PM EDT Tue Apr 14 2026

Light, stable flow is expected through Thursday with a weak pressure gradient over the area. Dense fog is expected to expand tonight over much of the lake and continue into Wednesday morning. There is low confidence in how quickly the fog will erode on Wednesday.

Southerly winds will develop and increase on Friday ahead of a deepening low pressure, 30% chance for gales over the eastern lake.
This low will push through over the weekend bringing a cold front and the potential for northwesterly gales (around 50% chance Saturday night into Sunday).

HYDROLOGY
Issued at 350 PM EDT Tue Apr 14 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. Additional rain chances continue, mainly Wednesday night and Friday night. Rainfall Wednesday night will likely be less than a quarter inch but heavier rainfall is possible for Friday night. NBM has a 10-30% chance for an inch of more of rainfall Friday night. Colder weather is expected for Saturday night and Sunday which should slow the melt of any remaining snow.

Flooding in the wake of snowmelt and multiple heavy rain events continued over the south-central U.P. today. Though the snowpack is mostly gone in the south-central; swamps, creeks, low lying areas and rivers remain full/high and additional showers and thunderstorms are possible Wednesday night. This could exacerbate the ongoing flooding though widespread heavy rainfall is not expected.

For the north and east snowmelt and potential rainfall will continue the flooding threat though the week with the analysis and observations showing over a foot of SWE in the higher terrain.

Rivers in the far western U.P. were beginning to fall and anticipate that the Flood Watch will be able to expire Wednesday morning.

Will be extending the Flood Watch for all but the far western U.P.
until Thursday night. This may need to be extended further in time with future updates as even warmer temperatures and higher dew points, along with increasing winds are expected for Thursday and Friday.

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

Dense Fog Advisory from 11 PM EDT /10 PM CDT/ this evening to 8 AM EDT /7 AM CDT/ Wednesday for MIZ001>007-009>014-084- 085.

Flood Watch through Wednesday morning for MIZ002-009.

Lake Superior...
Dense Fog Advisory until 8 PM EDT this evening for LSZ265>267.

Lake Michigan...
None.