Marine Weather and Tide Forecast for Copper Harbor, MI

SHORT TERM /THROUGH MONDAY NIGHT/
Issued at 411 PM EDT Sun Aug 10 2025

Afternoon WV and RAP analysis show a deep trough over the much of the Plains with embedded shortwaves lifting NE toward the Upper Great Lakes. Another trough over far N Ontario has an associated sfc low around 1002mb beneath it with a cold front draped S into the Midwest, currently just W of the CWA Right now radar is fairly quiet with returns mostly confined to WI where an embedded shortwave is located. For the remainder of today, expect iso/sct shra/tsra to drift over the UP as this shortwave lifts overhead. The latest SPC mesoanalysis indicates plenty of instability in the UP with SBCAPE up to 1500-2000j/kg. That said, wind shear is lacking ~25-30 kts and lapse rates are struggling to reach 6.5C/km, so strong to severe storms are not likely. The area which storms could produce some small hail/gusty sub-severe winds is over the west late this afternoon/evening ahead of a cold front. Otherwise, muggy conditions continue with Tds in the upper 60s to mid 70s and temps in the 70s to low 80s.

Tonight, the LLJ strengthens to 35-45 kts over the E supporting increased coverage of shra/tsra. CAMs are not in the greatest agreement on exact placement of the LLJ max, but areas underneath could get up to ~1" given the limited elevated instability (few hundred j/kg of MUCAPE) and favorable warm cloud layer ~13kft with PWATS of 1.5-2" over the E. Will want to monitor areas N of M-28 and E of Munising for minor flooding concerns highlighted in the WPC Marginal outlook as higher soil moisture is noted in that region.
Otherwise widespread QPF is light, ~0.25" or less. Temps settle into the 60s.

Monday brings additional chances for shra/tsra over the E thanks to afternoon lake breezes and embedded shortwaves moving overhead.
Lapse rates will be better in the lowest 3km compared to today, but the mid level remains unfavorable and instability will be lacking (the NAM struggles to reach 500j/kg of MUCAPE). This leaves strong to severe storms unlikely once again. Precip amounts up to ~0.1" are fcst. Otherwise expect another day in the upper 70s to mid 80s.
Another concern for the start of the work week is Canadian wildfire smoke returning to the region. As a result, the Michigan Department of Environmental Quality has issued an Air Quality Advisory for Mon August 11th through noon EDT on August 12th (Tue), for elevated levels of fine particulates (PM2.5). Pollutants are expected to be in the Unhealthy for Sensitive Groups range. See the latest Air Quality Alert for additional information.

Dry weather looks to briefly return Mon night with the loss of diurnal heating. Lows will be in the upper 50s to mid 60s.

LONG TERM /TUESDAY THROUGH SUNDAY/
Issued at 411 PM EDT Sun Aug 10 2025

Precip returns to the forecast on Tue as a deeper trough extending from MN up along the Manitoba/Ontario province line will be at the W flank of the CWA by 12Z Tue. This trough shifts over Ontario, bringing a ~996mb sfc low across far N Ontario and pivoting the southern end of the trough and attendant cold front over the UP during the day. This system brings better instability, bulk shear, and forcing for convection, but is lacking in deep available moisture. Will want to watch this round regardless as it does present some potential for strong to severe storms.

From there a dry period sets up for mid week as a mid level ridge over the N Plains moves over the Great lakes and high pressure tracks over E Canada, extending ridging down into the Great Lakes.
Slightly cooler temps are expected in the wake of the cold front on Tue with highs Wed/Thu in the 70s and lows Wed night in the 40s to mid 50s, coldest interior. This rebounds back above normal for the end of the work week into the weekend as low level S flow returns.
Quazi-zonal flow aloft returns into the weekend which lowers predictability, but passing shortwaves keep chance PoPs in the fcst.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/
Issued at 715 PM EDT Sun Aug 10 2025

VFR conditions dominate for IWD and CMX throughout the period, but MVFR cigs may hang around SAW until later this evening, which guidance seems to have a tough time capturing. If, however, the model guidance is correct on cigs lifting to VFR here at SAW shortly, will amend the TAF to VFR sooner than 5z this evening. Some showers and maybe (but doubtful) a thunderstorm or two could move over SAW this evening, but convection looks to quiet down later tonight. In addition, some BR/FG could be seen at SAW late tonight; reflected this in the TAF by dropping cigs and vis to IFR/MVFR, but could be down to as low as airport mins potentially (worst-case scenario). Conditions at SAW improve to VFR a few hours after dawn Monday morning and are expected to continue the rest of the day.

Generally southwest to westerly flow dominates the TAF period, although winds could be fairly light and calm tonight.

MARINE
Issued at 411 PM EDT Sun Aug 10 2025

Southerly flow will largely prevail through mid-Tuesday across Lake Superior thanks to the persistent broad troughing positioned just upstream in the Northern Plains. Surface troughs will press through tonight and again Tuesday, which will support a period of westerly winds afterwards. Northwesterly winds establish themselves Tuesday night after the cold front finally swings through. Winds will largely fall in the 15-25 kt range in this period save for gusty winds associated with passing thunderstorms. Thunderstorm potential mostly focuses this evening through tonight across the east half of Lake Superior and then a slow moving, west to east line of showers and storms late Monday night into Tuesday. Hazards with any of these storms will be lightning and visibility reductions from potential heavy rain and post-rain fog that may develop.

MQT WATCHES/WARNINGS/ADVISORIES
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.