Marine Weather and Tide Forecast for Grand Marais, MN

DISCUSSION
Issued at 315 PM CDT Mon Apr 21 2025

Low pressure lifting into north-central Ontario decreases sky cover over the Arrowhead and the South Shore over the next few hours as short-lived high pressure ridge sets up over northern Minnesota this evening. Expect a wind shift from northerly today to southeasterly Tuesday as the next weak front lifts northeastward Tuesday morning. As that front embedded in a shortwave trough lifts northeastward early Tuesday morning, a band of rain will enter first in the Brainerd Lakes a few hours before sunrise that lifts northward through the morning hours.
Chances of a quarter inch of rainfall persist in north-central Minnesota into the afternoon hours, with much lighter (less than a tenth of an inch) rain extending into the Twin Ports and far western Wisconsin. A weak nose of cape is progged on global deterministic guidance to create the slightest chance (10 percent) for embedded rumbles of thunder in east-central Minnesota and the Brainerd Lakes. Widespread thunderstorms are not likely though tomorrow.

A pronounced easterly breeze off the Big Lake keeps many North Shore to Twin Ports and east-facing parts of the South Shore cooler Tuesday.

Seasonable to slightly above normal temperatures and dry conditions Wednesday give way to a low pressure moving through the Lower Midwest late Wednesday into Thursday creating chances (40 to 60 percent) of scattered rain showers along and south of the Iron Range. This Thursday time period also sees better chances of thunderstorms working into northwest Wisconsin as CAPE values seen on medium range global guidance ranges from 50 to 250 J/kg. Strong to severe storms are not likely with this Thursday system though.

Seasonable temperatures persist early this weekend as a very dry airmass slides overheard from Canada. Saturday will be a day to watch for very low relative humidity in northern Minnesota.

Ensemble guidance continues to show signals for a late weekend to early next week weather system bringing an additional chance of rainfall to the region.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
Issued at 1223 AM CDT Tue Apr 22 2025

VFR conditions overnight alongside light and variable to calm winds. Already seeing some areas of IFR to MVFR fog develop over portions of north-central Wisconsin that should persist into the early morning today, but the probability of impacting HYR has decreased to less than 10 percent.

Banded light rain showers will move in from the southwest associated with a front extending southeast from a low pressure centered over North Dakota. Expect BRD to be the first to see this rain by around 08Z and affecting Brainerd through the morning. Scattered rain showers then spread northeast through the Northland terminals for the morning and afternoon before exiting locations near the International Border later this evening. Expect ceilings to drop to MVFR and then IFR with these showers and then remain low as MVFR or near-IFR for the evening, with visibilities in the showers as VFR to MVFR. BRD and HYR should see conditions scatter out to VFR later this afternoon and evening and precipitation ends first for those locations.
There is also an expectation for much lower ceilings and visibilities in fog/low stratus near the end of the current TAF period for terminals near Lake Superior given onshore winds, with a 20 percent chance for LIFR conditions.

Winds will increase from the southeast daytime today, with gusts of 15-20 kt through this afternoon.

MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/
Issued at 232 PM CDT Mon Apr 21 2025

Northwest winds under 15 knots today become east-northeasterly Tuesday morning. Expect winds gusting in the low-20 knots range Tuesday afternoon in the southwestern arm of the lake. A Small Craft Advisory may (60-70% chance) may be needed at the head of the lake Tuesday afternoon and evening. Another wind shift to southwesterly occurs Wednesday, but winds remain below 20 knots under a stable lake warm air advection regime.

For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt.

DLH WATCHES/WARNINGS/ADVISORIES
MN...None.
WI...None.
MARINE...None.