Marine Weather and Tide Forecast for Grand Marais, MN

DISCUSSION
Issued at 241 PM CDT Fri May 15 2026

Today through Saturday - Critical Fire Weather Conditions: We are observing red flag conditions this afternoon with gusty winds and low relative humidity. As of 1 PM, humidity ranges from around 17 to 25 percent for most of northeast Minnesota and between 23 percent and 41 percent in northwest Wisconsin. Winds are especially gusty in northeast Minnesota with widespread gusts in the 25 to 35 mph range, and there have been some gusts in the 40 to 50 mph range along the International Border. Winds are a bit less gusty in Wisconsin so far, but we still have several hours of afternoon left for drying and mixing to take place. Expect these red flag conditions to persist into the early evening, but winds will eventually start to subside around sunset and humidity will rise a bit overnight. Aside from the fire weather, skies are mostly clear and it is a warm/hot summer-like day.

Tonight, expect quiet weather for the most part. Relative humidity will likely struggle to recover much for many places with the dry air mass remaining in place. Some places may stay in the 40-50% range.

An exception to the quiet weather tonight is that we will have a cold front passing through, and while we are contending with a dry air mass, there is some moisture and instability to work with around or just southeast of Price County. Isolated thunderstorms may be possible there this evening, and severe weather is not expected.

On Saturday, winds become a bit more west-northwesterly following the cold front. An upper-level trough passing along the Canadian Border may bring some clouds north of US-2 in Minnesota, along with cooler temperatures, and this should keep relative humidity a little higher. Further south, expect another dry but less windy day with humidity falling to around 20 to 25 percent during the afternoon. Near-critical fire weather conditions are likely for these areas.

Saturday night through Tuesday - Rain and Severe Weather: Brief ridging aloft and surface high pressure over Ontario will keep the weather quiet Saturday night, but southerly flow aloft will develop ahead of a potent Colorado low that will track straight for the Northland. Expect increasing clouds and eventually showers and thunderstorms to develop Sunday afternoon as warm air and moisture advect northward aloft. This storm will pull in deep moisture from the Gulf of America in several waves through Tuesday with PWATs rising into the 1-2" range. Sunday night through early Tuesday morning, we can expect both heavy rain and severe weather potential, so I'll break each down below:

Heavy rain and minor flooding threat: With the 1-2" PWAT values expected along with multiple rounds of rain, we are looking at some appreciable rainfall over a couple days. It is looking like we will see the initial burst of warm- frontal showers and storms through Sunday night, then perhaps a slight break for most places Monday morning, and then a resurgence of rain and storms Monday afternoon into Monday night coupled with diurnal heating. As low pressure moves northeast on Tuesday, we will be left with some wraparound moisture, but the bulk of the accumulating rain should be about done by then. With this setup, we are not looking at training of thunderstorms over a particular area for enough time to cause a widespread or substantial flooding threat. However, heavy rainfall rates with any thunderstorms could certainly lead to some localized and minor flooding issues.

As for event-total rainfall, ensembles have a somewhat high spread at individual locations, and given that thunderstorms will be producing pretty localized amounts, forecasting exact amounts at precise locations is difficult. With that said, models hover around 1-3" rainfall amounts pretty much across the region. It would not be surprising to see locally higher amounts approaching 4" or so for a few places. Despite some flooding concerns, this rain will be highly beneficial for reducing the fire weather conditions we've had.

Severe weather threats: Elevated instability is expected to build Sunday afternoon and into the night. Instability may be in excess of 1000 J/kg with the initial rounds of rain moving in, so embedded thunderstorms may be capable of producing some large hail and perhaps a lesser threat of damaging winds. This very well could be a threat that persists through the overnight and possibly into Monday morning.
The greatest threat for severe weather will be in our southern areas.

It's possible we may see a brief break at some point Monday morning, at least for some areas, but with a continuous surge of warm air and moisture, this isn't a guarantee. With diurnal heating and low pressure continuing to move northeast, expect a resurgence of rain and thunderstorms Monday afternoon. In our area, expect there to be a bit of a gradient with the severe weather threat, with the best chances in northwest Wisconsin and a progressively lesser threat moving northwest as we get more into elevated instability. If we can tap into surface-based instability, all hazards will be at play Monday afternoon and evening with large hail (potentially golfball size or higher), damaging winds (potentially 70 mph or higher), and perhaps tornadoes as there should be plenty of low-level veering winds and streamwise vorticity ingestion into updrafts.

The severe weather threat may continue into the evening and will likely start to wrap up overnight as low pressure moves northeast and a cold front passes through. We will then be left with some wraparound showers, mostly in northeast Minnesota, for Tuesday into Tuesday night. I know nobody wants to hear the "s" word anymore, but some wet snowflakes could mix in along the International Border as cold air filters in behind the low Tuesday afternoon and evening.

Extended Outlook - Wednesday into next weekend: Following the storm, we may have a day or two of high pressure and relatively quiet weather. There are hints of a possible weaker low around Thursday/Thursday night that could bring some rain chances. The upper-level pattern generally looks pretty wavy going into the weekend, so we may see more rain/storm chances going into the weekend as well. We may see some ups and downs with temperatures with this pattern as well.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/
Issued at 620 PM CDT Fri May 15 2026

VFR with decreasing westerly winds overnight. Pockets of LLWS this evening. Westerly winds increase again Saturday before turning more northerly towards the end of the TAF forecast.

MARINE /FOR NEARSHORE WATERS OF WESTERN LAKE SUPERIOR/
Issued at 241 PM CDT Fri May 15 2026

Gusty southwest winds are expected to persist around the nearshore waters through early this evening. Around sunset, winds will decrease pretty quickly. Higher waves may persist around Grand Marais to Grand Portage into tonight. Small Craft Advisories remain in effect.

Breezy northwest winds are likely along the North Shore Saturday afternoon. Small Craft Advisories may be needed.

An extended period of strong northeast winds is expected Sunday into Sunday night as a strong low pressure system approaches.
Gales are possible (~50-60% chance) Sunday afternoon and evening. Winds will likely remain gusty through Tuesday.

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

FIRE WEATHER
Issued at 241 PM CDT Fri May 15 2026

Critical fire weather conditions will persist through this evening due to very low relative humidity and strong winds. Red Flag Warnings remain in effect through this evening.
Southwesterly winds will gradually shift more westerly overnight as a weak cold front passes through. Wind speeds are expected to drop off somewhat quickly after sunset tonight. Humidity may not recover well with many places staying at 40-50% humidity or lower through tonight as the dry air mass remains in place.

Expect near-critical fire weather conditions again on Saturday, especially along and south of US-2. An upper level trough may bring some clouds around the International Border, which may keep minimum relative humidity above 25 percent. Further south, relative humidity may fall into the 20-25% range. Winds will be less of a concern Saturday with west-northwest winds gusting to 20 mph for most places, except perhaps up to 25 mph along the North Shore and Arrowhead.

Widespread rain and thunderstorms will move in Sunday afternoon and evening with increasing clouds and moisture on Monday.
Widespread rainfall around 1 to 3 inches is expected across the region through Tuesday with some locally higher amounts possible. Severe weather will be possible at times Sunday and Monday as well.

See the Fire Weather Forecast product for a more thorough breakdown of fire weather conditions.

DLH WATCHES/WARNINGS/ADVISORIES
MN...Red Flag Warning until 9 PM CDT this evening for MNZ010>012- 018>021-025-026-033>038.
WI...Red Flag Warning until 9 PM CDT this evening for WIZ001>004- 006>008.
MARINE...Small Craft Advisory until 10 PM CDT this evening for LSZ121- 141>148-150.
Small Craft Advisory until 4 AM CDT Saturday for LSZ140.