textproduct: Duluth

KEY MESSAGES

- Strong thunderstorms are possible late this afternoon into this evening along and north of Iron Range.

- Inland northwest Wisconsin and east-central Minnesota could (30% chance) see a period of significant severe weather Monday late afternoon and into the evening hours. Very large hail exceeding ping pong ball size is the primary hazard, but damaging winds, and a tornado cannot entirely be ruled out.

- Areas of dense fog will continue tonight. Most likely lasting in the Arrowhead tonight.

DISCUSSION

Issued at 230 PM CDT Sun Apr 12 2026

A complex and active spring weather pattern has taken hold of the Northland, bringing multiple rounds of thunderstorms and localized flooding along the South Shore. This afternoon, a warm front lifting through the region has placed our area into a warm sector, allowing temperatures to soar into the 70s for far southern locations while Lake Superior keeps the shorelines in the 40s and 50s. We are watching the Iron Range closely this afternoon, as a sharp gradient exists for storm development. Between 5 PM and 8 PM, storms are expected to fire along an incoming cold front. Unstable cumulus clouds over Hubbard and Wadena Counties are already forming in the narrow pocket of most likely initiation ahead of the front. This area then pushes into Northland over the next hour or two. Right now the the storm initiation region appears to be the greater Cass/Itasca/west- central St Louis County area early this evening from 4-6 PM. These storms then become more intense into central St. Louis County along or just south of the Iron Range around sunset and move into the Arrowhead. There will be a fairly short window in this time period for those strong thunderstorms to potentially lead to an isolated severe thunderstorm as large hail around the size of a Quarter. The strongest thunderstorms exit the area from 10PM to Midnight tonight through the Arrowhead.

Ongoing dense fog in the Arrowhead this afternoon may mix out from high res model guidance suggestions this evening as the rain showers and thunderstorms pass overhead. As we head into tonight, the concern shifts back to fog. These conditions are currently covered by a Dense Fog Advisory issued earlier today and runs through Midnight tonight. I would not be surprised if after the winds decrease and temperatures drop tonight post- front that the dense fog moves at least into the inland Arrowhead regions. This creates a low-end chance of needing extensions in time or areal coverage expansions of the Advisory. Travelers should be prepared for rapidly changing visibilities to near zero at times.

A Flood Warning for the Tyler Forks River near Mellen was issued today for the combination of rain and rapid snowmelt forecast to create Minor Flooding impacts. These would primarily be held to the State Highway 169 north of Mellen as it crosses over the Tyler Forks River. The flood stage is currently forecast to begin Monday morning, crest Tuesday daytime and begin to recede below flood stage late Wednesday. The rest of Ashland and Iron Counties, along with Bayfield, remain under a Flood Watch for the ongoing snowmelt that may interact with heavy rainfall Monday evening and overnight.

Monday brings a much more significant severe weather threat as a potent low pressure system moves in from the Central Plains. High instability and strong wind shear will create an environment favorable for supercells. The primary risk area sits south of the Northland. The exception though is for inland northwest Wisconsin stretching from Burnett through Price Counties and Pine County in east-central Minnesota (Storm Risk of 3 out of 5). Very large hail, potentially the size of golf balls or larger, will be the main threat for any of these counties. Depending on the location of the warm front tomorrow afternoon, southern reaches of Douglas through Iron Counties (Storm Risk of 2 out of 5) could not be ruled out either for more notable storms tomorrow. The confidence in any severe thunderstorms largely diminishes though for any locations along and north of US Hwy 2 even in the Marginal Risk (Level 1 of 5). Any very large-capable supercells Monday PM that are able to anchor onto the warm front could then also be associated with a damaging wind threat and limited tornado threat too for the late afternoon and evening hours. Heavy rainfall rates within these storms will only add to the ongoing flooding concerns.

While severe weather is expected to stay to our south, a few thunderstorms cannot be ruled out Tuesday. Much of this week will also feature notable lake breeze temperature gradients with 40s to 50s for shoreline locations and 60s inland. By late Friday into the weekend, a shift to a much colder air mass is expected. This could reintroduce snow to the region, with light accumulations possible Friday night as lows drop into the 20s. Any snow will be short-lived, however, as e remain in a highly progressive and moist pattern heading into next week.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1242 PM CDT Sun Apr 12 2026

Warm front moved across the area this afternoon and is triggering widespread rain showers and a few thunderstorms in northern Minnesota. Prevailing southwesterly winds will occur for a 6 to 9 hour period under this warm sector ahead of an incoming cold frontal passage west to east this evening. An isolated severe thunderstorm late this afternoon through this evening cannot be ruled out for HIB/INL and into the Arrowhead. Fog is likely to again setup tonight, with possibly lingering dense fog in the Arrowhead still from today. Winds shift to northerly and become light tonight from 06-12Z. Guidance is pointing towards lifting ceilings from 14-17Z tomorrow ahead of the next round of strong to possibly severe thunderstorms for areas south of US Hwy 2 after 20Z Monday.

MARINE /FOR NEARSHORE WATERS OF WESTERN LAKE SUPERIOR/

Issued at 233 PM CDT Sun Apr 12 2026

A Dense Fog Advisory remains in effect for all nearshore waters this evening. As westerly winds take hold and dewpoints decrease behind the cold front later tonight, the dense fog may decrease in coverage along the North Shore. Expect visibilities below one nautical mile through early Monday morning though along the South Shore where the Advisory lingers last. Northeast winds will increase to 15 to 25 knots Monday night, creating hazardous conditions for small craft in the southwest arm of Lake Superior. Small Craft Advisories are very likely to be needed Monday evening and overnight.

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

FIRE WEATHER

Issued at 235 PM CDT Sun Apr 12 2026

There are no fire weather concerns at this time. An active weather pattern for the next few days will keep rounds of rain and thunderstorms in the forecast. Expect a few strong thunderstorms this evening near the Iron Range and Arrowhead of northern Minnesota. Scattered severe thunderstorms are forecast south of US Hwy 2 Monday PM for mainly inland northwest WI, but also east- central MN districts. Very large hail the size of a ping pong ball is possible, along with a lower chance of damaging wind gusts.

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

HYDROLOGY

Issued at 345 AM CDT Sun Apr 12 2026

No changes to the Flood Watch for Bayfield, Ashland, and Iron counties in Wisconsin for this evening through early Wednesday morning. The watch remains medium confidence as it will be less the traditional sense for flash flooding potential and more into the potential for around 1-2" of rain over several days combined with the potential for 1-5 inches of snow water to melt out of the remaining snowpack. Given the convective nature of the precipitation, some pockets of locally higher and lower rainfall totals will be possible. The precipitation from this morning will set the stage for subsequent rounds of flooding potential. However, the QPF trends continue to shift further southeast with each model subsequent model run. The main threat still looks to be Monday night as a low pressure system moves across MN. A few of the deterministic models are painting 0.50-1.00" within a 12 hr period.

We will still need to monitor for river rise/flood concerns along the North Shore as well given the deeper snowpack to 12-24"+ of snow depth and snow water equivalents of 5-7"+ there. However, the trend has been for the heaviest rain to remain south of the North Shore. Additionally, despite temperatures forecast to be above freezing for several days in a row, Lake Superior will keep the North Shore high temperatures about 10-20F colder and low temperatures 5-15F colder than areas farther inland. This should slow the snowmelt process there relative to the South Shore. Should precipitation forecasts and/or temperature forecasts increase for the North Shore for tonight through Wednesday, then flood headlines may be needed.

As for river and stream concerns, the highest potential for minor flooding remains with the Tyler Forks near Mellen, which could see minor flooding by late Monday or early Tuesday depending on how heavy the first couple rounds of rain are. The Bad River and Nemadji Rivers also have some potential to rise into action stage in the Monday to Tuesday timeframe depending on heavy rain locations and amounts.

DLH WATCHES/WARNINGS/ADVISORIES

MN...Dense Fog Advisory until 1 AM CDT Monday for MNZ020-021. WI...Flood Watch through Wednesday morning for WIZ002>004. MARINE...Dense Fog Advisory until 1 AM CDT Monday for LSZ140>145-148. Dense Fog Advisory until 1 AM CDT Monday for LSZ142. Dense Fog Advisory until 10 AM CDT Monday for LSZ146-147-150.