textproduct: Duluth

KEY MESSAGES

- Warm weather with isolated to scattered showers and storms through Labor Day. Areas of fog overnight.

- Thunderstorms are possible with a cool front Tuesday and Tuesday night.

- Cooler temperatures and scattered rain showers expected Wednesday through the rest of the week. Frost Advisories may eventually be needed.

DISCUSSION

Issued at 416 AM CDT Sun Aug 31 2025

Early this morning...

High pressure near the surface remains in place over the western Great Lakes. Aloft there is a subtle shortwave trough and lobe of cyclonic vorticity evident on GOES-East water vapor imagery. The latest RAP13 forecasts continue to feature a very subtle ripple in 700 mb heights associated with this feature. Isentropic ascent was maximized over the Arrowhead in the 296-302K layer and was aiding ascent in that area. There appears to be a pocket of 100 to as much as 500 J/kg of elevated potential instability from the Arrowhead to the I-35 and US-53 corridors. A persistent cluster of showers and occasional thunderstorms continued to percolate near the Twin Ports as of 08Z. Additional showers and occasional storms developed farther north into the Arrowhead and northwest Ontario over the past few hours. The showers/storms were moving toward the south- southwest at 15 to 20 mph. The latest KDLH radar estimates suggest rainfall amounts of a few hundredths up to around a quarter inch of rain per hour with the precipitation. Storm total accumulation revealed a few swaths of 0.5 to over 2 inches where the heaviest showers were located. Expect the showers to continue to bubble with occasional lightning discharges through late this morning.

Elsewhere the story is similar to yesterday morning. We continue to watch and wait for fog to develop under mainly clear skies and light winds. Brainerd saw variable visibility between unlimited and 1 mile so far. Aitkin, Bigfork, Longville, and Hinckley each had reduced visibility as well. It appears the pressure gradient is slightly tighter than last night which is contributing to low, but not calm winds. Will continue to monitor. A Dense Fog Advisory is not out of the question, though there would need to be a rapid and more widespread decease in visibility to warrant a headline.

Rest of today through Monday night...

Not much change from yesterday expected with today's conditions. Temperatures will climb into the middle 70s to low 80s with mostly sunny to partly cloudy skies initially. By this afternoon diurnal heating will contribute to MLCAPE of 500 to 1500 J/kg with the greatest values forecast over the Arrowhead. Convergence over the Arrowhead near the Lake Superior shore should contribute to isolated to scattered showers and a few thunderstorms. Effective shear is forecast to be quite anemic at around 10 to 20 knots therefore pulse type convection is most likely and severe weather is not expected. Slow storm motions toward the southwest may produce brief periods of locally heavy rain. Isolated rainfall amounts of 2 to 4 inches are possible wherever the heaviest showers occur, although most locations will see far less precipitation and much of the Northland will be dry.

Small chances of showers and occasional thunderstorms persist overnight. Overall trend PoPs downward a bit due to uncertainty in location and coverage. Patchy fog will be possible once again where skies are clear and winds calm.

Labor Day Monday will see weak southerly return flow will develop in the low levels. Afternoon isolated to scattered showers and a few thunderstorms appear likely, although coverage is uncertain and warranted slight chance and chance PoPs in the forecast. MLCAPE of 500 to 1500 J/kg is forecast again with weak effective shear. Slow storm motions will provide a few narrow and localized areas of heavy rain. Temperatures will be in the middle 70s to low 80s.

The diurnal convection will persist into Monday night and may increase in coverage in response to isentropic ascent over northern Minnesota.

Tuesday through next weekend...

A cold front will sag southward across the Northland on Tuesday. Showers and storms are likely to accompany the front. Modest potential instability and limited shear will set the stage for isolated non-severe storms. A closed upper-level low will follow the front on Wednesday and will take up residence over the western Great Lakes for the remainder of the week. Look for autumnal temperatures with highs in the 50s to low 60s Wednesday through Saturday and mainly cloudy skies. With cold air advection and cyclonic flow aloft expect scattered showers through the period. Anyone over northern Minnesota and awake during the overnight hours may see the season's first "conversational" snowflakes Wednesday night and Thursday night. The colder temperatures may also warrant Frost Advisories if skies can clear and winds become calm.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 628 AM CDT Sun Aug 31 2025

Variable visibility between MVFR and LIFR expected at BRD until 13Z. Scattered showers near DLH and HIB will persist until the 14-16Z timeframe. Showers north of the Canadian Border will sink south and may affect INL before 16Z. Look for isolated showers and storms to develop over northern Minnesota this afternoon, mainly over the Arrowhead. If a shower or storm moves over INL, HIB, or DLH, expect visibility less than 1 mile for short durations. Chance of those conditions impacting the terminals is less than 30 percent thus omitted explicit weather and visibility reductions with this forecast. Fog may develop at the terminals again tonight provided skies clear out and winds become calm.

MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/

Issued at 416 AM CDT Sun Aug 31 2025

High pressure will remain in place over the region for the next few days. This will keep winds generally less than 10 knots from the southwest. Isolated showers and storms are likely today and tonight. Occasional cloud-to-water lightning will be the main threat from the storms.

A cold front is forecast to move southeastward across western Lake Superior on Tuesday. Showers and thunderstorms are expected with the front and winds will veer northwesterly and increase in speed behind the front. Conditions will become hazardous for small craft. Cool air will continue to pour into the area through the end next week. Seasonably warm water temps will contribute to persistent stronger winds and conditions hazardous for smaller vessels.

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.