textproduct: Duluth

KEY MESSAGES

- Spotty showers and thunderstorms through tonight along with some fog developing overnight.

- Showers and thunderstorms are expected at times Friday and Friday evening. A few strong to severe storms are possible along with heavy rain that could lead to localized flooding.

- Occasional rain chances into next week with potential for thunderstorms on Tuesday.

DISCUSSION

Issued at 1255 PM CDT Thu Jul 10 2025

This afternoon and tonight:

An initial round of showers and storms this morning has capped off convection from developing this afternoon for the most part. Storms had been largely redeveloping along their outflow boundaries. CAMs have had a really hard time keeping up with this activity, and with a similar favorable instability but low wind shear environment expected to persist into tonight, the forecast confidence for additional showers and thunderstorms is rather low. We should have continuing warm air advection and we already have plenty of moisture in place (PWATs around 1.0"-1.5"). The question of where the cap may bust in and around our region is still in question, and without much for organized fronts around until we get a cold front Friday evening, we can expect more of the same shower and storm activity through tonight. This means that spatial coverage of any showers/storms should be generally isolated, but anything that pops off could develop an outflow boundary that could kick off more storms around it. But right now, it looks like the best instability (MUCAPE ~2-3 kJ/kg) may confine itself to north-central Minnesota, thus giving that area the best chance (~60%) for storms later this evening into tonight. With wind shear topping out around 15-25 kt, severe threats are going to be limited to some brief large hail and maybe some gusty winds (a ~5% chance isolated threat, per SPC outlooks).

Another thing we've been observing with this morning's storms is some pretty hefty rainfall rates around or perhaps slightly exceeding an inch per hour as storms that form (with plenty of moisture to work with) simply aren't moving very fast. WPC has outlined a marginal risk for rainfall exceeding flash flood guidance through tonight. In other words, while flooding is generally unlikely, there's ~5% chance that any storms that form could produce some localized minor flooding.

Friday and Saturday:

Going into Friday, a bit of rinse and repeat with the storm chances except that we will have a bit more of a focus for convection out ahead of the slowly approaching cold front from the northwest. Shear looks to remain on the low side, but instability should remain in place and PWATs may increase a bit to around 1.5" to nearly 2.0". We also might have a brief window Friday late afternoon and early evening where there could be a brief collaboration between increasing wind shear just ahead of the cold front and lingering instability to increase chances for severe weather slightly. There may be enough dry air aloft to promote the large hail threat and perhaps some damaging winds. It's tricky to say how big of hail there could be since there are going to be some conflicting ingredients, like high freezing heights (hail melts more as it falls) but also plenty of instability (up to 2-3 kJ/kg; makes for bigger hail aloft). Uncertainty in how much moisture entrainment there will be also lends uncertainty in potential hail size, but all things considered, perhaps up to around 1.5" in diameter could be possible in the largest of storms. Any that do form to this intensity should be pretty short-duration with the low wind shear though.

Rainfall in general should be a bit more widespread with higher moisture and pre-frontal forcing. At this time, there are not any high signals in the models favoring substantial rainfall totals (e.g. NBM probabilities for 2"+ are only up to ~10%). That said, what we've observed with storms this morning is that where they do form, they are certainly capable of dropping a lot of water. Thus, a nonzero threat for flash flooding does exist. WPC currently has upgraded most of the region to a slight risk for rainfall exceeding flash flood guidance (~15% chance). Localized minor flooding is possible, and if there is an area of storms that develops and persists, then there could still be potential for rainfall totals upwards of 3-4". There is very low predictability of where or if this will happen, even at this short time window, so for now, keep an eye on the forecast and monitor conditions Friday afternoon and evening in case such a scenario plays out somewhere in the Northland.

Showers and storms should decrease in overall coverage and intensity Friday night as diurnal instability goes away and the front passes through. It's still looking like we could see some wraparound showers and perhaps some non-severe storms on Saturday with a trough passing through overhead, though drier air filtering in may limit this potential. Any lingering showers or storms are not expected to produce substantial rain.

Sunday into next week:

Broad but low amplitude ridging develops going into Sunday, so it's looking like a largely quiet weather day, and also a bit warm with highs in the 80s. There are some hints that a weak trough could pass through around Monday night into Monday morning, bringing some shower/storm chances, but not all models are on board with this. A warm air advection regime looks like it'll persist going into Tuesday, then maybe an upper-level trough with a cold front going into Wednesday. Tuesday might be a day to watch for some storm potential with increasing moisture, instability, and shear. It's too early to say if there could be any severe weather, but this looks to be the next best chance in the near future after Friday's storms. Some cooler temperatures may follow Wednesday into Thursday.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 702 PM CDT Thu Jul 10 2025

A broad and diffuse warm front will lift northeastward across the Northland tonight. Areas of fog will likely develop where rain fell earlier today and winds become calm. High-res models diverge with respect to shower and storm chances tonight. Opted to keep a mention of rain and storms in the forecast with this update. A nocturnal low-level jet is forecast to develop over portions of northwest Minnesota, eastern North Dakota, and adjacent areas of Manitoba and Ontario overnight. Convergence on the nose of the jet may lead to thunderstorms overnight which would move into INL and HIB after 11.08Z. A cold front will sag southeastward across the Northland Friday and may touch off another round of thunderstorms.

MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/

Issued at 334 PM CDT Thu Jul 10 2025

Expect occasionally breezy east to northeast winds through around sunset. Gusts up to 15 to 20 kt are possible at times, but are expected to decrease quickly early this evening. Winds are expected to become more light and variable on Friday, though predominantly remaining northeasterly. Periods of rain and thunderstorms are expected, mainly in the afternoon and evening hours, which could lead to gusty and erratic winds at times. Other hazards include heavy rain, cloud to water lightning, and a small chance for large hail. After a cold front passes through Friday night, winds are expected to shift to westerly to southwesterly. Some gusts up to 15 to 20 kt are possible on Saturday as well as Sunday.

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.