textproduct: Marquette

KEY MESSAGES

- Smoke from upstream wildfires will continue to impact Upper Michigan. Air Quality Alerts remain in effect today trough midnight tonight. Consider limiting strenuous outdoor activity or remaining indoors when possible.

- Strong to severe thunderstorms capable of producing damaging winds and large hail are anticipated this afternoon and evening. Those with outdoor plans should continue to monitor forecast updates.

- The Storm Prediction Center has maintained a Slight Risk (level 2 of 5) for severe weather across the entire UP today with an Enhanced Risk (level 3 of 5) extending into much of the west-central.

- Cooler and breezy conditions arrive on Tuesday. Gales are expected over Lake Superior along and east of the Keweenaw Tuesday morning through the evening. This will also result in dangerous swim conditions for the Lake Superior beaches.

DISCUSSION

Issued at 256 PM EDT Mon Jul 20 2026

Strong thunderstorms marched across the northern portions of the U.P. this morning bringing marginally severe hail and isolated strong winds gusts. A possible wake low had developed behind the thunderstorms bringing strong winds over Lake Superior, particularly in the Grand Marais area where gusts reached 60 mph. Visible satellite had showed clearing skies over the central and western U.P. with the exceptions of a weakening line of showers and thunderstorms east of the Keweenaw. This has allowed the western part of the U.P. to warm well into the 80s with dewpoints in the upper 60s to low 70s, making it feel muggy. Surface pressure analysis showed low pressure moving across southern Ontario with the associated surface trough extending south into northern MN and the central Plains. At the upper levels a well defined shortwave was evident over southern Ontario with a strong jet rounding the base of the trough. Southwest flow at the surface was helping to advect the smoke out of the area with likely continued improvement through the day and tonight.

Low pressure over southern Ontario will move east to near James Bay by Tuesday morning, dragging a cold front across the U.P. Ahead of the front the atmosphere will continue to become more favorable for thunderstorms, some of them strong to severe. WOFS shows mlcape 1500- 2500 J/kg along with 45-50kt of deep layer shear. While a cap remains in place, with most of the ongoing convection of Lake Superior owing to large scale ascent, the cap will weaken through the afternoon. Any storms that develop this afternoon could be discrete supercells with all thunderstorm hazards on the table. The latest WOFS run shows distinct helicity tracks across the central U.P. indicative of discrete supercells. There is a non-zero tornado threat, especially over the central U.P. where hodographs are deeply curved and 0-1 SRH could reach or exceeds 300 m^2/s^2. However, the main threats will be large hail (potentially 2" or greater) and strong damaging winds (potentially as high as 80mph). As the front moves into the area this evening could see the storms build upscale into a linear system. If this happens the storms will transition to mainly a wind threat has they move east from the central U.P. through the eastern U.P. There is still uncertainty as to the coverage of thunderstorms. Please continue to monitor the forecast and have a way to receive severe weather warnings.

The main hazard is expected this afternoon into the evening as a fairly volatile atmosphere for our neck of the woods shapes up. As strong synoptic support spreads over the area and airmass recover takes place, CAM ensembles suggest MUCAPE values climbing near 2500 j/kg. What is most impressive is the kinematic environment. Strong mid-level flow will increase bulk shear between 45-55 kts and sickle shaped low-level hodographs support 0-1 km SRH upwards of 100-200 m2/s2 (150-250 1-3km SRH). As storm coverage increase ahead of and along a surface cold front, all severe weather hazards are on the table, including tornadoes should isolated supercells be maintained. Steep lapse rates aloft will contribute to a sizable hail threat in supercells, potentially 2" or greater. Once storms grow upscale into a more linear segment, damaging winds will then become the main threat. SPC has maintained a Slight Risk (level 2 of 5) for the entire UP with an area of the west and central UP in an Enhanced Risk (level 3 of 5) for severe weather. All of this is to say that if you have outdoor plans today, especially in the afternoon and evening, have a way to receive a warning and a plan should one be issued.

Expect cooler conditions on Tuesday into Wednesday behind the cold front that will sweep through the area tonight. High temperatures will be mainly in the 70s with 60s possible close to Lake Superior. It will be breezy on Tuesday with north winds potentially gusting to 30 mph over the land areas and over 45 mph over the Great Lakes. Some lingering showers are likely for the NW wind "snowbelts" and upslope favored areas on Tuesday as 850 mb temps cool between 5-10C. This may aid in lake-enhanced showers as the nearshores and areas of the west and central lake have warmed between 15-20C. Swim conditions will become dangerous on Tuesday for the Lake Superior beaches of Marquette and Alger County.

The area remains under northwest flow aloft into the early part of the weekend with a ridge building back over the central U.S. This will bring the opportunity for showers and thunderstorms as weak disturbances in the flow push across the U.P. Afternoon temperatures will be seasonable, upper 70s to low 80s, with lows in the 50s. Temperatures will warm to the mid 80s on Sunday as the ridge shifts east over the Upper Great Lakes.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 200 PM EDT Mon Jul 20 2026

Radar imagery as of 18z depicts the latest round of showers and thunderstorms clearing the Keweenaw and pushing into central Lake Superior. Expect some lingering stratus to produce MVFR cigs at KCMX through about 19z. Otherwise, mainly VFR over most of the rest of the UP for now as this morning's activity exits to the east, though still currently seeing some smoke and locally reduced visibilities to around 3 miles in the KSAW observations. The next round of showers and thunderstorms will develop over the western and central UP later this afternoon and push east through the evening, warranting PROB30 for TSRA at all sites after 21z. Some of these storms could be strong to severe as clearing skies help to build instability back up in the near term. All modes of severe will be possible, with large hail and damaging winds gusts possible at the terminals. Severe threat will diminish after 01-02z as activity exits to the east, yielding VFR conditions through most of tonight. Expect another batch of showers to develop 09-12z Tuesday morning, accompanied by MVFR cigs at all sites into the end of the TAF period.

MARINE

Issued at 256 PM EDT Mon Jul 20 2026

It will be breezy across the lake through this evening with southwest winds of 20-30kt expected. A few rounds of thunderstorms are expected through the evening as a deep low pressure moves through Ontario and a cold front approaches the lake. Some of the thunderstorms could be severe with large hail and high winds this afternoon and evening.

Late tonight the thunderstorms threat will diminish and winds will shift northwesterly as the cold front pushes through the area. Strong pressure rises behind the front of 6-8 mb/6hr will result in strengthening winds. Gales are expected for most of the lake along and east of the Keweenaw on Tuesday, as high as 40kt. Over the west expect winds in the 20-30kt range.

Winds fall below 20kt over the west for Wednesday with 20-30kt Northwest winds continuing over the east, before settling down below 20kt late Wednesday night as the flow turns back to the southwest. Southwest winds will continue through Saturday, mainly between 15 and 25kt.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Beach Hazards Statement until 10 PM EDT this evening for MIZ014.

Lake Superior... Gale Watch from Tuesday morning through late Tuesday night for LSZ244>251-265>267.

Lake Michigan... None.