textproduct: Marquette

KEY MESSAGES

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

- Strong to severe thunderstorms capable of producing damaging winds and large hail are anticipated today, especially in the 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.

DISCUSSION

Issued at 318 AM EDT Mon Jul 20 2026

Early morning GOES satellite and RAP analysis reveals a vigorous upper level shortwave in the vicinity of Lake Winnipeg diving southeast towards the northern Great Lakes. At the surface, a deepening low pressure stacked below the parent wave will continue north of Lake Superior today. Mid to upper level ascent on the nose of a 100kt 300mb jet streak will be the forcing mechanism for a first round of potentially strong to severe storms this morning into the early afternoon. As of ~2:30 am edt, convection has been ongoing in upstream Ontario and a few thunderstorms are working across eastern Superior. CAM guidance suggests a line of showers and thunderstorms developing in MN and knocking on our western waters/shorelines by ~12z this morning, however, there remains some uncertainty in the potential severity of this round given meager instability forecasted then. At this time thinking a few strong storms may be possible in the west half after daybreak given increase strong synoptic ascent, but confidence remains low.

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.

Strengthening southerly winds on will result in building waves over Lake Michigan, as high as 7 feet by late afternoon along the beaches of Schoolcraft County. This will bring a high rip current threat and dangerous swim conditions.

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 likely become dangerous on Tuesday for the Lake Superior beaches of Marquette and Alger County. Smoke could also increase again with the northerly flow.

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 /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 159 AM EDT Mon Jul 20 2026

Southwest winds much of the 6Z TAF period help lift lingering wildfire smoke out of the region. That said, MVFR vis restrictions persist this morning as smoke in WI lifts over the UP. Winds increase during the day to around 15 kts with gusts into the 20-30 kt range, strongest at CMX and SAW. Otherwise PROB30 groups for SHRA/TSRA remain in the TAFS for two rounds of storms today. The first round of TSRA arrives in the west around 11-13Z this morning, likely weakening before reaching SAW. The second round kicks off with a passing frontal boundary, possibly impacting all sites into this evening. This second round has the potential to be severe. Additional wildfire smoke may filter back into the west at the end of the TAF period behind the front. However, confidence in vis restrictions below 6SM was too low to include at this time.

MARINE

Issued at 318 AM EDT Mon Jul 20 2026

Marine Dense Smoke Advisories are being allowed to fall off this morning as gusty south to southwest winds push dense smoke concentrations back to the northeast. Cant rule out some areas of reduced visibility, but overall vis should be improved nicely today.

A deep low pressure working north of Lake Superior today will aid in SW wind gusts between 20-30 kts today. A few isolated gales to 35 kts may be seen in the western arm of the lake (30% chance). In addition to the winds today, there will likely be two rounds of thunderstorms, with the second having the greatest chance of seeing strong to severe storms capable of producing winds >50 kts and large hail upwards of 2" in diameter. The first round is most likely to reach the western lake after day break before continuing east and ultimately fizzling out. Uncertainty remains high on the potential for severe thunderstorms with this first wave, but some strong to severe cannot be ruled out. The second round develops this afternoon ahead of and along a surface cold front before departing the eastern lake late tonight.

Behind the cold front, very strong NW winds for this time of year are expected to develop as the strong pressure rises of 6-7 mb/6hr and modest cold air advection occurs. Ensembles continue to maintain a 50-90% chance for Gales of at least 35 kts largely east of the Keweenaw Peninsula. A Gale Watch is now in effect for areas east of the Keweenaw beginning Tuesday morning. Gales will contribute to significant wave heights growing 7-12 ft, highest along the lakeshores between Marquette and Whitefish Point. Winds of 20-30kt will linger Wednesday morning over the eastern part of the lake but expect winds to fall below 20kt by evening with light winds for Thursday and Friday.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Beach Hazards Statement from 8 AM EDT this morning through this evening for MIZ014.

Lake Superior... Dense Smoke Advisory until 8 AM EDT /7 AM CDT/ this morning for LSZ240>251-263>267.

Lake Michigan... Dense Smoke Advisory until 8 AM EDT this morning for LMZ221- 248-250.