textproduct: Marquette

KEY MESSAGES

- The warmest airmass of the season so far will impact the UP with highs in the 90s Sunday-Tuesday. Muggy dew points in the 60s and low 70s as well as overnight lows in the 60s and 70s will make cooling off more difficult. People sensitive to heat should make preparations for these conditions.

- There is a chance of thunderstorms Sunday with the warm and unstable airmass. The SPC has outlooked a Marginal Risk (category 1 of 5) for severe thunderstorms (5-15% chance).

UPDATE

Issued at 339 AM EDT Sat Jul 11 2026

The going forecast remains mostly on track this morning. GOES-East Nighttime Microphysics RGB imagery just shows a few scattered, short- lived patches of low clouds over the region,with otherwise clear skies under a RAP-analyzed 1016 mb high that extends from the UP to Hudson Bay. Besides a slight chance of diurnally-driven rain showers this afternoon per CAM guidance, should be a fairly quiet day today as temperatures continue to warm, but except for a few spots that get downsloping winds, most should remain below 90 degrees today. The warming trend is also seen in tonight's overnight lows, which should remain above 60 degrees for most.

Sunday, 500mb heights continue to build as ridging over the plains exceeds the maximum of climatology for this time of year (per NAEFS). EFI and Shift of Tails both are elevated for both max and min temps, as NBM highs climb to the 90s for much of the UP. Dew points in the 60s will lead to heat indices approaching triple digits. In addition to the heat, the longer-range CAMs are showing some early indications that thunderstorms may develop along a ridge- riding boundary of some sort and take advantage of the warm, moist air that allows instability to build to a Euro ensemble-mean MUCAPE of 1500 to 3000 (!) J/kg. The shear profile looks ok as well with some curvature in the hodographs, though the speed shear is lacking somewhat and there is a fairly significant spread in the ensembles by the afternoon hours. What CAM output there is has a significant spread in the location and timing of thunderstorms (expected, given the meager synoptic forcing), so confidence is low, but the ceiling of impacts is high enough that the SPC has introduced a Marginal Risk of severe thunderstorms.

The heat comes to a head Monday and Tuesday as the upper level ridge extends overhead from the west. If the LREF mean 500 mb height of 600 dam verifies at the Green Bay balloon site, it would be the highest 500mb height recorded in the period of record that includes over 51 thousand soundings since 1953. As 1000-500mb thickness is proportional to temperature, a record 500mb height would mean record high temperature records are also in play. The usually cool-biased LREF shows up to 35% chances of exceeding 100 degrees in some interior locations while the NBM (which can be warm biased) shows some pockets of up to 60% chances of exceeding 100 degrees. This combined with dew points in the 60s to low 70s will also lead to heat indices climbing into the triple digits for many. People with sensitivity to heat and/or without air conditioning should make preparations to contend with the heat and stay hydrated. Overnight lows in the upper 60s to low 70s may make it challenging to keep cool overnight without AC.

Differences in how ensembles handle the troughs that bookend the ridge result in significant spread from Wednesday onwards, with LREF 10th to 90th percentile spread of at least 15 degrees (the difference between highs cooling to the mid 70s or low 90s heat lingering). Thus, did not deviate from the NBM in that time period.

DISCUSSION

Issued at 339 PM EDT Fri Jul 10 2026 Amended at 339 AM EDT Sat Jul 11 2026

The main focus of the forecast period continues to be heat as upper level ridging strengthens over the central CONUS through the weekend. Widespread mid to upper 80s are expected by today with some areas hitting the 90 degree mark by Sunday. Most intense heat is still on track for Monday and Tuesday with NBM guidance showing between 90-100% chance to exceed 90 degrees on Monday and 60-70% chance to exceed 95 degrees in pockets across the interior west and southeast inland. Tuesday, that 60-70% chance of exceeding 95 degrees becomes concentrated over the south-central and southeast. Meanwhile, even though not as humid as the late June heat wave, dew points will still soar into the 60s/low 70s, resulting in some triple digit heat indices across the southeast sector on Monday. Do not expect much reprieve at night, either, with overnight lows in the 60s and 70s from Saturday night through Tuesday night. As a result, headlines for dangerous heat will likely be issued with future forecast issuances for Monday and Tuesday. By midweek, model guidance begins a downward trend in temperatures as a low pressure system traversing Canada flattens the ridge a bit. Nonetheless, temperatures will still be above normal with highs in the 80s through the extended period.

In tandem with the heat will as usual be some shower and thunderstorm chances during the peak heating of the days. But, chances will be enhanced today and Sunday due to weak perturbations along the ridge. Any lake breezes that do form could be triggers for convective development.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 728 AM EDT Sat Jul 11 2026

Mainly VFR conditions and light winds will persist at all the terminals through the forecast period with high pressure overhead. A few showers will form along a lake breeze off of Lake Superior this afternoon. There is up to a 30% chance for SAW/IWD to be impacted by one of these showers. Any showers will diminish during the evening with loss of daytime heating. Winds will be generally light and variable at around 5 kt or less.

MARINE

Issued at 339 PM EDT Fri Jul 10 2026 Amended at 339 AM EDT Sat Jul 11 2026

Light winds of 15 kt or less will prevail into the weekend as Lake Superior remains under the influence of surface high pressure. There will, however, be an uptick in winds starting Sunday night as the pressure gradient tightens while a strong low moves along the high pressure ridge. Southwesterly winds will increase to 25-30 kt over the central portions of the lake, persisting through the first half of next week and expanding to include western and eastern portions of the lake as well. Models continue to trend toward a few gale force gusts Monday into Tuesday across the central portions of the lake.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... None. Lake Superior... None. Lake Michigan... None.