textproduct: Marquette

KEY MESSAGES

- Benign, sunny weather continues through today with highs near seasonal norms. There is a slight chance of showers and thunderstorms both Saturday and Sunday, but no severe weather is expected.

- A warming trend is forecast as high temperatures increase daily through early next week. Highs near or above 90 are becoming more likely from Sunday through Tuesday.

UPDATE

Issued at 258 AM EDT Fri Jul 10 2026

The going forecast remains on track this morning. GOES-East Nighttime Microphysics RGB imagery shows marine fog over a relatively cool Lake Superior while only patches of fog are noted on land at 06Z, notably along the shores of eastern Alger County and Luce County and isolated patches of the interior west. While a return of some fog is expected as conditions are ripe for efficient radiational cooling to the dew point, drier air and increased subsidence from advancing upstream ridging do cast some doubt on the coverage of fog. Will hold off on any advisories and react accordingly if widespread fog does form, though that scenario is doubtful.

Once the morning fog clears, benign weather takes hold of the region as ridging gradually builds over the Upper Midwest through Monday morning. By Monday, LREF 500mb height reaches the 99th percentile of climatology, and the building atmospheric thickness (as well as efficient diurnal heating with high surface pressure leading to clear skies) will allow temperatures to slowly climb. The LREF, which can sometimes run cool on high temp forecasts, is already calling for up to 40% chances of breaking 90 on Sunday and up to 60% chances of breaking 95 degrees on Monday and Tuesday for much of the interior UP. With LREF mean dew points in the 60s on Monday, heat indices into the triple digits will be in play (NBM mean apparent temperature does reach 100 in a few spots Monday and Tuesday), though there is enough moving parts in the setup to cause confidence in the forecast to be low. Accompanying the heat will be near-daily slight chances (15-30%) of rain and thunder in the afternoon with diurnal heating building instability, subtle ripple troughs in the 500mb flow, and lake breeze fronts, but widespread precipitation is not expected.

Confidence in the forecast deteriorates further for Wednesday and beyond as spread in how ensemble members resolve the strength and placement of a potential kicking trough over the Pacific Northwest. Should the trough not be strong enough or take a suboptimal path, the heat and lack of meaningful precip may last into the midweek period. On the other hand, the kicking trough may shift the ridge into a placement that brings more seasonable temperatures to the UP as well as more precip chances. LREF 10th-90th percentile spread is nearly 20 degrees by Wednesday evening, so confidence in the forecast is too low to deviate from the NBM at this time.

DISCUSSION

Issued at 349 PM EDT Thu Jul 9 2026 Amended at 258 AM EDT Fri Jul 10 2026

RAP analysis shows surface high pressure beginning to build in over Lake Superior as it extends southward from Hudson Bay and northern Ontario. This will promote dry and pleasant summer conditions through today as high temperatures increase into the upper 70s to mid 80s across the area for this afternoon.

Temperatures continue to gradually increase through the weekend as expansive upper level ridging builds from the Intermountain West into the central CONUS, sending highs solidly into the 80s across the UP on Saturday afternoon and pushing 90 degrees for at least the interior areas by Sunday. Will retain a slight chance of showers and thunderstorms both Saturday and Sunday as a few weak disturbances transit the periphery of the upper ridge this weekend, but with MUCAPE only around 500 J/kg and relatively meager shear would not anticipate any strong to severe thunderstorms.

Heat remains the primary forecast concern early next week as 500 mb heights rise above 590 dam, near or above the climatological max for mid July per multiple ensemble suites, while 850 mb temps climb to 25-27 C or higher. This will likely result in widespread readings in the 90s across the UP for Monday and Tuesday, with the NBM depicting a greater than 75% chance to exceed 90 away from the immediate shorelines and even the often low-biased LREF showing a 60-75% chance in these locations. Humidity will not be as high as in the late June heat wave as low level trajectories will have more of a westerly component, but dewpoints into the 60s will still support potential 100 degree heat indexes in some interior locations per the NBM. This coupled with high overnight low temps in the 60s to perhaps even 70 degrees will correspond to a major HeatRisk across much of the UP for Monday and Tuesday. There remains uncertainty as to the duration of the heat later into the week as medium range guidance continues to hint at a strong upper trough flattening out the ridge as it moves into the vicinity of Hudson Bay Tuesday into Wednesday of next week, increasing shower and thunderstorm chances again across the area as we head into the middle of next week.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1253 AM EDT Fri Jul 10 2026

VFR conditions will deteriorate late tonight as the low levels cool under clear skies and light winds, which will combine with low level moisture to produce widespread fog. Confidence is increasing in the development of dense fog and IFR/LIFR conditions through the early morning hours. After sunrise fog will begin to mix out, with VFR expected by mid-morning and continued light winds.

MARINE

Issued at 349 PM EDT Thu Jul 9 2026

Surface high pressure building over the lake from the north will maintain light winds of 15 kt or less into the weekend. Patches of dense fog will likely linger over parts of the lake, especially the eastern half, through at least Friday morning. There is some indication that the pressure gradient will tighten across the lake early next week as string high pressure resides over the Lower Great Lakes while a strong low approaches from the northwest. This will likely result in 25-30 kt southwesterly winds over the western half of the lake during the first half of next week, with the NBM showing a 15-25% chance for a few gale force gusts Monday into Tuesday.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... None. Lake Superior... Dense Fog Advisory until 11 AM EDT /10 AM CDT/ this morning for LSZ162-250-251-263>267.

Lake Michigan... None.