textproduct: Marquette

KEY MESSAGES

- The warmest airmass of the season so far will impact the UP with highs in the 90s Sunday through Tuesday. High dewpoints and poor overnight recoveries will increase cumulative impacts. 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).

DISCUSSION

Issued at 408 PM EDT Sat Jul 11 2026

Today continues the ongoing warming trend: current surface temps are on track to reach toasty levels 5-10F above normal. With RAP surface analysis showing the UP under 1018mb of high pressure and light winds, interior locations in the east and west are hitting high 80s across the board, while Great Lakes shoreline temps remain more tolerable in the 70s. Highs today are projected to touch 90F interior and reach the low 80s along shorelines. With dewpoints in the 50s east and 60s elsewhere, apparent temperatures remain in the mid to high 80s. Radar shows a lake breeze initiated around 1745Z from the Lake Superior shoreline heading toward the central UP, so some relief may be felt this evening in those parts.

Over the next few days, the robust Four Corners high amplifies and shifts northeast toward the Upper Great Plains. As the high approaches the Upper Great Lakes on Monday, its northward progress is deflected eastward as a sub-arctic trough over the Hudson Bay deepens and an upper-level jet streak moves over the Canadian Prairies. Thus, continued anticyclonic flow advects extremely anomalously warm air toward the region for several days before steering flow shifts it south. The NAEFS ESAT is currently showing 500 hPa mean geopotential height at 100% of climatology for most of the UP for Monday afternoon through late Tuesday.

For Sunday's ramp-up period to this extreme heat, a Heat Advisory has been issued for noon through 9PM for the western UP given widespread apparent temperatures (heat indices) reaching 90F-100F. The NBM has over 50% probability of high temps greater than 90F for nearly all of the CWA, with the exception of south shore of eastern UP whose high temps will be influenced by light, onshore southerly flow off Lake Michigan. Portions of far western UP and Keweenaw have highest NBM probabilities of over 90% chances of greater than 90F, and over 50% chance of greater than 95F. NBM MaxT interdecile spread for Sunday tops out at 9F, which puts most of UP in the mid-80s at the low end. Southwesterly surface flow indicates extra warming is possible via downsloping for the central UP coast, from Copper Harbor to western Alger County. With NBM mean dewpoints in the mid to high 60s for the second half of Sunday through Monday morning, this puts apparent temperature on the first day of this heat streak at 90F-100F for the western UP, and in the upper 80s in the eastern UP.

Along with the warm, moist airmass, thunderstorm potential is nonzero for Sunday afternoon. HREF mean SBCAPE ranges from 1500-3000 J/kg tomorrow evening, concentrated in the western UP and including the Keweenaw. HREF bulk shear magnitude values increase to moderate through the day as the jet moves in from the NNW, though directional shear (from HRRR soundings) is largely unidirectional, veering from NW'ly to N'ly through the night, above the low-levels. With scant synoptic forcing and high pressure moving in, any lake breezes which form may be a focus for convection. Though CAMs struggle to arrive at consensus with respect to time and placement, the environment is supportive of isolated severe storms; thus, SPC's Marginal Risk for severe thunderstorms tomorrow.

Sunday evening has poor recoveries from the heat with apparent temps only decreasing down to the high 60s and low 70s by early Monday morning. Should widespread thunderstorms manifest Sunday afternoon and evening, cloud cover and recent rainfall may increase mugginess. With recent NBM runs trending overnight minimum temperatures higher with the latest model runs, this may worsen cumulative heat-related impacts.

The UP is set to experience widespread apparent temperatures in the high 90s and triple digits on Monday and Tuesday, the worst of which will be felt between 1PM and 8PM each day. Between MinT's decreasing only to the low 70s and dewpoints in the high 60s, Monday's overnight period recovers particularly poorly with apparent temps in the mid 70s. As the mid-level ridge begins to flatten out toward midweek, the warmest airmass shifts south of the CWA, though it's possible that above-average heat will remain through the week. The NBM shows widespread, significant interdecile spread (>15F) for temperatures after Wednesday night.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 228 PM EDT Sat Jul 11 2026

VFR conditions to prevail for duration of TAF period with light winds as Upper Michigan remains under high pressure. A few showers cannot be ruled out still later today along any lake breezes that may form, but confidence is not high enough to include mention at this time. Any showers that do form will diminish during the evening, though, with loss of daytime heating. Winds will be generally light and variable at around 5 kt or less.

MARINE

Issued at 408 PM EDT Sat Jul 11 2026

Light winds of 15 kt or less will prevail through tonight as Lake Superior remains under the influence of surface high pressure. There will be an uptick in winds starting Sunday as the pressure gradient tightens while a strong low moves along the high pressure ridge. Southwesterly winds will increase to 15-20 kt on Sunday and to 25-30 kt over the central portions of the lake by Monday, 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 late Monday into Tuesday across the central portions of the lake.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Heat Advisory from noon EDT /11 AM CDT/ to 9 PM EDT /8 PM CDT/ Sunday for MIZ001>005-009>011-084.

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