textproduct: Marquette

KEY MESSAGES

- Showers and thunderstorms will be possible (up to 50%) along a cold front tonight into Tuesday.

- Temperatures will be close to seasonal averages most days through next week, with highs in the 70s and lows in the 40s and 50s.

DISCUSSION

Issued at 256 AM EDT Mon Aug 17 2026

GOES-East Nighttime Microphysics imagery shows just some patches of low to mid level clouds over the UP now that the previous day's showers are all east of the region. Scattered METAR reports of 1/2 mile to 1 mile visibility have been reported, but are not consistent spatially or temporally, so no advisory is planned, however, will continue to monitor in case the coverage becomes enough to impact the Monday morning commute.

Per RAP analysis, the upper air pattern consists of an expansive 500mb high over much of the southern CONUS with deep troughs off of each coast and one in northern Manitoba. Through Tuesday afternoon, a 500mb trough will deepen and become a closed low as it swings along the Hudson Bay shoreline from Manitoba to far northwest Ontario. Falling 500mb heights ahead of this closed low will lead to the formation of a surface trough that will once again bring rain shower chances to the UP tonight. CAMs show some convective activity in Minnesota and northwest Ontario ongoing at 00Z Tuesday, though there is significant spread on the continuity of the line of showers along the front as well as the intensity therein. If convection survives crossing the lake and reaching the UP, it will be moving into stable air (HREF mean MUCAPE between 100-250 J/kg), though it will be a shear-rich environment as HREF mean 0-3km SRH balloons to 100-200 and deep speed shear is present (including the presence of a 100+kt jet at 250mb). Model soundings show meager lapse rates but plentiful deep moisture (LREF mean PWAT grows to about 1.25 inches, around the 75th percentile of climatology). Thus, if any thunderstorms can get going, some heavy rain rates could be observed, but severe thunderstorms seem unlikely given the timing of the showers not lining up well with diurnal destabilization and the best forcing being displaced from the UP. Unfortunately for the areas of growing drought for the UP, this rainfall does not look to be widespread, as LREF probabilities of 0.1 inch of rain by 00Z Wednesday are 20-40% for the west half and 40-65% for the east half.

Another dry spell then kicks off early Wednesday morning through at least Thursday evening. Models diverge significantly for the late week period, though the passage of another deep trough from the northwest looks to be the next mechanism for bringing shower and thunderstorm chances to the UP late this week into next weekend. With the continued background northwesterly flow aloft pattern, temperatures generally remain seasonal with highs in the 70s and lows in the 50s.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 721 AM EDT Mon Aug 17 2026

With the morning fog clearing out, VFR conditions will prevail at all sites throughout the period. Generally westerly to northerly winds 5-10 kt will becoming southerly to southwesterly this evening ahead of a cold front that will bring some showers to the UP overnight, though chances of rain are only up to 60% at IWD, 45% at CMX, and 25% for any given hour at SAW. Chances of thunder are only above 15% at IWD and with the peak chance of thunder at only 20%, will leave TSRA out of the TAF at this time.

MARINE

Issued at 256 AM EDT Mon Aug 17 2026

Wind gusts around or less than 20 kt on Lake Superior this morning last through tonight (with the notable exception of southwesterly wind gusts funneling between Isle Royale and Thunder Bay Monday afternoon to 20-25 kt). A cold front passing over the lake tonight into Tuesday will have gusty westerlies for the east-central portion of the lake to 20- 25 kt for Tuesday afternoon. Winds falling below 20 kt again Tuesday night will remain thus until the next disturbance arrives late in the week.

MQT WATCHES/WARNINGS/ADVISORIES

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