textproduct: Marquette

KEY MESSAGES

- Widespread moderate rain chances (30-60%) this afternoon into Sunday, along with low thunderstorm chances (15-20%) during the overnight hours. Severe weather is not expected at this time.

- Dry weather late Sunday through Monday before rain chances resume Tuesday through early Wednesday.

- High temperatures are expected to be in the mid-70s to low 80s into next week, with low temperatures generally in the 50s to low 60s.

DISCUSSION

Issued at 309 AM EDT Sat Aug 15 2026

GOES-East Nighttime Microphysics RGB imagery shows mostly clear skies over the UP with the exception of mid-level clouds streaming above the far western UP ahead of multiple disturbances to the west. RAP analysis shows 1024mb high pressure centered over northeastern Ontario with 500mb showing a shortwave over the KS/NE/CO triple point and a line of convection along the MO/IA border with falling 500mb heights there, in addition to the well-advertised trough currently over Saskatchewan. This Canadian trough will be the mechanism for rain chances in the forecast, though models have trended much slower with the onset of rainfall arrival in the past 24-48 hours. Especially as the prior two disturbances down south cut off any Gulf connection for moisture transport, precip will have some difficulty starting as the better forcing will be over Canada. The HREF now shows a mean onset time for measurable precipitation over the western UP around 00Z Sunday, then 06Z Sunday for the central UP, with the eastern third not seeing precip on average until 12Z Sunday. With 200-500 J/kg of MUCAPE (per Euro ensemble mean) to work with, a few rumbles of thunder will be possible, but the severe threat remains low with the aforementioned forcing and moisture deficiency as well as 20-30 kt of sfc-500mb shear. Most in the UP will see at least some precip by the time showers exit to the east, with HREF probabilities of at least measurable precip at over 70% for all except a few pockets of the south-central, though the chance of a quarter of an inch of rain is only about a coin flip (higher chances along Lake Superior, lower between the US-2 and M- 28 corridors).

As the trough and associated showers depart late Sunday, the UP is once again in northwesterly flow aloft with gently-sloping ridging upstream. This will lead to dry weather for the UP through Monday, but will also keep temperatures around normal with highs in the 70s to low 80s and lows in the 50s (60s near the shores, upper 40s interior).

By 12Z Tuesday, a deep 500mb closed low over Hudson Bay will send at least 1 trough across northern Ontario and towards the Great Lakes. While spread remains high on the details, LREF probabilities of a quarter inch of rain per 24 hours is above 50% for the southern UP and in excess of 33% as far north as Marquette. Euro mean MUCAPE values around 500 J/kg indicate some thunderstorm potential, though a fair amount of ensemble spread limits the confidence in severe potential. Ensemble spread increases sharply following Wednesday as confidence in ridging over the Four Corners is high, but details on any of the surrounding troughs is low.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 752 AM EDT Sat Aug 15 2026

A disturbance will brings SHRA and TSRA chances to the terminals near the back half of this TAF period along with gradually deteriorating ceilings and perhaps visibility conditions as well. An assortment of PROB30s covers the approximately 30 percent chances of TSRA as well as of visibility of at least MVFR, though chances of ceilings falling to MVFR or lower are much greater (greater than 75%). For the daytime today, the ongoing airport minimums at SAW should be short lived now that the sun has risen, so a one hour TEMPO will cover that (and if the fog remains stubborn, the TAF will be amended as needed). Otherwise, VFR conditions should persist at all sites through the daytime hours. Southeast to east winds of 5- 10kt with gusts up to 15 kt will veer towards the west as the disturbance passes.

MARINE

Issued at 309 AM EDT Sat Aug 15 2026

Wind gusts will be sub-20 kt this morning on Lake Superior. This afternoon immediately east of the Keweenaw Peninsula, east to southeast wind gusts to 20-25 kt will form ahead of an approaching disturbance. Winds fall sub-20 kt as the disturbance passes, but reinvigorate to near 25 kt northwesterlies over the east half of the lake behind the front. Winds fall below 20 kt Sunday night through Tuesday night (except for a few southwesterlies above 20 kt as winds funnel between Isle Royale and Thunder Bay on Monday). Wednesday, wind gusts of 20-25 kt out of the north will be along the shores of the UP out to 10-20 miles in the wake of a mid-level trough before falling sub-20 kt Wednesday night.

MQT WATCHES/WARNINGS/ADVISORIES

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