textproduct: Marquette

KEY MESSAGES

- Chance of rain (30-50%) for the south half of the U.P. Friday afternoon into at least Saturday morning. There is a slight chance (~10-25%) of amounts exceeding an half an inch, mostly limited to Menominee County south of US-2.

-There is uncertainty in how far north the precipitation will reach, but totals are expected to be low if precipitation does occur in the northeastern U.P.

-Temperatures are expected to remain at or just below average through midweek.

DISCUSSION

Issued at 228 PM EDT Thu Sep 17 2026

Latest visible satellite imagery shows cumulus clouds developing thanks to diurnal heating over the central and western U.P., with scattered midlevel cloud cover across Lake Superior. The latest water vapor imagery shows a fairly dry zonally-oriented airmass across the U.P. and much of the eastern US-CA border, which is reflective of the generally zonal flow across the area at 500mb. Lows tonight are expected to fall into the mid to low 40s, which could result in some patchy fog in the southwestern U.P.

As the 500mb low currently over northern Manitoba continues to progress eastward this evening, 500mb ridging is expected to build over central Canada. Combined with the effects of the high pressure center currently centered over AR, this will result in ridging over the central US and generally northwesterly upper level flow across the western Great Lakes region tonight through Friday morning. A shortwave trough is expected to move across the largescale ridge to our west tonight, arriving just south of the CWA by Friday afternoon and bringing our next best chance of rain. The NBM continues to keep the heaviest rainfall south of the U.P., which is in agreeance with the latest CAMs guidance. LREF chances for 24-hour rain totals greater than 0.01 inches between 00z Saturday and 00z Sunday are between 20-40% for the northern and eastern U.P., and increase to upwards of 60% for the central southern U.P. Probabilities decrease significantly with increasing totals, with a 10-25% chance of totals exceeding 0.5 inches for Menominee County.

On Sunday, a 500mb ridge is expected to build over MN in advance of an eastward-moving 500mb low currently over northern CA. This ridge will progress over the area Monday, bringing clearing skies. Tuesday, the aforementioned low weakens due to the influence of the ridge as it progresses into our region and split flow develops around the weakening low and amplifying ridge.At this time, there is still some uncertainty as to the exact track of this split flow, however, the U.P. is currently projected to be under generally high pressure, which would result in dry weather and seasonable temperatures through midweek.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 143 PM EDT Thu Sep 17 2026

VFR conditions expected through the TAF period as surface high pressure strengthens over Upper Michigan through Friday. Can't rule out some patchy fog in the west tonight, including at KIWD where there is a ~30% chance for MVFR visibility into early Fri morning. Winds remain below 10 kt through the period, turning easterly Fri afternoon ahead of a system passing south through Wisconsin.

MARINE

Issued at 228 PM EDT Thu Sep 17 2026

Lake Superior: Tonight, winds remain below 20kts and are expected to shift from westerly to northerly around 04z Friday. On Friday, winds are expected to become easterly at up to 20kts. On Saturday, expect a shift to southeasterly winds slowing to under 15kt for the east, remaining easterly and up to 20kts in the west, especially the western arm of Superior, which could see winds exceeding 25 kts near Duluth. On Sunday, northeasterly winds are expected to reach 20- 30kts in the south and west. Uncertainty remains as to whether winds will exceed gale conditions in the southern portion of the western arm, with the latest NBM run projecting around a 30-40% chance of exceedance. Wave heights are expected to remain below 3ft until Sunday, when they build up to 3-6ft. For Monday and Tuesday, the strongest winds (up to 30kts) will remain in the western arm of the lake, while most areas will see winds at or below 20kts.

Northern Green Bay and Northwestern Lake Michigan: Winds remain under 15kts and generally northerly until Saturday morning, when they strengthen to around 15kts and shift to easterly. On Sunday, northerly winds return, with speeds up to 25kts possible. On Monday, winds will weaken slightly to around 20kts and shift easterly, with similar conditions expected to last through midweek. Wave heights are not expected to exceed 2ft until Sunday, when they build to 3 ft. 2-3ft waves remain in the forecast through Tuesday, and reduce to 1-2ft or less Wednesday.

MQT WATCHES/WARNINGS/ADVISORIES

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