textproduct: Marquette

KEY MESSAGES

- Ongoing rain showers early this morning end by noon, rain totals generally less than a tenth of an inch.

- Rain becomes likely (>50% chance) for the south half of the UP Friday afternoon into at least Saturday morning. There is a slight chance (~20-40%) of amounts exceeding an inch, mostly limited to Menominee County south of US-2. There is uncertainty in how far north the precipitation will reach.

DISCUSSION

Issued at 316 AM EDT Thu Sep 17 2026

KMQT radar returns at 05Z show a bit more widespread rain shower coverage over the western UP than forecast 24 hours ago as the shortwave low over northern Manitoba has more pronounced troughing along its southern periphery. Despite this trend upwards in shower coverage, intensity remains low as the showers are having to fight subsidence from a surface high of 1026-1028 mb that remains over the region, though is now centered around southern James Bay. 00Z HREF 75th percentile QPF by the time showers end around 12Z is still less than a tenth of an inch for all except for the Watersmeet area. Confidence in any measurable rainfall this morning decreases sharply over the east half of the UP, with the HREF PoPs east of the M-94 corridor mostly sub-15%. The additional low level moisture from these showers may lead to a few patches of fog, but widespread dense fog is not expected as HREF chances of visibility less than 1 mile is only 10-20% this morning.

Elsewhere, the 500mb pattern consists of 600 dam ridging over Memphis bounded by deep troughs centered over northern California and the Bahamas in addition to the aforementioned northern Manitoba trough. The first key feature to watch will be a ridge-riding shortwave currently over the UT/CO/WY triple point that will track a surface low south of the UP this weekend and bring chances of rain to the UP Friday and Saturday. The NBM continues to trend the core of heavy rainfall south, though the LREF has wavered back and forth some over the past few runs. The 00Z RRFS doesn't even guarantee precip for the vast majority of the UP, only showing measurable precip for southern Menominee County and pockets of the interior west. While that solution is on the dry side of the distribution, it is within the realm of possibilities. Current chances of a tenth of an inch of precip or higher in the LREF are around 50% or higher for the US-2 corridor and south. The 25th-75th percentile precipitation accumulation remains high as the 25th percentile shows very little precip for all except for Menominee County, though the 75th percentile shows up to half an inch for Iron River/Escanaba and over an inch for the southern half of Menominee County, so some heavy rainfall remains possible but is far from guaranteed.

In the wake of the disturbance, the western CONUS trough will shift into the Northern Plains, weakening slightly. At the same time, ridging to the north of the trough amplifies, causing split flow. At this time, the favored solution is for the UP to be affected by the northern branch of this split flow which will lead to persistent high pressure and dry weather and near-normal to slightly below normal temperatures for Sunday through at least the first few days of next week until ensemble spread increases for the midweek and beyond.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 123 AM EDT Thu Sep 17 2026

VFR conditions are expected to prevail through the TAF period. A weak shortwave will move across the area through early morning bringing mid-level cloudiness along with a band of light showers. Confidence was high enough to include a TEMPO group early in the TAF period at the sites. Overall, showers are not expected to impact flight categories. Winds will be light though the period.

MARINE

Issued at 316 AM EDT Thu Sep 17 2026

High pressure keeps winds below 20 kt through tonight. Friday and Saturday, low pressure passing by to the south combined with a high to the north will result in prolonged northeasterly flow into the western arm of Lake Superior, with winds increasing locally to 20-30 kt and waves of 2-3 feet. A stronger high building to the north on Sunday looks to expand coverage of 20-30 kt winds to much of the southern half of Lake Superior. Models disagree about gale potential, with the Euro ensemble probabilities of gales only around 10% over the western arm while the NBM projects gale chances of around 40%. Waves increase to near 3 feet over northern Lake Michigan and Green Bay on Saturday as well due to prolonged easterly flow approaching 20 kt.

MQT WATCHES/WARNINGS/ADVISORIES

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