textproduct: Marquette

KEY MESSAGES

- The combination of 4-8 inches of snow and strong winds of 30-40 mph will result in hazardous conditions this afternoon through Saturday for the Keweenaw and eastern Upper Michigan. - Dangerous wind chills late tonight and Saturday are expected for parts of western Upper Michigan.

- Gales and heavy freezing spray are expected on Lake Superior late this afternoon into early Sunday.

- Below normal temperatures continue this weekend before a warm up above freezing next week.

DISCUSSION

Issued at 307 AM EST Fri Dec 12 2025

Weak surface trough is currently stretching across eastern Lake Superior with an 850mb airmass between -10 to -13C. Within northwest to north-northwest flow, lake effect snow showers have been common into the traditional northwest wind snowbelts. Model soundings show inversion heights of 5k feet or less, which matches the lack of significant organization observed in the shower activity on KMQT. Webcams across the region also reinforce this, highlighting only light snow accumulations so far overnight. Temperatures have been observed in the teens and 20s so far. Cloud cover so far has limited cooling, but if we are able to see breaks, interior areas may dip into the single digits above zero.

The forecast area sits to the west of a broad upper level low positioned over northern Maine and downstream of a large ridge stretching up the West Coast. Within the northwest flow aloft, a mid- level ridge is currently stretching north from Minnesota to Hudson Bay with a surface low positioned in north-central Manitoba and a cold front draped south into North Dakota. Ahead of the front, lake effect will lift northeast as flow becomes more southwesterly with surface high stretching southeast through Wisconsin. The cold front will press into the west this afternoon and through the east this evening as the surface low moves through Ontario. Current CAMS support a band of 925-850mb fgen resulting in a sharp uptick in snow intensity along the front into the Keweenaw/west in the 18-20z timeframe and then near 1-3z this evening into eastern Alger/Luce 1- 3z. Behind the front, strong cold air advection will enable 850mb temps to fall from near -11C to -24C by Saturday morning. This will support a post-frontal lake effect event that will continue through the weekend for areas downwind of Lake Superior. When combined with the frontal passage, snow accumulations could eclipse 5 inches in many areas of the higher terrain in the Keweenaw/Spine this afternoon and tonight, and tonight and Saturday in Alger, northern Schoolcraft, and Luce counties. Additionally, the cold air and the post frontal pressure gradient will result in strong winds developing. These 30-40mph winds will be enough to support areas of blowing snow and hazardous travel. Opted to issue Winter Weather Advisories for the Keweenaw and eastern counties because of this combination.

The airmass will support below normal temperatures through the weekend. Specifically tonight, sub-zero lows across the interior west are expected, with single digits above north-central, Keweenaw, and parts of the interior east. Daytime temps on Saturday don't climb much for the west half, which are likely to remain in the single digits above. The east looks to warm into the teens. Combined with wind gusts of 30-40 mph in the Keweenaw and by Lake Superior tonight and through Saturday, 20-30 mph elsewhere, dangerous cold, blustery conditions are expected. Windchills between -10 to -20F are expected through Saturday across the west half, with colder values of -30 to -25F being possible Saturday morning. Given this risk, opted to issue a Cold Weather Advisory for the coldest spots. Right now this is limited to Gogebic and Iron counties, but this could be expanded later today should model trends elsewhere fall. The cold will linger through the weekend while winds lighten. Dangerous wind chills below -10F are expected to continue into Sunday morning for the west half.

Monday into Monday night, another shortwave caught in the northwest flow may kick off another round of snow, mainly in the Keweenaw and east. Mid-level flow across CONUS becomes more zonal afterwards, allowing a system to move through central Canada Monday and Tuesday. There's really good agreement among the various deterministic packages that this surface low will lift a warm front through the region. Warm air advection behind it may help the forecast area warm above freezing Tuesday and Wednesday afternoons. We should fall below freezing both nights though, so significant snowpack loss isn't expected.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 653 AM EST Fri Dec 12 2025

MVFR/VFR conditions prevail this morning at all sites ahead of a shortwave and attendant cold from crossing through MN this morning. As this front passing through Upper Michigan this afternoon, light snow will overspread the, bringing down cigs/vis to MVFR. Once the front clears the lake, lake effect snow will begin to increase for the NW wind snowbelts, mainly impacting CMX and IWD. There, moderate to heavy lake effect snow will sock in IFR to LIFR vis in blowing snow as WNW winds pick up between 25-35 kts, highest at CMX. Meanwhile at SAW, occasional snow showers are expected, but IFR conditions will likely not be seen. NW flow lake effect snow showers continue tonight and through Saturday.

MARINE

Issued at 307 AM EST Fri Dec 12 2025

Southwest flow will increase today to near 30kts ahead of a cold front this afternoon and evening. The airmass behind the front and the lingering strong pressure gradient will be enough to support gales and heavy freezing spray. Current thinking is that northwest winds fall below gale west of the Keweenaw this evening, but remain 35-40kts north and east of the Keweenaw into Sunday morning. Even though winds fall below gale west of the Keweenaw, the cold airmass will still be enough to support heavy ice accumulation rates from spray. Because of this, opted to hoist Gale Warnings and Heavy Freezing Spray Warnings for most of Lake Superior. Winds fall below 20kts lake-wide Sunday afternoon.

Southwest flow will then increase Sunday night into Monday to 25- 30kts for most of the lake. Some gale potential does exist, but current ensemble guidance varies greatly what that potential is. For example, latest NBM suggests 20-30%, latest EC 50-80%, and latest GEFS 40-60% chance for gales. There's good agreement though on winds falling below 20kts by Monday evening. Another period of elevated winds looks to follow Tuesday with what could be a stronger event in the Wednesday/Thursday time frame. There's already good agreement that this mid-late week event could be a gale (at least 50%) and there's guidance suggesting Storm potential.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Saturday for MIZ001>003.

Winter Weather Advisory from 7 PM this evening to 7 PM EST Saturday for MIZ006-007-085.

Cold Weather Advisory from midnight tonight to 9 AM CST Saturday for MIZ009-010.

Lake Superior... Heavy Freezing Spray Warning from 4 PM EST /3 PM CST/ this afternoon to 1 AM EST /midnight CST/ Sunday for LSZ162.

Heavy Freezing Spray Warning from 7 PM EST /6 PM CST/ this evening to 7 AM EST /6 AM CST/ Sunday for LSZ240>244-263- 264.

Gale Warning from 7 PM this evening to 1 AM EST Saturday for LSZ242-243-263.

Gale Warning from 7 PM this evening to 7 AM EST Sunday for LSZ244-264.

Gale Warning from 10 PM this evening to 7 AM EST Sunday for LSZ245-246-248>251-265>267.

Heavy Freezing Spray Warning from 1 AM Saturday to 7 AM EST Sunday for LSZ245-248>251-265>267.

Lake Michigan... None.