textproduct: Marquette

KEY MESSAGES

- A burst of light to moderate snowfall is expected over the Keweenaw and east half of the U.P. late tonight into Monday morning. Accumulations mainly less than 2 inches.

- Southwest gales of 35 knots are expected over the western lake late tonight into Monday. Heavy freezing spray is also expected over the far western lake tonight.

- Temperatures start climbing early this week, with above freezing highs expected by Tuesday.

- Multiple gale events could be seen across Lake Superior this week.

- A strong Clipper low could bring high winds and a flash freeze setup across the area Thursday. Continue to monitor the forecast as impacts could change depending on the strength and track of the low.

DISCUSSION

Issued at 418 PM EST Sun Dec 14 2025

The forecast is an active period including a multitude of mid level waves, increasing in strength and vigor, as they traverse the Upper Great Lakes this week. The pattern change to more zonal flow across the CONUS allows better periods of warm air advection to support precip, but also result in widespread above freezing temps returning for the first time in weeks on Tuesday/Thursday. Beyond this coming weekend, temps hover around normal and ensemble guidance leaves potential for several weak disturbances around the holiday timeframe, but with lesser impacts and much lower confidence in timing/track. Starting this afternoon, GOES water vapor imagery shows the mid level trough has made it to New England with a broad ridge over the west CONUS. At the surface, strong high pressure near 1040 mb over the Mid Mississippi River Valley is extending ridging up into the Upper Great Lakes. This has already deteriorated thermodynamic profiles, but will also back winds out of the southwest into this evening. This ends lingering light LES showers over the east by tonight. Additional snow accumulations this afternoon around 1 inch or less.

This inbetween period won't last long as a subtle wave currently atop the ridge over the Canadian Prairie approaches the region tonight. WAA and isentropic ascent support a round of light snow as high pressure ridging gives way into Monday with brief weak trailing LES. A quick passing f-gen max over the central may support higher amounts into the 2-4 inch range on the cold side (eastern UP), but confidence is not great as available deep moisture is not impressive and is short lived. Particular focus is on Keweenaw, Alger, and Schoolcraft counties where there is a 25% chance for +3 inches and less than a 10% chance for +4 inches. While this will be a quick burst of light to moderate snow with possible visibility restrictions down to 1 mile (50-75% chance), opted not to hoist any Winter Weather Advisories. Additional LES amounts up to 1 inch over the Keweenaw and northeast on Monday. Otherwise temps settle tonight into the single digits above to low teens, warming into the upper teens to 20s on Monday. A brief ridge passes over Monday evening into Monday night, ending LES and increasing southwest flow. Temps mainly hold in the teens, hitting their lows shortly after midnight.

On Tuesday, a clipper system tracks across northern Ontario. Strong WAA brings back widespread highs in the 30s with some low 40s in downslope flow areas. Southwest winds increase with the tightening pressure gradient, becoming breezy, particularly in the aforementioned downslope flow where gusts in to the 25-35 mph range are expected. A warm front and trailing isentropic ascent may provide marginal lift to produce some drizzle/freezing drizzle late in the day, but once again the available moisture is unimpressive. Better PoPs (20-40%) arrive overnight into Wednesday when the shortwave and cold front track through. This cooler period introduces LES back into the wintry mix. All measurable accumulations at this point look marginal, if at all. Also could see some gusts up to 40 mph with the passing cold front and strong pressure rises, particularly near Lake Superior (30-60% chance). Expect precip to end by Wednesday afternoon as ridging returns. Highs will be closer to normal on Wednesday in the upper 20s to mid 30s.

This dry period will not last long as the most prominent feature of the forecast arrives. A mid level trough over the Northern Rockies on Wednesday tracks along the southern end of the Great Lakes Basin Thursday night into Friday, sending a strong low pressure system somewhere over the Upper Great Lakes on Thursday. There remains plenty of ensemble spread in the surface low track at this point, so varying levels of impacts are possible. The main story is that WAA initially warms temps above freezing into the 30s late Wednesday night into Thursday. This alongside isentropic ascent kicks off a wintry mix of rain and snow showers into Thursday. As the low tracks through on Thursday, a cold airmass quickly slams in from the west, transitioning precip over to snow from west to east. This is a good set up for a flash freeze as models indicate 15-20F changes in 6 hours or less with lows Thursday night in the single digits above to mid teens, coldest interior west. The combination of any snowmelt and prior rain to this cold front likely would create hazardous roads and sidewalks should this pan out. The amount of snow accumulation late Thursday into Friday with the trailing LES will depend on the system track. Depending on how far the low ends up tracking, this could speed up the p-type transition period, or mostly circumvent it altogether like the 12Z GFS. This uncertainty is captured well by the latest NBM percentiles. The 75th percentile has 4-8 inches over the northwest wind snowbelts while the 25th struggles to reach 1 inch. What does seem more certain is the winds with this system. The strong pressure gradient/pressure rises on the back side with strong CAA support strong northwest winds, potentially as high as 50 mph across the Keweenaw and along the Lake Superior shoreline (20-40%). These strong winds, in conjunction with any icing that occurs, could bring some power outages and minor lakeshore flooding and beach erosion to the Lake Superior shoreline late Thursday into Friday morning.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 653 PM EST Sun Dec 14 2025

Lingering lake effect has mostly tapered off this evening, yielding prevailing VFR conditions at Upper Michigan terminals as the next weak system approaches from the west. Expect cigs to trend downward back towards MVFR 05-08z Mon as southwest winds increase to 10-15 kt, with snow returning to KCMX and KSAW while guidance only depicts around a 20% chance for precipitation at KIWD. Snow along with winds gusting to 20-25 kt will bring variable MVFR/IFR conditions to KCMX at times on Mon. Snow will taper off from west to east and winds will begin to ease as conditions trend back towards VFR at all terminals towards the end of the period.

MARINE

Issued at 418 PM EST Sun Dec 14 2025

A very active period is expected across Lake Superior during the next 7 days. Southwest winds increase through tonight to 20-30 kts across the lake with gales to 35 kts expected over the west tonight into Monday morning. In addition, heavy freezing spray is expected over the far western waters. Winds veer northwest through Monday, gradually falling below 20 kts from west to east by Monday night as a weak ridge moves through.

A stronger clipper system moves north of the lake on Tuesday, once again increasing southwest winds tuesday morning to 20-30 kts lakewide, further strengthening to gales of 35-45 kts by the afternoon (20-40% chance of at least 40 kts), strongest winds over the west. Winds veer northwest Tuesday night as the cold front progresses through, with strongest winds to 35-45 kts now over the east (30-50% chance of at least 40 kts). Winds weaken once again to 20 kts or less by Wednesday afternoon as another ridge quickly passes through the area. A Gale Watch is likely needed with the next forecast package if confidence and timing certainty increase.

The main concern of the forecast occurs Wednesday night continuing through Thursday night. A strong low pressure system is progged to track somewhere across the Upper Great Lakes on Thursday. This brings the best chances for gales in the forecast with 50-75% chances for at least 35 kts during the event. Southerly winds increase Wednesday night into Thursday to 20-30 kts as the pressure gradient strengthens. During this period there is a 30-60% chance of gales to 40 kts over the east half. As the system tracks through, a strong surge of cold air moves in from the west and winds quickly turn northwest to north into Thursday night; chances for 40+ kt gales increase lakewide to 40-70%. Depending on where the storm tracks will impact the strength of the winds, but latest probabilities of storm force winds are at 15-30% over the central and eastern waters Thursday afternoon and night. Widespread moderate to heavy freezing spray is anticipated with this system.

A high pressure moves across the Upper Great Lakes on Friday, briefly returning winds to around 15-25 kts, but this quickly is replaced with another low pressure from the west over the weekend with more 20-30 kt winds and gale potential. That said, there is plenty of timing and track uncertainty at this point in the forecast.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... None. Lake Superior... Heavy Freezing Spray Warning until 4 AM EST /3 AM CST/ Monday for LSZ162.

Gale Warning from 11 PM EST /10 PM CST/ this evening to 7 AM EST /6 AM CST/ Monday for LSZ162-263-264.

Lake Michigan... Heavy Freezing Spray Warning from 2 AM to 9 AM EST Monday for LMZ221.