textproduct: Marquette

KEY MESSAGES

- Patchy, locally dense fog will be possible tonight, especially over the interior west.

- High temperatures be around 10 degrees above average through midweek with highs in the 70s.

- A storm system tracking through Ontario will bring rain chances back into the U.P. on Tuesday night into Wednesday night, followed by cooler, more seasonable temperatures.

DISCUSSION

Issued at 308 PM EDT Sun Sep 27 2026

This afternoon water vapor imagery and 500mb model height analysis showed the blocking ridge continued to eroded as shortwaves moved across the northern periphery of the remaining ridge. Downstream an upper level low associated with the nor'easter was nearly stationary over New England. Troughing was expanding over the western half of Canada with the southern extent of the trough splitting over the Pacific Northwest. At the surface high pressure continued to bring pleasant fall weather to the U.P. with temperatures warming into the 60s and 70s along with light winds. Clouds were spreading over the western half of the U.P. but struggling in their eastward march as they encounter a dry, stable airmass.

Upper level ridging will continue to break down through tomorrow with troughing expected for the midweek. The surface high will hold on until tomorrow before shifting southeast away from the region. This will result another day of light winds and continued warm temperatures (10-15F above average). With the dry air expect cool night tonight and Monday night along with the potential for fog with strong radiational cooling. For tonight fog is likely to form over the western half of the U.P. (some cloud cover should limit cooling in the central/east) for the early morning hours Monday. The fog could be dense and folks may want to leave themselves additional time for their morning commute. Fog will be possible over the entire U.P. Monday night, especially over the interior locations.

For Tuesday into Wednesday west-southwest flow will overspread the region as troughing moves into central Canada and the northern plains. Meanwhile, the trough over the Pacific Northwest will cut off over the four-corners region and track into the southern Plains. This will bring increasing Pacific and Gulf moisture transport northeast into the U.P. with PWATs reaching up to 1.25" (90th percentile from climo) Tuesday night through Wednesday. With dewpoints pushing 60F on Wednesday it will feel a bit humid for fall. There will be multiple opportunities for precipitation Tuesday night through Wednesday night as warm, moist air advection increases along with a 40-45kt low level jet providing a focus for large scale ascent. Then a cold front will push through the area by Thursday morning with additional showers preceding it and cooler, drier air behind it. As far as rainfall amounts, NBM probabilities are around 20-50% for 0.5"+ of rainfall (highest in the east) and 50-60% for 0.25"+ across the entire U.P. With deep moisture would expect that some locations will overachieve with localized heavy downpours.

Expect cooler, more seasonable temperatures to finish out the week and into next weekend with highs in the low 60s. Wouldn't rule out lake effect rain showers, especially over the eastern U.P. on Thursday night into Friday morning as a passing shortwave brings the potential for deeper inversion heights and colder 850mb temps. The GEFS is the most aggressive among the ensembles with a mean of 0C at 850mb while the LREF (EC/GEFS/CMC) mean sits around 3C with 0C falling into the 10th percentile. With lake temperatures sitting around 13-16C would expect a high potential for lake effect cloudiness and a few light showers even with the warmer, mean solution.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 127 PM EDT Sun Sep 27 2026

A weak shortwave moving around the western edge of an upper level ridge over the Upper Great Lakes was spreading cloudiness into the western half of the U.P. along with MVFR cigs at IWD. Expecting that cigs will lift to VFR over the next few hours before scattering out all together later in the afternoon. Elsewhere expect VFR conditions through the evening hours along with light winds.

Clouds clear out from west to east overnight with fog formation likely at CMX and IWD under optimal conditions for strong radiational cooling. This will bring a period of early morning IFR with VLIFR also possible should dense fog form (40% chance).

A shift to weak northerly winds behind a boundary tonight will result in a period of MVFR cigs at SAW with favorable upslope flow and moisture in the low levels.

VFR conditions will return by mid-morning on Monday.

MARINE

Issued at 308 PM EDT Sun Sep 27 2026

High pressure will continue to bring light winds to Lake Superior and northern Lake Michigan through Monday. Thereafter the high will shift southeast, away from the Great Lakes as a surface trough overspreads the region. This will bring strengthening southerly flow with winds to 25kt Tuesday and possibly Wednesday. A cold front pushes across the area on Wednesday night with cold air advection and a tighter pressure gradient favoring gusty winds for Thursday with gales possible over the eastern half of Lake Superior (40-50% chance).

MQT WATCHES/WARNINGS/ADVISORIES

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