textproduct: Marquette

KEY MESSAGES

- Widespread dense fog is expected this morning during commuting hours. If you're on the road, slow down and leave extra following room.

- Today will be warm and dry with gusts to 20 mph in the west. This will result in borderline elevated fire conditions in the western UP.

- Scattered rain showers are possible (20-40%) along the southern tier on Wednesday.

DISCUSSION

Issued at 341 AM EDT Tue Sep 1 2026

GOES water vapor imagery this early morning shows a stream of Pacific monsoonal moisture trailing across the UP as a closed 500mb low enters into the province of Ontario. With most stationary land and marine observation platforms showing near dead calm and dewpoint depressions of 0 degrees, fog is pervasive across the CWA tonight. All TAF sites currently show visibilities persistent at 1/4 mi or less and ceilings at or below 200 feet, and METAR sites are reporting fog or dense fog. With widespread fog currently evolving, have hoisted a Dense Fog Advisory for most of the CWA.

High surface moisture should be alleviated into the morning hours as the Ontario low tracks east, moving subgeostrophic flow and subsidence over the area. The tighter pressure gradient associated with the center of the low comes into closer proximity, causing winds to increase as diurnal heating kicks in. All this to say, fog is not expected to linger long into the morning. In fact, high temperatures well into the 80s and resultant deep mixing with a dry airmass aloft will lead to RHs dropping down into the high 20- percents over the west this afternoon (40s/50s in the east). The NBM shows over 90% probability of highs above 85F for much of the western and southern UP, making this the warmest day the UP has had in a while. Given gusts to 20 mph in the western and central UP (higher in the Keweenaw), spots of borderline elevated fire conditions may occur for a short while this afternoon.

As the Ontario low track east toward Quebec throughout the day today, a weak front swings down from the northwest. As of now, a few of the CAMs are suggesting isolated rain/thunder cells between 22Z- 00Z. Soundings are showing elevated CAPE above a small inversion during the evening hours and a far from saturated atmosphere. Thus, opted not to include this possibility in current PoP issuance.

Weak warm frontogenesis will occur Tuesday night/Wednesday morning to our south as PWATs increase again to 1.25-1.50 inches, with guidance mixed on whether associated rainfall will reach far enough north into the UP. Best chances (up to 40%) over the south.

For late week into the Labor Day weekend, ridging builds over the northern Plains, while a deep trough evolves over the Canadian Maritimes. While this pattern is generally favorable for subsidence over the local area, as evidenced by a high pressure ridge building in from the northeast, western parts of the UP may be close enough to the moisture/instability reservoir to see convection at times. Currently capping out at 20-30% PoPs though, so the evolution is far from certain.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 134 AM EDT Tue Sep 1 2026

Apart from stray high level cloud cover, skies are largely clearing over the UP. Clear skies and light winds are in turn leading to the development of fog and low stratus, with LIFR/VLIFR already at the TAF sites; these conditions are expected to continue through the night. An improvement to VFR is expected by mid- morning Tuesday as skies clear out. Otherwise, light and variable winds overnight will increase out of the west to southwest Tuesday afternoon; gusts to 20 kts will be possible.

MARINE

Issued at 219 PM EDT Mon Aug 31 2026

Lake Superior: There is the potential for dense fog at times through tonight and will continue to monitor conditions for potential marine dense fog headlines. Winds will be SE to 15 to 20 kts over the eastern half of the lake today. Expect light winds of 20 kts or less to return to Lake Superior tonight. However, SW winds of 20 to 25 kts could return between Isle Royale and the Keweenaw on Tuesday before becoming 20 kts or less again Tuesday evening. The light winds remain until potentially late on Thursday when NE winds of 20 to 25 kts possibly return to the western arm.

Northern Green Bay and northwestern Lake Michigan: Winds will generally be southerly 5-10kt today. A few strong to severe thunderstorms are possible this afternoon and evening which could product large hail and strong winds, however the probability is only around a 5% chance. Expect mainly light winds to continue through the rest of the week, although more showers and storms could return on Wednesday.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Dense Fog Advisory until 9 AM EDT /8 AM CDT/ this morning for MIZ001>007-009>011-013-014-084-085.

Lake Superior... Dense Fog Advisory until 2 PM EDT this afternoon for LSZ245>247-251-265>267.

Dense Fog Advisory until 11 AM EDT /10 AM CDT/ this morning for LSZ162-243-244-263-264.

Lake Michigan... Dense Fog Advisory until 2 PM EDT this afternoon for LMZ221- 248.