textproduct: Marquette

KEY MESSAGES

- Showers and thunderstorms will exit the area this morning. Areas of dense fog are possible through mid-morning, especially in the higher elevations.

- Showers and thunderstorms are possible this afternoon. There is a marginal risk (~%5 chance) of severe thunderstorms over the southcentral UP this afternoon.

- Drier weather with above normal temperatures and higher humidity is expected for much of the rest of the week.

DISCUSSION

Issued at 307 AM EDT Mon Aug 31 2026

Early this morning GOES water vapor imagery and 500mb model height analysis showed an upper level high pressure over the southern states and an upper level low pressure over southern Saskatchewan. Ahead of the low pressure shortwave ridging extended through the western Great Lakes. Monsoonal moisture from the southwest U.S. was streaming northeast into the midwest. Warm air advection had initiated a line of showers and thunderstorms over the southern and western U.P. which was moving northeast. It was mild and humid with temperatures and dewpoints generally in the mid 60s. Fog had developed over the area, especially in favorable areas with east- southeast upslope flow such as the Keweenaw and higher elevation of the north central UP. Behind the showers fog could become more widespread and dense, will continue to monitor for the potential need for fog headlines.

The upper level low pressure over southern Saskatchewan will move east to western Ontario by late tonight, weakening as it continues to occlude. Showers and thunderstorms will exit the area this morning (a few heavy downpours can be expected as moisture is abundant, with PWATs over 1.5"). Expect fog and low clouds to lift through mid-morning with some peaks of sun at times through the day. With deep moisture in place and relatively steep mid-level lapse rates instability will be on the rise through the day, to as much as 3000 J/kg over the south-central. Shear also increases through the day with 35-40kt shear by late this afternoon. The combination of instability and shear will be sufficient for a strong to severe thunderstorm should a storm develop. However, large scale ascent is fairly weak and most models keep the atmosphere capped through the afternoon and evening, hindering thunderstorm development. SPC maintains a marginal risk in the south-central for severe thunderstorms (~5% chance). The main hazards with any stronger storms will be large hail, damaging winds and heavy rainfall. Maintained low pops, mainly over the south-central.

It will feel very warm and muggy today with highs reaching into the mid 80s and dewpoints well into the 60s to low 70s. Overnight tonight the deeper moisture will begin to shift east resulting in more comfortable conditions as the night progresses, with lows in the 50s west and low 60s east.

The forecast trends drier on Tuesday as Upper Michigan becomes situated between low pressure over northern Ontario and high pressure over the Tennessee Valley, which another day of highs in the 80s expected. The ridge then reamplifies over the central CONUS for the latter half of the week as the low over Ontario moves east to the Canadian Maritimes, placing the UP back into a northwest flow regime with temperature moderating into the 70s into next weekend. This will favor generally drier weather through the end of the week, though a few periods of showers can't be ruled out with any embedded disturbances passing through the region.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 731 AM EDT Mon Aug 31 2026

Flight restrictions will continue through the morning due to low cigs/vsby at the TAF sites with improvement expected through the early afternoon. Expect MVFR conditions at times this morning at IWD, improving to VFR by early afternoon. Moist, upslope flow was bringing fog and low cigs to CMX and SAW but this should improve as the morning moves on and winds become more southerly along with diurnal heating/mixing, with VFR expected by mid to late afternoon. Cannot rule out a thunderstorm this afternoon/evening with a moist and unstable airmass in place at SAW which is mentioned with a PROB30.

The next challenge is fog development again tonight. Probabilities for MVFR vsby is highest at SAW and CMX (60% chance) while IWD is less likely to see fog, only around 20% chance.

MARINE

Issued at 352 PM EDT Sun Aug 30 2026

Lake Superior: NE winds increase to 15-25 kt over the western lake this evening as a warm front approaches, with a few small craft headlines in place for western Lake Superior nearshores through 8 PM EDT. As the showers and storms associated with the front start to move in tonight from the SW, expect the winds to dwindle over the western lake while increasing from the SE to 20 to 25 kts over the eastern half of the lake on Monday. Expect light winds of 20 kts or less to return to Lake Superior Monday night. 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: Light winds of 15 kts or less look to continue until Monday. Meanwhile, some showers and storms could be seen through tonight, with some potentially marginally marine severe weather possible tonight (gusty winds up to 34 kts and hail up to dime sized). We could see some S'rly winds of 15 to 20 kts over the area on Monday before winds return to 15 kts or less Monday evening. The light winds continue through the rest of the week, although some more showers and storms could return on Wednesday.

MQT WATCHES/WARNINGS/ADVISORIES

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