textproduct: Marquette

KEY MESSAGES

- Isolated showers and thunderstorms this afternoon and evening, mainly near Lake Michigan.

- Temperatures will be close to seasonal averages most days through the week, with highs in the 70s and lows in the 40s and 50s.

- Showers and thunderstorms are possible (40-70% chance) late Thursday into Friday as a weak system moves through the area.

DISCUSSION

Issued at 249 PM EDT Tue Aug 18 2026

The general pattern through the forecast period and toward the end of August places the UP under northwest flow aloft. This yields seasonal to slightly cooler than normal temps, captured by the CPC 6- 10 day temp outlook. The mid level closed low over northern Ontario and Hudson Bay gradually makes its way to northern Quebec for Thursday into the weekend, but likely will be replaced by another deep trough early next week. Model discrepancies exist regarding the timing and placement of this trough (or if another closed low develops), but this currently does not yield significant changes to the northwest flow anticipated for over the Upper Great Lakes.

Afternoon observations have placed the cold front now over central and eastern Upper MI with temps in the 70s to low 80s ahead of it. Tds in the upper 50s to low 60s and PWATs struggling to reach 1.2 inches are not terribly impressive, but steep low level lapse rates and SBCAPE values up to 1500 J/kg are present over parts of the east half. Strong bulk shear is present up to 50 kts on the latest SPC mesoanalysis page. As low level f-gen increases with colder 925 mb temps pressing south from eastern Lake Superior, isolated convection continues. These could bring gusty winds and small hail, but severe weather is not expected until outside the CWA.

A much drier airmass moves in tonight behind the cold front. Mostly clear skies and light winds support (between 5-10F) colder than normal temps. Lows are expected in the 40s to mid 50s, coldest interior west where upper 30s are anticipated. High pressure builds in over the Great Lakes through Wednesday, keeping dry and comfortable conditions going. The blended guidance mean has been running several degrees too warm during recent cool nights, thus have opted for the lower end of the distribution, 10th percentile for low temps tonight and tomorrow night. Highs in the 70s on Wednesday will once again be followed by lows in the 40s to mid 50s, coldest interior west where temps dip into the mid to upper 30s.

High pressure over the Great Lakes Thursday morning shifts southeast, giving way to a shortwave and weak sfc trough the west. WAA reintroduces rain chances into Thursday night and a trailing shortwave continues PoPs on Friday. Strong to severe storms are not expected given that probabilities of 1000 or greater CAPE values struggle to reach 30% until Friday when bulk shear falls off. As far as rainfall amounts go, 24 HR NBM probabilities for 0.25 inches or more are in the 30-60% range with 15-25% chances for at least 0.75 inches. While any storms that do form could put down locally heavy rainfall, a widespread heavy rainfall is not expected. Thus not expecting appreciable improvements to the ongoing drought conditions over the south and west. A cold front on Saturday yields one more day of showers and non severe storm chances (15-30%) before high pressure returns with mostly dry weather into early next week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 119 PM EDT Tue Aug 18 2026

VFR will be the predominant flight category for the duration of the TAF period. The only exception could be brief MVFR conditions at SAW later this afternoon, but with most if any convection expected south and east of the area, will leave out of the TAF. Meanwhile, winds are veering northwesterly with the passing front, with gusts up to 20kts possible mainly at SAW and CMX through the rest of the afternoon.

MARINE

Issued at 321 PM EDT Tue Aug 18 2026

Lake Superior - Southwest winds of 15-25 kts are expected over the west, particularly between Isle Royale and the northwest shores where winds are funneled. Winds shift northwest tonight as they fall below 20 kts lakewide. High pressure building in through Thursday morning keeps winds below 20 kts through Friday. A cold front on Saturday increases northwest winds to 15-20 kts lakewide, particularly over the east where gusts approach the 25-30 kt range. Northerly winds remain elevated until Sunday night when high pressure brings back calmer conditions. A few thunderstorms are possible in the west Thursday evening, but strong to severe storms are not expected.

Northern Bay of Green Bay and northern Lake Michigan - Overall expect winds less than 20 kts through Thursday night. Scattered showers and storms are expected into this evening as a cold front pushes through the area. These could bring marginally severe wind gusts up to 35 kts and small hail. A system Thursday night and Friday brings back shower and storm chances, but strong to severe weather is not expected. Southwest wind gusts up to 25 kts are expected ahead of this system on Friday, particularly near Manistique. Winds diminish Friday night, then become northwest for Saturday, once again increasing gusts up to 20-25 kts for the weekend.

MQT WATCHES/WARNINGS/ADVISORIES

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