textproduct: Marquette

KEY MESSAGES

- Showers and thunderstorms will be possible (up to a 50% chance) along a cold front tonight into Tuesday.

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

- Showers and thunderstorms are possible (up to a 75% chance) Thursday night into Friday as another front moves through the area.

DISCUSSION

Issued at 217 PM EDT Mon Aug 17 2026

It was a pleasant afternoon across the UP with sfc observations showing temperatures generally in the low to mid 70s along with dewpoints in the 50s to near 60. Satellite imagery showed fair weather cumulus had formed with diurnally driven instability resulting in partly cloudy skies. Model height analysis and water vapor imagery showed an upper level low over the Hudson Bay with broad troughing over much of Canada, extending south across the northern tier of the U.S. Multiple subtle shortwaves were evident in the flow with a few thunderstorms over northwest MN.

Overall the UP will remain under northwest flow aloft through next weekend bringing seasonal temperatures along with a few passing cold fronts. The upper level low pressure over Hudson Bay will slowly move east, reaching eastern Quebec Friday night as yet another upper level low pressure moves toward the Hudson Bay to take its place.

Thunderstorms are expected to develop and increase in coverage this afternoon to the west, over the central plains into MN as a cold front pushes southeast through the region. Thunderstorms are expected to move east through tonight and diminish as the approach the UP will loss of diurnally driven instability and an overall lack of forcing to sustain elevated convection. This will result in rather meager chances for appreciable rainfall, only about a 10-25% chance for a wetting rain (0.10" or more). As the morning progresses the front will sag south across the UP, reaching the far south- central late in the day. Additional showers and thunderstorms are expected to form along and immediately behind the front during the afternoon hours. HREF joint probabilities for mucape>500J/kg and shear(0-6km)>30kt are around 60% close to Lake Michigan and over the south-central in the early afternoon, rapidly decreasing over the east but higher probs lingering over the south-central into the late afternoon. Despite the higher shear thermodynamic profiles do not support hail growth but couldn't rule out gusty winds with any storms that due develop along with brief heavy rainfall.

Any lingering showers will exit the far south-central tomorrow night with cooler and drier air filtering into the area. This will result in a comfortable airmass with seasonable highs in the 70s for Wednesday and Thursday. Lows will be mainly in the 40s Tuesday night into Wednesday with parts of the interior west could fall as low as the mid-30s. 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 temperatures Tuesday night and Wednesday night.

The next chance for rain will be Thursday night into Friday. Warm air advection ahead of a deepening trough will bring increasing chances for showers on Thursday night. A shortwave and trailing cold front will continue precipitation chances into Friday. At time it appears the strongest instability will stay south of the UP with only about a 30% chance for enough cape/shear to support stronger thunderstorms. As far as rainfall amounts, NBM probabilities for 0.25" or more are in the 25-45% range. These probabilities quickly drop off though with only about a 10-25% chance for 0.34" or more. While any thunderstorms 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.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 116 PM EDT Mon Aug 17 2026

VFR conditions will prevail at all sites throughout the period. Generally westerly to northerly winds 5-10 kt will becoming southerly to southwesterly this evening ahead of a cold front that will bring some showers to the UP overnight, though chances of rain are only up to 60% at IWD, and up to 30% for any given hour at CMX and SAW. Chances of thunder are only above 15% at IWD and with the peak chance of thunder at only 20%, will leave TSRA out of the TAF at this time.

MARINE

Issued at 217 PM EDT Mon Aug 17 2026

Lake Superior - Southwesterly winds 20-25kt are expected through the early evening between Isle Royale and the Canadian shore where winds are being funneled. Over the rest of the lake southwest winds of 15- 20kt can be expected. Winds will shift northwest wind and increase to 25kt near/east of the Keweenaw late tonight into Tuesday. Thereafter winds will generally be less than 20kt through the remainder of the week. A few thunderstorms will be possible tonight and again on Thursday night and Friday but strong thunderstorms are not expected. Another period of northwest winds are expected on Saturday, 20-30kt, mainly along and east of the Keweenaw.

Northern Bay of Green Bay and northern Lake Michigan - Overall expect winds less than 20kt trough Thursday. Showers and thunderstorms are possible tonight into Tuesday (50% chance) as a cold front pushes through the area. Isolated thunderstorms Tuesday afternoon could produce gusty winds. Another front is expected to bring showers and thunderstorms into the area Friday night into Saturday. Southwest winds to 25kt are expected ahead of the front on Friday near and east of Manistique. Winds diminish Friday night, then shift northwest on Saturday increasing to 25kt.

MQT WATCHES/WARNINGS/ADVISORIES

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