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KEY MESSAGES

- Active weather returns continues through much of at least the first half of next week as several periods of showers and thunderstorms are poised to move through the region.

- A prolonged period of well above freezing temperatures and higher dewpoints will bring increased snowmelt. This, combined with periods of potential heavy rain and thunderstorms, will accelerate river rises and lead to ponding of water in areas with poor drainage. A Flood Watch remains in place for all of Upper Michigan through Wednesday morning.

DISCUSSION

Issued at 341 AM EDT Sun Apr 12 2026

Early morning remote sensing tools reveal widespread rain across the Northern Great Lakes region as strong WAA/isentropic ascent occurs ahead of developing low pressure system currently organizing in the High Plains. A few non-severe thunderstorms are noted across north- central WI on the nose of a ~55kt LLJ, but given meager elevated instability nothing more than a few rumbles of thunder and localized pockets of heavier rain are expected from them. Through the rest of the day, showers and embedded thunderstorms continue lifting through the UP much of the morning and afternoon, tallying additional rainfall totals upwards of 0.5-1", greatest south-central and east, and locally greater amounts between 1-1.5" where thunderstorms and heavier rain showers linger the longest. Precip largely wraps up from west to east this afternoon/evening as the parent shortwave and sfc pressure reflection lift north of Lake Superior. Today's temperature forecast is a bit uncertain. There will likely be a large gradient across the UP from east to west, with the east half being much cooler, potentially 15-20 degrees cooler than the WI/UP stateline. The NBM soars daytime highs into the mid to upper 60s across the west and 50s east. Have opted to kick temps down a tad given widespread rain and cloud clover, especially across the east half where cool S-SW flow off Lake Michigan will mute sfc temps despite 850 temps pushing 10-13C. Tonight, some additional light showers may be seen as the system's cold front pushes west to east late into Monday morning. Low temps fall into the 40s, though the some areas of the south-central may remain above 50 overnight!

Monday starts off fairly quiet with a brief period of zonal flow overhead and sfc high pressure nosing south across northwestern Ontario, however, troughing emanating out of the Rockies once again sends another surge of moisture into the UP Monday PM, kicking off another round of widespread showers and thunderstorms. Latest ensemble suites and NBM suggest a 50-70% chance for an additional 0.5" of widespread rainfall by Tuesday morning, though suspect locally higher amounts will be possible given PWATs pushing 1" and thunderstorm activity. Both SPC and WPC have the UP in a Marginal Risk (level 1 of 5) for severe thunderstorm and flash flood potential, respectively.

Looking into the mid to late week, global models and ensembles are in decent agreement on a continued active period with southwest flow aloft translating embedded shortwaves through the Great Lakes, mostly notably a stronger wave late Wednesday into Thursday. Continued SW flow will hold a warmer than normal temperature trend through the coming workweek. For additional information specifically on flooding concerns due to the combination of rain and snowmelt, please see the Hydrology section below.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 116 AM EDT Sun Apr 12 2026

VFR conditions will slowly deteriorate to MVFR from west to east through Sun 09Z as rain spreads into the region, with further deterioration to IFR/LIFR at the terminals by Sun 12z. Will continue to carry PROB30s for TSRA at CMX and SAW into this afternoon, but will only mention a TEMPO early this morning at IWD. Meanwhile, LLWS will continue to be an impact as LLJ moves overhead this morning, accompanied by gusty south winds at the surface. Rain showers slowly diminish in coverage in the west near mid to late morning, but expect cigs to remain MVFR or lower through this afternoon and possibly even into this evening.

MARINE

Issued at 341 AM EDT Sun Apr 12 2026

South-southeat wind gusts will be on the rise this morning as a low pressure lifts north of Lake Superior today. Gusts are expected to peak during the early afternoon between 30-35 kts across the east half of the lake. Gales >35 kts are not expected (<20% chance), though cannot rule out an isolated gale. Significant wave heights peak between 5-10 ft largely across the northern tier of the lake, falling tonight as winds diminish below 25 kts lake wide. A few strong showers and thunderstorms are possible tonight.

After a quick reprieve from the active weather during the day on Monday, another shortwave low moves over the Upper Great Lakes Monday night through Tuesday. Besides additional showers and thunderstorms potentially moving across Lake Superior, expect winds to back to the northeast to around 20 knots Monday night before weakening Tuesday. After another quick reprieve Tuesday night, a low pressure system could potentially move over Lake Superior on Wednesday. While this system could bring additional rain showers and thunderstorms to the lake, winds as of right now are still currently slated to remain at 20 knots or less before and after the low's passage. Weak high pressure ridging building in on Thursday looks to keep the winds and weather quiet over the lake as we begin heading towards the end of next week.

HYDROLOGY

Issued at 341 AM EDT Sun Apr 12 2026

The slow snow melt seen over the past few days gives way to accelerated melting through Wednesday morning as the latest NOHRSC analysis shows the remaining snowpack ripe for melting (snowpack temperature at freezing). In addition, with temperatures, dewpoints, winds, and heavy rainfall chances increasing, expect potentially significant river rises early next week given the expected rainfall and favorable melting conditions.

With a robust Gulf connection supplying very warm, moist air to the Great Lakes region early next week, expect temperatures to warm up generally into the 50s and 60s, save for maybe the northern Keweenaw after Sunday. Temperatures are expected to remain above freezing through the entire coming work week.

Today and Monday are the focus of highest temperatures, with forecasts ranging 10 to 20 degrees above normal (Normal Highs: 40s to low 50s, Normal Lows: 20s to 32) as parts of the U.P. get placed underneath the warm sector. The going forecast has highs in the 50s and 60s, warmest in the interior west today and in the south-central on Monday. There is a 30-60% chance of exceeding 70 near the WI/MI state line on today and Monday. Lows are expected in the 40s to mid 50s tonight and mid 30s to mid 40s Monday night (15 to 30 degrees above normal). During this period dewpoint temperatures soar into the 50s tonight, remaining elevated into Monday night even after the cold front of a shortwave low passes. Gusty south to southwesterly winds will support heat transfer near the surface today, increasing snow melt efficiency.

Periods of showers and thunderstorms are anticipated this weekend into the coming workweek. the ongoing precip event will bring an additional 0.25 to 1.25" by Monday morning (least west, greatest s- central and east, locally high amounts in thunderstorms. A second round of showers and thunderstorms moves through Monday night into Tuesday as shortwave low moves through the Upper Great Lakes. Mean rainfall amounts predicted with this shortwave's passage are between 0.5 to 1 inch of rain with stronger showers/storms reaching up to 1.25 to 1.5 inches of rainfall (as seen via NBM90th percentile). Additional precipitation is anticipated into mid next week as one final low pressure system is expected to move through Lake Superior on Wednesday.

All these factors lead to accelerated rate of snowmelt and increasing likelihood of ponding of water on low-lying/poor drainage areas as well as minor river flooding. A Flood Watch remains in effect for the entire U.P. tonight through Wednesday morning to account for these concerns. Moderate river flooding remains possible on the Paint River near Crystal Falls and the Sturgeon River near Alston (now up to a 45-60% chance in these locations); see the latest River Flood Statements for additional information. In addition, chances for at least Minor river flooding are increasing for areas such as the Black River at Bessemer, the Chocolay River at Harvey, the Middle Branch of the Escanaba River at Humboldt, the Eastern Branch of the Escanaba River at Gwinn, the Sturgeon River near Nahma Junction, and the Tahquamenon River near Paradise (now up to a range of 30-60%, save for near 90% at Gwinn, near Nahma Junction, and near Paradise). Those living near and planning to recreate around the rivers and low-lying areas of the U.P. early next week should keep up with the forecast and river levels as the snowmelt and rainfall amounts will determine flooding potential.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Flood Watch through Wednesday morning for MIZ001>007-009>014- 084-085.

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