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KEY MESSAGES

- Another round of showers and thunderstorms lifts into the UP tonight through Tuesday morning. There is a slight risk (level 2 of 5) for severe thunderstorms for the stateline border counties.

- Heavy rain will exacerbate ongoing flooding concerns. There is a marginal risk (level 1 of 4) for flash flooding with tonight's rainfall event.

- 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 338 AM EDT Mon Apr 13 2026

Early morning GOES water vapor imagery reveals a handful of embedded shortwaves lifting through the Great Lakes region within broad southwest flow aloft. At the surface, a weakening ~994 sfc low is lifting north of Lake Superior into James Bay, dragging its sfc cold front across the central UP (at the time of writing this discussion). Some light showers are noted on KMQT radar imagery along this boundary, though they have been slowly tapering off as the front becomes more diffuse and upper level support departs the area. These light showers may continue to skirt along the UP/WI border through this morning with not much more QPF expected. Otherwise, temps remain quite warm, hovering largely in the mid to low 50s though a few 40s are seen closer to the lakeshores and near 60 obs seen across the s-central. Patchy dense fog is also noted on area obs/webcams given the anomalously high moisture content. Impressively dense advection fog seen earlier this morning here at the WFO in Negaunee Township has since diminished, but wouldn't be surprised to see lingering fog come back in as winds diminish through sunrise.

Through this afternoon, a brief period of upper level zonal flow and northern Ontario sfc high pressure keep things mostly quiet under cloudy skies. Temps across the south-central and SW climbs into the low to mid 60s while the northern tier of the UP remains in the low to mid 50s, mid to upper 40s closer to Lake Superior. Another round of soaking rain and potentially some marginally severe thunderstorms arrives this evening into the overnight hours as sharp mid-level shortwave lifts out of the Rockies into the Upper Midwest, however, there is uncertainty regarding the spatial coverage of thunderstorms and thus the heaviest QPF axis. Isentropic ascent along and ahead of a surface warm front will be the focal point for showers and thunderstorms lifting northward along the stateline by ~10 PM EDT. Elevated instability between 500-1000 j/kg and effective bulk shear near 40 kts may support a few strong to severe storms capable of producing 0.5-1" hail, mainly closer to the stateline border counties. For this reason, SPC has included a level 2/5 Slight Risk for the UP/WI border counties with a level 1/5 Marginal Risk further north into the central and west where the threat for severe storms is limited. Additionally, given the anomalously high moisture content (PWATs in the 99th percentile of climatology), heavier thunderstorms will be efficient rain makers. With antecedent conditions already primed from recent rain and ongoing snowmelt, flooding concerns remain the greatest threat. WPC holds a level 1/4 Marginal Risk for flash flooding across the entire UP today. As mentioned previously, there remains uncertainty regarding the spatial extent of precip lifting into the UP tonight. Individual CAM guidance differs on the placement of the heaviest QPF axis, with the latest HREF suggesting a 40-60% chance for most of the s-central receiving an additional 1" of rain by Tuesday morning. Meanwhile the NBM (and a few CAMs such as the HRRR) ensemble shunts most of the QPF further south across central WI. Trends in CAM guidance will be closely monitored and the going forecast, which has a widespread 0.5- 1" across the central and eastern UP, may need to be altered.

Above normal temperatures and above freezing dewpoints (save for potentially the Keweenaw) remain through the rest of this week as an additional round of precipitation via a shortwave low looks to move into the area on Thursday. Similar flooding concerns are anticipated. Behind this third round of rain, expect the warmest temperatures of the week as highs potentially get into the lower 70s over the interior west by Friday (the NBM shows up to around a 75% chance of high temperatures above 70 for the interior west). With winds also predicted to intensify from the south ahead of a robust cold front, we could see more significant snowmelt across the area where snowpack still remains. Heavy rain showers and thunderstorms could also be seen along the cold front as it passes through the U.P. from west to east too, potentially bringing elevated flooding concerns once more.

However, behind the cold front, expect a pattern shift as more normal to below normal temperatures become realized. In addition, we may see the return of light lake enhanced to lake effect snow showers across the northwest wind snow belts next weekend. Should this occur, the colder air from behind the stout cold front will limit snowmelt and help to reduce flooding concerns as we head into next week.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 740 AM EDT Mon Apr 13 2026

Fog and low stratus across the UP continues to lead to IFR ceilings at CMX and SAW, with MVFR/IFR visibility there as well. At IWD, meanwhile, ceilings are lifting to MVFR. A slow improvement generally to MVFR is expected at CMX and SAW into the afternoon, but then another batch of showers and storms moving in tonight will bring all terminals down to IFR again between 00-03Z. As rain begins to taper from west to east after 06Z, lingering fog and low stratus will keep in IFR or even LIFR restrictions through the rest of the night.

MARINE

Issued at 338 AM EDT Mon Apr 13 2026

A passing cold front has largely shifted winds to the NW this morning, diminishing below 25 kts. A Marine Dense Fog Advisory remains in place through this morning and may be extended further into the day based on local observations and trends. Winds remain below 15 kts this afternoon, however, a low pressure lifting through the area kicks up breezy E to NE winds (largely below 25 kts save for the eastern arm of the lake) tonight with a chance for a few strong thunderstorms.

Moving through the rest of the week, winds look to mostly stay 20 knots or less across the lake. Another shot at showers and thunderstorms is possible on Thursday. More active marine weather returns next weekend. The latest ensemble guidance suggests a 30-50% chance for Gales to 35 kts Friday through Sunday with the passage of a few stronger systems, though there remains high uncertainty regarding the exact track.

HYDROLOGY

Issued at 338 AM EDT Mon Apr 13 2026

In response to the rainfall and widespread above freezing ambient and dewpoint temperatures through the the rest of the workweek, river rises are expected across Upper Michigan as the remaining snowpack melts away. In addition, the heavy rainfall at times may accelerate the liquid entering into the streams, rivers, and waterways of the UP, especially across the south-central UP where expected rainfall tonight in combination with yesterday heavy rain will exacerbate flooding already felt. River observations and forecasts have increased in measured and expected water level heights, with Moderate Flooding still expected for the Paint River in Crystal Falls the Sturgeon River in Alston; the latest River Forecast for Crystal Falls has the Paint River getting up to a height of 8.2 feet, but with the river observations already exceeding the river forecast, its possible record flooding could be seen (9.8 feet).

Elsewhere across Upper Michigan, other rivers have been put under a River Flood Advisory as they are expected to get to bankfull; however, uncertainty still remains on whether or not they will achieve flood stage as it will depend on the speed of snowpack melt and rainfall this week. The rivers are: the Black River near Bessemer, the Chocolay River at Harvey, and the Middle Branch of the Escanaba River at Humboldt. As of this morning, the Black River had over a 30% chance of getting into Minor Flood Stage. Meanwhile, the Chocolay at Harvey and the Middle Branch of the Escanaba River at Humboldt have over a 50% chance of reaching Minor Flood Stage later this week. Eastern Delta County has received enough rain yesterday that the latest observations already show the Sturgeon River near Nahma Junction already at bankfull; thus a River Flood Advisory remains for it until further notice. Outside of these spots, others like the East Branch of the Escanaba River at Gwinn and the Michigamme River at Witch Lake could get to bankfull or more later this week. This morning's HEFS guidance suggests there is a 70% chance that the Escanaba River in Gwinn gets to Minor Flood Stage. Outside of these rivers, there may be additional spots where flooding and bankfull stages could be achieved. In addition, expect the saturated soils over the U.P. to potentially keep the poor drainage and low-lying areas inundated with water. Therefore, if you see any flooding please report it to the NWS and go around it; turn around, don't drown.

Aside from the expected rainfall tonight, additional chance for precipitation are expected again later this week into the following weekend. With snowmelt continuing until a cold front passes Friday night, flooding concerns continue until colder air arrives by Saturday. With the warmest weather expected on Friday, expect snowmelt to accelerate as winds pick up from the southeast and south and dewpoints reach up to around 50 once again. Thus, we may see river rises intensify late this week as the rainfall along the cold front combined with the snowmelt could exacerbate river rises and flooding across the Upper Peninsula. However, after the cold front passes early Saturday, expect the snowmelt to become limited if not cease entirely as light lake enhance to lake effect snow moves over the northwest wind snow belts. With cooler and drier weather expected this upcoming weekend, we may see flood concerns start to alleviate by the end of the forecast period.

MQT WATCHES/WARNINGS/ADVISORIES

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

Lake Superior... Dense Fog Advisory until 11 AM EDT /10 AM CDT/ this morning for LSZ162-243>246-263>267.

Lake Michigan... Dense Fog Advisory until 8 AM EDT this morning for LMZ221-248- 250.