Area Forecast Discussion

KEY MESSAGES

- The threat for river flooding continues over the north central and east today with temperatures in the 40s. Snowmelt continues through the week as temperatures continue rising.

- With the surface drying out and temperatures increasing through the week, the chance for elevated fire weather conditions is starting to increase from today to Wednesday. However, expect temperatures and the later arrival of windier conditions today and the calm winds Tuesday and Wednesday to limit fire weather concerns.

- Southerly gales to 35 knots over the eastern third of the lake tonight, particularly near Caribou Island.

DISCUSSION

Issued at 306 PM EDT Mon Apr 20 2026

High pressure has shifted to the Lower Great Lakes today increasing low level southerly flow and warming temps much closer to normal in the 40s. A few spots in the west should climb into the low 50s. Despite the southerly flow, mixing has kept the low levels dry, evident in obs indicating Tds mainly in the teens. Resulting RHs have fallen into the 20s to 30s in the west, 30s to 40s east. This significantly dry airmass in the low levels is preventing a shortwave pressing into the UP from the west from precipitating. This feature is evident in GOES water vapor imagery as well as light reflectivities showing up on the radar mosaic. The mixed layer will continue to increase southerly wind gusts to 20-25 mph for this evening ahead of a cold front as the LLJ strengthens. Gusts up to 30 mph are expected where downslope flow is maximized, particularly near eastern Lake Superior. The combination of gusts and low RHs yields a brief period this evening of elevated fire weather conditions, however no SPS was issued due to the shortness of these conditions lining up as well as higher soil moistures from recent snowmelt. The lack of moisture will prevent any precipitation with the cold front as well. Otherwise lows tonight settle into the 30s for most as cloud cover moves over the UP.

A ridge currently over the PAC NW will have moved to the Plains for Wednesday with weak high pressure returning to the Great Lakes. This ramps up WAA through Thursday, bringing highs into the 50s/60s Tuesday/Wednesday with 60s/70s on Thursday. Lows Tuesday night will be in the 30s, warming even further the next two nights into the 40s to mid 50s. Tds will be dry Tuesday and Wednesday, lowering RHs back into the mid 20s to low 30s in the west. Thankfully winds don't look particularly gusty (mostly 15 mph or less), but will continue to monitor for additional elevated fire weather conditions. Moisture advection becomes more noticeable toward the latter part of the week when the mid level ridge moves over the Great Lakes. During this period, dry weather will at least mitigate melting, but a ramp up of snowmelt is expected regardless this week given the temp forecast. This results in river flooding persisting. A mid level trough moving into the rockies on Wednesday develops a surface low off the Northern Rockies, which pivots to Manitoba for Friday. Precipitation looks unlikely (<15% PoP) with the warm front late Wednesday night into Thursday. Higher PoPs hold off until late Thursday night into Friday when the cold front is forced through the region. This brings back showers and thunderstorms in a similar fashion to last Friday, but severe potential is lower because the amount of instability reaching the UP is questionable. Generally looking at 0.25 to 0.5 inches where embedded storms develop, but confidence on timing and amounts remains a bit blurry. Expect cooler, but near normal temps to return post cold front into early next week as the closed low spins over central Canada. Highs in the upper 40s to 50s and lows in the 30s.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 721 PM EDT Mon Apr 20 2026

VFR conditions will prevail for the duration of the TAF period. However, south-southwesterly winds will continue to gust up to 25 kts at IWD and SAW through this evening. Then there will be a LLWS threat early tonight at all TAF sites as a low level jet strengthens to 50 kt. Look for this low level jet to weaken by daybreak tomorrow.

MARINE

Issued at 344 PM EDT Mon Apr 20 2026

South to southwest winds continue increasing into this evening ahead of a cold front dropping over Lake Superior tonight. The forecast into tonight then becomes a bit complicated as a low level jet strengthens over the lake, but a warmer airmass also comes with it. This increases stability over much of the lake this evening, limiting winds to 20-25 kts over the western two thirds of the lake through tonight. Where the colder and less stable air lingers is the eastern third where gusts to 30-35 kts are likely, particularly near Caribou Island and along the international boundary waters east of Stannard Rock. Opted to Upgrade to a Gale Warning, shortening it by one hour to end at 4 AM EDT Tuesday.

Behind the cold front, winds fall below 20 kts Tuesday morning and remain light through Wednesday. Southeast winds over the east half increase to 20-30 kts on Thursday, holding into Friday. There is a 20-40% chance for gales to 35 kts Thursday night into Friday. Expect westerly winds behind the cold front, mainly 15-25 kts the remainder of the weekend. Some rain showers and thunderstorms could be seen with the cold front's passage Thursday night through Friday.

MQT WATCHES / WARNINGS / ADVISORIES

Upper Michigan... None. Lake Superior... Gale Warning until 4 AM EDT Tuesday for LSZ266-267.

Lake Michigan... None.