textproduct: Marquette

KEY MESSAGES

- The threat for river flooding continues over the north central and east today into Thursday as temperatures climb into the 60s and 70s. Snowmelt continues through the week as temperatures continue rising.

- Warming temperatures and RHs in the 20 to teen percents could create limited fire weather concerns over the west and portions of the interior east today and Wednesday.

- There is over a 40% chance for low-end gales over eastern Lake Superior Thursday evening through Friday morning.

DISCUSSION

Issued at 148 PM EDT Tue Apr 21 2026

Midlevel ridging over the western CONUS is supporting downstream surface high pressure over the Northern Plains and into the Great Lakes. This in turn is allowing for a sunny and quiet day, with afternoon visible satellite revealing hardly a cloud in the sky over the whole UP. Temperatures so far have been able to climb into the lower 60s over the interior of the central, western, and eastern UP, but only into the lower/mid 50s nearer to the shorelines of Superior and Lake Michigan as a lake breeze develops. Dewpoints are expected to drop precipitously into the late afternoon, particularly over the western UP where they could reach the teens. This leads to a limited fire weather concern, temperature, however, by light winds and wet soils. With temperatures also climbing into the 60s and even the 70s over the west half on Wednesday and soundings supporting another good afternoon dewpoint drop, a limited fire weather risk remains midweek. While the drier and warmer weather will help to evaporate moisture from the soil and remaining ponding water today through the middle of the week, river flooding is still looking to continue over at least the next couple of days as melting of the remaining snowpack continues over the north-central and east.

The pattern begins to change by Wednesday night/Thursday as a midlevel trough digs into the Rockies and a surge of warm, moist air from the Gulf enters into Upper Michigan. While the warmest weather of this week expected to come on Thursday (highs in the 60s over the east to potentially upper 70s over the west), expect the moisture content at the sfc to also increase with the surge of this more- tropical airmass as RHs during the day only potentially drop down into the 40 to 50 percents. In addition, we may see some rain showers and thunderstorms skirt the western U.P. late Wednesday night as the surge in Gulf air could help spark warm frontogenesis over western Lake Superior. However, the chances for precipitation remain low (20% or less) late Wednesday night into Thursday as the better forcing mechanics of the warm front look to occur over far northern Minnesota and by Thunder Bay.

Better chances for rainfall do look to occur Thursday night through Friday as a cold front progressively pushes from west to east across the U.P. Some of the guidance continues to suggest that some initial convection that forms along the cold frontal boundary Thursday evening will potentially out-run the boundary Thursday night into Friday. As a result, any other convection that forms along the boundary behind this initial wave of convection would be using 'worked over' air. Thus, while there may be a non-zero chance for a stronger thunderstorm or two near Ironwood Thursday evening courtesy of a hefty amount of shear and at least a few hundred j/kg of CAPE, thinking severe weather chances will be next to zero Thursday night through Friday everywhere else, with only heavy downpours in the strongest showers and thunderstorms being the biggest impact. Showers and storms taper off from west to east behind the front Friday night. Much of the guidance favors a quarter to half an inch of rain over the central UP by early Saturday morning, with higher totals over the western UP given the comparatively higher potential for thunderstorms to reach the area. Still, ensembles point to around a 20-30% chance for higher totals in excess of an inch where thunderstorms develop (again, highest over the western UP). Though preceded by a couple of dry days, rainfall accumulations could exacerbate flooding issues ongoing over the central UP.

Behind the cold front, expect temperatures that are more normal for late April to come into Upper Michigan (highs in the 50s to maybe low 60s and lows in the 30s). Some drier air seen immediately behind the cold front could bring RHs back down to 30% or less on Saturday (up to a 30% chance according to the LREF). However, with a deepening low pressure system looking to lift towards the Upper Midwest near the end of the forecast period, more moist if not rainy conditions may return by the middle of next week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 109 PM EDT Tue Apr 21 2026

VFR skies and light winds <10 kts persist through the TAF period.

MARINE

Issued at 148 PM EDT Tue Apr 21 2026

High pressure over the Great Lakes will keep winds below 20kts tonight through early Wednesday evening, gradually shifting from a more northerly direction this afternoon mainly over to the east by Wednesday afternoon. Then, winds turning to the southeast increase to 20 to 25 knots over the north central and eastern lake Wednesday night. The winds continue to build from the southeast Thursday into Thursday night as a cold front approaches from the west. Eventually, southeast gales up to 35 knots could start to occur Thursday evening over the eastern open lake, with chances for low-end gales becoming maximized to over 40% late Thursday night. While some rain showers are expected along and ahead of the cold front's passage Thursday night through Friday, no severe weather is really expected save for maybe a low-end chance for some stronger storms closer to Duluth early Thursday evening.

Behind the cold front, expect the winds to become westerly gusting up to 20 to 25 knots Friday night into early Saturday. After that, expect light winds of 20 knots or less to return to Lake Superior for the rest of the weekend thanks to a weak pressure gradient and high pressure ridging.

MQT WATCHES/WARNINGS/ADVISORIES

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