textproduct: Marquette

KEY MESSAGES

- A warming trend early this week may cause increased heat risk for vulnerable and sensitive populations.

- Thunderstorm chances (20-40%) persist in the forecast through Tuesday as multiple disturbances move through; however, confidence is low.

- Dry weather returns on Wednesday, likely persisting into the weekend.

DISCUSSION

Issued at 347 PM EDT Sun May 24 2026

The first half of the week contains multiple disturbances which complicate the forecast, but weather quickly becomes quiet for the latter part of the week as a persistent high pressure pattern sets up. Afternoon GOES water vapor imagery clearly highlights a mid- level shortwave pressing over the CWA from the west with quazi-zonal flow upstream. At the surface, weak high pressure is developing over the Great Lakes. Morning convection over the MN arrowhead has fizzled out as it moved toward drier and more stable air. SPC meso analysis indicates that instability is rebounding under the mostly sunny skies as low level lapse rates have soared to 8C/km and a diurnal-cu field has developed. Quiet and dry weather should persist through most of this afternoon as temps climb into the upper 50s to mid 70s, coldest eastern lakeshores.

The first disturbance arrives this evening. A 75 kt upper level jet left exit region quickly passes over the southwest while low level flow increases and a warm front lifts in from the southwest. HREF MUCAPE values are between 250-500 J/kg with bulk shear around 30-35 kts this evening when these ingredients align which would support thunderstorms, but CAMs are not in agreement of this round even happening or the placement of convection if it does. The NAM Nest is an extreme member with MUCAPE of up to 1000 J/kg, but the lack organization leaves strong to severe storms likely off the table with forecast uncertainty already high. Thus, added slight chance PoPs this evening into tonight over the west above the NBM (15-24%). Otherwise temps settle into the mid 40s to mid 50s.

A shortwave arriving near the WI/MI state line late tonight/early Memorial Day brings the next potential for showers/storms over the west/central UP. If the prior round does occur, this will work over the environment instability, but otherwise warm and moist air advection keep elevated instability overnight. Given the developing cap, not expecting strong to severe storms with this round. Anything that does develop should fizzle out as it progresses to the east late morning/early afternoon. WAA ramps up overnight into Monday, bringing high temps into the 70s to mid 80s for most; upper 60s in the east near Lake Michigan where there is moderating onshore flow. Diurnal convection ramps up in the afternoon as CAPE increases to 1000-1500 J/kg, highest in the west, with model soundings indicating the cap erodes by late afternoon. Strengthening low level winds could help convection break the weak lingering cap moving further east and helps increase bulk shear again to 35 kts. The proximity to the shortwave earlier in the day could leave much to desire for afternoon convection...noted in the limited CAMs response.

Better forcing for showers and storms arrives Monday evening/night. A shortwave diving across northern Ontario brings a low pressure system with it, sending a cold front southeast over the UP. This keeps PoPs in the forecast, but they remain low (15-30%) over the far west and north as dry air plays a limiting role. Afternoon instability set up from Monday does bring strong to severe storm potential with steep lapse rates, aforementioned CAPE up to 1000+ J/kg, and 30-35 kts of shear. Uncertainty quickly grows as this progresses over Lake Superior and the sun sets. The SPC has a Marginal Risk for large hail and damaging winds scraping the far western UP which matches where confidence begins to drop off. Temps stay mild in the 50s to low 60s.

WAA primes the region for a hot day on Tuesday with highs soaring into the 80s for most away from the Great Lakes. Lake Superior and eastern Lake Michigan lakeshores peak in the 70s, some interior south spots reach low 90s! This may cause increased heat risk for vulnerable and sensitive populations. Drier air in the wake of the cold front means instability does not climb quite as high as Monday mean values ~1000 J/kg or less, but afternoon showers and storms potentially kicked off from Lake Breezes are possible 15-30% chance...highest south-central UP. Dry weather returns Tuesday night as high pressure over western Hudson Bay builds southeast into the Great Lakes. Temps settle into the 50s.

A persistent high pressure pattern is expected to set up for late week into the weekend as an amplified mid level ridge becomes centered over the Midwest. An upstream closed low over the west CONUS may force this pattern northeast as it lifts north to Canada, this would briefly weaken the surface high pressure hold over the region. That said, the trough to the east and resulting surface low dropping over Quebec and New England likely will be too far east for precip to materialize over the Upper Great Lakes given the antecedent dry airmass in place. With that in mind, the GFS and GEFS suite likely too progressive to consider. Another high pressure is likely to return to the Great Lakes/Midwest early next week regardless, keeping the dry and warm pattern going. Expect highs late week and weekend in the 60s to low 80s, warmest interior west. Lows will be in the 40s to low 50s.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 740 PM EDT Sun May 24 2026

An area of showers and thunderstorms is skirting the MI/WI border and passing south of KIWD as of 00z Sun, but expect any TS to remain south of the state line based on current radar and satellite trends. Otherwise, expect VFR conditions through the period at Upper Michigan terminals as surface high pressure lingers over the region. Could see a few showers and thunderstorms develop across the west- central U.P. within a marginally unstable air mass Monday afternoon, but TS chances are too low to warrant inclusion in the TAFs. Will carry a PROB30 for -SHRA at KSAW after 18z Mon. Generally light southerly winds tonight will increase to around 10 kt out of the S- SW on Monday, gusting to 20 kt at times at a few sites.

MARINE

Issued at 347 PM EDT Sun May 24 2026

With abundant high pressure influence during the forecast, winds by and large remain 20 kts or less through next week. This keeps significant wave heights below 4 ft. The main focuses will be marine dense fog and thunderstorms.

Much of the low level moisture has diminished with clearing skies this afternoon; however, some lingering dense fog is noted on satellite over the northwestern waters, particularly near Isle Royale. Areas of dense fog are also expected to persist through tonight over the eastern lake. Given the patchy nature of the fog west of Stannard Rock, all Dense Fog Advisories were canceled except 266/267. What could impact additional fog development is shower/storm potential this evening into tonight over the western lake. Confidence is low, but strong to severe storms seem unlikely until Monday evening/night when a low pressure system to the north sends a cold front over the lake. This round could bring large hail and strong winds to western Lake Superior. Mostly dry weather is otherwise expected Wednesday through next weekend.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... None. Lake Superior... Dense Fog Advisory until 8 AM EDT Monday for LSZ266-267.

Lake Michigan... None.