textproduct: Marquette

KEY MESSAGES

- Hot and muggy conditions will continue this afternoon. Temperatures will remain very warm the rest of the week but likely below heat advisory criteria. Be sure to stay hydrated and have a way to cool off.

- There is a slight risk (15% chance) for severe thunderstorms this evening and tonight, mainly during the afternoon and evening. The main threat will be damaging winds though a few storms with large hail cannot be ruled out.

- There is a chance for thunderstorms again on Wednesday, some of which could be strong to severe with damaging winds and large hail.

- Additional thunderstorms are possible through the rest of the week, some of which could be strong to severe through Friday.

DISCUSSION

Issued at 154 PM EDT Tue Jun 30 2026

An upper level ridge remained over the UP this afternoon ahead of an upper level low pressure now centered over southern Manitoba. A strong upper level jet extended from the central Rockies through northern MN and into Ontario. Several impulses in the flow were helping to trigger convection with one area of storms that had been strong over north-central WI pushing east of Green Bay and weakening. While these stayed south of the UP they were sending mid and high level cloudiness across the central areas and thus helping to hamper warming a bit. Skies had cleared over the west with temperatures reaching to near or above 90F. Dew points were very impressive, in the mid 70s to 80F across the UP, with the highest readings in the central and south. This was resulting in extreme potential instability, with mucape of 7000 J/kg on the SPC RAP analysis. The atmosphere remained strongly capped in this area though, suppressing any thunderstorm development.

Late this afternoon into tonight the chance for thunderstorms will increase through there remains quite a bit of uncertainty with guidance in poor agreement with the spatial extent and placement of thunderstorms. The atmosphere will remain supportive for severe thunderstorms with effective shear over 40kt and mucape/sbcape as high as 4000 J/kg in the east and 2000 J/kg in the west. It may be hard to break the cap though as surface heating has been suppressed by cloud cover over the central and east. However, a clearing trend and boundary sinking south over western Lake Superior, additional boundary over WI pushing east could provide convergence and help to overcome the cap. Any storms that develop will be strong to potentially severe, with damaging winds and large hail as the primary threats. It will remain muggy tonight with lows in the 60s to near 70. Patchy fog may also develop late tonight, especially anywhere that received rainfall.

The pattern remains active with chances for showers and thunderstorms just about every day through the weekend. Some of the storms could be strong to severe, especially on Wednesday. The upper level jet will weaken this weekend and the risk for severe thunderstorms will go down.

It will remain very warm and muggy through Thursday with the heat index in the upper 80s to mid 90s. Dew points fall back into the low 60s with somewhat cooler highs in the low to mid 80s late week into the weekend, with heat indices staying in the 80s.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 144 PM EDT Tue Jun 30 2026

VFR prevail this afternoon, however, late afternoon to evening thunderstorm development will be the primary aviation hazard for the 18z TAF period. Latest satellite imagery reveals SKC across the west half with decaying high clouds from convection south of the UP moving into the east half. The big question is when and where this next round develops. Latest thinking is increased coverage of showers/storms across the south-central largely after 21z, though high spread in model guidance gives little confidence. Have opted to include a Prob30 at SAW from 21z-03z tonight. At CMX/IWD, capping may prevent thunderstorms altogether, thus leaving any mentions of storms there altogether for now.

MARINE

Issued at 154 PM EDT Tue Jun 30 2026

The main marine hazards over the next few days will be dense fog and thunderstorms, some strong to severe with high winds and large hail through Wednesday. A very humid airmass will continue to spread across the lake resulting in areas of dense fog, especially anywhere rainfall is occuring or occurs. Dense fog advisories continue across much of the lake. Additional thunderstorms are possible through the rest of the week but the potential for severe thunderstorms over Lake Superior will decrease on Thursday. Weak gradient flow will result in light winds, below 15kts through the weekend, with the exception of stronger winds in the vicinity of thunderstorms.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for MIZ002>007-009>014-084-085.

Beach Hazards Statement until 11 PM EDT this evening for MIZ014.

Lake Superior... Dense Fog Advisory until 11 AM EDT /10 AM CDT/ Wednesday for LSZ162-242>244-263>267.

Lake Michigan... None.