textproduct: Marquette

KEY MESSAGES

- 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 an enhanced risk (30% chance) for severe thunderstorms across the far southern UP and a slight risk (15% chance) for the remainder of the UP, mainly this afternoon and evening. The main threat will be damaging winds though a few storms with large hail cannot be ruled out.

- There is a marginal risk (<15% chance) for thunderstorms again on Thursday, 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.

UPDATE

Issued at 353 AM EDT Wed Jul 1 2026

Surface analysis early this morning shows a surface low focused over northwest Nebraska coinciding with a weak mid-level wave. Meanwhile, an associated stationary frontal boundary is extending northeastward through north Iowa, Wisconsin, and into central Upper Michigan. It is closest to this surface low/mid-level wave where reflectivities are currently lighting up early this morning on regional radar mosaic along with a few returns traveling ahead of the aforementioned stationary boundary. Therefore, local radar mosaic has been quiet so far across Upper Michigan despite very muggy conditions. Ground-based obs across the area are reporting widespread temps and dew points still in the 70s. So, focus remains on the upstream convection and its northeastward propagation into the Upper Midwest through the morning. And, if this does not materialize over the UP, there is potential for an additional round of thunderstorm development later this afternoon/evening dependent on the strength of the low-level jet. If isentropic lift becomes sufficient, it will have enough effective shear and instability to generate severe thunderstorms with the main threats being damaging winds and large hail, especially with another hot day of widespread upper 80s/low 90s for much of the UP. SPC continues to keep the southernmost portions of the UP in an enhanced risk for severe thunderstorms with the remainder of the CWA under a slight risk.

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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 739 AM EDT Wed Jul 1 2026

VFR conditions continue to prevail this morning and will likely prevail through much of the afternoon outside of any thunderstorms that do develop. And, afternoon convection remains the biggest aviation impact, which still has a window of time from 18Z onwards. Uncertainty still remains high, however, in exact timing and location with ongoing convection still over southern Wisconsin. So, will continue to highlight threats with PROB30s at both IWD and SAW. The highest confidence in thunderstorms remains at SAW, where chances of precip are mostly above 50 percent after 21Z and conditions are most favorable.

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... None. Lake Superior... Dense Fog Advisory until 11 AM EDT /10 AM CDT/ this morning for LSZ162-242>244-263>267.

Lake Michigan... None.