textproduct: Marquette

KEY MESSAGES

- Hot and humid weather is expected through much of the week, with the hottest period Monday through Wednesday. The heat index will reach the lower 100s over the west and south on Monday and much of the western and central U.P. on Tuesday. The very humid airmass will offer little relief and cooling Monday night, with the heat index staying at or above 70F. A heat advisory has been issued for the western and southern UP.

- Showers and thunderstorms are likely tonight across much of the UP. Some storms could be strong to severe with large hail near the MI/WI state line (5% chance for severe thunderstorms). There will be the chance for thunderstorms every day next week along with the potential for strong to severe thunderstorms.

DISCUSSION

Issued at 225 PM EDT Sun Jun 28 2026

Warm air and moisture advection in the mid levels set off a few light showers and sprinkles this morning but otherwise it was dry today. A large MCS pushed from MN to IA and far western WI bringing a shield of high clouds north over the western half of the UP. A few showers associated with the decaying MCS could move into the west this afternoon but overall activity will be isolated. Temperatures had warmed into the 70s to low 80s with southeasterly flow over the region in response to low pressure over the plains. Upstream, an upper level low was over the northern Rockies and north-central MT, with ridging continuing to build over the Great Lakes.

Gulf moisture surges north into the UP overnight under southerly flow. Instability will increase through the night as a warm front pushes north into the area. The front seems to be slowing down from yesterdays guidance which may keep the stronger and isolated severe thunderstorms south of the UP, over north-central WI. HREF updraft helicity tracks are confined mainly over WI but there are a few over the southern UP, particularly Menominee county. Plenty of updrafts are indicated across the UP and likely widespread showers and thunderstorms late tonight into the morning hours on Monday. MUCAPE will be in the 1000-2000 J/kg range with effective shear of 30-40kt. SPC has shifted the marginal risk for severe thunderstorms south, which now overlaps only parts of the UP near the MI/WI border where large hail can not be ruled out with a stronger storm. Heavy rain can also be expected with any thunderstorms that develop with a deep, warm airmass.

The upper level low will very slowly make its way from the Northern Rockies to northern Manitoba through Wednesday night. Ridging will continue to build ahead of the low pressure bringing southerly flow and increasing temperatures and moisture. By Tuesday and Wednesday 850mb temps warm up to 22-24C which will translate to highs well into the 80s to mid 90s across much of the UP. Humidity also begins to increase starting Monday with Gulf moisture surging north, bringing dewpoints to near or exceeding 70F at times. Heat impacts are expected this week, especially over the west Monday through Tuesday as lows remain warm (60s to low 70s) and daytime highs approach or break the 90F mark, combining with the humid airmass to bring heat indices into the 90-103F range. Heat advisories have been issued for the south and west and may need to be expanded tomorrow for the heat Tuesday into Wednesday. While the heat index remains borderline with respects to criteria, the extended period of heat and warm nights warrants the hazard and messaging. Those who will be exposed to the heat for prolonged periods and those who are sensitive to the heat should have a plan to stay cool and hydrated.

In addition to the heat, thunderstorms will be possible at times through the week. Potential instability will remain moderate to high through the week though the atmosphere will largely will remain capped and large scale ascent will likely be needed to trigger convection. ECMWF cape EFI is high on Monday through Wednesday with shift-of-tails of 1 over the Great Lakes Tue and Wed. Values are a bit lower with combined cape/shear but still notable and a few areas of SOT of 1 is now showing up over the UP. Overall, should convection develop during this period it could be strong to potentially severe but it is too early to pin down details. Should MSC activity occur, outflow boundaries and lingering cloud cover will likely impact the evolution of the proceeding day's convection and high temperatures.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 124 PM EDT Sun Jun 28 2026

VFR conditions prevail in this TAF period until shower and thunderstorm activity increases over the area tonight into Monday. Latest CAMS have delayed onset time by a few hours, so TAF reflects later shower/thunderstorm segments than previous forecast. Tempo and Prob30 groups were added to indicate scattered nature of convection and less confidence, respectively. Deep moist and warm layer suggests potential for high precip rates, which may reduce visibilities and lower ceilings to at least MVFR. Gusty south to southeasterly winds likely to accompany convective activity, especially at KIWD which may see gusts near 30kts outside of thunderstorms.

MARINE

Issued at 225 PM EDT Sun Jun 28 2026

Low pressure will continue to deepen over the central U.S, ahead of a upper level low pressure that will slowly move from the Northern Rockies to northern Manitoba through Wednesday night. This will result in a tightening pressure gradient over Lake Superior and increasing winds. Easterly winds of 20-30kt can be expected to develop this afternoon over the open water, turning south-southeast on Monday. Winds will remain southerly for Tuesday and Wednesday but generally 20kt or less. There is the potential for thunderstorms starting tonight, with chances each day through the week. Predictability on timing and coverage is too low but there remains a chance for strong to severe thunderstorms at times through the week.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Heat Advisory from noon EDT /11 AM CDT/ Monday to 8 PM EDT /7 PM CDT/ Tuesday for MIZ002>004-009>011-084.

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