textproduct: Marquette

KEY MESSAGES

- A warming trend continues through this weekend, bringing unseasonably warm temperatures and humid conditions into next week. This is leading to a potential for heat-related impacts to vulnerable populations.

- Showers and thunderstorms are likely Sunday night, some of which could be strong to severe with damaging winds and large hail (5% chance for severe thunderstorms). There will be the chance for thunderstorms every day next week.

DISCUSSION

Issued at 216 PM EDT Sat Jun 27 2026

Surface high pressure over the Upper Great Lakes this afternoon was bringing pleasant weather to the UP with sfc temperature observations in the 70s. It was cooler along the shoreline of Lake Superior and Lake Michigan where lake breezes had developed and dropped temperatures back into the 60s. GOES visible satellite imagery showed areas of fair weather cumulus. Upstream low pressure was moving through the Pacific Northwest with ridging developing over the plains and relatively zonal upper level flow over the Great Lakes.

The upper level low will move into the northern Rockies this weekend, lingering into early next week before slowly pushing north and east into Canada. Ridging will continue to build ahead of the low pressure over the Midwest, 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 likely next week 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 90-100F range. ENS 850mb temperature anomalies are not overly impressive though return intervals are in the 10-30 yr range. Thus the heat event looks impactful but not extreme for the UP. NBM bias corr could be overdoing temperatures as it has with previous warmer stretches over the last month. Did knock high temperatures down a few degrees from the NBM Sunday through Tuesday. Heat advisories may be needed next week and 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 a potential hazard starting Sunday night with continued chances through the week. Moisture and temperature advection increases as a warm front pushes through Sunday night. Most unstable CAPE increasing to 2000-3000 J/kg Sunday night with effective shear of 40+ kt, providing an environment favorable for organized convection as large scale ascent provides lift for elevated convection. The strongest upper level support remains north and west of the UP in an area of divergent flow aloft, ahead of the upper level low pressure over Montana. However, thunderstorms are still likely Sunday night and SPC has a marginal risk for severe thunderstorms over the western 2/3 of the UP, with the main hazards being large hail and damaging winds.

Potential instability remains moderate to high through the rest of the week, however, the atmosphere largely will remain capped and large scale ascent may 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. 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 convection and high temperatures.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 714 PM EDT Sat Jun 27 2026

VFR conditions will prevail through the TAF period as drier air and stronger winds will keep fog from forming overnight tonight. The best chances for sub-VFR conditions will be at IWD approaching 00Z Monday as rain chances approach from the west, though chances of rain prior to 00Z are only around 20% and chances of MVFR ceilings are only around 30%, so will keep mentions of both out of this issuance. Winds will be generally light until the late morning to early afternoon hours of Sunday where winds increase to around 10 kt out of the south to southeast with gusts near 20 kt.

MARINE

Issued at 216 PM EDT Sat Jun 27 2026

A large area of high pressure over the Great Lakes and eastern Canada will slowly move east through early next week as low pressure deepens over the central U.S, ahead of a upper level low pressure moving from the PAC NW to the Northern Rockies. This will result in a tightening pressure gradient over Lake Superior and increasing winds. Easterly winds of 20-30kt can be expected to develop Sunday afternoon, 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 Sunday night, with chances each day through the week. Some of the storms could be strong to potentially severe Sunday night into Monday (5% chance). Thereafter predictability is too low but there remains a non-zero chanced for strong to severe thunderstorms at time through the week.

MQT WATCHES/WARNINGS/ADVISORIES

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