Marine Weather and Tide Forecast for Bayfield, WI

DISCUSSION
Issued at 147 PM CDT Sat Jun 21 2025

Dangerously hot conditions this weekend will end with a cold front passage and at least a few thunderstorms, with a cooler, more seasonable weather pattern for the work week. Dry to start off the week, then precipitation chances return Wednesday into Thursday as a mid-level shortwave or two lifts from the central Rockies into the Upper Midwest helping to produce scattered to widespread showers and storms in the warm sector. There remains considerable uncertainty in the details of timing, but there is medium confidence in at least a wetting rain (tenth of an inch of precip or more) for the region and that the risk for severe weather is low (less than 10 percent) at this point. Later in the week into next weekend a deeper mid/upper level trough tracks east across the High Plains, Great Plains, and into the Great Lakes, with the possibility for some kind of severe weather threat to emerge. But there remains too much uncertainty to narrow down the location beyond somewhere in the northern Great Plains and Midwest at this time. Leaning warmer, but nowhere near the extreme heat values being experienced this weekend.

On the synoptic scale a fairly seasonable broad upper ridge/high exists over the Southeast US with a broad trough over the Great Basin and intermountain west. This pattern will amplify slightly into Sunday with the trough deepening eastward and the ridge building northeastward, with mid/upper level flow being southwesterly across the Great Plains and Upper Midwest. In this flow, a surface low will lift from the Great Plains northwest towards northern Minnesota and western Ontario on Sunday, with a very hot environment ahead of the low. 850mb temps are above the 99th percentile relative to climatology, and even with partly clear skies tonight, there will be little relief from the heat overnight tonight as lows only fall to the 70s in locations away from Lake Superior, especially east-central MN and northwest Wisconsin - record warm low temp values for Brainerd (72, forecast is 73) and approaching the record warm low at other sites away from Lake Superior. The cooler Lake Superior temperatures will result in a strong lake influence, cooling temperatures on the north shore especially. Highs on Sunday will be similar to today in the upper 80s to mid 90s, warmest in northwest Wisconsin where heat index values will reach the triple digits.

As the surface low approaches, the southerly low level flow will help to advect in elevated instability on the order of 3000 to 4500 j/kg MUCAPE - BUT with a very strong cap due to the warm temperatures. By 00z Sunday evening the warm front associated with the surface low will be north of the international border (or darn near it), and IF storms can develop in the warm sector across northern Minnesota, deep layer shear on the order of 40 knots would be more than sufficient for supercells producing all modes of severe weather, quickly merging into a linear mode with significant damaging wind potential. PWAT values in the 1.5-1.8" range means storms would be very efficient rainfall producers, with a localized minor flood threat driven by intense rainfall rates. In addition to the threat for storms closer to the warm front, additional thunderstorms are expected to develop in southwest Minnesota that could lift northeast into parts of the Northland overnight, but with a much lower threat for severe weather.

The severe threat on Sunday afternoon/evening is extremely conditional - IF storms develop they produce produce tornadoes, very large hail, and significant damaging winds. However, given the strong convective inhibition present, there is significant uncertainty in whether there will even be thunderstorms south of the US/Canada border - it's possible storms remain north of the border and just brush far northern Minnesota. Convection-allowing guidance is fairly conservative on the development of thunderstorms, but if storms do develop they could produce significant damage.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/
Issued at 627 PM CDT Sat Jun 21 2025

Largely VFR across the region this evening with a few pockets of MVFR ceilings across northern MN where a warm front continues to surge north. Some echoes may form off this boundary and propagate through the night. Not expecting much impacts from this as it will likely be drizzle with some lower ceilings possible. Through the overnight hours lower ceilings will envelope the region with some potential of fog impacting DLH/HIB. These ceilings will linger across northern MN through mid morning before dispersing. Additionally, a strong low level jet will lead to low level wind shear in HYR overnight.

MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/
Issued at 147 PM CDT Sat Jun 21 2025

Late today into tonight northeast winds increase and at least patchy fog will reduce visibility to a mile or less in some spots, with the wind gusts into the Small Craft Advisory range, so we issued a Small Craft Advisory for the Twin Ports and north shore tonight. A cold front moving west to east on Sunday night will lead to isolated to scattered thunderstorms, and some of these storms could produce gale- force gusts. West winds 10 to 15 knots on Monday in the wake of the cold front with skies becoming sunny. Next chance for thunderstorms mid-week.

For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt.

DLH WATCHES/WARNINGS/ADVISORIES
MN...Heat Advisory until 9 PM CDT Sunday for MNZ010>012-018-019-037.
Extreme Heat Warning until 9 PM CDT Sunday for MNZ025-026- 033>036-038.
WI...Extreme Heat Warning until 9 PM CDT Sunday for WIZ001>004- 006>009.
MARINE...Small Craft Advisory from 10 PM this evening to 4 AM CDT Sunday for LSZ140>145.