Marine Weather and Tide Forecast for Sturgeon Bay, WI

DISCUSSION
Issued at 239 AM CDT Sat Jul 25 2026

The latest RAP analysis and satellite imagery show shortwave energy pushing east across south-central Canada into northeast North Dakota and northern Minnesota, driving a cold front into northwest Minnesota. Thunderstorm activity ahead of this front has been weakening across northern Minnesota as it outruns stronger instability, though light showers continue to push into far north- central Wisconsin early this morning. Further south and west, a dominant subtropical ridge centered over the Intermountain West continues to build northeast toward the northern Plains and Upper Midwest, anchored by extreme heat over the Plains. Widespread low stratus is lifting northeast across the state in a low-level warm advection regime. Over the next 36 to 48 hours, the interaction between embedded northern-stream shortwaves propagating along the northern periphery of this building subtropical ridge and the advancing surface front will serve as the primary driver for convective potential and dangerous heat across the region.

Regarding thunderstorm potential, the decaying surface front will track east today, losing definition near Lake Superior. Morning cloud cover (and persistent light showers) over north-central Wisconsin should mix out by afternoon, allowing for surface heating and destabilization. Mid-afternoon CAPE values reaching 1000-2000 J/kg alongside lake breeze convergence will favor isolated thunderstorm development from 4 PM to 9 PM, primarily over far northeast Wisconsin. While weak overall convergence and capping will keep storm coverage sparse, any cell that develops could become conditionally severe, with large hail and damaging winds as the primary threats. A second, more organized round of convection is possible late night into Sunday morning as a 25-30 knot low-level jet over Minnesota supports a cluster of storms riding elevated instability around 2000 J/kg into north- central Wisconsin. Effective shear of 50-60 knots could organize these early Sunday storms capable of damaging winds and hail before dissipating. Depending on how morning convection modifies the airmass, afternoon re-development on Sunday remains conditional due to rising 700mb temperatures near 12C creating a stout cap.
Northeast Wisconsin remains the most favorable area for thunderstorm development on Sunday afternoon, which is an area on the edge of the mid-level cap. A third period of severe potential arrives Monday as a stronger shortwave trough and cold front sweep through the region, interacting with 2000-3000 J/kg CAPE and deep- layer shear exceeding 40 knots. Much of the area is in a slight risk of severe thunderstorms on Monday.

Regarding the heat threat, the expanding subtropical ridge will usher a hot, muggy airmass into the region on Sunday and Monday.
Afternoon high temperatures in the upper 80s to lower 90s combined with dew points climbing into the lower 70s will yield heat index values peaking in the middle to upper 90s on both days, particularly across central and east-central Wisconsin. While convective debris and thunderstorm coverage introduce some uncertainty regarding exact peak temperatures, conditions will remain dangerously hot and humid for those outdoors. Headlines for excessive heat may be required as confidence in storm coverage improves. A cold front will cross the region late Monday into Monday night, shifting winds to the north on Tuesday and delivering a reprieve from the oppressive humidity. Highs Tuesday through Thursday will moderate into the upper 70s to middle 80s with much lower dew points, before another disturbance brings renewed thunderstorm chances late Thursday into Friday.

AVIATION
for 06Z TAF Issuance Issued at 1056 PM CDT Fri Jul 24 2026

Skies ranged from mostly clear across central and east-central Wisconsin, with a BKN-OVC deck across the north ahead of a cold front and upstream convection. This cold front will approach from the north overnight, which could bring some lower clouds across the north along with some disorganized shower activity, affecting primarily RHI. CAMs indicate less of a chance for this activity to affect RHI; therefore, will only put a PROB30 group in this set of TAFs. Further southwards these showers are expected to diminish rapidly; therefore, no mention of showers was made at other sites for now.

Outlook...Isolated to scattered thunderstorms and lower flight categories are possible at times over Saturday evening and again Sunday as a warm and unstable airmass shifts into the region.

KOSH

Mostly clear skies with only some high clouds are expected overnight. An approaching cold front overnight into early Saturday could bring some disorganized showers into northern Wisconsin. Currently expect these showers to dissipate as they move southwards, with around 10-15% chance of some sprinkles reaching the site; therefore, did not add a mention of showers at this time.

Fair weather cumulus returns Saturday afternoon. Looking ahead of the current TAF period, Saturday evening will also bear watching as it may include some pop-up showers and scattered storms. Best signal remains west and northeast of the area, but will need to monitor the forecast going forward for convective potential over Oshkosh.

Winds will remain below 10 kts overnight. Southwest winds increase Saturday morning at 5-10 kts with some brief gusts up to 15 kts through early Saturday evening.

MARINE
Issued at 239 AM CDT Sat Jul 25 2026

Southern Green Bay buoy continues to gust from 20 to 25 kts so will hold onto the Small Craft Advisory until its 4 AM expiration. South winds will remain 15 to 20 kts for much of the day prompting persistent waves from 3 to 4 ft. With these waves, there is a moderate risk for rip currents on Lake Michigan beaches.

GRB WATCHES/WARNINGS/ADVISORIES
None.