Marine Weather and Tide Forecast for Sister Bay, WI

DISCUSSION
Issued at 219 AM CDT Mon Apr 20 2026

Dry and cool conditions continue today as upper ridging builds over the region. A short-wave, currently over northern Manitoba will work east across Canada today dragging a cold front across the western Great Lakes this evening. This will lead an increase in cloud cover this afternoon, however, with such a dry air mass in place the chance for even a sprinkle is less than 10%. Forecast soundings this afternoon do show a deeply mixed PBL which will lead to low relative humidity values of 20-30 percent, lowest across northern WI. Deep mixing is expected again on Tuesday and Wednesday with RHs similarly bottoming out around 20-30 percent. Whiles fuels are rather wet from recent rain these lower RHs will help dry them out and may lead to an uptick in wildfire activity through mid-week.

Main focus of the extended forecast is a round of showers and thunderstorms expected Thursday evening into Friday. Increasing southerly winds Wednesday night and Thursday will draw Gulf moisture into the area with PWATs reaching 1.2 to 1.5 inches, which is near the climatological max. Widespread ascent will overspread the region as a trough ejects out of the norther Plains Thursday reaching the western Great Lakes Thursday night. This will lead to scattered to widespread showers with embedded thunderstorms. Ensemble mean MUCAPE values increase to 500-600 J/kg. This could support isolated stronger storms, however, deep layer shear is expected to be maximized west of forecast area which may keep the severe weather threat generally over MN and western WI. Precipitation amounts will likely vary widespread due to localized convection with this system.
Current NBM probs show 30-50% chance for greater than 0.5" across most of the forecast area with high end amounts (95th percentile)
around 1.2-2" which would is reasonable to expect in areas that see the strongest storms.

Zonal flow becomes more favorable behind the cold front Friday into next weekend which may lead to a period of cooler temperatures and on and off showers.

AVIATION
for 12Z TAF Issuance Issued at 620 AM CDT Mon Apr 20 2026

VFR conditions will prevail through the TAF period. An area of high clouds is stating to stream into central WI early this morning and will overspread much of the region by this afternoon. Light southerly winds this morning will increase during the day reaching 10-15 kts this afternoon with gusts up to 25 kts. Tonight an period of LLWS is expected as winds a the surface diminish and winds around 2kft increase to 40-45kts.

HYDROLOGY
Issued at 219 AM CDT Mon Apr 20 2026

Minor to moderate flooding continues on many rivers, with major flooding expected to persist on parts of the Wolf River through Tuesday. Most of the river levels have crested, and with a prolonged stretch of dry weather anticipated through Thursday, water levels should gradually subside through the week.

Those living near rivers should continue to monitor the latest Flood Warnings and statements from the National Weather Service in Green Bay.

See the discussion section above for information pertaining to precipitation forecasts for the Thursday to Friday period.

GRB WATCHES/WARNINGS/ADVISORIES
None.