Marine Weather and Tide Forecast for Ephraim, WI

DISCUSSION
Issued at 1202 PM CST Tue Mar 3 2026

Mainly Dry Weather Expected through Thursday night:

High pressure will persist across the region through Wednesday, along with dry weather. There is some concern for fog development tonight, due to partly cloudy skies, light winds and low-level moisture from daytime melting of snow. The fog should be most extensive where a deep snowpack remains.

The next system is expected to have a glancing blow, with most if not all of the precipitation (rain) staying to our south and east on Thursday. Models are not in unanimous agreement on this, with the Canadian ensembles still fairly aggressive with rain over the southeast half of the area. Have kept 20-50% chances for rain over the south/southeast counties per the NBM; however, it wouldn't be shocking if these are lowered as we get closer to the event.

Friday/Saturday System with Thunder/Heavy Rainfall Potential:

The main system of concern will impact the area Friday into Saturday morning as a strong low pressure system moves from the central Plains to the western Great Lakes. Rain is the main concern in the mild air mass, with thunder possible as elevated instability (MUCAPE of 500-1000 J/kg) arrives in the SW CWA late Friday afternoon and regionwide Friday night. Forcing will be provided by strong WAA/ isentropic lift on the nose of a 35-40 knot low-level jet, strong FGEN, and a warm front lifting into the southeast part of the forecast area. This is followed by the passage of the surface low Friday night into Saturday morning.
PWATs surge to 1.0-1.3 inches across almost the entire forecast area, leading to the potential for moderate to heavy rainfall, especially where convection occurs. Could see minor flooding impacts due to runoff from frozen ground, especially in conjunction with any ice jam flooding that may be ongoing by that time.

Severe Weather Potential:

The severe weather potential late Friday afternoon into Friday night has increased some, as evidenced by the SPC Day 4 outlook surging the 15% severe weather potential into southern Wisconsin and at our doorstep. Instability has increased this run, with MUCAPEs of 500-1000 J/kg. Although bulk shear values are 60 knots, effective shear is a more modest 20 knots. Given the elevated nature of these storms the bulk shear is probably not a great indicator of the severe weather potential given the amount of shear below the steep inversion around 900 mb. At this point the severe weather potential is still low; however, it has increased from the previous forecast and the trend is further north. That being said, cannot rule out some strong storms during this period with gusty winds being the main threat given the very elevated hail growth zone and fairly skinny CAPE profiles.

Mild Temperatures/Fog Potential:

Much above normal temperatures are anticipated through the week, with highs in the 40s and 50s and lows in the 20s and 30s. Fog potential increases through the week as rising dew points and melting snow add low-level moisture. The greatest potential for fog development will be the northwest half of the forecast area, especially north-central Wisconsin, where a deep snowpack remains.

Ice Jam/Ice Floe Potential:

In addition to the previously-mentioned potential for runoff flooding from heavy rainfall with the Friday/Saturday system, there is a lesser threat of ice jam flooding. The ice jam threat should gradually increase through the week as warmer temperatures promote some break-up. The ice jam threat will be reduced a bit due to low water levels, though this could change if heavy rainfall occurs Friday/Friday night. An increased threat of ice floes on Green Bay could also develop later in the week, depending on how strong the Friday/Saturday system is. Wind directions look favorable for a time from Friday into Friday night, but there is some question about how strong the winds will be.

AVIATION
for 18Z TAF Issuance Issued at 1126 AM CST Tue Mar 3 2026

MVFR CIGs across central Wisconsin should give way to VFR as drier air breaks up the clouds across the region later this afternoon.
This breaking up the clouds and drier air are evident on satellite imagery and progressing eastward. Further north, MVFR/VFR CIGs will remain with some breaks in the clouds at times.

Partly cloudy skies, light winds and moisture from melting snow will combine to produce areas of fog, locally dense, late tonight.
The fog will be most extensive over the northwest half of the forecast area, where a deep snow pack remains. Any fog will then dissipate Wednesday morning.

GRB WATCHES/WARNINGS/ADVISORIES
None.