Marine Weather and Tide Forecast for Lake Koshkonong, WI

UPDATE
Issued 549 AM CST Sat Feb 28 2026

The frontogenesis with the snow band is starting to set up to the west across southern Minnesota into northeast Iowa. The northern edge of this area may become fairly sharply defined, as north winds push dry air against it. This may also help push this band a little further to the south than currently forecast into today.

Thus, the heavier snow rates of up to 1 inch per hour and 2 to 4 inch snow accumulations may end up a row of counties to the south of the current forecast, perhaps a little more. Most of the area should still see snow and 1 to 2 inch accumulations as this pushes through the area later this morning through early to middle evening.

For now, will wait for some of the 12Z models to come in and get one final look at where the best frontogenesis sets up before deciding on any Winter Weather Advisories.

After the main snow ends during the evening, there may be a period of lake effect snow with a single band that occurs for locations near Lake Michigan tonight into Sunday morning. There is uncertainty with where the single band may set up, and it may stay offshore. For now, kept 20 percent chances for snow showers for this period, and will see how things trend with this potential.

Wood

SHORT TERM
Issued 1204 AM CST Fri Feb 27 2026

Tonight through Saturday Night:

Gusty northwest winds in the wake of a cold front will diminish toward morning and then veer north during the day. Temperatures are slower to drop since the arctic air is taking its time, but lows are still expected to drop into the lower 20s for most areas.

Snow will spread into southern WI from the west from late morning through early afternoon, which is a later arrival time than previous forecasts. Steady snow is not expected in Madison until around noon. Dry air will initially limit snowfall reaching the ground and also snowfall rates. Once saturation occurs, snow should last 4 to 6 hours and then diminish from west to east during the early evening.

An east-west band of higher snowfall rates (potential of brief 1 inch per hour and IFR conditions) should develop along/north of I-94 and then exit to the east. There continues to be a high degree of uncertainty of where the heavier snow band will track.

Sloped frontogenesis from central IL to northern WI, weak vorticity advection, and the left exit region of the upper jet is coming together across South Dakota late this evening and this will translate across southern MN and into southern WI. The forcing is not perfectly organized/stacked, but should align enough to give everyone at least a dusting of snow. The focused band of snow, wherever it lands, will be associated with 850-700mb frontogenesis. The 00Z HRRR is showing a lower probability of 1" per hour snowfall rates than the 12Z run.

The forecast continues to evolve and models continue to struggle, even as the snow is already beginning in South Dakota. High pressure is quickly building into the Upper Midwest, with a decent push of dry, arctic air southward tonight. This will be difficult for frontogenesis to override, thus a southward shift may be developing. The NAM initialized with its precip shield too far north and the HRRR seems to be trending too far north at this moment as well. We will keep an eye on trends and snowfall rates through the night. Overall, a 3 inch snowfall in 6 hours does not warrant an advisory, but if there are 1 inch per hour snowfall rates for a couple hours, then a small area may need one.

Snow will taper off from west to east Saturday evening. Winds will start to shift northeast over Lake Michigan, and the convergence zone may help a lake effect snow band to develop.
The intensity of the band should not be strong due to minimal temp diff between air and lake, but nevertheless it may brush the shoreline of southeast WI late Saturday night. Lows Sat nt should range from single digits inland to around 20 southeast.

Cronce

LONG TERM
Issued 1204 AM CST Fri Feb 27 2026

Sunday through Saturday:

Arctic high pressure will finish building into Wisconsin on Sunday, sliding eastward and allowing winds to return to southeasterly overnight. Expecting highs in the mid 20s to near freezing on Sunday, with lows in the mid teens overnight.

Monday, southeasterly flow returns and winds increase as low pressure deepens across Ontario, bringing temperatures back into the upper 30s to low 40s. As low pressure occludes across the Hudson Bay Monday night, expect its trailing cold front to begin to interact with ejecting low pressure from the southern High Plains, allowing for a region of warm frontogenesis to build across the Middle Mississippi Valley and expand northeastward into southern Wisconsin overnight into Tuesday. With lows expected to be below freezing Monday night, potential develops for WAA aloft to bring in a period of freezing rain and sleet at the onset of precipitation, with snow towards central Wisconsin.

If phasing between the northern front and the southern Plains system is strong enough as currently portrayed on the major models, surface WAA will allow for temperatures to climb to near 40 degrees across southern Wisconsin during the day Tuesday, allowing most regions to transition to rain or a rain/snow mix.
Rain and snow will taper off into Tuesday night as low pressure in the southern Plains ejects eastward and a ridge of high pressure builds into the Upper Midwest. Expect lows in the upper 20s.

Wednesday, some return flow from the Gulf Coast states may allow for additional cyclogenesis over the Lower Mississippi Valley as low pressure develops in the lee of the Montana Rockies. Between these two features, general lift may develop across southern Wisconsin, bringing back chances for precipitation (20 to 30% chance). As cyclogenesis completes and the resultant low progresses northeastward, more widespread precipitation is possible Wednesday night (50-60%). With temperatures expected to remain just above freezing throughout the overnight time period, expecting primarily rain with a few snowflakes mixing in toward central Wisconsin.

Active pattern remains in place through Thursday and into Friday as low pressure ejects from Montana through the Upper Midwest.
Timing and intensity remains in question across models, as multiple shortwaves embedded in the mean flow may phase with the primary low and intensify it at various points in its development.
General PoPs in the 20-40% range continue through Saturday due to these uncertainties. However, confidence is high in this period primarily being focused on rain and perhaps a few thunderstorms.

MH

AVIATION
Issued 549 AM CST Sat Feb 28 2026

The snow band is starting to set up to the west across southern Minnesota into northeast Iowa. This band may end up pushing a little further to the south than currently forecast into today.
Thus, the heavier snow rates of up to 1 inch per hour and 2 to 4 inch snow accumulations may end up a row of counties to the south of the current forecast, perhaps a little more. Most of the area should still see snow and 1 to 2 inch accumulations as this pushes through the area later this morning through early to middle evening.

Visibility of 1 to 2 miles is expected with the snow, perhaps down to 1/2 to 3/4 mile at times in heavier snow bands. Ceilings should drop into the 1500 to 2000 foot AGL range as well. Winds will remain light out of the north to northeast later this morning into this evening.

After the main snow ends during the evening, there may be a period of lake effect snow that occurs for terminals near Lake Michigan tonight into Sunday morning. There is uncertainty with where the band may set up and it may stay offshore. Kept some 2000 foot AGL ceilings for the lakeshore terminals for now, and will see how things trend with this potential.

Wood

MARINE
Issued 549 AM CST Fri Feb 27 2026

Gusty northwest winds early this morning will become north to northeast and moderate today into tonight, as strong high pressure around 30.7 inches builds into the Upper Midwest. This high will gradually slide east Sunday into Monday. Expect lighter winds Sunday into Sunday night, before becoming south to southeast on Monday into Monday night. Winds may then become northeast to east toward the middle of next week.

For the nearshore waters, waves may reach Small Craft Advisory levels at times later tonight into Sunday morning south of North Point Lighthouse, and again Monday afternoon into Tuesday north of Port Washington. Waves may reach Small Craft Advisory levels again Wednesday night into Friday.

Wood

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM...None.