Marine Weather and Tide Forecast for Lake Koshkonong, WI

SHORT TERM
Issued 336 AM CDT Wed Apr 30 2025

Today through Thursday:

An area of low clouds developed near Green Bay late last evening and slowly expanded into east central WI overnight. The trajectory keeps them confined to Sheboygan and Fond du Lac counties early this morning, and then mixing will help them dissipate by mid morning. Temperatures dropped into the upper 30s across much of east central and southeast WI thanks to cool air from Lake Michigan on slightly enhanced northeast winds.
Winds were probably too high to allow for frost development.

There will be a large difference in temps between the lakeshore and western Waukesha County (and north-south of there) due to a steady east wind off Lake Michigan all day. Inland temps should reach the mid to upper 60s from Madison and westward.

Dewpoints are in the 30s and they are not expected to make much headway into the 40s today, per the upstream obs in IA and IL.
Therefore, min RH values will be in the 35 to 40 percent range.

The arrival time of the precip today looks slower than previously forecast due to all the dry air in place over WI.
The convection ongoing over MO will lift into the Upper Midwest later today. However, the nose of the LLJ (and vorticity advection with a southern stream upper trough) that are driving that convection is expected to split around southern WI. This means that one wing of the precip will track into northeast IL today and lower Michigan this evening; the other wing of precip will track northward into southern MN, following the right entrance region of the upper jet and a mid level shortwave trough.

Eventually, the southern stream shortwave trough will push into the mid Mississippi River valley and a more connected flow from there into southeast WI will develop overnight. Thus, that is when the more widespread showers will arrive in southeast and east central WI. However, the disjointed upper levels between the southern stream upper trough and northern stream upper trough means that south central WI and central WI will likely have lower precip amounts from this system. Total rainfall amounts are forecast to range from around 0.75 inch in southeast/east central WI to 0.35 inch in south central/central WI.

A surface low will develop over central IL as the MS River valley mid level shortwave trough gets closer. That surface low will slide across southern Lower MI during the day Thursday, and the steadier showers over southeast WI will taper off from west to east from Thursday afternoon through Friday evening.

Given that we will be on the northwest periphery of the main forcing of this system, our chance for thunder is very low. The steeper mid level lapse rates should be limited to right along the WI/IL border late tonight through Thursday. Elsewhere, lapse rates look moist adiabatic and thus quite stable.

Temps Thursday will remain cooler by the lake, especially toward east central WI due to steady northeast winds. Inland highs will be in the upper 50s, except lower 60s near the WI/IL border.

Cronce

LONG TERM
Issued 336 AM CDT Wed Apr 30 2025

Thursday night through Tuesday:

Meanwhile, the northern stream upper trough will be slow to make eastward progress. This will bring additional light showers to southern WI Thursday night. While shower chances continue through Friday due to the upper trough passing overhead, the dry air surging in from the north may win out and keep us dry. Any precip will not be a steady rain, but instead characterized by several waves of light to moderate showers, as various shortwaves rotate through the larger scale upper trough. Highs Friday will be a touch cooler, with readings in the mid to upper 50s to around 60.

The main upper level trough is expected to pass through the area Friday night, with high pressure building into the region on Saturday. Guidance is suggesting that an omega block will set up across the CONUS, with deep troughs/upper lows over the eastern and western US, and a strong ridge over the central part of the country. This suggests a stretch of quiet and warm weather as high pressure slowly drifts eastward, with highs early next week approaching the upper 70s and low 80s.

Boxell

AVIATION
Issued 336 AM CDT Wed Apr 30 2025

An area of low clouds developed near Green Bay late last evening and slowly expanded into east central WI overnight. The trajectory keeps them confined to Sheboygan and Fond du Lac counties early this morning, and then mixing will help them dissipate by mid morning. Northeast winds are elevated near Lake Michigan and lighter for inland areas. High clouds will continue streaming into southern WI from a storm complex crossing the MO and IL today.

Light rain chances should hold off for southern WI until evening, although virga is possible. Then more widespread showers should develop in southeast and east central WI overnight tonight. A few rumbles of thunder will be possible near the IL border.

VFR today. Ceilings will fall tonight as the rain moves in, with IFR expected after midnight and through at least Thursday morning.

Cronce

MARINE
Issued 336 AM CDT Wed Apr 30 2025

High pressure of 30.3 inches centered over Upper Michigan will cross Lake Huron today. Steady easterly winds will persist through Wednesday night, then increase Thursday as low pressure around 29.6 inches tracks from IL to southern Lower Michigan.

Winds will become northerly Thursday afternoon and westerly Friday afternoon as that low exits the region. High pressure around 30.2 inches will return to the Upper Great Lakes for the weekend, bringing quiet weather and light winds to the region.

Cronce

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