textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Scattered thunderstorms, possibly producing large hail, will continue through the afternoon.

- Areas north of the I-94 corridor may observe a glaze of freezing rain accretion Wednesday evening into Thursday morning, mainly on elevated surfaces. Highest potential is further north and west in the region. Slick spots are possible for the Thursday AM commute.

- Thunderstorms are possible once again Thursday afternoon and evening (level 2 out of 5 severe threat).

- Additional chances for rain and a few thunderstorms Friday afternoon into Saturday.

UPDATE

Issued 730 PM CDT Tue Mar 31 2026

High pressure nudges in tonight as the base of the high strengthens and pushes into eastern Ontario into Wednesday. Into the upper levels it largely looks like zonal flow but the large scale look appears to be in an area of weak ridging, particularly into the day Wednesday. Into the day Wednesday we will see predominantly northeast flow and we warm up a bit of a boundary/front feature develops and spreads down the lake. It appears to be a bit of a backdoor cold front type feature but in effect will just keep temperatures in eastern WI from increasing much. This will be as temperatures to the west increase into the mid to upper 40s thus just creating a fairly strong temperature gradient across the CWA. Otherwise no precipitation is expected Wednesday though we cannot rule out a brief period of light precip across parts of southern WI Wednesday morning as a result of a little shortwave energy aloft in the presence of some moisture. Given drier low to midlevels this would likely appear as virga but we cannot completely rule out a few flakes/sprinkles.

Kuroski

SHORT TERM

Issued 134 PM CDT Tue Mar 31 2026

This afternoon through Wednesday:

The slow moving cold front is now located over far srn WI but the new areas of convection from Green County to Ozaukee County are along the 925-850 mb front. Sfc-850 mb frontogenesis along and east of the 925-850 mb front will continue to generate showers and thunderstorms this afternoon as elevated CAPE of 1000 J/kg remains. The elevated front does linger a bit into the evening over far se WI so chances for showers and storms will continue there. The actual sfc cold front will shift entirely into nrn IL by 20-21Z with chilly temps to follow. Farther to the north and west of Madison, the rain threat is mostly over and some sunshine is expected this afternoon along with warming temps near 50F.

Nnely winds and cold advection will prevail tnt into Wed as polar high pressure moves across Ontario, reaching James Bay by 00Z Thu. Low temps in the lower to middle 30s tnt then only warming into the middle to upper 40s over south central WI on Wed, with lower 40s in the east.

Gehring

LONG TERM

Issued 200 PM CDT Tue Mar 31 2026

Wednesday night through Tuesday:

Deep Colorado low pressure will track northeastward on Wednesday, crossing central or north central WI Thursday afternoon before lifting into Canada. In advance of it's arrival, strong high pressure over Quebec Canada will force east to northeasterly flow off of Lake Michigan, cooling temperatures to around the freezing mark (particularly well north of the I-94 corridor), which could result in a wintry mix, predominantly rain and freezing rain. The arrival window for this activity would be roughly 6 to 11 PM Wednesday evening in a SW to NE manner, arriving as predominantly plain rain south of I-94 and wintry mix of sleet, freezing rain, and wet snow (with snow as the least likely of the three) further north. The majority of the rest of the event (after initial onset) should feature liquid-only hydrometeors judging by the ever- strengthening warm nose evident on forecast soundings. This would mean freezing rain where it is cold enough at the surface (generally in the same area, well north of I-94) and plain rain further south. Rising surface temperatures later Thursday morning will bring an end to any winter wx concerns, rapidly melting any ice that may have formed.

Precip type and travel impacts could swing one way or another with even just a tiny shift in the position of the low pressure system, or any modeled misrepresentation of the marine boundary layer to our east. Speaking of which, the latest model trends have been ever so slightly further north, with warmer temps and less wintry precip. That said, our current thinking is that areas south of I-94 will get away with zero wintry accumulations. The MSN/MKE metros and I-94 corridor have some slight potential for a thin glaze of ice if temperatures allow, but our best guess is little to no wintry impacts unless the system reverses trends and tracks further south. North of I-94 (Sauk through Ozaukee counties and counties further north) there will be better potential for slick spots, with potential for a glaze ice accretion from freezing rain, mainly on elevated surfaces. Values up to a quarter inch cannot be completely ruled out in portions of Sauk, Marquette, Green Lake, Fond du Lac, and Sheboygan counties, particularly further north and west in these counties, though this would be an outside chance (35% chance or less), and is growing less and less likely as the system tends to track slightly further north. Primary impacts would be to the Thursday AM commute. Precip is currently looking to arrive too late Wednesday to impact the Wednesday PM commute, though we'll have to narrow down the arrival window to be certain. Some minor sleet and wet snow accumulations (less than 1 inch total) may occur in this same area towards the onset of the event, but the most likely scenario is nearly zero measurable snow/sleet, with freezing rain as the only real concern.

Due southerly surface WAA will spread northward into the region Thursday, with continued rain showers and increasing thunderstorm chances (level 2 out of 5 severe storm threat). Temperatures soar into the 60s Thursday afternoon, around 70 towards south-central WI. Most models in the ballpark of 200 to 1,000 joules MUCAPE building into the CWA (highest further southwest) on Thursday, with the majority of modeled convection (as seen in QPF output) occurring in the warm sector (afternoon hours on Thursday), with the NAM suggesting additional activity along and just behind the cold frontal passage (Thursday evening), which fits with our conceptual model. Dry weather likely by midnight Thursday night as high pressure quickly crosses the region.

The preferred model solution is for yet another Colorado low pressure system to track northeastward across the region late this week, with precip expected late Friday into Saturday (90% chances). Predominantly an all-rain event (with thunder chances again). Included 10-30% precip chances Saturday night into predawn Sunday in the forecast, with some chance for a little snow to mix in with the rain as precip shuts off (no accumulation expected whatsoever at this time). Likely dry and cooler conditions (highs in the 40s) with passing high pressure on Sunday. Temperatures may slowly moderate upwards from there into mid next week under a less active weather pattern. That said, the ECMWF and GFS resolve a clipper system or shortwave trough leading to light rain chances either Monday or Monday night. Capping chances at 20% until this feature becomes clearer.

Sheppard

AVIATION

Issued 740 PM CDT Tue Mar 31 2026

High pressure nudging in tonight, which will largely clear low CIGS out of southern WI. However, with northeast winds off the lake moisture/low clouds will likely show some presence in southeast WI for periods this evening through the early morning Wednesday. There is some uncertainty in this potential but most models showed enough evidence to support some form of MVFR CIGS pushing in off the lake over the next few hours. Into Wednesday morning the rising sun will help raise these low CIGS with VFR conditions generally expected for the rest of the day Wednesday. Areas near the lake may continue to have lower CIGS but perhaps more in the 3500 ft range. As the next system pushes in Wednesday evening we will see more widespread MVFR/IFR CIGS (possibly even LIFR) push in from the south overspreading southern WI by the late evening with increases rain chances overnight. Cannot rule out some ice toward central WI as well. Rain and even some thunderstorms will be possible into the day Thursday. Southeast WI will see the best chance for a period of clearing skies (or at least dry) with the corresponding best chance for stronger storms later Thursday.

Kuroski

MARINE

Issued 134 PM CDT Tue Mar 31 2026

A slow moving cold front over southern Lake Michigan will reach the southern tip of the lake late this afternoon. Modest southerly winds south of the front will shift northerly and become brisk into Wednesday. Numerous thunderstorms will continue over the southern portion of the lake into early this evening.

Breezy easterly winds are then expected Wednesday night into Thursday between high pressure of 30.7 inches east of James Bay in Canada, and low pressure of 29.4 inches lifting from the Central Plains into Wisconsin. Gusts could approach gale force over far northern Lake Michigan on Thursday. The breezy easterly winds will shift southerly from south to north across the lake Thursday afternoon and evening with the passage of a warm front, then followed by the cold front with winds shifting westerly late Thursday night.

A Small Craft Advisory will remain in effect from Sheboygan to Winthrop Harbor for late this evening into late Thu nt for brisk winds and high waves.

Gehring

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646...10 PM Tuesday to 4 AM Friday.