textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Rain and embedded thunderstorms are expected to develop between 4 PM Tuesday and Midnight Tuesday night. Isolated strong to severe thunderstorms will be possible along and south of the I-94 corridor, especially towards the Illinois border (threat level 1 or 2 out of 5). Main concerns would be hail and frequent lightning.

- Rain will transition to a brief period of freezing rain and snow Wednesday morning (4 AM to Noon Wed transition from northwest to southeast). Up to a glaze of icing and 1 inch or less of slushy snow accumulation possible north of I-94 and west of Madison. Practically zero accumulation further south and east due to warm surface temps. Precip ends early Wednesday afternoon.

- High precip chances (65-85%) Thursday evening/night, with expectations for some snow to mix in with rain late overnight into Friday morning. Practically no snow accumulation expected.

- Additional precipitation chances develop Saturday into Sunday. High confidence in precipitation, but confidence in precipitation type and placement is lower. Snow is possible Sunday.

SHORT TERM

Issued 1100 PM CDT Mon Mar 9 2026

Today (Tuesday) through Wednesday:

A backdoor cold front is currently moving southward across southern WI, with northeast winds arriving behind it. The initial passage of this front (ongoing as of ~10:30 PM Monday) is practically cloud free as seen on GOES Nighttime Microphysics, with just a few unrelated high-altitude clouds passing by, but through this morning we expect a gradual onset of low-altitude clouds (moving in off the lake), which slowly spread inland through the course of the daytime hours. Some marine fog might briefly mix into the shoreline of far southeastern WI this morning, though most guidance prefers to keep it just offshore. CAA behind the backdoor front reinforced by the cooling effect of Lake MI will hold shoreline and east-central WI daytime high temps to the 40s today, moderating up to the low to mid 50s further inland and further southwest. Dry weather expected this morning and early afternoon despite the approaching clouds.

Low pressure will track northeastward from the central Great Plains today, dragging a warm front into Illinois. The aforementioned northeasterly CAA will stall this front in Illinois, likely around the I-80 corridor, with numerous showers and thunderstorms firing up along it. The marine layer (covering our region north of the front) will be extremely stable, reducing the tornado threat to zero, and significantly reducing the wind gust threat as well. That said, plenty of MUCAPE will be present north of the front (perhaps 1,000 to 2,000 joules near the WI/IL border, locally higher) allowing elevated thunderstorms with a hail threat to drift north towards our region. This threat is conditionally dependent on the exact placement of the front, which has changed from one model initialization to the next, but the I-80 corridor of Illinois seems to be a strong consensus for the warm front placement on the latest (00z) CAMs, especially given that the WRF-ARW (which handles early-season marine backdoor cold fronts well due to it's special boundary layer scheme) came into agreement with the HRRR, NAM, and WRF- FV3 on the 00z run. The NAM-NEST and RRFS favor roughly 1 county further south, but still roughly agree with this assessment. With the aforementioned levels of CAPE encroaching into far southern WI (mainly along and south of the I-94 corridor), and mostly unidirectional effective shear (~60 knots convective cloud-layer shear, 40-60 knot EBWD), the ingredients are forecast to be in place for a strong to severe storm with hail and frequent lightning, especially for the first 1 or 2 waves of storms reaching us (maybe even a left or right-moving supercell or two if all the ingredients align). We assess this threat as a level 1 out of 5 for much of the aforementioned area, with a level 2 out of 5 risk in the vicinity of the WI/IL borderline in southeastern WI.

As the low pressure system slowly ejects northeastward Tonight, light stratiform rain continues. A NW to SE rain to snow transition unfolds roughly 4 AM to Noon Wednesday, with slushy accumulations 1 inch or less possible north of I-94 and west of Madison, along with some slick travel possible for the Wednesday AM commute. A thin glaze of freezing rain ice accretion cannot be ruled out either. Further south and east, a transition to snow is not guaranteed, but we expect a few flakes to fly (with practically no snow or ice accumulation due to warm surface temps). Precip should slow down towards noon Wednesday, ending shortly thereafter. Though some flurries or drizzle might linger into the afternoon, air temps should be in the mid 30s to around 40, thus our best guess is smooth sailing for the Wednesday PM commute.

Sheppard

LONG TERM

Issued 1100 PM CDT Mon Mar 9 2026

Wednesday night through Monday:

Overall an active pattern is expected for the end of the week into the weekend.

Wednesday night into Thursday will see CAA behind the departing trough and see temps drop closer to normal as high pressure works across the region through the day Thursday. Looking at overnight lows Wednesday in the 20s and high temps only in the 40s for Thursday.

Meanwhile, a mid-level shortwave trough will begin to dig across the northern Plains through the day Thursday and trek across the Upper Midwest overnight into Friday morning. Models continue to track a sub-990mb low across northern WI. A bulk of the precip will be more anchored to the center of this clipper to our, but still will be a glancing blow of lighter precip across our neck of the woods. Best chances continue to be across our central WI counties, with diminishing chances further south. Thinking it will mild enough for initial round to start off as rain and stay mostly rain south of I-94, while looking a bit colder north of I-94 and mainly expecting wintry mix of rain and snow and potential for some all snow overnight into early Friday morning. Overall accumulations and amounts will be toward the lower end, but still could result in some pockets of travel impacts. Otherwise, this wound up system will also bring strong, gusty southwest winds turning west- northwesterly into Friday with winds gusts of 25-35 mph through the afternoon.

Will see a brief reprieve in the active pattern Friday night into Saturday as high pressure quickly works through the region and continuing the near normal temp trend.

Looking ahead to the weekend there continues to be signal for another deepening upper-level trough to develop across the central Plains and traverse into the Midwest. However, there continues to be a wide spread from the ensembles in the system's track, strength, as well as QPF amounts. The GFS, AIGEFS, and GEFS trends a bit weaker with a more elongated system, while the ECMWF, EPS, and AIFS trend stronger with the surface low undergoing cyclogenesis as it lifts across the Midwest. Additionally the spread in for the weekend system's QPF ranges from a few hundredths of an inch to over 2 inches with the largest spread seen on the NBM and GEFS members. Despite the varying solutions and uncertainty, will need to keep an eye on this system as still expecting increase precip chances with potential impacts.

Otherwise, cluster analysis and ensemble trends continue to favor Colder airmass to settle across the region into early next week with below normal temps.

Wagner

AVIATION

Issued 1100 PM CDT Mon Mar 9 2026

A backdoor cold front is expected to slide southward down the Lake Michigan shoreline (and southern WI as a whole, albeit weaker inland) overnight, shifting winds northeast. Said northeast winds gain speed into Tuesday morning, roughly 10 to 15 knot sustained winds with 20 to 25 knot gusts (mainly by the shoreline). Fuel Alt MVFR cloud ceilings (in the ballpark of 1,000 to 2,000 ft AGL) are expected to gradually arrive behind the front, with rough timing reflected in the TAFs (used SCT to indicate the earlier possible arrivals, and BKN for the expected ceiling arrivals), generally reaches the shoreline first then spreads inland through the course of Tuesday. Some marine fog may briefly roll into shoreline TAF sites late tonight / Tuesday as well, confidence is low.

The northeasterly breeze continues Tuesday afternoon and evening as a low pressure system drags a warm front into Illinois. Scattered to numerous thunderstorms are expected to fire up along and north of the warm front late Tuesday afternoon through Tuesday evening, and some of these showers / storms should drift north into southern WI (70-95% rain chances, highest further south and east). There is a conditional threat for frequent lightning and large hail. Ceilings will decline to IFR levels Tuesday evening, possibly LIFR Tuesday night. A gradual northwest to southeast transition from stratiform rain to stratiform snow is expected to unfold 4 AM to Noon on Wednesday, with winds backing from north to northwest. Snow and/or light freezing rain will struggle to accumulate due to the antecedent warmth, though 1 inch or less accumulations of slushy snow remain possible north of I-94 and west of Madison. Precip should end by early Wednesday afternoon.

Sheppard

MARINE

Issued 1100 PM CDT Mon Mar 9 2026

A backdoor cold front will continue southward across Lake Michigan through the overnight hours, bringing breezy northeasterly winds behind it. Pockets of marine dense fog may develop over southern portions of the lake overnight into Tuesday morning (mainly ahead of the front). Northeast winds behind the front should gradually clear out the fog (if applicable) by mid day Tuesday.

Low pressure around 29.6 inches develops in the central Great Plains and progresses into northern Illinois Tuesday night. There is some potential for thunderstorms across the southern third of the lake north of the associated warm front late Tuesday afternoon through Tuesday evening, with a continued northeast breeze. Low pressure ejects to the lower Great Lakes into Wednesday morning, turning winds northwesterly and allowing rain to slowly transition to snow. North to northwest gales are possible Wednesday morning through Wednesday afternoon, mainly over the south half of the lake. Winds gradually diminish into Thursday morning.

Another round of gales is possible Thursday night into Friday as a compact clipper low of 29.2 inches crosses northern Lake Michigan.

Sheppard

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643-LMZ644...3 AM Tuesday to 7 PM Wednesday.

Small Craft Advisory...LMZ645-LMZ646...10 AM Tuesday to 7 PM Wednesday.