Area Forecast Discussion

KEY MESSAGES

- Temps rise well above normal Tuesday through Thursday.

- Next chances (50-80%) for showers and thunderstorms Thursday night.

SHORT TERM

Issued 1130 PM CDT Mon Apr 20 2026

Today through Wednesday:

High pressure continues to trek eastward overnight with increasing southerly flow across southern WI. Expect southerly winds and low- level WAA to warm temps up for today with highs climbing into the low to mid 70s. given the trend, expect some deeper mixing to occur thus could see lower dewpoints as well. Otherwise, looking at a mid- level ripple of vorticity to work its way across the region during the afternoon along with a backdoor cold front extending off of the low tracking across Hudson Bay region. Also expecting PWATs to climb toward 0.7-1 inch and paired with cold front and a little bit of upper-level forcing, may be enough to spur a few showers along it across southeastern WI in the afternoon. Overall not expecting much from this activity maybe a few sprinkles or just enough to measure. Otherwise, the southward push off of the lake with enhance the cooler air behind the front cooling things off through the evening quicker than a typically diurnal pattern.

High pressure will build in behind the front overnight with lows dipping into the upper 30s/low 40s along the lake and low to mid 40s further inland. Wednesday is looking to another unseasonable warm day as the upper-level ridge axis builds over WI. expecting high temps to climb into the mid to upper 70s inland and would not be surprised to see a few spots crack 80F. However, temps remain cooler by the lake as the temp gradient between land and Lake Michigan paired with the lighter winds, will be conducive for a lake breeze to develop and push inland into the the afternoon. Temps will remain milder overnight into the upper 40s to upper 50s as WAA and ridge axis gradually work its way through the area.

Wagner

LONG TERM

Issued 1130 PM CDT Mon Apr 20 2026

Thursday through Monday:

Low pressure ejects into southern Manitoba on Thursday, allowing for continued warm, moist advection in the form of southerly winds gusting 20 to 30 mph throughout the day in southern Wisconsin. High temperatures in the upper 70s are expected away from Lake Michigan. Prefrontal/warm sector convection will develop in the eastern Missouri River Valley Thursday afternoon, becoming a line of storms progressing eastward during the late overnight hours Thursday into Friday morning. If these storms are able to tap into the available MUCAPE (~500 J/kg) and shear (~35-40 kt), a few pockets of damaging winds are possible along this line as it progresses eastward through the area. With the late overnight timing and borderline ingredients, as well as the parent low lifting into northern Manitoba away from the Midwest, not anticipating widespread severe convection with this activity. However, there remains a low chance (~10-20%) for rainfall over 1 inch. This may exacerbate any lingering river flooding. This level of rainfall is expected to be isolated, with more widespread accumulations around 0.5 inch.

A cold front will be progressing through the region Friday afternoon, bringing additional chances for precipitation (20-50%). However, amount of lift will be dependent on how much overrunning precipitation from the previous night lingers into Friday morning. Winds will shift to become northwesterly behind this front, bringing in clearing conditions by Friday night. Expect high temperatures Friday in the upper 60s to low 70s, with overnight lows in the mid 40s.

Cooler and drier conditions are expected into the weekend under high pressure, with highs in the low 60s and lows in the low 40s. Sunday night, low pressure ejects from the central Plains and brings the next chances for precipitation Sunday night through at least Monday. Model solutions diverge into Tuesday as some (notably the GFS) models show a deepening occluding low lingering over the Midwest through Tuesday night and other models (ECMWF/Canadian) indicate a more progressive low with only light showers lingering into Tuesday. Current indications are for southern Wisconsin to remain north of the warm sector, limiting severe potential, but flooding may become a concern.

MH

AVIATION

Issued 1130 PM CDT Mon Apr 20 2026

VFR conditions and light winds prevail tonight into Tuesday morning. Expect VFR conditions to persist through the day. May see some diurnal cu develop given the milder pattern. Otherwise, expect a backdoor cold front to work its way down Lake Michigan through the afternoon and will see winds pick up and turn as the front pushes through. Also may see a few sprinkles and/or light showers develop across southeastern WI as the front slides southward. Otherwise, light and variables winds are expected behind the cold front for Tuesday evening into Wednesday.

Wagner

MARINE

Issued 1130 PM CDT Mon Apr 20 2026

Lingering gusty winds and waves will keep small craft conditions overnight into the early morning hours for nearshore waters from Port Washington northward. Otherwise mainly expecting a wind forecast today through midweek as southerly winds during the day are expected to pick up before turning more northerly with a back door cold front through the afternoon and evening. Then light and variable winds behind the front for tonight into Wednesday as high pressure works its way through the region. Thursday will see southerly wind pick up as low pressure develops across the Plains and the pressure gradient increases. Expecting to see a cold front from this system work its way across the lake into Friday and will also bring the next chances for showers and thunderstorms as well.

Wagner

MKX WATCHES / WARNINGS / ADVISORIES

WI...None. LM...Small Craft Advisory...LMZ643 until 7 AM Tuesday.