textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Areas of fog possible over southern parts of the area late tonight.

- Well above-normal temperatures continue through Thursday.

- Periods of showers and storms expected late Thursday night into Friday. Widespread severe weather is not expected, though some storms could produce heavy downpours.

- Showers and thunderstorms return Sunday night through Tuesday.

SHORT TERM

Issued 1125 PM CDT Tue Apr 21 2026

Rest of Tonight through Thursday:

Synopsis/Mesoanalysis: Surface observations place a weak cold front along an approximate Prairie du Chien - Baraboo - West Bend axis late this evening. Nudged by a broad area of high pressure centered over the Lake Superior vicinity, the boundary will continue to drift south into the region through the remainder of tonight, bringing a light but steady north wind shift in its wake. The boundary's progress will slow as it approaches the Wisconsin-Illinois border during the predawn hours, keeping winds light and variable along and south of the I-94 and US-18 Corridors through daybreak. The light winds will combine with clear skies & efficient radiational cooling to support areas of fog development in locations most proximate to the slow-moving surface boundary during the predawn hours. Slow down & use low-beam headlights if encountering areas of fog during the early morning hours. Upper ridging will glide across the western Great Lakes during the day Wednesday, allowing for mostly sunny skies and continued well above-normal temperatures away from the Lake Michigan shoreline. A pronounced upper trough will eject from the northern Rocky Mountains on Thursday, encouraging surface cyclogenesis over the Dakotas. Remaining well east of the low, increasing southerly winds will allow for even warmer conditions across southern Wisconsin on Thursday afternoon. Precip impacts from the Northern Plains trough & surface low will hold off until Thursday night/the beginning of the long term period.

Rest of Tonight: Will be monitoring for areas of fog development after midnight. With clear skies and still modest moisture in the near-surface layer, conditions will be broadly favorable for visibility reductions with continued cooling. Tend to think the greatest potential for fog will be along & south of I-94 and US-18, where proximity to the surface front sagging into the region will result in light winds & the best chances for decoupling of the boundary layer. Have maintained fog mentions over the southern part of the CWA given these expectations. Will be monitoring visibility trends further north, though higher surface winds should preclude widespread fog potential over this part of the area. Whether or not any fog will become dense remains uncertain, and will likely be contingent on a complete stall of the encroaching surface front such that winds can remain calm for long enough in any given location(s). Will be watching trends through the remainder of the overnight.

Thursday: Continued low level warm advection will result another afternoon of well above-normal temperatures areawide. Trended forecast temperatures up slightly in the evening update, with widespread mid-upper 70s & low 80s anticipated across much of the area. Breezy southerly winds should keep the lake breeze from mixing too far inland, though the boundary may attempt to work inland during the mid-late afternoon hours. Could thus see locally cooler high temps near the immediate Lake Michigan shoreline. Think highs will remain just below April 23 records (83 in 1960 in Madison & 85 in 1960 in Milwaukee), though trends will continue to be monitored.

Quigley

LONG TERM

Issued 1125 PM CDT Tue Apr 21 2026

Thursday night through Tuesday:

Synopsis: The upper trough moving into the Northern Plains Thursday will progress from the Upper Mississippi Valley through the western Great Lakes during the Thursday night - Friday time frame. Attendant surface low pressure will concurrently occlude over the Canadian Prairies, with an occluded front moving across southern Wisconsin during the day on Friday. Thunderstorms will develop along the front to the west of the area Thursday evening, moving into southern Wisconsin after midnight as they steadily decay. Additional shower/storm development is possible during the daytime hours Friday as the occluded front crosses the area. Widespread severe weather potential is not expected in any thunderstorms during the Thursday night-Friday time period, though some storms could produce brief heavy downpours. Drier and cooler air will work into the region behind the departed front Friday evening, with passing high pressure maintaining dry conditions across southern Wisconsin through the majority of the weekend. A second upper wave will approach from the southwest Sunday night into Tuesday, bringing additional chances for showers and embedded thunderstorms to southern Wisconsin.

Thursday night: Expect strong to severe thunderstorms to erupt over the Missouri Valley during the late afternoon hours, with activity organizing into clusters and lines as it moves into Iowa and Minnesota during the evening hours. Expect that activity will work into southern Wisconsin near or after midnight, though it will be battling a waning instability pool & weakening wind shear as it attempts to migrate east. Thus not currently expecting a widespread or organized severe weather threat in Thursday night's thunderstorms. Will nevertheless need to monitor areas west of Madison, where a few storms with gusty winds could be possible if instability and/or wind shear trend higher in coming forecasts. A likely progressive & weakening nature to storms should limit the residence time of higher rainfall rates in any one given location, which should act to keep flash flooding potential low in Thursday night's storms. Could nevertheless see some hydro responses in rivers, streams and urban areas, where conditions remain full & saturated from last week's rainfall. Will continue to watch trends & provide more information as additional forecast guidance becomes available over the next 12-24 hours.

Friday: Given the slow progression of the upper wave & surface occluded front currently progged in global guidance, expecting some rejuvenation of early morning showers/storms and/or redevelopment of showers/storms from late morning into the afternoon hours. Persistent cloud cover should help to limit instability, though values could climb to sufficient levels to combine with overlapping wind shear to support an isolated stronger storm capable of hail and gusty winds. Will be monitoring trends regarding this potential over coming forecasts. Additional heavy downpours would be possible in any thunderstorm redevelopment.

Sunday night into Tuesday: Showers and scattered storms return to the region ahead of the next upper disturbance. Precip will be focused by an abundance of synoptic ascent ranging from positive vorticity advection in the mid-levels to warm advection & frontogenesis in the lower levels. While there is little uncertainty regarding the aforementioned abundance of forcing, there remains considerable uncertainty regarding the precise timing of its passage amongst global guidance. This is contributing to the wide temporal range of mentionable precip probabilities in the evening update, with the expectation for mentionable probabilities to contract a tighter window(s) as this portion of the period draws closer & the timing of best forcing clarifies. Passage of the upper wave near or just south of the region will place the best overlap of instability and wind shear in the Ohio and mid-Mississippi River Valleys, which is where machine learning-based forecast guidance is placing the highest potential for severe thunderstorms. Thus initially thinking that the primary impact from any storms during the Sunday night - Tuesday time frame would be heavy downpours, but will nevertheless be monitoring trends.

Quigley

AVIATION

Issued 1125 PM CDT Tue Apr 21 2026

Primarily VFR flight categories prevail through the period as high pressure currently centered near Lake Superior migrates east toward Lake Huron. The passing high will lead to mostly clear skies through Wednesday morning, with FEW-SCT upper level clouds gradually moving in on Wednesday afternoon. The clear skies will combine with light & variable winds tonight to support areas of fog, particularly across the southern half of the region. Have inserted prevailing mentions in the 00Z update at all terminals along and south of I-94, and will continue to monitor trends further north. Whether or not dense fog will occur remains uncertain, with trends being monitored through the evening and overnight hours. Any areas of BR/FG should quickly dissipate following sunrise Wednesday morning. Light and variable winds will trend east-southeasterly during the day Wednesday.

Quigley

MARINE

Issued 1125 PM CDT Tue Apr 21 2026

A weak surface boundary will continue to work south into the southern third of Lake Michigan tonight, leading to light and variable winds with breezier winds further north. The light winds could lead to areas of fog over the southern third of the open waters through the overnight hours, with trends being monitored for possible dense fog advisories through this evening. Light north- northeast winds will become established over all of Lake Michigan after sunrise on Wednesday, trending east-southeasterly during the second half of the afternoon hours.

Southerly winds will increase over the open waters Wednesday night through Friday morning as 990 mb low pressure develops over the northern Great Plains. While winds will be breezy, gales are not anticipated at this time. The low will pull a cold front across Lake Michigan Friday afternoon and evening, resulting in a breezy north- northwest wind shift. Periods of showers and embedded thunderstorms will accompany the approaching/passing surface low & front Thursday night through Friday. Severe weather is not anticipated at this time.

North to northeast winds will continue through the weekend across Lake Michigan. 1000 mb low pressure will approach the open waters from the Great Plains during the day on Monday, resulting in a breezy east wind shift. The low will cross Lake Michigan Monday night into Tuesday, bringing a northwest wind shift by Tuesday evening. Don't anticipate widespread gale potential as of this forecast, though trends will continue to be monitored over coming updates.

Areas of fog are possible in nearshore zones tonight. Some fog could become dense, with trends being monitored for potential headlines through this evening. Southerly winds will increase in nearshore zones ahead of low pressure in the northern Great Plains Thursday evening through Friday, resulting in elevated wave heights. Some waves could approach Small Craft Advisory thresholds, particularly from North Point to Sheboygan. Periods of showers and thunderstorms are expected Thursday night into Friday, with severe weather not anticipated at this time. Trends will be monitored for possible headlines in coming forecast updates. Additional Small Craft Advisory wind gusts and wave heights are possible over all nearshore zones Sunday night into Tuesday.

Quigley

MKX WATCHES/WARNINGS/ADVISORIES

WI...None. LM...None.