textproduct: Milwaukee/Sullivan

KEY MESSAGES

- Chances (20 to 50 percent) for showers this afternoon. There could be a few rumbles of thunder with the showers this afternoon as well. This setup may occur again Thursday and Friday afternoon.

- Cooler temperatures are expected through the end of the week, with lows in the lower to middle 30s each night tonight into Friday night. A Frost Advisory may eventually be needed each night for most of the area.

UPDATE

Issued 617 AM CDT Wed Apr 29 2026

Showers have developed into a broken like of light rain across southeastern Wisconsin, with patchy drizzle to the west. Expecting rain to end within the next few hours, with a brief break before a shortwave propagates southeastward through Wisconsin midday into this evening. With this wave and slight instability (~100 J/kg SBCAPE), an isolated thunderstorm is possible. However, more likely will be isolated to scattered showers (20-50% coverage). Highs in the upper 50s inland and in the lower 50s to upper 40s near Lake Michigan.

MH

SHORT TERM

Issued 1146 PM CDT Tue Apr 28 2026

Overnight through Friday night:

Middle to high clouds will continue to push northeast through the area overnight into Wednesday. Winds will shift northeast overnight as a backdoor cold front shifts southwestward. Winds will increase from the northwest to north on Wednesday, with a northeast turn in the afternoon near Lake Michigan.

There will be small chances (around 20 to 30 percent) for showers to occur overnight, as some frontogenesis response in the 850 mb to 700 mb layer moves through southern parts of the area, with some differential CVA aloft from a passing shortwave trough. There is a fair amount of dry air to overcome initially, though forecast soundings do saturate toward sunrise and may allow for a few showers to reach the ground.

The shower chances (20 to 50 percent) linger into Wednesday, as another vorticity maximum rotates through with a more elongated 500 mb trough in the region. This will bring more differential CVA, along with some weak instability with daytime heating and steep low level lapse rates. Left small (around 20 percent) chances for thunder in the afternoon, as there may be enough low level CAPE reaching the -10 degree Celsius level to bring some rumbles of thunder.

Lows overnight should drop into the lower to middle 40s, with highs Wednesday in the middle to upper 50s inland, with 40s to lower 50s closer to the lakeshore.

Cyclonic flow around a deep 500 mb low to the northeast of the region should remain into Thursday and Friday. Various 500 mb vorticity maxima should rotate through the area at times, with forecast soundings showing a similar look to this afternoon with weak instability during peak heating. Thus, kept small chances (20 to 30 percent) for showers Thursday afternoon in parts of the area, and may need to add some for Friday afternoon eventually. A rumble of thunder is possible again Thursday afternoon, and perhaps Friday afternoon as well.

Ensembles suggest temperatures will remain a little below seasonal normal values through Friday night. Lows Wednesday night, Thursday night and Friday night should drop into the lower to middle 30s for most areas away from the lakeshore, so frost is expected to develop each night. A Frost Advisory may eventually be needed each night for a good portion of the forecast area.

Wood

LONG TERM

Issued 1146 PM CDT Tue Apr 28 2026

Saturday through Tuesday:

500 mb cluster analysis shows the deep and anomalously below normal low slowly shifting east across Quebec Saturday. This feature then gets enveloped with another 500 mb low to the west and maintains a deep and broad 500 mb trough over the region into early next week.

This would suggest northwesterly cyclonic flow at 500 mb during this period, with high pressure at the surface Saturday shifting east and perhaps allowing for additional shortwave troughs and surface lows to move southeast through the region.

Ensembles support 20 to 30 percent chances for showers at times during this period, so left them in the forecast for now. Ensembles suggest that temperatures may moderate slowly this weekend into early next week in this setup, as winds try to turn more south to southwest by later in the weekend and early next week.

Wood

AVIATION

Issued 617 AM CDT Wed Apr 29 2026

VFR conditions are expected to prevail, with a brief period of MVFR ceilings possible mid-morning into midday as a weak low pressure system progresses through the area. Isolated to scattered showers (20-50% coverage, with the most widespread activity in central to southeastern Wisconsin) will develop midday and continue on and off through the afternoon and early evening before dissipating. An isolated thunderstorm is possible within these showers (~20% chance). Dry conditions are expected overnight.

Expect predominately northwesterly winds today, with gusts up to 20 kt in southwestern to south-central Wisconsin. A lake breeze will keep winds northerly near Lake Michigan, and will progress inland this afternoon to turn winds northeasterly. Winds will diminish this evening and shift to be light and northwesterly through Thursday morning.

MH

MARINE

Issued 1146 PM CDT Tue Apr 28 2026

High pressure around 30.3 inches over the Canadian Prairies will gradually shift southeastward into the western Great Lakes by the end of the week. Winds will shift to the north northeast overnight, as a backdoor cold front moves southward across the lake. These winds should linger into Wednesday morning, before weakening in the afternoon.

As the high pressure system approaches and moves into the region by the end of the week, winds will generally remain light. Light showers will be possible at times through the rest of the week, as weak low pressure areas move through.

Wood

MKX WATCHES/WARNINGS/ADVISORIES

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