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FXUS63 KMKX 230237 AAA AFDMKX

Area Forecast Discussion...UPDATED National Weather Service Milwaukee/Sullivan WI 937 PM CDT Mon Apr 22 2024

KEY MESSAGES

- Scattered thunderstorms possible Tuesday afternoon. Cannot rule out seeing a stronger storm or two capable of producing small hail and localized gusty winds ahead of the cold front.

- Potential for frost/freeze concerns return Tuesday night and Wednesday night.

- More active pattern with thunderstorm potential Friday into the weekend.

UPDATE
Issued 937 PM CDT Mon Apr 22 2024

Scattered light showers will continue this evening, generally coming to an end across the area by around midnight. Still a lot of dry air in the low levels, so most places will likely see only a trace of precip. Already seeing some breaks in the clouds across the northwest forecast area, with at least partial clearing working into the area through the overnight hours. Low temps look on track for tonight, staying on the milder side given the clouds and continued breezy southerly winds.

DDV

SHORT TERM
Issued 341 PM CDT Mon Apr 22 2024

Tonight through Tuesday night:

Upper-level ridging today will slide east as mid-level trough digs into the Upper-Midwest. Ahead of the main trough will be a broad shortwave with a vort max ripple working across WI later this afternoon and evening and be the main focus for scattered shower activity. Trends continue to favor shower development along the mid- level feature aligning with a a developing LLJ around 40-55 kt this evening. All the 12z CAMs pick up on trend along with the global models, with the greatest chances across the northern half of the CWA However, rainfall totals remain light with HRRR and NBM have medium to high probabilities (50-70%) of seeing measurable rain north of I-94, but seeing 24hr QPF exceeding 0.1" remains low (<40%). Main window for this activity will be between 23z-05z.

Otherwise, with the strong LLJ and tighter pressure gradient as the associated low tracks across southeastern Manitoba/western Ontario, southwesterly winds will remain elevated. Also will bring much warmer overnight temps with lows in the mid 40s to low 50s.

Tuesday will be another warm day with breezy southerly winds as the main upper-level trough swings and drags a cold front across the region. While there will upper-level dynamics aligning with deep layer shear exceeding 50 kt, min SBCAPE around a few hundreds of J/kg along with some CAMs hinting at a few showers/storms developing, any chances remain more scattered in nature. Dewpoints will be tough to crack the lower 40F and PWATs will remain less the 0.7", thus moisture will be limited. However if we are able to get a thunderstorm to develop and grow upscale, they could potential produced localized gusty winds given the steep low-level lapse rates indicated in the model soundings along with some small hail. Will need to monitor trends over the coming hours, but the latest 18z HRRR is favoring the drier solution.

Nevertheless, a cold front will slide through Tuesday afternoon/evening with a secondary backdoor cold front sliding southward overnight Tuesday. The secondary front will bring the colder airmass into southern WI Tuesday night dropping lows into 30s. Given the CAA, the is a higher potential (60-80% chance)
to see frost/freeze conditions Tuesday night/early Wednesday morning.

Wagner

LONG TERM
Issued 341 PM CDT Mon Apr 22 2024

Wednesday through Monday:

As we enter the middle of the week, dry weather returns to southern Wisconsin. Behind the exiting cold front Tuesday night, high pressure will build into the Great Lakes Region from the Northern Plains. This upper level ridge will mosey through the state Wednesday into Thursday. Eventually exiting Thursday evening/night.
Wednesday will likely (70-80%) be the coldest day of the week with cold air advection kicking in behind the cold front. High temperatures Wednesday are expected to be in the 40s along Lake Michigan to mid 50s further inland. With gusty east to northeast winds coming off Lake Michigan, the cool air will have an easier time traveling inland which will keep more than just the immediate lakeshore cool. These cool conditions will be short lived as the upper level ridge moves east of the state bringing a return of warm air advection and clear skies to allow for more diurnal heating.
Thursday through Sunday will remain warm with temperatures expected to be in the 60s to 70s.

For the end of the week and through the weekend, there will be multiple chances for rain. Two separate troughs will advect out of the Southwest CONUS toward the Great Lakes Region in the extended.
The first of which is expected to advance toward Wisconsin Friday into Saturday. There are still some discrepancies between timing and location on this low pressure system. The GFS has been a bit faster and further north than the EURO and Canadian. Regardless of track there is higher confidence (50% or greater) that southern Wisconsin will get rain regardless of the track issues. The shifts that are occuring are relatively small with the upper level trough and mid level low pressure systems traversing the state, however the track will play a roll in the duration, amount of rainfall expected, and potential for any strong/severe thunderstorms.

As this system pulls out of the Great Lakes Region, right on its heels will be that second trough advecting out of the southwestern CONUS. This will bring the state another round of rainfall Sunday into Monday. There is quiet a bit of uncertainty with this system especially in regards to timing and location. This has created an extended forecast dominated by POPs of roughly 40-90%. As the weekend gets closer expect the timing for rain/storms to firm up a bit with the added detail. Definitely a rainy weekend, but not necessarily a washout at this point.

Patterson

AVIATION
Issued 937 PM CDT Mon Apr 22 2024

Scattered showers will continue this evening, coming to an end west to east by around midnight. At least partial clearing is expected overnight, with sct to bkn mid and high level clouds lingering. Breezy southerly winds will persist overnight as the low level jet moves overhead. Winds are expected to be strong enough aloft for low level winds shear late evening and overnight, despite the continued breezy conditions at the surface.

Scattered showers will be possible again Tuesday afternoon into early evening. Could be a few rumbles of thunder with this round as well. Breezy southwest to west winds tomorrow will become north west to north by early/mid evening behind a passing cold front.

DDV

MARINE
Issued 341 PM CDT Mon Apr 22 2024

Southwesterly winds have picked up over Lake Michigan as low pressure tracks across southeastern Manitoba/western Ontario overnight. Gusty winds will persist overnight into Tuesday as the surface low and cold front slide into the Upper Great Lakes through Tuesday afternoon. Small craft conditions expected during this time and cannot rule out a brief gale force gust at times. Also could see a few thunderstorms with the frontal passage as well. Expect gusty winds to turn more northerly through the afternoon from north to south. While cannot rule out a few gusts to gale force at times, especially Tuesday evening, potential and coverage remains low enough to hold back on any headlines at this time. Winds will begin to lighten up Wednesday through the second half of the week as high pressure builds down across the upper Great Lakes. Then southerly winds increase heading into the weekend as another storm system approaches.

Wagner

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM
Small Craft Advisory
LMZ643-LMZ644-LMZ645-LMZ646 until 7 PM Wednesday.

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