Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
401 FXUS63 KMKX 180501 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 1201 AM CDT Tue Aug 18 2026 .KEY MESSAGES... - Chance of showers and storms today; coverage remains uncertain. A few stronger storms with hail and gusty winds are possible in the mid to late afternoon. - Dry and pleasant conditions Wednesday through Thursday. Rain chances return Friday, but overall nice weather is expected for the weekend. && .SHORT TERM... Issued 1201 AM CDT Tue Aug 18 2026 Rest of Tonight through Wednesday: The storms in MN this evening are focused along the nose of the low level jet (LLJ). The jet will shift into WI overnight, veer to the west, and have a weakening trend; thus the storms will too. However, these diminishing showers could get a boost Tuesday morning over south central WI as low-level, moist, warm advection focuses over us. The RAP is showing a slight increase in CAPE (up to 500 j/kg) and modest bulk shear up to 40 kt during the morning hours (between 8 and noon). This would be enough forcing to justify general thunder. Coverage of these showers/storms is still uncertain due to them moving into an already-dry environment. A mid level shortwave trough and coincident right entrance region of an upper jet that is currently over southeast Montana will track into southern WI around midday Tuesday. This stronger synoptic forcing will give us a better environment for thunderstorms during the mid afternoon to early evening hours, but there is a lack of focus for these storms. There will have to be be very small-scale feature such as an outflow boundary or MCV that plays a role in where these storms pop. Depending on how much/little cloud cover lingers over southern WI during the day, we could build up to 1500 j/kg CAPE with continued bulk shear around 40 kt. This would be enough for a few near-severe gusts or small hail. Since precipitable water values are going to be increasing to around 1.5 inch by late afternoon, heavy rain with any storms is likely. The upper trough and slow-moving surface front will finally exit southern WI by Wednesday morning. Expect sunshine with diurnal cumulus clouds and highs in the upper 70s. Light winds under high pressure will allow for a weak lake breeze as well. With the dry air mass in place, Wed nt lows will drop into the mid 50s for inland areas. Cronce && .LONG TERM... Issued 1201 AM CDT Tue Aug 18 2026 Thursday through Monday: Northwest flow at 500 mb is generally expected across the Western Great Lakes region during this period, with a digging shortwave trough/low shifting through Lake Huron and southeast Ontario Saturday night into Sunday. Another digging shortwave trough may move southeast into the region early next week. Ensembles suggest that high pressure at the surface Thursday will push off to the southeast Thursday night into Friday, with low pressure shifting east southeast through a similar path to the digging shortwave trough later Friday/Friday night, then shifting southeast on Saturday. This should bring a cold front southeast through the area, with some low level warm air advection ahead of it. Forecast soundings are showing some tall skinny mean layer CAPE developing ahead of the front Friday afternoon, though deep layer bulk shear is modest at best. Ensemble members are generally showing measurable precipitation later Friday into Friday night, so will continue to mention chances for showers and thunderstorms in the forecast. Some of this could linger into Saturday if the frontal passage is a little slower, or the shortwave trough helps bring some scattered showers behind it. Ensembles suggest temperatures near seasonal normal values with dew points into the 60s Friday into Friday night ahead of the cold front. High pressure should then bring quiet weather for Saturday night into Sunday night or Monday, depending on when the next digging shortwave trough approaches the region from the northwest. Wood && .AVIATION... Issued 1201 AM CDT Tue Aug 18 2026 A line of diminishing thunderstorms might hold together as they get into south central WI around 12Z Tue. Scattered showers and a few weak thunderstorms are possible during the mid-late morning, but there is less certainty in these occurring now. With minor storm chances all day, I tried to pick a 4 hour window to include thunder and decided on the late afternoon to early evening time. Any storms during this time will be widely scattered and brief but would have gusty winds and heavy downpours. Cronce && .MARINE... Issued 1201 AM CDT Tue Aug 18 2026 A slow-moving low pressure trough of around 29.9 inches will slide across Lake Michigan during the day Tuesday. Winds will be predominantly westerly. A few storms are possible within the vicinity of the trough/front through Tuesday night. An isolated stronger storm with gusty winds and hail cannot be ruled out. High pressure of 30.0 inches will move through the western Great Lakes Wednesday through Thursday, with light and variable winds prevailing across the waters. The next thunderstorm chances arrive Friday afternoon and evening, when the next cold front is expected to move across Lake Michigan. Cronce && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && $$ Visit us at weather.gov/milwaukee Follow us on Facebook, X, and YouTube at: www.facebook.com/NWSMilwaukee www.x.com/NWSMilwaukee www.youtube.com/NWSMilwaukee