136 FXUS63 KMKX 200339 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 1039 PM CDT Thu Jun 19 2025 .KEY MESSAGES... - A thunderstorm complex developing over Minnesota overnight is expected to spread into south central Wisconsin Friday morning, but severe storms are not anticipated. - Hot and humid conditions are expected Saturday through Monday. Maximum heat indices of 100 to 105 degrees are forecast each day. Highest confidence in reaching 105 degree heat index in southeast WI so an Extreme Heat Warning is in effect there. && .UPDATE... Issued 1032 PM CDT Thu Jun 19 2025 A couple chances for additional scattered shower and thunderstorm activity tonight into Friday morning. Could see the ongoing thunderstorm activity southeast of Eau Claire continue to develop and track southeastward into our CWA within the next couple of hours. If a storm or two can tap into the elevated MLCAPE, cannot rule out seeing some hail possibly up to quarter sized. Otherwise the complex of storms up across west central MN and the Dakotas are progged to continue to develop overnight and congeal into an MCS. 00z CAMs prog this complex to track southeastward across southern MN/IA before pushing into the Upper Mississippi River Valley around daybreak. Better thermodynamics look to remain to the west of southern WI and models hint at a downward trend as it moves into WI. However cannot rule out storm reinvigorating as it slides across the area through late Friday morning as things try to recover. Overall the timing of this activity moving through during the morning will limit an additional development later in the afternoon/evening, thus limiting severe potential. If things do happen to weaken more before pushing through (in opposition to the model trends) and the environment can recover, then cannot rule out an afternoon/evening round of activity. Wagner && .SHORT TERM... Issued 352 PM CDT Thu Jun 19 2025 Tonight and Friday: An area of showers and thunderstorms (that rolled in from a weak storm complex that developed over northwest WI this morning) is now tracking through southeast Wisconsin. Efficient mixing is causing gusty winds up to 40 mph with these low-topped storms. Another area of storms is developing in the Eau Claire area and that may also clip our northern counties from the Dells to Sheboygan during the late evening. The next complex is expected to develop along the nose of the low level jet over southeast MN early Friday morning, around 3 or 4 AM. That complex will track east-southeast into southwest and south central WI Friday morning. The strongest portion of that complex should remain just to the west of our forecast area, toward northeast IA and maybe Grant County WI. Nevertheless, with the low level jet leaning over into southern WI, any more robust thunderstorm could mix down winds up to 50 mph for areas west of I-94. Instability will be lacking, but shear will be strong Friday morning. Gusty southwest winds are expected Friday from mid morning through mid afternoon due to mixing. Temperatures will be similar to today with highs in the lower 80s. The 12Z GFS tries to light up showers and storms along the warm front that will be sliding northward through southern WI Friday night. This is the only model that is doing this so far. There is a better chance of storms over northern WI. Cronce && .LONG TERM... Issued 352 PM CDT Thu Jun 19 2025 Saturday through Thursday: The weekend looks hot and humid. A 500 mb 594 dm ridge is expected to develop across the SErn CONUS on Saturday and expand to include most of the eastern half of the country by Sunday. A surface high will also be centered across the SE US. To the NW, a surface boundary will linger through the weekend from the central High Plains to the Red River Valley. Gusty SWrly winds will exist between these features which will pump warm and humid air into the area through the weekend. 850mb temps are forecast to climb to the mid 20s on Saturday and Sunday which equates to surface temps in the low/mid 90s. Areas of far SE WI will see downsloping from the Kettle Moraine which boosts temps a few degrees resulting in weekend high temps in the mid/upper 90s. The SW winds will also transport a much more humid air mass into the region with dew points in the low/mid 70s through the weekend. The combination of air temps in the 90s and dew points in the 70s will produce peak afternoon heat index values near 100 degrees each afternoon. Areas of far SE WI may see heat index values approach 105 degrees due to the expected warmer air temps. In addition to the hot daytime temps, overnight lows are forecast to remain quite warm in the mid/upper 70s both Saturday and Sunday night`s. It is possible that record high and/or record warm low temperature records are set over the weekend. Record high temps are more likely at MKE than MSN, but warm low temp records are possible at both locations. With the gusty southwest winds, dewpoints may be lowered a bit, which would affect the heat index values. We took this into account by blending the NBM with CONSMOS, so dewpoints are conservative around 70 near the lakeshore each afternoon. We have the highest confidence in southeast WI reaching heat index values of 105 each afternoon Sat-Mon, and it is also a vulnerable area that is used to having the lake breeze cool them down. Without a lake breeze these days, this heat will feel very extreme. Therefore, issued an Extreme Heat Watch for Milwaukee, Racine and Kenosha Counties Sat afternoon through late Monday afternoon. Additional counties may need to be added. A Heat Advisory will be needed elsewhere each day. The upper level pattern begins to break down on Monday, but a hot and humid day is once again expected with similar temp and heat index conditions as from the weekend. The surface boundary is forecast to approach from the NW late in the day representing the next chance for showers and storms. The upper level flow becomes more zonal by the middle of next week which would imply the boundary will no have much of a push north or south. The forecast for the remainder of the week depends on the position of that boundary. This could result in multiple rounds of showers and storms, but it is far too early to attempt to pin down timing or location. Locations south of boundary will remain warm and humid. BMiller/Cronce && .AVIATION... Issued 1032 PM CDT Thu Jun 19 2025 Overall tonight should remain VFR with light and variable winds. However, showers and storms southeast of Eau Claire may work their way into southern WI bring a brief window for showers and possible a thunderstorm, mainly for MSN/JVL. But confidence remains low. Otherwise, ongoing activity upstream in SD/ND/MN continues to congeal and shift southeastward overnight into Friday morning bring more widespread showers with some embedded thunderstorms mid Friday morning. This activity will spread eastward late Friday morning, but is progged to weaken and dissipate/push out by early afternoon. With any shower and thunderstorm activity, can expect to see a brief window of lower visibility and ceilings approaching MVFR level. Otherwise, generally expecting VFR conditions into Friday with increasing southwesterly winds. Wagner && .MARINE... Issued 352 PM CDT Thu Jun 19 2025 Gusty southwest winds are expected Friday late morning through early afternoon over land areas, and could impact the NSH area within the first mile of the lakeshore. Not enough confidence in Small Craft conditions being met, so no advisory at this time. There is higher confidence for Small Craft Advisory criteria to be met along the lakeshore Saturday and Sunday with gusty southwest winds. Cronce && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && $$ Visit us at weather.gov/milwaukee Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSMilwaukee www.twitter.com/NWSMilwaukee www.youtube.com/NWSMilwaukee