FXUS63 KGRB 091817 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 117 PM CDT Thu Jul 9 2026 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Scattered showers and a few thunderstorms will come to an end by early this evening over parts of central and east-central Wisconsin. Severe storms are not expected. - Patchy to areas of ground fog are forecast to develop late tonight into Friday morning, which may result in localized travel impacts due to reduced visibilities. - Building heat and humidity early next week will bring a period of minor heat-related impacts, with heat index values forecast to rise into the middle to upper 90s on Monday and Tuesday. && .DISCUSSION... Issued at 116 PM CDT Thu Jul 9 2026 A weak surface cold front is currently draped across central and east-central Wisconsin early this afternoon, acting as the primary focus for scattered convective activity across the region. North of this boundary, high pressure and a much drier airmass are already filtering into northern Wisconsin. Looking at the broader synoptic setup, water vapor imagery reveals an intensifying mid- level ridge centered over the western United States. This ridge is forecast to amplify and expand northeastward toward the western Great Lakes over the weekend and into the early part of next week, becoming the main feature to impact the weather across north- central and northeast Wisconsin for the remainder of the forecast period. The near-term forecast through this evening centers on the scattered shower and isolated thunderstorm activity along the slow moving front. The latest RAP analysis and satellite/radar imagery show the boundary stretching from near Wisconsin Rapids to Appleton and Kewaunee. Despite widespread cloud cover, a reservoir of boundary layer moisture and surface temperatures in the middle to upper 70s are generating mixed-layer CAPE values in the 500 to 1000 J/kg range. This environment will continue to spark scattered showers and isolated storms through the late afternoon before the front fully sags south of the area. Given weak forcing, severe weather is not anticipated; however, high precipitable water values will allow any storm to produce heavy downpours and lightning. Most of the shower activity will quickly come to an end early this evening with the loss of diurnal heating. As the frontal boundary pushes south, focus turns toward fog potential late tonight. Drier air settling behind the front will mix out dewpoints into the 50s across far northern Wisconsin, thereby lowering the risk for dense fog. However, surface dewpoints will be slow to mix out across central and east-central Wisconsin this afternoon. Clearing skies and light winds under the building surface ridge will create optimal radiational cooling conditions, favoring the development of ground fog late tonight. The highest probability for dense fog resides across central Wisconsin, though east- central locations will likely see patchy fog as well. Any ground fog will burn off relatively early between 8 AM and 9 AM Friday, giving way to a fair-weather cumulus field by late morning. Friday afternoon will feature pleasant summer conditions across the region with highs in the low to mid 80s and comfortable humidity levels. For the extended period, the weather story is dominated by the arrival of the upper-level ridge and a subsequent warming trend. As the ridge builds closer over the weekend, a weak boundary is forecast to sag into northern Wisconsin, bringing a low 20 to 30 percent chance for scattered afternoon showers and thunderstorms on both Saturday and Sunday. By Monday and Tuesday, very warm temperatures aloft, with 700 mb temperatures climbing to 13C to 14C, will establish a strong capping inversion that will shut down precipitation chances. Projections of 925 mb and 850 mb temperatures support surface high temperatures expanding into the lower to middle 90s on both Monday and Tuesday. The NBM initialization shows dewpoints in the middle to upper 60s during this timeframe, which looks to be on the lower side of guidance. Bumped dewpoints up slight based on non-bias corrected data. This will yield widespread heat indices in the middle to upper 90s, bringing a threat for minor heat- related illnesses. A pattern shift toward the middle to end of next week is expected to break down the ridge and bring cooler relief. && .AVIATION...for 18Z TAF Issuance Issued at 1205 PM CDT Thu Jul 9 2026 A weak cold front is dropping south from roughly Wisconsin Rapids (ISW) to Appleton (ATW) late this morning. A mix of ceilings ranging from IFR to VFR exist along the front and across much of central, east-central, and far northeast WI. Skies are clearing across far northern WI as a drier airmass moves in the low levels. Widely scattered showers and isolated storms will be possible along and ahead of the boundary through 00Z. The IFR/MVFR ceilings are expected to gradually rise, but MVFR ceilings could persist through 20-22Z along the front. Brief downpours could drop visibilities to IFR in the heaviest shower activity. Skies are anticipated to clear tonight which will set up a favorable ground fog scenario. The most favored area for ground fog will be across central WI and parts of the Fox Valley where dewpoints will struggle to mix out this afternoon. LIFR/IFR flight conditions will be possible in the ground fog from 08-13Z Fri. Fair weather clouds are expected to build after the fog burns off later Fri morning. Light winds are expected over the TAF period. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....MPC AVIATION.......MPC