FXUS63 KGRB 150508 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1208 AM CDT Wed Apr 15 2026 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - Flooding continues in some urban, low-lying, and poor drainage areas across central and east-central Wisconsin through late tonight. - Minor to moderate river flooding is ongoing or forecast to occur on several area rivers. Expect many rivers to rise this week due to additional rain and runoff from Upper Michigan, with the greatest impacts expected on the Menominee River, where some locations may see major flooding during the mid to late part of the week. - Additional rounds of rain and thunderstorms are expected at times Wednesday through this weekend. && .DISCUSSION... Issued at 405 PM CDT Tue Apr 14 2026 Severe Storm Potential Late This Afternoon/Evening...A surface boundary (warm front) was orientated west-east just on the southern edge of the forecast area this afternoon. This boundary will gradually lift north into the southern portion of the forecast area this afternoon due to persistent southwesterly flow, ushering in moist, unstable air. The atmosphere will be primed across the southern portion of the forecast area with steep mid- level lapse rates, 50-60 kts of deep-layer shear, and around 1000 to 2000 J/kg of MUCAPE, supporting the potential for severe thunderstorms with large hail and damaging winds being the main hazards. However, just along the southern portion of the forecast area, CAMs and current surface analysis indicate some surface- based CAPE of 1000 to 1500 J/kg, effective SRH of 100-200 m2/s2, and steep low-level lapse rates, favoring a tornado threat in addition to the large hail and damaging winds. After coordination with SPC and surrounding offices, a Tornado Watch was issued for Waushara, Winnebago, Calumet, and Manitowoc counties until 10 PM tonight (Tuesday). Depending on how far north the boundary lifts, the tornado threat could reach into the next northern tier of counties. PWATs of 1-1.25 inches are forecast with these storms, causing a risk of at least additional flooding in urban, low- lying, and poor drainage areas, and a risk of flash flooding, especially where ongoing flooding impacts from Monday evening's storms remain. Possible Dense Fog Tonight...Following this evening's showers and thunderstorms, models indicate low-level moisture/stratus expanding into the area from the northeast. Given the low-level moisture and the ongoing low-level moisture over the area already, fog is likely going to occur. Models indicate visibilities may drop as low as 1/4 mile at times. A Dense Fog Advisory may be needed late tonight into Wednesday morning. Rain and Thunderstorms Wednesday-Monday...A surface low is forecast to lift into the Upper Mississippi Valley Wednesday into Thursday, bringing another round of rain and possible thunderstorms. MUCAPE of 200-400 J/kg looks to stay confined to the southern portions of the forecast area leaving a marginal risk for severe storms. Although rainfall amounts with this system look less impressive, any additional rainfall will still add to the ongoing flooding risk. A more dynamic trough is slated to impact the region late Friday into early Saturday, bringing additional widespread rainfall and storms. The northward extent of greater instability is somewhat uncertain with this system, impacting severe weather potential, but this will be something to watch in the coming days. Cooler air will trail behind this system, which may bring potential for snow across the far north on Saturday associated with the wrap-around moisture from the main low pressure system. && .AVIATION...for 06Z TAF Issuance Issued at 1205 AM CDT Wed Apr 15 2026 A stationary warm front remains positioned across the southern Fox Valley tonight. Scattered showers and isolated thunderstorms continue to impact northeast Wisconsin, primarily affecting KGRB, KATW, and KMTW through 08z. While the severe threat has diminished, brief reductions in visibility remain possible in any stronger cells. Following the departure of the precipitation, low-level moisture and stratus will expand across the region from the northeast. Flight conditions are expected to deteriorate rapidly to LIFR or VLIFR at all terminals overnight. Dense fog is anticipated over areas which received rain this evening, from central to east- central WI, with visibilities frequently dropping to 1/2SM or less. Confidence is high in these poor flight conditions persisting through at least 14z-15z Wednesday. Conditions will be slow to improve Wednesday morning. Fog and ceilings are forecast to lift more quickly over north-central Wisconsin (KRHI) than areas further south and east. Persistent MVFR ceilings are expected to linger through Wednesday afternoon across east-central Wisconsin, while KMTW may remain IFR for much of the day due to onshore flow. Another round of showers and thunderstorms is possible Wednesday night as additional energy moves into central Wisconsin, likely leading to a return of IFR conditions. && .HYDROLOGY... Issued at 405 PM CDT Tue Apr 14 2026 Despite no precipitation falling from this morning through early this afternoon, several locations across east-central WI were still dealing with flooding impacts where a maximum of 4.5-5.5 inches of rainfall fell from Monday's storms along an axis from Stevens Point to Bonduel, with a more broad swath of 1-3" south of HWY 8. An additional 0.5-1" of rain is expected across east- central WI this afternoon/evening, which will only exacerbate flooding concerns. Runoff from snow melt in Upper Michigan is also still expected to bring moderate to possibly major flooding on the Menominee River, especially during the mid to late part of the week. If you live near a river or stream, keep a close eye on water levels this week and monitor the latest Flood Warnings from the National Weather Service in Green Bay. && .GRB WATCHES/WARNINGS/ADVISORIES... Flood Watch until 7 AM CDT this morning for WIZ022-035>040-045- 048>050. && $$ DISCUSSION.....Kruk AVIATION.......MPC HYDROLOGY......Kruk