FXUS63 KGRB 151134 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 634 AM CDT Wed Apr 15 2026 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Another round of showers and thunderstorms are expected late this afternoon and evening. 1+ inch hail is the main severe hazard. - Additional rainfall will continue to exacerbate any ongoing flooding. If thunderstorms train over areas that have seen multiple inches of rain the last two days flash flooding would be likely. - 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. - Addtioanl rounds of rain and thunderstorms are expected Friday through this weekend. && .DISCUSSION... Issued at 240 AM CDT Wed Apr 15 2026 Short Term...Today...Tonight...and Thursday Fog this morning.. Dense fog with visibilities as low as 1/4 mile has spread across much of the lake and bayshore counties overnight, while dense fog is more patchy further west. The coverage of fog will continue to expand over the next few hours before fog starts to dissipate. Fog will be quicker to burn off across central WI compared to eastern and northern WI. Areas along the lake and bay as well as far northern WI may see fog linger into the early afternoon. Rain and Thunderstorm Chances Today... A stalled frontal boundary snaking from east-central WI back toward central IA will continue to spur on isolated showers this morning, however, most locations should remain dry. Chance for precipitation increases again this afternoon as a surface low lifts into the region. Main concern with this next round of precipitation is how additional rainfall will exacerbate ongoing flooding or lead to new flood concerns given soils are saturated and rivers and streams continue to run high. REFS LPMM shows another 0.25-0.5" of rain with this system through Thursday morning south of a Stevens Point to to Marinette line. However, if more persistent convection is able to develop over this area could see rainfall totals closer to REFS 90th percentiles of 1-1.5" in localized areas. If those higher end amounts do play out in areas with ongoing flooding or areas that have had flooding issues over the past two days flash flooding would be likely. The severe storm threat late this afternoon and evening is more muted compared to the past two days. Forecast soundings do show elevated MUCAPEs of 200-400 J/kg late this afternoon along with 50-60 kts of unidirectional 0-6km shear. This may lead to a marginal risk for 1+ inch hail across part of central and east- central WI. The risk for damaging wind gusts or tornados is very low given a stable boundary layer. Long Term...Thursday Night Through Tuesday The latest ensemble means continue to indicate a break in this incredibly wet pattern is forecast this weekend into the middle of next week. Until this time range, the final system to move through the region arrives late Friday afternoon and departs on Saturday. A brief lull in the rainfall is likely on Thursday night into Friday morning as the region will reside between systems. However, that changes by late Friday afternoon when a 35 to 45 kt low level jet advects precipitable water values up to the 99 percentile into the northern Mississippi Valley. Models show precipitation is forecast into expand on Friday afternoon as large scale ascent and moisture increases over the course of the day. Instability increases between 400-700 j/kg on Friday night when the surface low pressure and pwat axis moves through. Because instability peaks at night, the severe risk will likely be muted somewhat due to a capping inversion. But given the wind profiles and some instability, small hail and gusty winds in excess of 40 mph appear possible. Greater concern revolves around rainfall and flooding potential. Probabilities for a 1/2 inch of rain ranges from 40-60% while probabilities for 1 inch of rain ranges from 5-20%. So, most likely looking at precipitation of 1/2 to 1 inch of rain, with locally higher amounts where thunderstorms occur. Given the moisture laded soils, the most flood prone areas may see renewed flooding potential. After the system passes, much colder air arrives on Saturday. A change over of precip from rain to snow remains possible. The probability of a 1/2 inch of snow over Vilas county ranges from 20 to 40% on Saturday, so little to no impacts are expected. But gusty winds in excess of 30 mph appear possible. Thereafter, high pressure will move across the region late in the weekend into early next week. This should result in a period of little to no precipitation into Wednesday. && .AVIATION...for 12Z TAF Issuance Issued at 634 AM CDT Wed Apr 15 2026 Blanket LIFR conditions across the region early this morning as low status and dense fog have develop across much of the region overnight. Expect vsbys to gradually improve this morning. Cigs across central and northern WI are expected to rise mid to late morning and become MVFR, however, further east persistent easterly flow off the lake along with ample low-level moisture will keep LIFR/IFR cigs across east-central WI for much of the day. Isolated showers may lift into central and east-central WI this morning, but should have little aviation impact. Showers are expected to become more scattered this afternoon along with the development of a few isolated thunderstorms south of a ISW to GRB line. Any thunderstorms will be capable of producing heavier rain and lower vsbys as well as hail up to 1". Thunderstorm active will wane this evening, but scatter showers may linger across the region through Thursday morning as a surface low exits the region. Along with the rain overnight expect another round of IFR/LIFR status and areas of fog overnight into Thursday morning. && .HYDROLOGY... Issued at 240 AM CDT Wed Apr 15 2026 Widespread flooding continues across parts of central and east- central WI, where flood warning remain in place, due to multiple rounds of thunderstorms that have produced 3 to 6 inches of rain over the last 48 hours. Extensive road closure remain where the heaviest rain has fallen. Multiple dams have also been over topped at times due to high flows on rivers and streams. Runoff from snow melt in Upper Michigan is also still expected to bring moderate to 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... Dense Fog Advisory until 10 AM CDT this morning for WIZ011>013- 019>022-030-031-035>040-045-048>050-073-074. && $$ DISCUSSION.....GK/MPC AVIATION.......GK HYDROLOGY......GK