108 FXUS63 KGRB 291952 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 252 PM CDT Tue Oct 29 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Well above normal temperatures continue through Wednesday. Besides several record highs already set this afternoon, record highs will be possible again over many locations again on Wednesday. - There is potential for heavy rainfall and thunderstorms from Wednesday afternoon through Thursday morning. Localized urban flooding will be possible, especially where storm drains are clogged by fallen leaves. Isolated strong wind gusts will also be possible with any thunderstorms or heavier showers. - An extended period of hazardous boating conditions will continue through Thursday evening. && .DISCUSSION... Issued at 251 PM CDT Tue Oct 29 2024 Short Term...Tonight and Wednesday The latest RAP analysis and satellite/radar imagery show deep southwest flow across the western Great Lakes ahead of a potent trough centered over the intermountain west. At the surface, a warm front is lifting north across central Wisconsin where temperatures are in the middle and upper 70s south of the front, but remain only in the lower 70s north of the front. Not too far upstream, a cold front is draped from southwest Minnesota to far northwest Wisconsin early this afternoon. Skies are mostly clear south of the warm front, while partly to mostly cloudy conditions exist along the cold front and north of the warm front. Focus in this part of the forecast revolves around record temps and shower/thunderstorm trends. Tonight...While the warm front lifts north into the Upper Peninsula, the cold front will remain nearly stationary as a wave of low pressure travels along the boundary and into southern Minnesota. Strong southerly flow of 40-50 kts will transport increasing amounts of low level moisture northward across the region. This moisture will boost elevated instability over the course of the night. However, due to a large cap centered around 8000 ft, much of this instability exists well above the inversion, and therefore, chances of thunderstorms look relatively low. Furthermore, ample dry air exists in the mid-levels and consequently, convective allowing models have backed off of precip coverage tonight. Have therefore trended precip lower tonight. In terms of temps, very mild temperatures are forecast. Record high min temps range from the lower 50s to lower 60s on October 30. With lows forecast to range from the upper 50s to nearly upper 60s, most locations are expected to shatter their record high mins. Wednesday...The wave of low pressure will continue to track northeast across northwest Wisconsin and the Upper Peninsula of Michigan. This surface wave along with height falls aloft will give the cold front a push to the east and arrive over north- central Wisconsin by midday and central Wisconsin in the afternoon. With arrival of the front, rain chances will increase from northwest to southeast starting around midday in the north. While not that impressive, instability of 300-500 j/kg will be developing over northeast WI ahead of the front, but some capping will likely hold back convection until late in the afternoon. If thunderstorms develop, it will probably be close enough to peak heating to where gusty winds to 40 mph and small hail will be possible. Temperatures ahead of the front will be most favorable for record highs ie. the Fox Valley and lakeshore. Highs are forecast to range from the middle 60s in the north to middle 70s over the Fox Valley. Long Term...Wednesday Night Through Tuesday Main focus of the long term forecast revolves around a dynamic low pressure system that is progged to cross the region Wednesday night through Thursday. Periods of moderate to heavy rainfall along with isolated thunderstorms are expected as this moves across the area. Precipitation...WAA/f-gen driven rain is likely to be ongoing to start the long-term period as a closed upper-low progresses northeast across the northern Plains. Frontogenetic forcing is expected to strengthen late Wednesday night into Thursday morning just ahead of a slow moving cold front. Ample low and mid-level moisture will advect into the area ahead of the aforementioned cold front with PWATs forecast to reach 1.25-1.50", which would exceed the daily climatological max. The strong forcing and ample moisture will likely lead to efficient warm rain processes resulting in periods of heavy rain through Thursday morning. Most long-range ensembles members and deterministic models show the heavies band of rainfall developing from the WI/MN/IA tri-point through northeast WI. Rainfall should lighten up Thursday afternoon/evening as the strongest forcing exits the region, but scattered showers may persist as the cyclonic flow around the low lingers over the region. NBM probs show an 80-90% chance for greater than 1" of rain through Thursday evening for areas north and west of the Fox Valley, with a 40-60% chance in east-central WI. Locations in central and northeast WI, where the heaviest rain is expected, have a 40-60% chance for greater than 2". While most may welcome the rain given the on-going drought conditions there is a chance for minor urban and street flooding, especially if storm drains become clogged with fallen leaves. As 850 temps cool to -4 to -5C there is a chance for lingering showers to become a rain/snow mix then all snow across far north-central WI Thursday night into Friday morning. There also appears to be a brief window overnight where winds turn to the northwest which may help to induce some lake effect snow across northern Vilas County. Snowfall amounts are still widely variable, however, there is a decent signal (50-70% chance) that areas of north-central will see their first measurable snowfall of the year. Expect a return to dry weather for much of Friday and Saturday as a brief period of high pressure sets in over the region. The next chance for rain (40-60%) looks to come late Saturday into Sunday as a WAA regime and surge of Gulf moisture move over the region. At this point the risk for any thunderstorms during this time looks low. Winds...In addition to the rain, Thursday will be another breezy day across the region. With a tightening pressure gradient due to the passing surface low and winds just off the surface (2-3kft) around 35-40kts there will the potential for gusts to reach 25-35mph, strongest in the Fox Valley. Expect winds to weaken by Friday with calmer conditions expected for this weekend. && .AVIATION...for 18Z TAF Issuance Issued at 1132 AM CDT Tue Oct 29 2024 Late this morning, a cold front remains draped from southwest Minnesota to far northwest Wisconsin. VFR conditions prevail along the front with ceilings above 10 kft south of the Upper Peninsula border. A warm front is lifting north across central Wisconsin with only scattered cirrus south of the front. As the warm front continues to lift north, VFR conditions will prevail through the evening, although a scattered 5000 ft cloud deck may develop by late this afternoon over north-central WI and ahead of the cold front. This 5000 ft cloud deck is forecast to spread southeast according to forecast soundings. Dry air wedges in the column will like keep showers northwest of the region, and trended drier in this forecast. Ceilings will likely lower to MVFR over north-central on Wednesday morning. Gusty south winds will decouple early this evening, resulting prolonged low level wind shear through mid-Wednesday morning before the gusty winds aloft get transferred to the surface. && .MARINE... Issued at 251 PM CDT Tue Oct 29 2024 Will extend the Small Craft Advisory through Wednesday night, but it will likely need to be stretched out through Thursday evening. Gusts to 25 to 30 kts will be possible through much of the period, but stable conditions over the water should limit potential for gale force gusts. Waves will build to 5-9 feet on Lake Michigan and 3-6 feet on the bay. There may be a brief lull in the in winds over Green Bay on Wednesday night. But am reluctant to end small craft advisories given a quick wind shift to the northeast is expected. && .CLIMATE... Issued at 251 PM CDT Tue Oct 29 2024 Unseasonably warm air will push into the region, bringing record or near warmth through Wednesday (10/30). Several high and high minimum temperature records may be reached. Here is a look at the record and forecast highs for the GRB climate sites: Green Bay Date Record High Forecast High ------------------------------------------------------ 10/30 75 (1901) 77* On record, the latest 80 degree temperature during the fall occurred on Oct 23, 1899 (81F). Rhinelander Date Record High Forecast High ------------------------------------------------------ 10/30 79 (1950) 70 Wausau Date Record High Forecast High ------------------------------------------------------ 10/30 78 (1950) 73 On record, the latest 80 degree reading during the fall occurred on Oct 27, 1927 (80F). * Record high temperature forecasted. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....MPC/GK AVIATION.......MPC MARINE.........MPC CLIMATE........MPC