Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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657 FXUS63 KGRB 181743 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1243 PM CDT Tue Jun 18 2024 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - Hot and humid weather is expected today, with heat indices in the low to mid 90s in most places. A few places in the Fox Valley and west of the bay could have heat indices in the upper 90s. It will be considerably cooler near the Lake Michigan shore. - Gusty south winds could create large waves and strong currents at Lake Michigan beaches this afternoon and tonight. A Beach Hazard Statement has been issued. - The gusty south winds will also create conditions hazardous to small craft on the lake and bay today and tonight. - Thunderstorms are likely in central and northcentral Wisconsin tonight, and in eastern Wisconsin Wednesday. Some storms could produce strong winds and torrential rains. && .DISCUSSION... Issued at 413 AM CDT Tue Jun 18 2024 Short Term...Today...Tonight...and Wednesday The surface warm front was approaching the Michigan border at 09z. Wisconsin will be in the warm sector of the surface low lifting north across the Plains states today. The models really do not show any significant upper air or surface feature to trigger thunderstorms today, though there is plenty of warmth and moisture in the atmosphere. There could be isolated storms this afternoon, perhaps along a lake breeze, but left them out due to low probability. Hot and humid weather is expected today, except near the lakeshore. Heat indices will be mostly in the low to mid 90s away from the lake, with a few places in the Fox Valley and west of the bay reaching the upper 90s. It will be much cooler near the Lake Michigan shore, with highs in the lower 70s but with a gusty wind. Thunderstorms will move into central and northcentral Wisconsin tonight as the cold front moves into northwest Wisconsin. A few storms with strong winds and torrential rain are possible. High dewpoints and clouds will make for a very mild night, with lows in the 70s in most places. Thunderstorms will arrive in eastern Wisconsin Wednesday as the cold front moves slow across the state. Highs will range from the middle 70s in northcentral Wisconsin to the low 80s in the Fox Valley. Long Term...Wednesday Night Through Monday An unsettled pattern is forecast to persist through much of the extended period with low to middle end PoPs (30-70%) progged for each day through Sunday. With the chance for successive rounds of showers and storms and anomalously high available moisture, minor flooding as well as rising levels on area rivers and streams looks to be the main impact through the extended period. Wednesday night through Sunday...A few showers and thunderstorms may linger across east-central WI into Wednesday night as a cold front departs the region. Expect mostly dry conditions across the rest of the region overnight into Thursday morning as cold air advection behind the front brings an area of widespread subsidence. This dry spell looks to be rather short lived as models show return flow bringing a surge of warm moist advection into the upper-Midwest. An upper-level right rear jet quad is progged to provided additional synoptic scale ascent during this period. The severe weather potential during this period looks rather low given weak instability and the lack of a more robust forcing mechanism. A developing low-level jet overnight Thursday into Friday morning may be able to sustain some isolated to scattered showers, but with nocturnal stabilization this may be another period during which the region could see a lull in the precipitation. The chances for widespread rain with embedded thunderstorms then increase Friday with another surge of warm moist air out ahead of a developing low pressure system. With PWATs forecast to approach 1.75-2 inches (near 99th percentile of climatology) periods of heavy rain fall will be possible, particularly along warm front which is forecast to set up across northern WI. The severe weather potential does increase Friday afternoon and evening compared to Thursday, especially across central WI where SBCAPE are forecast to reach 1000-1500 J/kg and effect shear values range from 25-30 kts. However, with widespread cloud cover expected and a lack of a clear cut forcing mechanism there are pitfalls that may hinder storm development during this period. As the axis of anomalously high available moisture and low pressure system continue to propagate across the region through Saturday periods of heavy rain are expected to continue. The best chance for severe weather during the extended period may come Saturday afternoon and evening as the attendant cold front sweeps across the region. There is a high level of uncertainly with the severe potential during this period, but currently long range guidance is showing upwards of 2000 J/kg MUCAPE and effect shear of 20-30 kts which could support some stronger to severe storms. Behind the cold front perception should become more scattered with areas of showers lingering into Sunday as the region remains in the cyclonic flow, but the threat to any severe weather Sunday looks minimal at this time. In terms of the flooding potential, long range ensembles are forecasting about 2-2.5 inches of QPF from Wednesday night through Sunday across the region. Locally higher amounts may be possible if heavier rainfall hits the same area multiple times. WPC has introduced a slight risk (15%) for excessive rainfall across northern WI and a marginal risk (5%) across central and east-central WI both Friday and Saturday. Rest of the extended...Long range ensembles are in decent agreement with a broad low amplitude ridging moving over the region Monday. Expect this ridge to bring a more prolonged period of dry and seasonal weather to start next week. Temperatures...While temperatures may trend a few degrees above normal each day during the extended there is only a minor risk of heat related impacts. && .AVIATION...for 18Z TAF Issuance Issued at 1243 PM CDT Tue Jun 18 2024 A mix of high-end MVFR/low-end VFR cu field across the region early this afternoon, but expect most cigs to be in the 3500- 5000 ft level for the rest of the afternoon into this evening. A cold front is forecast to slowly move into western WI later tonight and bring a chance of showers and thunderstorms into central WI. Cigs will lower into the MVFR range once the precipitation reaches the area and it is possible for a brief period of IFR conditions under any storms. Mainly MVFR conditions to persist through Wednesday morning as the cold front slides through the region and pulls up stationary over southern WI late in the day. There will still be a chance of showers and thunderstorms with the front in the vicinity, but the north should begin to dry out in the afternoon. In fact, cigs should return to the RHI/AUW/CWA TAF sites by the afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement through Wednesday morning for WIZ022-040- 050. && $$ DISCUSSION.....RDM/GK AVIATION.......Kallas