739 FXUS63 KGRB 161937 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 237 PM CDT Thu May 16 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Thunderstorms are possible across the forecast area through early this evening. A few storms may become strong across central and east-central Wisconsin. Small hail and strong winds are the main hazards. - Patchy to areas of fog are expected overnight with clearing skies and light winds. The fog may reduce visibilities at times, making travel hazardous. - Isolated thunderstorms are possible Saturday, but most of the area will be dry during the day. Lightning and isolated wind gusts will be the main concern with any storms. - Next chances for widespread active weather will be in the region early next week. It's too early to determine severe potential. && .DISCUSSION... Issued at 237 PM CDT Thu May 16 2024 Short Term...Tonight and Friday An area of showers and thunderstorms is currently exiting the lakeshore counties with light showers continuing across north- central Wisconsin. Hi-res models develop another area of showers and thunderstorms with the occluded front as it sweeps through the area this afternoon into the early evening in an area of MUCAPEs currently building from southwest Wisconsin north to western Wisconsin. Although MUCAPEs are forecast to jump to 1000 to 2000 J/kg across central and east-central Wisconsin ahead of these showers and thunderstorms, this seems a bit generous given the extensive cloud cover, cool temperatures, and low dew points across the region. A more realistic instability forecast would be in the realm of 500 to 1000 J/kg or about half of the current model guidance. In addition, bulk shear late this afternoon into early this evening is expected to be modest at 20 to 30 knots. Most of the mesoscale models generally keep any thunderstorms in check as they track across the area late this afternoon into this evening; which makes sense given the relatively limited dynamics associated with the front itself and limited available shear. Any strong storms that do develop could contain small hail and gusty winds, but this should be the exception rather than the rule. Once the occluded front and showers/thunderstorms move off to the east, clearing skies and light winds should rule during the overnight hours. This will provide for ideal radiating conditions, when combined with the recent rainfall, should lead to patchy to areas of fog overnight. Although the models are targeting different areas for visibility reductions overnight, they generally agree that there will be fog somewhere across the area. Therefore, will introduce fog across the area overnight. Lows tonight are expected to range from the lower 40s across the north, to around 50 across east-central Wisconsin. A weak ridge of high pressure will track through the area on Friday, which should keep the area dry for much of the day. The only exception could be far north-central Wisconsin as a warm front develops across the northern Great Lakes on the backside of the departing high. Otherwise, Friday will be around 10 degrees above normal as highs range from the middle 70s across north- central, to 75 to 80 along and west of the Fox Valley, with 60s near the lakeshore. Long Term...Friday Night Through Thursday Precipitation trends remain the focus of the extended. However, with the Saturday forecast trending drier, attention now turns to the potential rain for early next week, which could be another more active pattern. Saturday...Unstable air near the surface coupled with the passage of weak cold air advection aloft will be the main two factors that could produce some scattered precipitation on Saturday. Instability values see CAPE get to around 600-900 J/kg in the afternoon as high temperatures head towards the upper 70s and lower 80s. However, to get precipitation the dewpoints will also need to be on the increase during this period, but this will be at odds with the increase mixing with some of the drier air aloft. All in all, the forecast is trending to just isolated precipitation associated with some pulsy storms but severe storms are not currently expected. Dry conditions then follow behind this for Sunday. Early next week...The mean pattern will see broad ridging over eastern CONUS while an upper low sets up over southern Alberta and Saskatchewan. For us, this means general southwesterly flow and a couple of rounds of active weather as a series of shortwaves crosses into the area. As of this forecast issuance, models have to come in to better agreement in the passage of two systems, one during the day Monday and the next Tuesday evening. That said, this type of pattern can be somewhat volatile in terms of timing systems this far out, so if you have plans early next week be prepared for changes in the details. && .AVIATION...for 18Z TAF Issuance Issued at 1212 PM CDT Thu May 16 2024 Showers and thunderstorms will track through the east-central Wisconsin TAF sites early this afternoon, with additional showers and thunderstorms possible later this afternoon into early this evening as an occluded front tracks through the region. Any remaining showers and thunderstorms will end from west to east during the afternoon and early evening as the occluded front moves to the east and high pressure builds in from the west. Flight conditions will likely vary from VFR where there isn't much shower or thunderstorm activity, to MVFR/IFR in shower and thunderstorm activity. Clearing skies are expected overnight along with light winds. This will provide ideal conditions for fog development given the recent rainfall. Therefore will put in low clouds and fog across the TAF sites overnight with IFR/LIFR conditions, with the fog expected to dissipate by 15Z Friday. VFR conditions are then expected after the fog lifts on Friday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski/Uhlmann AVIATION.......Kurimski