Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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277 FXUS63 KGRB 211915 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 215 PM CDT Fri Jun 21 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Several rounds of thunderstorms with heavy rain are likely across central and east-central Wisconsin through Saturday evening. The heavy rain could result in flash flooding, especially in urban areas. A Flood Watch for flash flooding is in effect through early Saturday evening along and south of Highway 29. - Strong to severe thunderstorms are possible across central and east-central Wisconsin Saturday afternoon and evening. Damaging winds, a few tornadoes and torrential rainfall will be the primary threats. - Additional strong to severe thunderstorms are possible Monday night into Tuesday evening. && .DISCUSSION... Issued at 210 PM CDT Fri Jun 21 2024 Short Term...Tonight and Saturday Several rounds of showers and thunderstorms are expected across the region through Saturday as a warm front slowly lifts north across the western Great Lakes region. Although the CAMs models aren`t in great agreement regarding exact timing and placement of this activity, there seems to be some consensus that another round will track east through the area later this afternoon into early this evening, then again Saturday morning, and yet again Saturday afternoon. The initial rounds should not be surface based, which will limit the severe weather potential. However, moderate to heavy rain is possible from these rounds of rainfall into the early part of the weekend. Although the first rounds of convection are not expected to be severe, the third round Saturday afternoon could be problematic based on where the warm front ends up. There are some indications the warm front could lift as far north as southern portions of central and east- central Wisconsin, which would mean an increased threat for severe weather as model soundings are quite impressive. Specifically, SBCAPEs could be as high as 1-2 J/g with 0-1 km SRH values of 300 to 600 and Supercell Composite numbers of 3 to 6. There will be quite a bit of instability and low level helicity near the warm front, which will mean an increased threat for wind damage and tornadoes given the curved hodographs. Large hail will not be as big of a threat given the skinny CAPE profiles in the hail growth zone and wet-bulb zero heights of 12-14k ft. That being said, if the warm front ends up being further south due to the convection pushing the front further south, the severe weather threat across our area would be de minimis. Long Term...Saturday Night Through Friday The main forecast concerns revolve around thunderstorm and severe weather threats Saturday evening and Monday night through Tuesday evening. Models show low pressure and an associated warm front moving through EC WI Saturday evening, along with a potential severe weather and heavy rainfall threat. There is some concern about the degree of instability that will be present, as earlier convection could hold the front just south of the area. If everything comes together there could be a damaging wind/tornado/flooding threat in east central WI during the early evening. Short-wave energy moving through northern WI will also support continued showers and isolated storms there. Although Sunday still looks like the overall better weekend day, a short-wave moving through during the afternoon and early evening is expected to generate scattered showers and a few thunderstorms. After a brief break in the precipitation Sunday night into Monday, a warm front will bring a chance of storms back into the area Monday night. Substantial instability will develop across the forecast area later Monday night into Tuesday. Strong to severe elevated storms are possible later Monday night, with surface based storms possible ahead of a cold front Tuesday into Tuesday evening. Mainly low-impact weather expected for the latter half of the work week. && .AVIATION...for 18Z TAF Issuance Issued at 1158 AM CDT Fri Jun 21 2024 Periods of showers and thunderstorms are expected during the TAF period as a warm front slowly lifts north from northern Illinois. After this first round of thunderstorms moves through early this afternoon, additional thunderstorm timing is problematic as CAMs models each have a different solution. Most of the models seems to be honing in on additional thunderstorms moving in later this afternoon and again sometime Saturday morning. Conditions are expected to fall to MVFR and eventually IFR as low level moisture and showers increase across the region. Significant rain is possible at times, with moderate to heavy showers. && .HYDROLOGY... Issued at 210 PM CDT Fri Jun 21 2024 Rainfall reports from this initial batch of thunderstorms that moved through this morning and early this afternoon indicate that anywhere from 0.70 to around 1 inch of rain fell from this activity. Several more rounds of rainfall are expected later this afternoon through Saturday, each round possibly producing 0.50 to 1 inch of rain, for a total of 1 to 3 inches with locally higher amounts possible. The highest amounts appear to be across central and east-central Wisconsin where the heaviest rains will likely hit these areas several times. Therefore, will issue a Flood Watch for central and east-central Wisconsin through Saturday. && .GRB WATCHES/WARNINGS/ADVISORIES... Flood Watch through Saturday evening for WIZ030-031-035>040-045- 048>050. && $$ DISCUSSION.....Kurimski/Kieckbusch AVIATION.......Kurimski HYDROLOGY......Kurimski