


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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409 FXUS63 KGRB 041907 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 207 PM CDT Fri Jul 4 2025 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Although most of the region will remain dry, isolated thunderstorms are possible through early this evening. A strong storm is possible that could produce small hail and gusty winds. - A better chance for widespread rain and storms will occur Saturday afternoon and Saturday evening. A few severe storms are possible that could produce damaging wind gusts. Heavy rainfall is also possible that could produce localized urban and low- lying flooding. - Very warm and muggy conditions will result in heat indices in the middle to upper 90s over central and northeast Wisconsin through early this evening, and over eastern Wisconsin on Saturday. Those with outdoor plans should take precautions for the heat. && .DISCUSSION... Issued at 207 PM CDT Fri Jul 4 2025 Satellite imagery indicates quite a bit of clouds across the area, which has held down temperatures across much of the region this afternoon. Despite a mid level ridge building across the western Great Lakes region, there are some CAMs that develop some isolated showers and thunderstorms late this afternoon into early this evening. Given the abundant instability (2-3 J/g) across the region along with an uncapped atmosphere and a plethora of outflow boundaries will keep a low chance (20 percent) of showers and thunderstorms across the region late this afternoon and into early this evening. Despite the small chance for showers and thunderstorms, there is a high confidence that much of the area will be dry for fireworks events this evening. Dangerous Heat Potential: Clouds have not really dissipated across much of the region today, which has kept temperatures in check for the most part. There are some areas across central Wisconsin and the Fox Valley which have soared with some clearing, which could easily spread to the rest of the area if the clouds can dissipate. Any areas that clear out will easily hit the lower to middle 90s for heat index values and should stay below headline criteria. Heat indices on Saturday are expected to hit the lower to middle 90s across east-central, northeast, and portions of central Wisconsin ahead of an approaching cold front. These hot temperatures should then tumble with the cold front or any showers and thunderstorms that develop ahead of the front. Severe/Heavy Rain Potential Saturday and Saturday night: A positively tilted shortwave trough will push a weak low pressure system northeast across the northern Plains and western Lake Superior on Saturday. A cold front will then slide east across north-central Wisconsin on Saturday afternoon and through the rest of the area Saturday night. The chance of showers and thunderstorms will rapidly increase during the early to middle afternoon hours over north-central WI before spreading to northeast Wisconsin late in the afternoon or evening. An unstable airmass (1-2 J/g of instability) will remain present ahead of the front. Deep layer shear of 25-30 kts and precipitable water values near the climatological max will be present ahead of the front. Deep warm cloud depths and downdraft capes to 800 j/kg will support a heavy rain/damaging wind threat. HREF Probability Match Mean indicate potential for 1-3" of rain over north-central and central Wisconsin Saturday afternoon into the early evening and increased rainfall amounts from the NBM. There will be a marginal threat for severe weather Saturday afternoon and evening given the aforementioned instability and shear with damaging winds the primary threat. The threat for severe weather will wane later in the evening and into the overnight hours with the loss of instability as the event transitions to mainly a heavy rain threat. Low MBE velocities (under 10 kts) and high warm cloud depths (up to 13,000 ft) will lead to efficient rainfall production and potential for training cells. While latest rainfall forecasts are not impressive, heavy rainfall ingredients tell a different story so will continue to advertise in the HWO. Storms will taper off to light rain overnight before ending late Saturday night or Sunday morning. Some localized flooding will be possible given the potential for heavy rainfall, especially for areas with recent heavy rainfall like portions of central Wisconsin. Rest of the forecast: Behind the front, temperatures will return closer to normal through the end of the next week. Despite a reprieve from the warm and humid airmass, a shortwave will be moving across the region during the Monday night/Tuesday timeframe, which could interact with diurnal instability upwards of 1000 j/kg for a chance of strong thunderstorms. This will be the next period to watch. && .AVIATION...for 18Z TAF Issuance Issued at 1159 AM CDT Fri Jul 4 2025 Debris and convective clouds will affect the TAF sites at times through this evening. While some clouds will clock in at MVFR at times, the majority of the time should stay at VFR. Isolated showers and thunderstorms will be possible through the early evening; however, confidence in coverage and timing is too low to include in this set of TAFs. An approaching cold front will bring showers and thunderstorms from west to east on Saturday, only affecting KRHI in this TAF issuance but will include in the rest of the TAF sites with subsequent issuances. Low level wind shear will increase over north-central and central Wisconsin tonight, and dissipate Saturday morning. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski AVIATION.......Kurimski