


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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681 FXUS63 KGRB 291838 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 138 PM CDT Sun Jun 29 2025 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - Sub-severe wind gusts (40-50mph) are possible for a few hours early this morning as a line of storms moves across northern WI. - Scattered thunderstorms will likely re-develop this afternoon. These storms may pose a severe wind and hail threat through the evening. - Thunderstorms could bring locally heavy rainfall to the area this afternoon , with rainfall rates of 1 to 2 inches per hour resulting in localized flooding especially in urban areas. - Temperatures and humidity will trend back above average today, with near to above average temps continuing into next week. && .DISCUSSION... Issued at 232 AM CDT Sun Jun 29 2025 Mesoanalysis... A persistent MCV producing sub-severe wind gusts (40-50mph) is moving east across northern WI this morning. With a well established cold pool, favorable low-level shear orientation, and 1000-2000 J/kg MLCAPE this MCV should maintain its strength for a few more hours despite RAP analysis showing 200-300 MLCIN. Additionally a few pop-up cells have developed ahead of the MCV along a north/south oriented warm front that is draped across central WI. Will need to monitor any cell mergers for any possible QLCS type spin-ups. Convective active with this MCV should start to wane as it moves into northeast WI around daybreak where dew points are only in the low 60s. Afternoon/Evening Severe Weather Threat... The slower start to last nights convection over Minnesota has complicated this afternoon and evenings severe threat to some degree. Current thinking is that convective initiation will be focused along a remnant cold pool from this mornings convection as well as any differential heating boundaries that result from this mornings cloud cover. The cold pool is currently sagging southeast ward across northwest Wisconsin and eastern Minnesota and is progged to be draped from northeast to southwest WI by this afternoon. The primary driver of any thunderstorms this afternoon will be robust instability (SBCAPE 2000-3000 J/kg). This should result in rapidly developing updrafts capable of producing large hail and up to 60 mph wind gusts. However, with a relative lack of deep layer shear and disorganized hodographs updrafts should quickly cut off from the surface by their associated down draft. CAMs do show signs that clusters of cells may also grow upscale into a line segment which may also increase the severe wind threat ahead of any bowing segments. The severe threat should begin to wane this evening as instability decreases. Given the complexity of the environment today confidence remains relative low with the finer details of this event. In addition to severe weather threat there is a marginal risk for minor flooding today primarily if any back building or training storms develop over any urban areas. PWATS around 1.6" are near the 90th percentile for this time of year and warm cloud depths are over 13kft. This may result in periods of 1-2" hour rainfall rates. Monday`s Thunderstorm Potential... Broad ascent related to an upper level trough and jet streak moving over the state Monday may set the stage for another round of scattered thunderstorms. Thermodynamics are forecast to be favorable for a few marginally severe storms as SBCAPE build to 750-1000 J/kg and low-level lapse rates steepen to 7-7.5 C/km ahead of an approaching cold front. 40-45kts of 0-6km shear will also be in place which may allow for some storms to become organized. Result is shallow inverted-v soundings and straight elongated hodographs which support strong wind gusts and up to 1" hail with an storms that do develop along or just ahead of the front late Monday morning through the afternoon. A few CAMs also indicate a few post-frontal storms may develop. With the cooler mid-level air behind the front these storms may also be capable of producing hail. Rest of the Week... Global ensembles show prevailing northwesterly upper level flow through the middle of the week as a ridge builds over the Canadian Prairie. This pattern should bring generally quiet weather to the region, however, any ridge riding short-waves that happen to coincide with peak diurnal heating could kick of a round of isolated to scattered showers or storms. The resolvability of these features is very low at the moment so kept NBM PoPs and thunder probs. Otherwise temperatures should remain relatively steady through the end of the week with highs in the middle 70s to 80s each day. && .AVIATION...for 18Z TAF Issuance Issued at 1228 PM CDT Sun Jun 29 2025 MVFR CIGS over portions of central and northeast Wisconsin will rise into the VFR category by mid afternoon. Otherwise, another round of thunderstorms are expected later this afternoon, arriving at KRHI/KAUW/KCWA after 22z until 02z. A few storms could develop near KGRB/KATW/KMTW around 21z, but the main storm activity is expected between 00z and 04z. Some of the storms could contain strong winds and hail along with blinding rain. Additional shower activity may linger for an hour or two after the main complex moves through the area. Otherwise, VFR conditions will prevail later tonight except for some patchy fog in a few spots from 09z-13z. The chances of showers and storms return tomorrow morning and continue into the afternoon. Gusty winds over 30 knots and hail will be possible with the stronger storms. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....GK AVIATION.......Eckberg