


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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972 FXUS63 KGRB 300358 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1058 PM CDT Sun Jun 29 2025 New Information added to update section .UPDATE... Issued at 1057 PM CDT Sun Jun 29 2025 Cold front is slowly shifting into northern WI. One last area of isolated showers and a few lightning strikes are noted near the front. May see a few more showers and non-severe storms, mainly north, for the rest of the night. Light winds and recent rainfall along with partial clearing could lead to fog later tonight. Fog will be most likely where rain occurred today, but have put a mention of patchy fog in all areas. && .KEY MESSAGES... - Slight chance of thunderstorms rest of tonight. Brief heavy downpours and gusty winds main hazards. - More scattered thunderstorms on Monday afternoon. Gusty winds and large hail are main hazards. - Temperatures will be near to above average this week. && .DISCUSSION... Issued at 139 PM CDT Sun Jun 29 2025 Short Term...Tonight and Monday The first band of thunderstorms exited northeast Wisconsin shortly after sunrise this morning. In the wake of the complex of storms, a hefty inversion was noted on the KMPX and KGRB soundings. This inversion and no real trigger has inhibited any storms from redeveloping during the late morning into the early afternoon. However, the KGRB sounding indicated a convective temperature of 87F at Green Bay. Forecast high temperatures near 90 are expected across central and northeast Wisconsin which should allow for convection to redevelop. The combination of heat and humidity, a cold front moving across the area combined with an upper level disturbance should trigger thunderstorm redevelopment during the mid to late afternoon and lingering through the evening. Bufkit soundings indicated 2,000 to 3,000 J/KG of CAPE to support strong or severe storms. 0-6km shear values are only around 20-25 knots, thus storms will be more pulsy in nature with damaging winds as the main threat. A few storms could produce hail up to one inch (quarters). Torrential rainfall is possible with rainfall rates of 1 to 2 inches per hour. The greatest risk of heavy rains is across northeast and east-central Wisconsin, including the Fox Valley. A new wrinkle in the complexities of summer forecasting is the 12Z NAM has come in dry for most of the area through 12z Monday. The previous run had 1 to 2 inches of rain across the Fox Valley. Current thinking is convection will develop across northeast and east-central Wisconsin where these locations will approach or reach the convective temperature. Also, boundaries from the outflow from this morning or lake breeze may aid in the initiation of convection. The main forcing mechanism late this afternoon and evening will be the 500mb impulse moving east across the state. This feature will be the main focus for convection as a band of storms moves across the area. Once the main feature exits the area around 1 am Monday morning, some lingering showers are still possible but will be isolated in nature. Long Term...Monday Night Through Sunday Monday severe storm chances... An mid-level trough will amplify as it approaches the Great Lakes Monday morning, with broad ridging over the Intermountain West and closed low off the west coast. This trough paired with favorable location under the right rear quad of an upper jet will be the main drivers for our storm chances late Monday morning through the afternoon. Current thinking is that best chances for convection popping along the front will be over east-central Wisconsin early Monday afternoon as instability (~1,000 J/kg SBCAPE) builds within deeper moisture and low-level lapse rates steepen to around 9C/km. Inverted-V soundings would suggest gusty/downburst winds as the primary threat. CAMs then hint at a scenario in which diurnally-driven storms develop behind the front Monday afternoon. With synoptic support provided by the aforementioned trough and jet streak, some stronger pulse storms would be within the realm of possibility during this time as well. Hail threat increases during this time as post-frontal temperatures lower both the freezing level and wet bulb zero heights (~7 to 9k ft). This would be further evidenced by elongated hodographs produced by 40 to 45 knot bulk shear. Rest of the week... Remainder of the week will be characterized by low confidence storm chances as northwest flow regime sets up along the leading periphery of persistent upper ridging. We will thus be afforded a brief break from showers and storms by around mid-week. Ridge rider activity then ramps up during the Thursday/Friday timeframe, resulting in the return of storm chances. However, resolvability of these features remains volatile; will therefore continue to carry low-end PoPs and slight chance thunder in the forecast. Otherwise, steady-state temperatures in the 70s and 80s prevail through the end of the work week. Any deviation to above/below average temperatures will likely hinge on FROPA timing and cloud cover. && .AVIATION...for 00Z TAF Issuance Issued at 707 PM CDT Sun Jun 29 2025 Showers and embedded thunder will continue to impact the Fox Valley to east-central WI early this evening. Brief drops to IFR are possible during the storms. Also, isolated showers and storms will track across far northern WI, but will stay mainly north of RHI. Otherwise, conditions will be VFR through late this evening. Patchy fog may occur overnight where rain was most widespread this afternoon. Have included TEMPO groups at GRB/ATW/MTW. Conditions generally VFR on Monday. However, a few pop-up showers and storms may occur during peak heating of the afternoon. Coverage too low to include now, but may need to add in later TAFs. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE.........JLA DISCUSSION.....Eckberg/Goodin AVIATION.......JLA