


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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837 FXUS63 KGRB 141950 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 250 PM CDT Mon Jul 14 2025 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Near-surface Canadian wildfire smoke is most likely over north- central WI through this evening. - Isolated showers and storms into early this evening. Scattered storms across northern WI late Tuesday afternoon into Tuesday night. Severe storms are possible far north central during the evening. Heavy rain also a risk. - Staying active with showers and a chance of storms Wednesday through Wednesday evening. Marginal risk of severe storms and heavy rainfall. Lingering scattered showers on Thursday, then dry for the end of the week. - Very warm and humid through Wednesday. Heat index values peaking in the lower 90s on Tuesday. Cooler and less humid late this week. && .DISCUSSION... Issued at 250 PM CDT Mon Jul 14 2025 Lingering smoke and thunderstorm chances and impacts are main focus points through midweek. Smoke: Today opened up with smoke farther south than was projected by HRRR/RAP smoke models last 24 hours, with many 5-7 mile vsby observed as far south as east-central MN into central WI. Even with the trends, visibility is not as low as yesterday and air quality is not as poor. Using the HRRR/RAP guidance as guide, but adjusting it, kept mention of patchy to areas of smoke. Most of the smoke later this afternoon into early this evening that could result in poorer air quality will be advected into far northern WI from northeast MN. This is where an Air Quality Advisory is in effect until 6 pm this evening, though only for Vilas County in our forecast area. Still looks like approaching frontal boundary over northern Plains and associated southwest flow ahead of it will eventually push the smoke to the north later tonight. Thunderstorm Chances and Impacts: Weak ripple showing up as scattered mid clouds shifting across northern WI along with weak wind shift will interact with MLCAPES over 1000J/kg to yield a few showers and perhaps a storm over especially far northeast WI this afternoon. No severe weather is expected. 12z PWAT on GRB sounding not even reaching the 75th percentile, so heavy rain seems like minimal threat as well, so long as storms keep moving at decent clip. Next chance for storms arrives late Tuesday as weak low pressure system pushes cold front from South Dakota to northern Minnesota. Strongest dynamics and wind energy aloft stays to the north which could limit organization and coverage, but there is a modest low- level jet intersecting the approaching front along with building instability as MLCAPEs reach 1500-2000J/kg over northwest WI during peak heating on Tuesday afternoon. Ahead of the front, effective shear is 25-35 kts which could support loosely organized storms, marginal severe risk with damaging wind gusts and small hail. Storm motions will be slower and PWATs will be over 1.75 inches which is well over the 90th percentile for the day. Warm cloud depths of 11-12kft are also favorable for warm rain processes. Overall it seems there could be a few storms late Tuesday over northwest WI that could produce damaging wind gusts and heavy rain. Eventually these will reach north-central WI early to mid Tuesday evening, though the severe risk should wane later into the evening as instability lowers and the low-level jet weakens. Heavy rain could still be an issue though with training storms over the north even into the overnight hours as the showers and storms shift east. WPC is highlighting northern WI for a Slight Risk of Excessive Rainfall. Later Tuesday night, shortwave over the Dakotas, maybe combining forcing with convectively generated shortwave out of storms that form on Tuesday afternoon over the Dakotas, will be shifting toward Upper Mississippi Valley. By daybreak Wednesday, the wave (kind of looking like an MCV in some of the guidance) will be running into what looks to be a complex diffuse frontal boundary somewhere over Wisconsin. Gradient of MLCAPE will be over or just south of the forecast area. Storms motions will be from southwest to northeast, so either by track of upstream complex of storms and/or developing storms ahead of shortwave, portions of area will see showers and storms on Wednesday. Severe potential will depend on how far building instability extends from the south, but given the presence of decently defined wave, think there is a potential. Latest SPC Day3 outlook has shifted the risk farther north, which looks good based on location of instability gradient. Heavy rain a continual issue with PWATs at least as high, if not higher, pooling ahead of approaching system and along the frontal boundary. NBM probabilities for rainfall can be on the low side when dealing with qpf with summertime storms, but 90th percentile which offers reasonable high-end scenario, shows 24hr total QPF for Wednesday and Wednesday night up to 1.75 inches over central and north-central WI with amounts over 2 inches not that far off to the west. Trends on this have come up over the last couple days. As Tuesday night looks more active mainly over the north, Wednesday into Wednesday evening are looking more active over much more of the area, including the urban areas of the Fox Valley which can be more prone to flooding. WPC shows all our area in a Marginal Risk for Excessive Rainfall. Temperatures and Heat Impacts Through Wednesday: Ahead of the approaching front which brings the more active weather late Tuesday through Wednesday, a very warm and humid airmass will surge into the region. Highs reach the mid 80s today, with readings nearing 90 on Tuesday. These temps combined with dewpoints 69F to 71F will yield heat index values into at least the lower 90s, if not mid 90s locally on Tuesday. Nighttime lows will only drop into the mid to upper 60s tonight, with most areas staying in the upper 60s to near 70 on Tuesday night just ahead of the front. Exception Tuesday night will be over the far north with more rain cooled air. Though it will remain muggy on Wednesday, more clouds and chances for showers and storms will keep highs in the mid 80s. Overall, heat index values into Wednesday will remain below criteria and there is no enhanced signal showing up when looking at the heat in terms of relation to this time of year climatology and/or duration of the heat (NWS HeatRisk output). Thus, no headlines issued for the heat at this time. Outlook: Frontal boundary shifts east by Thursday. Could still be a few lingering showers on Thursday morning, but risk of severe and heavy rain will be east of the area by that time as high pressure settles over the western Great Lakes. The high will bring cooler and less humid, more comfortable conditions to the region. The break in the weather will not last long as west-northwest flow aloft and series of weak fronts will result in chances for showers and at least isolated storms. Its early, but at this point, greater instability is forecast to stay mainly west and south of the area, keeping severe potential on the lower side for the coming weekend. Temperatures look seasonable with highs upper 70s to lower 80s and lows in the mid 50s to lower 60s. && .AVIATION...for 18Z TAF Issuance Issued at 1255 PM CDT Mon Jul 14 2025 Smoke from Canadian wildfires will impact AUW/CWA/RHI the rest of the afternoon. Scattered cu will occur, but will mainly be VFR. A few showers and storms developing over northern WI may graze central WI TAF sites, but coverage is very isolated so will leave it out for now. Approaching front may lead to scattered low clouds late tonight and around daybreak on Tuesday over northern WI, including at RHI. Rest of Tuesday will feature scattered VFR cu. Pop-up showers and storms are expected late Tuesday afternoon into Tuesday evening over northwest WI. Some showers and storms may eventually reach into northern WI Tuesday evening, including at RHI. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA AVIATION.......JLA