


Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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054 FXUS63 KGRB 231136 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 636 AM CDT Mon Jun 23 2025 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - The intense heat will come to an end from west to east today as a cold front, along with showers and thunderstorms spreads eastward across the area. The heat index will climb to around 100 degrees over northeast Wisconsin before the rain arrives. - Strong or severe storms are possible this afternoon into this evening with damaging winds and torrential rainfall the primary hazards. Localized flooding is possible. - Periodic chances of showers and thunderstorms will continue Tuesday into next weekend. It is too early to determine if or when any of the storms would become severe. - Locally heavy rainfall is possible at times on Wednesday and Thursday where probabilities of receiving over an inch is between 40-80%. Probabilities of receiving over 2 inches is 20-40% over central and east-central WI and less than 20 over the north. && .DISCUSSION... Issued at 349 AM CDT Mon Jun 23 2025 Short Term...Today...Tonight...and Tuesday 595+ dam 500mb ridge centered over the Ohio Valley persists through tonight. Meanwhile, a sharp trough over south central Canada shifts toward Hudson Bay, lowering heights over the western Great Lakes and pushing a cold front across the region. The front will bring an end to the heat and generate showers and storms this afternoon and evening. Some storms will be strong to severe, with damaging wind gusts and torrential rain shaping up to be the main hazards. Much cooler weather is expected behind the front on Tuesday. Last day of the heat...Deja vu but once again very warm this morning as 3 am temps are still in the mid 70s to around 80 over much of the area. Cold front pushing in from the west could lead to isolated showers and storms as early as this morning over the far north, but overall the front will be slow enough to allow for one more day of heat. The hottest temps in the lower 90s and heat indices around 100 will occur from the Fox Valley to far northeast WI and to the lakeshore, including Door County as southwest wind direction will keep lake cooling to a minimum all day today. No changes to heat headlines. Depending on how quick the showers and storms develop central, likely will be able to end the Heat Advisory there early. Heat indices all areas fall below 80 by late evening. Lows later tonight will fall into the 50s north, but will remain in the upper 60s to 70 from the Fox Valley to the lakeshore. Even though that is still warm, it will be nothing like the last few nights. Severe storms this afternoon and evening...Not a true uniform cold front passage as sfc front moves through late afternoon into early evening, while 925-850mb temp drop and wind shift occurs after midnight. There also is really not strong shortwave trough, just a gradually lowering of heights. This all adds up to limited pre- frontal effective shear, likely less than 30 kts, which could limit storm organization and longevity. Instead looking at more of a pulse-type environment as MLCAPEs are still at least 1500j/kg if not 2000-2500j/kg. Some CAPE in hail growth zone, but higher freezing levels and weaker shear would tend to favor non-severe hail sizes. Damaging wind potential is there with unidirectional flow and sfc-delta theta-e values well over 20 in the lowest 15kft, suggesting downdrafts could accelerate when stronger cores aloft develop. Low LCLs and outflow boundaries could lead to spin up, but 0-1km/0-3km helicity values up to 100 are not too favorable. Overall think wind is the main severe threat, supported by recent NCAR NN output as well with most favored time between 3-8 pm. Heavy rain parameters still look very favorable. PWATs rising up over 2 inches (exceeding the daily max for the day) along with warm cloud depths surging to 12-14kft and MBE vectors slowing to less than 5kt are concerning if there are training storms. Supported by hints from HREF probs over over 1"/hr, seems greatest risk for heavy rain would be across the more vulnerable urban areas of the Fox Valley. HREF/NBM probs for 1" and 2" of rain this afternoon through tonight stay mainly southwest of our southern cwa, lined up with slight risk of Excessive Rain from WPC. Yet, glance through available models does support narrow swaths of 1-2" QPF over areas generally south of highway 29. 1hr-3hr Flash Flood Guidance that are lowest over Fox Valley point to needing only 1-2" in 3hr to cause some issues, so this will need to be monitored later today along with severe potential. MUCH COOLER on Tuesday...Cold front fully moves through late tonight with nw winds after midnight shifting northeast on Tuesday morning. Northeast winds may gust to 10-20 mph for a time close to the bay and along Lake Michigan. Mostly cloudy skies expected and some post frontal showers and storms could develop south of highway 29, but better chances will be south. Highs will be much cooler, with readings reaching mainly low to mid 70s. Warmer exception of near 80 would be over central WI if there is more sun. Cooler exception will be near the immediate lakeshore where the onshore winds may keep temps in the mid to upper 60s. As they say, what a difference a day makes!. Long Term...Tuesday Night Through Sunday 500mb ridge across the southeast United States is expected to flatten some during the week, resulting in lower 500mb heights. However, the western Great Lakes region will be in the ring of fire with periodic chances of showers and thunderstorms from Tuesday into next weekend. The main focus for heavy rain is in the Wednesday and Thursday time frame. Still a lot of uncertainty in where the axis of heavy rain will set up, but current thinking is that central and east-central Wisconsin currently have the greatest chance of seeing the heaviest rainfall totals. Based on the NBM, the probabilities of receiving over an inch is between 40-80%. Probabilities of receiving over 2 inches is 20-40% over central and east-central WI and less than 20 over the north. Determining the risk of severe weather is difficult this far out, but current thinking is that the front will be south of the area which would lower the risk of severe weather. The ECMWF has been most consistent with timing of the heavy rain which would support at least two rounds if not three rounds of heavier rain from late Tuesday night into Thursday night. It will be much cooler compared to the last several days with highs in the 70s to lower 80s Tuesday through Thursday, warming into the 80s Friday into next weekend. && .AVIATION...for 12Z TAF Issuance Issued at 636 AM CDT Mon Jun 23 2025 LLWS of 40-45 KT is expected early with gusty southwest winds just off the surface. Isolated showers and storms over western WI will slowly fill in as the day progresses as a cold front moves in from the west. A line of showers and storms will shift northwest to southeast across the state this afternoon and evening. The storms should reach north- central Wisconsin late this morning through midday, central Wisconsin and northeast Wisconsin early afternoon, and east- central Wisconsin late Monday afternoon. The showers and thunderstorms will lower CIGs to MVFR at times, with MVFR conditions expected behind the cold front. Some storms could be strong to severe as they track through the area this afternoon and evening. The primary hazards will be wind gusts to 50 kts and torrential rain. Behind the front tonight, expect cigs to fall to IFR over east- central WI (GRB/ATW/MTW). && .GRB WATCHES/WARNINGS/ADVISORIES... Heat Advisory until noon CDT today for WIZ005-010-011-018-019. Heat Advisory until 7 PM CDT this evening for WIZ012-013-020>022- 030-031-035>040-045-048>050-073-074. Beach Hazards Statement through this evening for WIZ022-040-050. && $$ DISCUSSION.....JLA/Eckberg AVIATION.......JLA