050 FXUS63 KGRB 020314 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1014 PM CDT Sun Jun 1 2025 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - Elevated wildfire smoke will lead to hazy skies through Tuesday night. The smoke may reach the surface at times from Monday afternoon through Tuesday night, but confidence is low regarding how widespread the smoke will be. - Elevated fire weather conditions continue across mainly northern WI through early this evening and also on Monday due to warm temperatures and low humidity. - Increasing south winds and building waves will result in hazardous conditions for small craft on Lake Michigan from Monday afternoon through Tuesday night. Dangerous swimming conditions will also develop on Lake Michigan beaches from Monday afternoon into Tuesday Night. - Showers/thunderstorms are expected Tuesday into Tuesday night. There is a marginal risk of excessive rainfall (urban flooding) and severe thunderstorms. && .DISCUSSION... Issued at 215 PM CDT Sun Jun 1 2025 Short Term...Tonight...Monday...and Monday Night The latest RAP analysis and satellite/radar imagery show surface high pressure stretching across the western Great Lakes and Ohio Valley early this afternoon. Other than hazy sunshine from smoke aloft in the atmosphere, skies are clear across the region. Looking upstream, lower visibilities reside across eastern North Dakota to central Iowa where smoke is reaching the surface. The next cold front is moving east across eastern Montana and due to move into the region on Tuesday. Forecast concerns revolve around near surface smoke potential and thunderstorm potential through Monday night. Surface Smoke Potential: While hazy skies will continue due to smoke aloft through Monday night, potential for near surface smoke doesn`t return to north-central WI until late tonight or Monday morning and eastern WI on Monday afternoon or evening. It seems like the potential for greatest impacts would occur late Monday afternoon into Monday night, but this is highly uncertain. Indications would suggest that the most likely impacts would be patchy at this time. So added patchy smoke to the forecast. Thunderstorm Potential: Warm advection will increase tonight across the western Great Lakes. Due to abundant dry air across the region, chances for rain will remain over the Lake Superior and northern Upper Peninsula where saturation and lift are more robust. The front will advance into the northern Mississippi Valley on Monday and into northwest Wisconsin on Monday night. Forecast soundings remain quite dry on Monday across northeast WI, so kept the area dry. But increasing large-scale ascent and moisture will bring a chance of rain into north-central WI after midnight on Monday night. No severe weather is expected. Temperatures: Will be trending warmer over the next 36 hours. Remained on the cold side of guidance tonight due to light winds and mostly clear skies, but no threat of frost with lows in the 40s and 50s. Highs on Monday will be in the 80s away from Lake Michigan. Fire Weather: Elevated fire weather conditions will continue through early evening over north-central and far northeast WI where minimum humidities will bottom out in the 20-30% range. After good humidity recovery tonight, warming temps combined with gusty winds to 20 kts and minimum afternoon humidities around 30% will lead to elevated fire weather conditions on Monday. Coordination with the DNR revealed they are concern about areas along and north of Hwy 8 (Rhinelander to Iron Mountain), which are on the verge of green up. Will pass along to mid-shift to issue a SPS for Monday. Long Term...Tuesday Through Sunday Focus in this part of the forecast remains on the weather impacts from Monday night through Tuesday night when a potent cold front moves across the region. Potential impacts include excessive rainfall and severe weather from thunderstorms, high waves, dangerous currents on Lake Michigan. Thunderstorm potential: Height falls across the northern Plains will push a strong cold front across the region on Tuesday. Timing of the front has changed little over the past 24 hours, reaching north-central Wisconsin around midday and eastern WI in the afternoon. Decent moisture convergence, mid-level fgen, and high precipitable water values 200% of normal will accompany the front, which will lead to a high chance of rain (greater than 80%) across the region. While not excessive, instability of 500 to 1000 j/kg will lead to a chance of thunderstorms. Most guidance paints a picture of the heaviest precip would lie post-frontal. Therefore expect precip to arrive in the morning over north-central WI and end of northeast WI by late Tue night. Severe Weather and Excessive Rainfall Potential: Despite favorable dynamics from a strong and broad low level jet, QG forcing from the upper trough, and convergence along the front, severe weather chances remain difficult to decipher. This is mainly due to uncertainty with surface heating and relatively warm temperatures aloft leading to poor mid-level lapse rates (less than 6 C/km). Cloud cover and light precip ahead of the front could make it difficult for low levels to destabilize with the warm temps aloft and forecast soundings indicate a narrow, skinny cape profile. Modifying a NAM forecast sounding at 18z sounding over GRB for a 81/65 surface parcel indicates cape of about 1300 j/kg. That seems more like a high end scenario if there is good solar insolation. Cape from 500-1000 j/kg seems more realistic, like the SREF indicates. Paired with 30-40 kts of deep layer shear, and can see a low end severe threat developing, which could become more significant if the warm sector ahead of the front is clear. Given the wind fields aloft, seems like strong winds would be a greater threat rather than hail. Eastern WI also appears to have a higher risk than central WI due to later arrival of the front and low precip potential early in the day. Conditions will also be favorable for heavy rainfall on Tuesday and Tuesday night. High freezing levels around 14 kft, precipitable water values 200% of normal, low level winds parallel to the front, and skinny instability profiles support potential for heavy rainfall. Probabilities indicate widespread precip from 0.50" to 1.50" is most likely (25-75 percentiles). Flooding concerns increase if precip amounts could reach above 1.50". For now, this looks like more of an isolated threat given low confidence of training thunderstorms. High Waves and Dangerous Current Potential: South winds will increase on Monday and remain gusty and times on Tuesday until the cold front passes. Gusts from 20-30 kts will be possible on the Bay and Lake, leading to poor boating conditions. A Small Craft Advisory and a Beach Hazard statement has been issued for Lake Michigan as waves reach 5-8 ft. && .AVIATION...for 06Z TAF Issuance Issued at 1014 PM CDT Sun Jun 1 2025 Elevated wildfire smoke will continue to spread across the region through Tuesday. Some reductions to surface visibility are possible overnight and especially Monday afternoon/evening, as the HRRR/RAP/Canadian near-surface smoke forecasts all have patches/areas of surface smoke. Will continue to have 6SM FU across eastern WI sites where confidence is highest, but we may have to add other sites and/or lower VSBYs slightly. Otherwise, VFR conditions expected through the TAF period. Showers and embedded storms will approach central and north central WI around 06z Tuesday. South to southwest winds will stay under 10 kts overnight, then increase Monday morning and gust to around 20 kts by mid to late morning and continue through the afternoon. Some gusts over 15 kts will continue into Monday evening but reduced mixing will limit the higher gust potential. As a LLJ works into the area, LLWS will become a concern from west to east Monday night as winds at 2000 ft increase to 40-45 kts. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement from Monday afternoon through Tuesday evening for WIZ022-040-050. && $$ DISCUSSION.....MPC/MPC AVIATION.......Bersch