Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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643 FXUS63 KGRB 211825 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 125 PM CDT Sat Sep 21 2024 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - Unseasonably warm temperatures will continue today, then will return closer to normal Sunday into middle of next week before trending above normal again late next week. - There is a Marginal risk of severe storms with strong winds and hail across central and north-central WI late this afternoon and early this evening. - A period of gusty north winds and building waves Sunday into Monday morning will likely bring a period of hazardous conditions to small craft on Green Bay and Lake Michigan. && .DISCUSSION... Issued at 352 AM CDT Sat Sep 21 2024 Short Term...Today...Tonight...and Sunday Main forecast concerns will be assessing chances for showers/storms this afternoon into Sunday, the potential for strong or possibly severe storms and fog early today. The long stretch of well above normal temps continues today then cooler air arrives on Sunday. Severe Weather Potential & Shower/Storm Chances: Areas of elevated showers and storms have developed across MN and western/northern WI during the early morning hours, associated with steep mid-level lapse rates of 7.5-8.0 C/km, FGEN/WAA and the nose of a low-level jet. This area should continue to develop/percolate through the morning hours, with some of the activity making it to central and north central WI. Then as the nocturnal effects wane after sunrise, most of the showers/storms should come to an end. This will set the stage for the next round of showers and storms ahead of a cold front and shortwave. Still some uncertainty on timing and degree of instability, along with whether a weak capping inversion will limit activity, but looking like isolated to scattered showers/storms should arrive after 4pm central and north central WI. The broken line of storms will track southeast across the area during the late afternoon and evening hours. MUCAPE of 500-1500 J/kg, SBCAPE up to ~600 J/kg, deep layer shear of 30-40 knots, and 0- 3 km helicities of 150-250 support potential for a few strong to marginally severe storms with gusty winds and hail. Inverted-V signatures on soundings will promote gusty winds of 30-45 mph making it down to the surface, with some higher gusts, along with some hail, possible in the stronger storms. SPC has kept the Marginal risk west of a Rhinelander to Wautoma line, where the best instability and shear will reside late this afternoon and early evening (4-10pm). Decreasing instability and a strengthening low-level inversion will end the severe threat in the late evening, but the showers/storms will continue to spread southeast across the area, but uncertainty remains on just how widespread the activity will be. On Sunday, showers and a few storms are expected, especially in the morning as the front slowly completes its trek across the area. The last of the showers look to end by around sunset over far east central WI. Most spots will see under a half inch of rain, but localized higher amounts will be possible as locally heavy rain will be possible with the storms as PWATs climb to ~1.5" ahead of the front. The fairly quick moving nature of the storms will limit any flooding threat. Fog Potential/Trends: Recent rain, low-level moisture, light winds, clear skies and a low-level inversion has allowed from some patchy ground to form early this morning, mainly across northern and central WI. The patchy fog will continue through a little after sunrise, then will burn off/mix out. Temperatures: The stretch of well above normal temps will last one more day, as 925mb temps remain between 20-23C today. Clouds will hinder temps at times, especially this afternoon over the west/north, with possible showers/storms knocking down temps over north central WI. Won`t make much change to the highs, with most spots in the upper 70s to mid 80s. If we get a little more sun over the east, some upper 80s will be possible. Lows tonight will range from the upper 40s across north central WI to the upper 50s and low 60s in east central WI. A return to near normal temps arrive on Sunday as 925mb temps fall to between 10-14C and more clouds/precip, with highs in the 60s to around 70. Long Term...Sunday Night Through Friday A fairly tranquil period is expected. 500mb trough moving across the western Great Lakes region could bring a small chance of showers to east-central Wisconsin Monday night and Tuesday. Once the trough exits the area, building 500mb ridge late next week will result in dry conditions with above normal temperatures returning. For Sunday night, some patchy fog is possible north and west of the Fox Valley. Patchy frost is also possible across north- central and far northeast Wisconsin, especially near the Upper Michigan border. Patchy frost may also be possible Monday night across north-central Wisconsin. Latest numerical guidance is suggesting that high temperatures by the end of next week could run as much as 10 to 15 degrees above normal. Also, the Climate Prediction Center 8-14 Day Outlook is calling for greater chances of above normal temperatures continuing. && .AVIATION...for 18Z TAF Issuance Issued at 125 PM CDT Sat Sep 21 2024 VFR conditions prevailed across the area early this afternoon, as high clouds spread from the west from thunderstorms in western/west-central WI. Given all guidance does not have this area of showers and thunderstorms at this time, based the early hours of the TAFs on satellite and radar trends. Therefore, confidence is not high for the evolution of these showers and storms into this afternoon. Based on trends, anticipate the central WI TAF sites to see the best chance for thunderstorms this afternoon, with a lower chance at the RHI TAF site. These storms will struggle to move eastward this afternoon due to a lack in instability. However, anticipate these storms to remain with VFR cigs. Another chance for thunderstorms, with MVFR cigs, will move across the area from northwest to southeast, in association with a cold front, mainly between 00z and 06z Sunday. A few of these storms may be strong and produce hail and gusty winds, especially at the central and north-central WI TAF sites. Additional showers are possible in east-central WI Sunday morning. Decided to include ceilings lowering after midnight as models continue to show this solution. Winds will turn north after midnight into Sunday morning following the cold front. Gusts up to 20 kts will be possible for Sunday morning. && .MARINE... Issued at 352 AM CDT Sat Sep 21 2024 A period of hazardous conditions for small craft looks to develop on Sunday as gusty north winds develop behind a cold front. Could have a burst of stronger winds close to/behind the front as the initial surge of cold air advection arrives, then a little lull during the day, with stronger winds arriving aloft later in the afternoon which should mix down. Gusts to 25-30 kt are expected with waves generally building to 2-5 ft, highest toward the open waters of Lake Michigan and south of Chambers Island on the bay. Winds and waves will slowly decrease Monday morning. && .CLIMATE... Issued at 352 AM CDT Sat Sep 21 2024 The record stretch of consecutive days in the 80s during September continues at Green Bay and Wausau. High temperatures are expected to climb into the 80s today, so one more day will be added to the record. The streak will end today as much cooler air works into the region tonight and Sunday. At Green Bay, the high on Friday was 85 degrees, marking the 10th consecutive day in the 80s. The old September record of consecutive days in the 80s was 9 days set from September 16-24, 1891 and from September 1-9, 1933. At Wausau, the high Friday was 80 degrees, marking the 10th consecutive day in the 80s.The old September record of consecutive days in the 80s was 8 days set from September 4-11, 1978 and from September 17-24, 1908. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Bersch/Eckberg AVIATION.......Kruk MARINE.........Bersch CLIMATE........Eckberg