Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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999 FXUS63 KGRB 172351 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 651 PM CDT Mon Jun 17 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - There is a slight risk of severe storms across the region through this evening. The best chance of severe storms will be across parts of central and east-central WI, with large hail being the main threat. - There is a slight risk of excessive rainfall through this evening. There is a continued risk of excessive rainfall from Wednesday through Friday. - Well above average temperatures and humid conditions are expected Tuesday, with heat indices climbing into the 90s. Some locations in east-central and far northeast WI may see heat index values approaching 100. - Periodic thunderstorm chances will continue throughout much of the week. Strong storms and locally heavy rainfall may be possible. && .DISCUSSION... Issued at 444 PM CDT Mon Jun 17 2024 Short Term...Tonight and Tuesday Precipitation/Thunderstorm Potential: This afternoon`s surface analysis had a stalled cold front/outflow boundary situated east-west from Clintonville to Kewaunee. Thunderstorms developed along and southwest of the front in east- central WI where a healthy 2000-3000 J/kg of SBCAPE and dew points in the low 70s prevailed. This will leave a severe threat in east- central WI for the remainder of this afternoon with hail being the main threat. Torrential rainfall is also expected with these storms due to PWATs of 1.75 inches. The cold front is expected to gradually pivot and lift north as a warm front late this afternoon into this evening. This will allow the pool of instability to increase across central and east-central WI. While thunderstorms are expected to develop and spread into central WI and continue in east-central WI, the severe potential will gradually decrease as the evening goes on due to a lack in deep- layer shear and instability becoming elevated. A marginal hail threat will remain in place for the evening as a result. The showers and thunderstorms will shift north into north-central and far northeast WI late this evening and overnight before exiting WI into Upper MI by early Tuesday morning. With the front well to the north of the area, dry conditions are expected for the remainder of Tuesday. However, some guidance is indicating an embedded shortwave/MCV will lift north into southeastern WI and produce some light showers or thunderstorms in far eastern WI. Included some slight chance PoPs for thunderstorms in east-central WI for now. Temperatures/Winds: Warm and humid conditions are expected to continue overnight as the frontal boundary lifts north and low-level southerly flow continues. This will result in well above normal low temperatures ranging from the middle 60s to low 70s. The hot and muggy conditions will continue into Tuesday with high temperatures rising into the upper 80s and low 90s. With dew points expected to be in the low 70s, heat indices will soar into the 90s to near 100. The highest heat indices are expected in east-central and far northeast WI. Decided to hold off on a Heat Advisory with this forecast issuance, as there is some uncertainty with temperatures and dew points. Forecast soundings indicate afternoon mixing will occur and bring gusty south winds to the surface, with gusts to 30 to 35 mph. Long Term...Tuesday Night Through Monday An active pattern will persist through the majority of the extended with several rounds of rain and storms possible through mid-week. Some strong to severe storms will be possible across north-central Wisconsin Tuesday evening and overnight. Main threats with stronger storms would be gusty winds, hail, and locally heavy rainfall. Mid-level flow will then flatten out toward the end of the week, resulting in an active westerly flow regime across much of the Midwest. Tuesday evening storm chances... As a surface low passes across Ontario, additional storm chances will enter the forecast area Tuesday evening along a trailing cold front. Most medium-range model guidance keeps decent instability (between 2,500 and 3,000 J/kg CAPE) out ahead of the cold front through 00Z Wednesday. This would be enough to sustain convection into early Tuesday night due to lingering heat and humidity before storm activity gradually decreases overnight. Heavy rainfall and localized flooding will once again be a concern given a strong signal for 1.75" to 2" PWATs from central to north-central Wisconsin. Rest of the extended... Expect a brief dry period on Thursday as the cold front departs to the southeast, leaving an area of large-scale subsidence and weak high pressure in its wake. A more robust system will then trek across the upper Mississippi Valley to start the weekend, bringing another round of potentially strong storms Saturday into Sunday. It is too soon to determine severe potential. Additionally, models are struggling to handle how long the high pressure will stick around, and are thus disagreeing about precip timing this far out. Will continue to monitor as we get closer to the event. && .AVIATION...for 00Z TAF Issuance Issued at 651 PM CDT Mon Jun 17 2024 VFR conditions prevailed across the area early this evening, as the afternoon showers/storms exited/weakened across east-central WI. Attention turns to convection continuing to expand across west-central and central WI as instability slowly builds northward along/south of the stalled/slowly lifting north boundary across the area. These storms look to impact AUW/CWA and eventually RHI later today, with some MVFR and possibly IFR conditions in/around the stronger storms. Still some uncertainty on just how long the storms will last as instability slowly decreases through the night. VFR conditions are expected further south. Surface winds will remain under ~10 kts tonight, with LLWS expected overnight as winds at 2000 ft increase to around 30kts. It will be a hot and humid Tuesday, with VFR conditions expected. Breezy south winds are expected, gusting to 30 kts. A few higher gusts are possible during peak mixing. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kruk/Goodin AVIATION.......Bersch