Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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775 FXUS63 KGRB 162145 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 445 PM CDT Sun Jun 16 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Thunderstorms are possible tonight. A few storms may become severe, especially over north-central Wisconsin. Large hail, gusty winds and heavy rainfall will be the main threats. - Well-above average temperatures are expected through Tuesday. Heat indices may reach the lower to middle 90s at times Monday and Tuesday across central, east-central, and portions of far northeast Wisconsin. - Periodic thunderstorm chances are possible through much of the upcoming week. Some strong storms and locally heavy rainfall may be possible at times. - There is a marginal risk of excessive rainfall across portions of north-central and central Wisconsin from tonight through Tuesday. This may lead to localized flash flooding and rapid rises in river levels. && .DISCUSSION... Issued at 445 PM CDT Sun Jun 16 2024 Short Term...Tonight and Monday Precipitation/Thunderstorm Potential: This afternoon`s surface analysis had a surface low pressure system located over central MN with its warm front extending over central WI. Conditions remained dry under partly to mostly cloudy skies this afternoon due to capping in place. However, thunderstorms began to develop at a triple point north of the surface low center in far northern MN. How these thunderstorms evolve with the movement of the surface low and its cold front over the next couple of hours will be the deciding factor for the forecast area to see thunderstorms. Based on the latest guidance, thunderstorms will remain tethered to the front and have it progged to sag southeast into north-central WI this evening. As the front reaches north-central WI, it will enter an area of 3000 J/kg of MUCAPE, steep mid-level lapse rates, and deep-layer shear of 30-35 kts. This will produce thunderstorms capable of large hail, gusty winds, and heavy rainfall. Confidence for severe storms decreases across the remainder of the forecast area as the front will move into an area where deep-layer shear is less supportive for long-lived storms. However, the potential for showers and thunderstorms will continue across the remainder of the forecast area through the night, but coverage will become scattered. Any showers or thunderstorms will also contain heavy rainfall as PWATs will remain between 1.50 and near 2 inches. The front is progged to settle somewhere across the central part of the state Monday morning. Another surface low will then move across the Central Plains and cause the front to lift north as a warm front. Additional showers and thunderstorms may develop along the warm front as a result, but where they develop is still in question due to the uncertainty where the front will stall over the state Monday morning. Limited PoPs to chance wording Monday afternoon because of this. Temperatures: Despite the cold front progged to move over the region, an abnormally warm airmass will remain over the area and keep above normal temperatures in the forecast. A mild night is expected with lows ranging from the low 60s to low 70s. Temperatures will climb into the 80s for most locations on Monday, in addition to dew points in the middle 60s to low 70s. This will make for another humid day with heat indices reaching into the low 90s for some locations across east-central WI Monday afternoon. Long Term...Monday Night Through Sunday Models are in good agreement with the placement of a strong upper high just off the mid-Atlantic states and an upper trough that extended from south-central Canada to the Pacific Northwest at the start of the period. The resultant southwest flow into WI will bring periodic chances for showers and thunderstorms as several shortwaves move across the area where plenty of moisture to reside. This upper high eventually weakens and shifts south, thus allowing for the upper trough to shift east and bring more rain chances to northeast WI next weekend. Temperatures will run above normal for much of the upcoming week, including humid conditions through Wednesday. Monday night and Tuesday... A warm front initially over central WI early Monday evening is forecast to gradually lift north into northern WI late evening and into Upper MI by daybreak. Expect showers/thunderstorms to accompany this front, thus highest pops to be placed over northern WI. PW values of at least 1.5 inches with dew points in the 60s, could bring locally heavy rain, so will need to watch for localized flooding across the north. On the flip side, parts of central and east-central WI may not see any rain, just a warm and muggy night in the warm sector. Min temperatures to range from the middle to upper 60s far north/near Lake MI, lower to middle 70s south. Northeast WI to reside in this warm sector on Tuesday with the warm front to the north and an approaching cold front into the Upper MS Valley. While no trigger is apparent, increasing instability with MUCAPES > 2K J/KG could kick off random thunderstorms during peak heating. The vast majority of the forecast area will be dry Tuesday and quite warm/humid. Look for max temperatures to be in the lower 80s along Lake MI, middle to upper 80s north and upper 80s to lower 90s south. Tuesday night and Wednesday... The cold front is progged to slowly move east and reach north- central to west-central WI by late Tuesday night. Even though the air mass will not be as unstable due to the loss of daytime heating, shear will be on the increase (25-35 knots). These factors, combined with lift from both the cold front and the right entrance region of the upper jet and hints of a mid-level shortwave moving northeast into the region all point to another round of showers and thunderstorms over the northwest half of WI. Right now, the strongest storms are expected to our west, but will need to watch the potential of stronger storms in later forecasts. Eastern WI should stay dry Tuesday night with min temperatures to range from the lower to middle 60s north-central WI, to the lower 70s east-central WI (cooler near Lake MI). This cold front will move into northeast WI on Wednesday, but the question becomes how far south and east this front can get before stalling as it encounters the mid-Atlantic upper high. As long as this front is is in our vicinity, we will have chances for additional showers and storms. More clouds, more rain and a wind shift to the west behind where the cold front passes will take temperatures down a bit with readings on Wednesday in the middle to upper 70s north- central, middle 80s east-central WI (inland from Lake MI). Wednesday night and Thursday... The nearly-stalled frontal boundary to remain parked over central (or southern) WI depending on which model you buy into. Either way, this boundary will be the focal point for more showers and storms Wednesday night and Thursday. PW values of 1.5 to 2.0 inches dictate that more heavy rains will be possible and depending on how much rain had fallen earlier in the week, flooding concerns (both urban and river) will need to be monitored. Max temperatures Thursday to be in the lower to middle 70s north/near Lake MI, upper 70s to lower 80s south. Thursday night and Friday... The frontal boundary to languish across WI through Friday, although there a signs that the boundary may lift north a bit into northern WI on Friday. Have no choice but to keep a chance of showers/thunderstorms in the forecast for both Thursday night and Friday. Max temperatures Friday to be in the middle to upper 70s north/near Lake MI, lower to middle 80s south. Friday night and Saturday... Precipitation chances may taper off a bit headed into next weekend, assuming the frontal boundary does become a warm front and lifts north of the forecast area. This would leave northeast WI in the warm sector and with plenty of moisture still over the region, cannot rule out pop-up showers/thunderstorms, especially on Saturday. Max temperatures to be in the middle to upper 70s north/near Lake MI, lower to middle 80s south. Saturday night and Sunday... By the latter half of the weekend, the Pacific Northwest upper trough to have traveled east and is forecast to be moving across the Upper MS Valley, accompanied by a cold front and more rain chances. Max temperatures for next Sunday to be in the middle to upper 70s north/lakeside, upper 70s to lower 80s south. && .AVIATION...for 18Z TAF Issuance Issued at 110 PM CDT Sun Jun 16 2024 Lingering showers over far eastern WI early this afternoon will continue to exit in the next couple hours. While VFR conditions will prevail in its wake across the east-central WI TAF sites through late this evening, MVFR cigs will prevail at the central and north-central WI TAF sites. Some clearing is also expected at times across the central and east-central WI TAF sites through this evening. A cold front is forecast to drop southeast into north-central WI sometime this evening and continue sagging southeast through the night. Low cigs/vsbys, showers, and thunderstorms are anticipated to accompany the front. However, guidance is struggling to agree on the timing of the frontal passage. Based on current guidance and trends, have the showers and storms moving through the RHI TAF site between 02z and 06z, central WI TAF sites around 03z to 06z, and the east-central WI TAF sites around 06z to 09z. Confidence in timing decreases as the front moves further southeast through the night. Additional showers and thunderstorms are possible on Monday, but will depend on where the cold front will stall out over the area. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement until 4 AM CDT Monday for WIZ022-040-050. && $$ DISCUSSION.....Kruk/Kallas AVIATION.......Kruk