Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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527 FXUS63 KGRB 152341 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 641 PM CDT Sat Jun 15 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - A round of showers and thunderstorms is expected to move across the area this evening through late Sunday morning. Heavy rainfall is likely, especially north and west of the Fox Valley. High rainfall rates may result in localized flooding and ponding on roads. - Another round of thunderstorms is possible late Sunday afternoon into Sunday night. Some storms may become severe across central Wisconsin with damaging winds and hail as the main threats. - Well above average temperatures are expected Sunday through Tuesday. Heat indices may reach the mid 90s at times. - Periodic thunderstorm chances are possible through mid-week due to high heat and humidity. Some strong storms and locally heavy rainfall may be possible at times. && .DISCUSSION... Issued at 421 PM CDT Sat Jun 15 2024 Short Term...Tonight and Sunday Precipitation/Thunderstorm Potential: Upper-level ridging and a surface high will continue to depart the region late this afternoon into this evening and make way for widespread rainfall this evening through midday Sunday. Outside of a few light showers or sprinkles falling out of a 12k ft cloud deck this afternoon, an area of rain associated with an embedded shortwave and increasing f-gen and WAA, was gradually shifting into western WI this afternoon. This area of rain is expected to spread and lift northeast across the forecast area this evening through late this evening. Rainfall amounts during this time should stay confined to west and north of the Fox Valley with about 0.10 to 0.30 inches for most locations and up to 0.50 inches in far north-central WI. Thunderstorm potential during this time will be very low due to limited instability. A small lull in the rainfall is likely once the f-gen rain lifts northeast out of the region, however, an isolated shower cannot be ruled out before the next round of rain arrives from the west around 4am (09z) Sunday. Moderate to heavy rainfall is possible as it tracks east across the region due to support from a strong southerly LLJ (45 to 55 kts), low-level WAA, and PWATs of 1.50 to 1.75 inches. By midday Sunday, additional rainfall amounts of 0.25 to 0.75 inches are expected. Total rainfall amounts have decreased slightly from the previous forecast, but central and north-central WI will still see the highest total amounts, where locally higher amounts up to 1 inch are possible. Elevated instability will increase to a couple hundred J/kg Sunday morning and bring the potential for a few thunderstorms capable of some small hail, but severe weather is not expected. The rainfall will come to an end from west to east by early Sunday afternoon. The remainder of Sunday will be a challenge to determine when precip will occur or not occur as the surface warm front will be residing over the area. Despite SBCAPE increasing to 3k-4k J/kg Sunday afternoon, decided to go dry for the remainder of Sunday as forecast soundings indicate a cap will develop between 700-800mb and prevent thunderstorm develop. The first signs of the cap breaking are during Sunday evening. Temperatures: The southerly flow will bring warm, moist air to the region for Sunday. Sunday`s highs will be the first day will well above normal temperatures climbing into the middle to upper 80s. Additionally, humid conditions are also expected as dew points will rise into the upper 60s to low 70s, resulting in heat index values in the upper 80s to middle 90s Sunday afternoon. Long Term...Sunday Night Through Saturday Focus for the extended remains on an active pattern bringing several rounds of rain/storms to the forecast area followed by building heat and humidity through mid-week. Some strong to severe storms will be possible Sunday evening as a cold front sweeps across the area. Periodic chances for storms will then continue throughout the week as a high amplitude mid-level pattern brings persistent southwest flow to much of the Midwest, maximizing chances for diurnally-driven convection. This warm and moist ridging regime has the potential to bring heat indices up into the low to mid 90s across portions of central to east-central Wisconsin Monday and Tuesday. Sunday evening storm chances... Confidence is increasing in potential for strong storms Sunday evening as a fast-moving shortwave passes through the upper Mississippi Valley. Models continue to show strong instability (3,000 to 4,000+ J/kg CAPE) through Sunday evening as well as decent 0 to 6 km shear (25 to 30 knots). Damaging wind and hail would likely be the main threats with stronger storms. Current thinking is that it would be difficult to get severe hail due to the warm environment and wet bulb zero heights around 12,000 ft, although non-severe hail will definitely be possible. This being said, abundant moisture and an open Gulf will place a corridor of 1.75" PWATs across central and east-central Wisconsin, suggesting that any storms that do develop would be efficient rain producers. There is still some uncertainty regarding whether or not thunderstorm activity Sunday morning will affect how the warm front behaves later in the afternoon, which would consequently impact instability/storm re- development due to airmass recovery time. Overall, thinking that best chances for strong storms would be in central Wisconsin overnight along a cold front approaching from the northwest. The SPC currently highlights portions of central Wisconsin near Marshfield and Wisconsin Rapids under a slight risk for receiving severe weather. Rest of the extended... On and off storm chances are expected to continue Monday and Tuesday as the cold front exits to the southeast. There are still some questions about timing and location of storm development, especially since ridging across the eastern US may keep most thunderstorm activity off to our west. However, a persistent warm and moist airmass may be enough to drive diurnal convection, especially on Tuesday. This airmass will likely cause additional problems through mid-week as temperatures potentially climb into the low 90s Monday and Tuesday. Portions of east-central Wisconsin, mainly centered around the Fox Valley, are under an extreme heat risk on Tuesday as heat indices soar into the mid 90s. && .AVIATION...for 00Z TAF Issuance Issued at 641 PM CDT Sat Jun 15 2024 VFR conditions will continue this evening, with mainly high- based light showers and sprinkles spreading across parts of the region. This activity will lift northward through the evening hours, with AUW/CWA/RHI seeing the most persistent rain. A lull in the rain is expected for a period later this evening and overnight (shortest at RHI), with another push of WAA and strong LLJ producing an additional round or two of showers (briefly moderate to heavy) and embedded storms overnight into Sunday morning. Ceilings are forecast to drop into the MVFR category across central and northern WI, with some IFR conditions possible at times. Mainly VFR ceilings are expected across eastern WI with a period of MVFR possible Sunday morning. The chances for elevated storms arrive after 04z, with chances increasing into Sunday morning. Have continued with the small windows for thunder where the best chances exist with the first wave of showers, but these may need to be shifted/extended with a second wave possible later in the morning. Storm chances on Sunday afternoon/evening are dependent on if the cap can break, but it appears it won`t, with maybe some elevated convection possible later in the day, but too much uncertainty to include a mention. South to southeast winds will continue tonight. Winds aloft will be increasing, so a few gusts to 20 kts are possible, but an inversion will likely limit the gustiness. When surface winds are not gusting, LLWS is expected overnight as winds at 2000 ft increase to around 40 kts. South to southwest winds are expected to gust to 15-25 kts on Sunday. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement from 1 AM CDT Sunday through late Sunday night for WIZ022-040-050. && $$ DISCUSSION.....Kruk/Goodin AVIATION.......Bersch