Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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999 FXUS63 KGRB 122306 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 606 PM CDT Wed Jun 12 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - There is a chance of strong to severe thunderstorms across all of north-central and northeast Wisconsin after 9 pm tonight. Overall confidence in the severe weather threat is medium-low, but a few of the strongest storms may produce strong to damaging winds and hail. - Well above normal temperatures are forecast from Sunday into the middle of next week. Heat indices may surpass 90 degrees at times. - The next chance for widespread rainfall arrives Saturday, with the best coverage Saturday evening through the overnight. It is uncertain if these storms would become severe, but locally heavy rainfall will be possible. && .DISCUSSION... Issued at 242 PM CDT Wed Jun 12 2024 Short Term...Tonight and Thursday The latest RAP analysis and satellite/radar imagery show relatively fast zonal flow in the mid and upper levels across the US-Canadian border with embedded shortwaves within said flow. In fact, the 200mb and 500mb flow is upwards of the 97.5 percentile. This flow is above a warm front lifting northeast across Minnesota and a trailing cold front across North Dakota. An area of showers ahead of these features is slowly decaying over northern WI, while more intense thunderstorm activity resides across southern Minnesota and southwest Wisconsin. These thunderstorms are expected to continue to move southeast and bypass central Wisconsin. The area behind these showers and storms over northern Minnesota is where greater concern lies as this area has seen strong solar insolation and destabilization this afternoon. Storm initiation is expected in the 3-4 pm timeframe in this area. Evolution of these storms and the severe storm potential are the focus of this forecast. Precipitation Trends and Severe Thunderstorm Potential: While it`s possible that some additional shower and storm activity could redevelop behind the ongoing convection over central and southern Minnesota, odds appear considerably reduced as the atmosphere will have little time to destabilize prior to peak heating. If storms redevelop, the airmass over central Wisconsin is considerably more stable and likely to keep the severe threat very low. A considerably higher potential for severe weather is likely to arrive from the storms that initiate over northern Minnesota. These storms are forecast to track southeast towards north-central WI in the 9 pm to 11 pm time frame. The airmass will be more stable over northern WI than upstream by this time, and the storms will likely be in the weakening process. Despite this, most unstable capes upwards of 1000 j/kg will likely lead to a severe threat continuing as storms arrive into north-central WI, especially with deep layer shear from 40-50 kts. With such strong wind fields aloft, strong to damaging winds will be the primary threat tonight, but updrafts may be strong enough for large hail to remain possible, at least over north-central WI. The threat of damaging winds will likely persist, however, as forward propagating vectors indicate a storm motion of 55-70 kts. The chance of storms will end towards the middle of the overnight. Thunderstorm Potential and Gusty Winds on Thursday: Thunderstorm activity will likely push the cold front into southern Wisconsin or northern Illinois by Thursday morning. However, ahead of a secondary front and shortwave trough, models indicate 1000-1500 j/kg of cape developing over central and east-central WI by late morning to early afternoon. Think widely scattered showers or storms could develop in this unstable airmass and have added a small chance to the forecast. Strong wind fields aloft could lead to a gusty wind threat if storms develop. Deep mixing through 6-8k feet should tap into strong winds aloft, resulting in west winds gusting to around 30 mph in most areas. Gusts should not be as strong over Lake Michigan, due to more stable conditions over the relatively cool waters. Thus, expecting gusts to remain below the 25 knot threshold for a Small Craft Advisory. Long Term...Thursday Night Through Wednesday The two concerns in the extended period will be the potential for another round of impactful weather moving through the region Saturday and the much warmer weather anticipated by the end of the weekend into early next week. Saturday... After a quiet start to the extended, active weather returns to the region as southerly flow picks up again. As warm air advection increases, showers are expected to develop across the region Saturday afternoon. Although initial rain will only have a minimal chance for thunder, the overall potential for stronger storms increases as we get into the overnight hours. A strong low level jet is expected to develop in the evening hours, helping to sustain and strengthen any ongoing showers. With lingering MLCAPE around 1000-1250 and strengthening shear, wouldn`t be surprised to see an increase in elevated thunderstorm coverage. Whether instability and shear remains sufficient for severe weather remains uncertain. PWATs during this time will also push to around 1.8-2.0, which will make heavy rainfall a concern, especially if these storms start training along the warm front. A few showers and storms may linger on to start off Sunday, which may skew the high temperatures expected in the region. Temperatures... The push of the warm front from Saturday will bring with it some well above normal temperatures. Highs could be well into the 80s by Sunday, although this may change slightly depending on how quickly clouds and active weather move out of the region Sunday morning. Dewpoints during this time are also expected to push towards the upper 60s which may make for one of the muggier days so far this year. Behind the Sunday system, temperatures early next week will remain well above normal, with highs into the upper 80s both Monday and Tuesday. A few of the warmer spots may even hit 90 during this timeframe. With several days of very warm temperatures in the forecast, make sure you have a way to beat the heat!. && .AVIATION...for 00Z TAF Issuance Issued at 552 PM CDT Wed Jun 12 2024 Showers and thunderstorms developing upstream across Minnesota are expected to congeal into a squall line and track through the area from northwest to southeast late this evening and into the overnight hours. Strong straight line winds and IFR vsbys will impact flight operations if thunderstorms hold together as planned. Confidence in these thunderstorms tracking through the area is medium (around 50 percent) with a lower confidence in the storms still being strong to severe when they track through (5 percent). In the wake of the storms, IFR low clouds may stick around for a time over far northern WI, including RHI, but then clear for a time on Thursday morning. Convective clouds are then expected to build over east-central WI by late morning, which could lead to scattered showers developing. Gusty west winds to 25 kts are possible at the taf sites on Thursday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....MPC/Uhlmann AVIATION.......Kurimski