Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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665 FXUS63 KGRB 220859 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 359 AM CDT Sat Jun 22 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Occasional thunderstorms with heavy rain are likely today. The heavy rain could result in flash flooding of urban areas and small streams. A Flood Watch is in effect through early this evening along and south of Highway 29. - Strong to severe thunderstorms are possible during the late afternoon and early evening, mainly south of highway 10. a few storms could produce damaging winds, and possibly tornadoes. - Many rivers and streams will continue to rise into early next week due to runoff from todays rainfall. - Additional strong to severe thunderstorms are possible Monday night into Tuesday evening. && .DISCUSSION... Issued at 359 AM CDT Sat Jun 22 2024 Short Term...Today...Tonight...and Sunday The potential for flooding rain is the main concern for this forecast period. Forecast soundings have precipitable water values of as much as 2.15", which is close to the all time record for June. Some upstream sites in southern Minnesota and northern Iowa had an inch to an inch and a half of rain in an hour early this morning, and this will likely happen here today. The computer models have very different forecasts for the axis of heaviest precipitation. Some of them even have two axes, one across northern Wisconsin and one across the central part of the state, with a relative minimum in between. This is plausible given split jet streaks moving across the area today. We will keep the flood watch going for the area south of highway 29, as one and three hour flash flood guidance is lowest there. In addition to the heavy rain, there is some chance of severe storms along and just north of the warm front, which will be moving north through the Fox Valley during the late afternoon. Storms with damaging winds are possible, and low LCL heights would suggest some tornado potential if we can get rotating storms. The rain will end from west to east this evening, with skies remaining cloudy overnight. A strong jet moving through the cyclonic flow aloft will likely produce some showers and low top thunderstorms Sunday. The atmosphere will be much drier than today, so additional rain will be modest. Rain from today will produce rising streams and small rivers, which will empty into the larger rivers in the next couple of days. So there is some flood potential early next week as well as today. Long Term...Sunday Night Through Friday A few showers and thunderstorms may linger into Sunday night as a transient short-wave departs the region. Monday should trend mostly dry as a brief period of high pressure develops over the region. Southerly winds Monday afternoon will help bring temperatures back up into the upper 70s to middle 80s. The main period to watch for potential impactful weather during the long-term is Monday night through Tuesday. Medium range models are in decent agreement with a low pressure system traveling across central Canada lifting a warm front across northern WI Monday night with an area of mid-level convergence developing along the noise of a low-level jet. Forecast soundings show robust elevated instability and strong effective layer shear during this time creating an environment that could conditionally support stronger to possible severe elevated storms. However, with nocturnal stabilization and a cap likely over much of the region the best chance for stronger storms will be in close proximity to the warm front. If thunderstorms are able to develop large hail and strong winds gusts look like the primary hazards. A second wave of thunderstorms may then be possible Tuesday afternoon/evening as a cold front comes across the region, however, the timing of these feature is still uncertain. Additionally, Tuesday looks like the hottest and most humid day next week with highs forecast to reach the middle 80s to around 90 degrees. Once the cold front is through the region Tuesday night a period of quieter weather is expected as a high pressure system takes control of the region during the middle of next week. Temperatures should trend closer to normal next Wednesday and Thursday. && .AVIATION...for 06Z TAF Issuance Issued at 1110 PM CDT Fri Jun 21 2024 Poor flying conditions will prevail through much/all of the TAF period as periods of showers and storms, low clouds and fog are expected with MVFR/IFR/LIFR conditions. A lull in the heavier rain/storms will continue late this evening. Another more widespread batch of showers and storms is expected to spread west to east overnight into Saturday morning. Heavy rain and lightning will be the main threats from this activity. Another round is expected Saturday afternoon/early evening, but questions just how far north the more significant storms will be able to form. Trends have been to keep most of the activity south of the area, possibly clipping ATW/MTW, which looks to a more favorable outcome as the large area of showers/storms in southern MN and northern IA should help keep the front from working northward. && .GRB WATCHES/WARNINGS/ADVISORIES... Flood Watch through this evening for WIZ030-031-035>040-045- 048>050. && $$ DISCUSSION.....RDM/GK AVIATION.......Bersch