Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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991 FXUS63 KGRB 071153 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 653 AM CDT Tue May 7 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Periods of showers and embedded thunderstorms are expected this afternoon and tonight. If sufficient breaks in the rain occur, conditions may become supportive for a few strong storms late this afternoon into early this evening. The best chance for strong storms will be south of a Marshfield to Waupaca to Oshkosh line. - Conditions hazardous to small craft are expected on Lake Michigan south of Two Rivers through early this evening due to gusty southeast winds. - Areas of frost are expected to develop over parts of central and north-central Wisconsin on Thursday night. && .DISCUSSION... Issued at 423 AM CDT Tue May 7 2024 Short Term...Today...Tonight...and Wednesday The main forecast concerns will be precipitation trends and potential for a few strong thunderstorms in the southwest part of the forecast area later today. A deep upper level low was situated over the western Dakotas, with a potent negatively-tilted short-wave trough lifting northeast toward the western Great Lakes. A weakening band of showers and embedded thunderstorms was moving through SE MN and eastern IA, ahead of the short-wave, and coincident with a strong and persistent area of frontogenetic forcing and deep moisture convergence. This band is poised to reach the far southwest part of GRB CWA by 12z/Tue. Today, strong forcing with the short-wave and frontogenesis will push the band of moderate showers through the SW part of the forecast area between 12z-15z, and through most of NE WI between 15z-18z. Little or no instability is expected with the main rain band, so only expect isolated embedded thunder at best. However, with PWATs increasing to 1.0-1.25 inches, much of the area could see a quick half to three-quarter inch of rain. The most difficult question for today is how much clearing and developing instability will occur in central WI before an occluded front approaches the area late in the day. Most models show a small area of marginal instability (SBCAPE of 250-750 j/kg) developing in parts of central WI and the western Fox Valley; roughly along and south of a line from Marshfield to Waupaca to Oshkosh. Scattered storms could develop in this region as the occluded front arrives during the late afternoon/early evening. Given that deep layer shear will be decreasing rapidly during this time frame, confidence in severe weather development is low. However, a few strong storms with gusty winds, small hail and heavy downpours will be possible. The weakening short-wave and occluded front will lift into northern WI during the evening, taking lingering showers and isolated storms with it. Small precipitation chances will remain across the north overnight into Wednesday. Sunshine, warmer temperatures and developing weak instability may result in a slight chance of thunderstorms in our southwest counties Wednesday afternoon. Temperatures will be a tough call today, and will be heavily moderated by showers and cloud cover. Most of the CWA should see highs in the middle 50s to middle 60s, with the warmest temps over the far north (heating before the rain band arrives) and far south (recovery in the afternoon after the first band moves through). Lows tonight should be in the middle 40s to lower 50s. Highs on Wednesday should range from the upper 50s/lower 60s far north to the lower to middle 70s south. Long Term...Wednesday Night Through Monday Relatively low impact weather is expected from Wednesday night into early next week as the upper flow veers to the northwest and temperatures fall below normal. The highest impacts will likely occur via rain chances, low temps cold enough for frost, and gusty winds at times. Precipitation chances: Elongated upper troughing will extend from the central Plains to Quebec from the Wednesday night through Thursday night time frame. Surface low pressure will be moving east across the mid-Mississippi Valley. Light rain chances are expected to redevelop over Minnesota within the deformation zone of the upper trough and north of the surface low track on Wednesday night before tracking east towards central and east-central Wisconsin late on Wednesday night through much of Thursday before exiting Thursday evening. Rainfall amounts of a tenth to a quarter inch appear possible. Another chance of rain will arrive on Friday night into Saturday when a sharp upper trough digs southeast across the western Great Lakes. There will be a slight chance of thunderstorms, but meager instability means no chance of severe weather. Temperatures: Colder temperatures are forecast to arrive on Thursday which will persist into the weekend. Low temps are forecast to become cold enough for frost over north-central WI on Thursday night. But northwest winds 5 to 10 mph may limit coverage to sheltered areas. Patchy frost could also develop over north- central WI on Saturday night. Gusty wind potential: Breezy northeast to north winds could produce gusts to 30 mph on late Wednesday night into Thursday. There is a 60- 80% chance of gusts greater than 25 mph over the Fox Valley and Lakeshore south of Sturgeon Bay. Conditions hazardous to small craft will be possible. Gusty north winds will also be possible on Saturday that could lead to conditions hazardous to small craft. && .AVIATION...for 12Z TAF Issuance Issued at 645 AM CDT Tue May 7 2024 A band of moderate showers will overspread the forecast area from SW to NE this morning through midday, with flight conditions deteriorating to MVFR. The steady showers will only last 3 to 4 hours at any given location before moving out, but MVFR conditions will persist in some areas after the rain departs. Showers will linger into tonight across northern WI, along with potential for flight conditions to drop to IFR. Farther south, scattered showers and storms may redevelop in the late afternoon and early evening, followed by improving flight conditions overnight. Gusty SE winds and some LLWS will occur across the region this morning. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/MPC AVIATION.......Kieckbusch