Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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992 FXUS63 KGRB 031138 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 638 AM CDT Wed Jul 3 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Some rivers and streams over portions of east central Wisconsin will continue to run above bankfull due to the heavy rain that occurred on Tuesday evening. - Rain/storm chances will arrive from the west Thursday afternoon, becoming more widespread overnight. This has the potential to impact fireworks displays the night of the 4th, especially across central and north-central Wisconsin. - On and off chances for rain/storms continue through early next week as upper-level flow remains unsettled. && .DISCUSSION... Issued at 347 AM CDT Wed Jul 3 2024 Short Term...Today...Tonight...and Thursday Today and tonight...Most showers have exited northeast WI early this morning. Main impact left from the heavy rain that occurred on Tuesday evening (2-3 inches of rain in last 24 hours in good portion of Winnebago and Calumet counties) will be smaller rivers and streams running above bankfull before slowly dropping this afternoon and tonight. Fog early that is most dense over central WI will fade by daybreak as dry air aloft moves across and winds shift more westerly. Expect a much warmer day across the board with highs well into the 80s. Forecast soundings and MOS guidance signal breezy winds developing early to mid afternoon with gusts reaching 30 mph at times over central WI. No big changes from previous forecast in terms of rain chances today. Still a small chance of pop-up showers this afternoon into early evening. CAMS are quite spotty in coverage, but all show some hint at some showers due to lower convective temps (75-78F) being achieved rather easily along with steeper low-level lapse rates and sfc dewpoints still mainly in the 60s giving at least 500J/kg of MLCAPE. Though a rumble of thunder could occur, very low chance, so just went with the shower mention. Rest of tonight looks quiet with min temps as low as mid 50s north and as warm as mid 60s for Fox Valley to the lakeshore. 4th of July...The holiday starts out dry but then becomes more unsettled as the day progresses. Main culprit is shortwave trough tracking from the plains to the upper mississippi valley by late in the day. Small chance of showers through midday from the southwest as elevated instability will be shifting toward WI and warm/moist advection will be increasing even as low-level jet remains tame. As we have seen multiple times, sometimes these elevated showers will outpace the greater instability and expand farther east than you expect. That could happen again during the morning as some models show. At the least, should see thickening clouds (highs will still touch the lower 80s for most locations) but again could also see some light elevated showers from this regime. Better chances for showers and possible rumbles of thunder on track for the afternoon, again spreading in from the southwest as shortwave trough draws closer and a warm front works into southwest WI. Chances for rain will start to eclipse 55-60 percent after 4-5 pm west of a line from Wausau to Waupaca to Wautoma with chances increasing further from west to east as we work into the evening of the 4th. SPC does have our far southwest CWA within a marginal risk for severe, but at this point even though MLCAPES will be near 1000J/kg, strongest low- level and mid- level winds (effective shear) stay well to the southwest across IA, so think the severe risk over central WI will stay on the lower side. Long Term...Thursday Night Through Tuesday Focus for the extended will be on rain/storm chances the evening of the 4th as a robust shortwave drags a surface low across the northern Plains. Rain is expected to arrive from the west Thursday afternoon before becoming more widespread overnight, potentially impacting fireworks displays especially across central and north- central Wisconsin. An unsettled pattern containing several shortwaves and accompanying chances for rain will then remain in place through early next week. Thursday evening through Saturday rain/storm chances... Closed upper-level energy will dig across the northern Plains mid-week before spinning up a surface low over the upper Mississippi Valley Thursday evening. Warm air advection precip will then spread west to east Thursday evening through Friday morning, bringing additional chances for heavy rain to the forecast area. Current ensemble guidance shows a 30 to 50 percent signal for exceeding 1 inch of rainfall in central Wisconsin through Friday evening. While storm potential doesn`t look too impressive, cannot rule out some rumbles of thunder given modest instability (700 to 900 J/kg) Thursday evening. This being said, better storm potential looks to be Saturday afternoon with wrap-around shower activity as the surface low departs to the east. Coverage will likely be spotty given the absence of any surface features, although surface dewpoints in the mid 60s and resultant CAPEs nearing 1,500 J/kg may be enough to generate some thunderstorms during peak heating. Rest of the extended... On and off chances for showers will continue through early next week as agitated mid-level flow persists. After dropping into the mid 60s to low 70s following Friday`s precip, temperatures will then rebound heading into the weekend before plateauing in the upper 70s to low 80s to start the week. Expect temperatures during this time to run right around average for this time of year. && .AVIATION...for 12Z TAF Issuance Issued at 637 AM CDT Wed Jul 3 2024 IFR/MVFR cigs will lift early, then scatter out by mid morning. High based cumulus will form midday through the afternoon. Small chance of a pop-up shower especially north-central to northeast WI, but too low in coverage to include at this time. Southwest to west winds will become breezy this afternoon with gusts 20-25 kts at all terminals. Mostly clear with light winds tonight. Rain chances will increase from southwest to northeast on the 4th, especially in the afternoon and evening hours. Conditions will stay VFR during the daytime on the 4th. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA/Goodin AVIATION.......JLA