Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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355 FXUS63 KGRB 042109 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 409 PM CDT Thu Jul 4 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Areas of showers and embedded storms are expected this evening into Friday. Some storms across central Wisconsin may become strong to severe through early this evening, with the main threats being flooding, gusty winds, and small hail. - Elevated potential for flooding this evening into Friday. River and stream levels will likely be on the rise, with some urban flooding also possible depending on where swaths of heaviest rain occur. - On and off chances for rain/storms continue through early next week as upper-level flow remains unsettled. && .DISCUSSION... Issued at 409 PM CDT Thu Jul 4 2024 Severe & Heavy Rain Threat / Precip Chances: Area of light rain and sprinkles, along with an embedded storm or two, will continue to track northeast across the area through the mid and late afternoon. Some additional activity will continue to peculate to our south and drift towards/into the southern counties through sunset. Instability has built up to 800-1000 J/kg despite the cloud cover, with an area of higher instability just to our south. While widespread severe weather is not expected, can`t rule out a strong to severe storm south of Hwy 29 through early evening as any storm taps into this instability to our south. A more organized area of convection will continue to develop across southeast MN and northeast IA and work east toward our area, as the main shortwave and surface/upper low track eastward. This looks to push east across the southern 2-3 row of counties later this evening. Instability will be slowly waning through the evening, so the severe threat will lower as we head toward midnight. Current timing has this area just to the west of the Fox Valley around firework time, but locations to the west will likely be impacted by these showers/storms. The shortwave/low will slowly work across the area on Friday, keeping scattered showers and isolated storms going for much of the day. With a north/northeast wind kicking in, it is not looking like the best early July day for outdoor activities. The shower/storm activity will diminish toward sunset and end across far eastern WI by midnight. Complex flood threat this afternoon into Friday as areas of convection will bring locally higher totals (0.5-1.0" per hour rates) across parts of central and east-central WI, and locations in the comma head will see a more steadier rain over far northern WI. Favorable antecedent soil moisture conditions exist across parts of central and east central WI due to recent heavy rain events. But we have had 1.5-3+ days in between heavy rain events which has allowed many rivers/streams to decrease. But the ground is still pretty saturated, with flash flood guidance (FFG) still between an inch or two in the Fox Valley, slightly lower in parts of Brown Co. This looks to be the most vulnerable area. Parts of central WI will need to be monitored as well with FFG between 1.5-2.5". But with the rounds/bursts of heavier rainfall expected to be separated by a few hours and models trends for a more progressive first round (or possibly missing some of the area), will hold off on a flood watch but continue to highlight in the HWO. If the heavier rain (1-2 inches) occurs across the areas with the lower FFG this evening, some flood advisories may be needed. Plus, the locations where the heaviest rain falls tonight will be more susceptible to flooding on Friday. Saturday is still looking mainly dry, aside for a few light showers or sprinkles in the afternoon/evening, as high pressure makes a brief stop over the western Great Lakes. A stray storm will also be possible some instability builds through the day. Have bumped up cloud cover as plenty of daytime cumulus are expected as well. The pattern turns unsettled once again Sunday into at least Tuesday as another large trough slowly rotates across the western Great Lakes. Some bouts of heavy rain will once again be possible with PWATs climbing back to near 1.75", possibly creating additional flooding concerns. Fog / Temps: Some fog will be possible tonight as winds will stay on the light side and recent rain. But with plenty of rain/clouds around, it looks to not be dense. There will be additional fog chances during the overnight and early morning hours this weekend, especially after the heavier rain events and if/when skies clear. A brief cool down arrives on Friday with highs stuck in the 60s across much of northern WI and low to possibly mid 70s further south. Temps rebound quickly to close to or slightly above normal for the weekend and into next week. && .AVIATION...for 18Z TAF Issuance Issued at 1244 PM CDT Thu Jul 4 2024 VFR conditions will continue early this afternoon, with an area of sprinkles and showers spreading across the area. A rumble of thunder can`t be ruled out. Then flight conditions will deteriorate to MVFR/IFR this evening into Friday morning as additional areas of showers and isolated/scattered storms spread across the region. A few LIFR conditions are possible overnight into Friday morning. Still a little challenging to pin down the best chances for thunder, but will pick 2-4 hour windows where probabilities are the highest. These will likely need to be adjusted as the mesoscale trends become more clear. Additional thunder chances may need to be added for Friday morning as well. Winds are forecast to remain mainly 10 knots or less this afternoon into tonight, with a few higher gusts possible Friday morning. Locally higher winds will be possible in/around any heavier shower or thunderstorm. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Bersch AVIATION.......Bersch