Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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794 FXUS63 KGRB 072321 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 621 PM CDT Fri Jun 7 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Showers are expected overnight into early Saturday afternoon. - There is a slight chance of thunderstorms Saturday afternoon, mainly across northern Wisconsin. Severe weather is not expected. - Below normal temperatures are forecast through early next week, then go above normal latter half of the week. && .DISCUSSION... Issued at 333 PM CDT Fri Jun 7 2024 Short Term...Tonight and Saturday Main forecast challenge to be timing of precipitation onset late tonight, ending Saturday afternoon and whether additional showers and storms can redevelop later Saturday afternoon. The 19Z MSAS surface analysis showed a weak area of high pressure that extended from ND to the Upper Midwest. Otherwise, surface features were rather diffuse which is typical of summer. Visible satellite imagery indicated fair weather cu over northeast WI with middle and high clouds to our west. across the Plains. Clouds will be on the increase this evening as a weak surface boundary and mid-level shortwave trough move across the Upper MS Valley. An uptick in both moisture transport and mid-level Q-G forcing will bring a swath of showers toward central WI after midnight and perhaps reach eastern WI toward sunrise. Instability is essentially nil, thus no mention of thunder for later tonight. Min temperatures to be in the upper 40s to around 50 degrees north, lower to middle 50s south. This band of showers will continue to move across the forecast area Saturday morning before forcing shifts east with the shortwave trough. Exactly how has this precipitation (and its associated clouds) moves will set the stage for additional precipitation chances Saturday afternoon. A faster exit would allow for some clearing to occur and bring a minor increase in instability (200-400 J/KG) mainly to northern WI (maybe into parts of central and east-central WI). Shear is forecast to be in the 30-50 knot range north, so despite the weak instability, cannot rule out a slight chance of thunderstorms to pop-up in the afternoon. Severe weather is not expected. All of this would be mute if we cannot clear out the clouds, thus there is still some doubt to the forecast overall for Saturday afternoon. Max temperatures to continue running below normal with readings in the lower 60s along Lake MI, mainly upper 60s inland. Long Term...Saturday Night Through Friday The main focus for the forecast period is resolving the precipitation trends for the late weekend and early next week. Saturday night through Sunday...A few lingering showers are possible Saturday evening before dry conditions return to the region overnight. Sunday, another weak shortwave will round the upper low to our northeast, bringing some brief stronger CAA in the afternoon. Short term models do develop a couple showers as a result, relying mainly on some meager instability from the surface. While the instability may suffice for a brief rumble of thunder, would still expect that overall and rain will be light, brief, and fairly small in areal coverage. Rest of the extended...The precipitation trends for early next week will rely heavily on the evolution of the upper pattern over the weekend. Previous model runs featured a shortwave riding across the Northern Plains, leading to the development of a closed low south of Wisconsin and light precipitation on Monday. More recent trends now go the other way however, keeping the aforementioned shortwave closed off in Canada while upper ridging builds eastwards behind the cold air advection. This will keep us dry Monday until the shortwave finally arrives behind the ridging sometime on Tuesday. It`s important to note that regardless of which way the precipitation comes through, the overall impact will be low as neither solution has potential for any severe weather in our area. Additionally, both still see some more modest return flow beyond Tuesday, which would see the return of some warmer temperatures to the region. && .AVIATION...for 00Z TAF Issuance Issued at 621 PM CDT Fri Jun 7 2024 VFR cumulus clouds from 4K-5K ft will dissipate early this evening. Mid and high clouds are forecast to quickly overspread the region this evening into the overnight period as a frontal boundary and shortwave trough approach from the west. Chance of showers to reach central WI toward daybreak with cigs/vsbys lowering into the MVFR category. These MVFR conditions would then spread east into eastern WI Saturday morning, along with the rain showers. Cigs could briefly dip to IFR under any of the heavier showers in the morning. Some improvement is expected Saturday afternoon with cigs returning to VFR. Depending on amount of clearing, a few showers/storms could pop up mainly over northern WI in the afternoon. West/northwest winds gusting to 30 kts will dissipate early this evening around sunset. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kallas/Uhlmann AVIATION.......Kurimski