729 FXUS63 KGRB 072331 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 631 PM CDT Wed Jun 7 2023 Updated aviation portion for 00Z TAF issuance .SHORT TERM...Tonight and Thursday Issued at 315 PM CDT Wed Jun 7 2023 The main forecast focus will be on a developing upper low over the Great Lakes late this weekend into early next week and its associated precipitation trends. Other than Sunday and perhaps Monday, temperatures should be at or slightly above normal. The 19Z MSAS surface analysis showed high pressure extended from northern Ontario south across Lake Superior. Visible satellite imagery indicated clear skies across northeast WI with less smoke overhead compared to earlier in the day. Any precipitation was located well to our west along a stationary boundary. High pressure will continue to build south from Ontario through WI tonight, bringing mainly clear skies, light winds and a rather dry air mass. Despite nighttime hours at a minimum this time of year, temperatures are expected to quickly fall this evening with readings by daybreak to range from the middle to upper 30s north- central WI, to the middle to upper 40s over east-central WI. Based on these temperatures, have maintained the Frost Advisory for north-central WI through 7 am Thursday. Other than a slight backing of the winds to the north, Thursday's weather looks to be a copy of Wednesday's weather with plenty of sunshine and temperatures close to normal for early June. The only concern would be the low afternoon humidity values of 15 to 25 percent. The lack of significant winds is the only reason for not having any fire weather headlines. Plan to issue a SPS for the elevated/near critical fire weather conditions across the forecast area. .LONG TERM...Thursday Night Through Wednesday Issued at 315 PM CDT Wed Jun 7 2023 Models insist on a blocky pattern through the upcoming weekend with a strong upper ridge over the eastern Pacific, a weakening upper ridge over the central CONUS and closed upper lows over the southwest CONUS and eastern Canada. The main forecast focus will be on a developing upper low over the Great Lakes late this weekend into early next week and its associated precipitation trends. Other than Sunday and perhaps Monday, temperatures should be at or slightly above normal. Thursday night and Friday... Even with the high pressure still in control of our weather Thursday night (and still over WI), temperatures aloft are starting to warm a bit. Thus, despite another night of mainly clear skies and light winds, temperatures will not be a cold as Wednesday night. Look for readings to range from the upper 30s to lower 40s north, middle to upper 40s south. While a few of our colder locations may see patchy frost, do not anticipate any additional headlines. The high pressure is forecast to move southeast into the OH/TN Valleys on Friday with winds becoming west, but still fairly light (10 mph or less). There is a cold front situated well to our north from south-central Ontario into ND, but this feature will not impact northeast WI yet. Other than a few more clouds around, Friday will be another pleasant day over the region with max temperatures in the lower to middle 70s near Lake MI, middle 70s to around 80 degrees inland. Afternoon relative humidity values away from the lake to be in the 20 to 30 percent range, thus elevated fire weather concerns to persist. Friday night and Saturday... This cold front is progged to sag south into northern sections of the Great Lakes Friday night and roughly bisect WI, reaching the HWY 29 corridor by late Saturday afternoon. Based on this timing, chance pops will become necessary over northern WI Friday night mainly in the form of showers as instability is weak at best. A better chance of showers and some thunderstorms to occur on Saturday with the cold front in the vicinity and more instability to be present. Models hint at MUCAPES around 1K J/KG with 0-6km bulk shear around 30 knots. This may support a few stronger storms in the afternoon. Max temperatures on Saturday to be in the lower to middle 70s north/near Lake MI, mainly upper 70s south. Saturday night and Sunday... Chance of showers/storms to continue into Saturday night over our southern counties until the cold front pulls farther away to the south. As this is occurring, models show an upper trough over Ontario moving southwest and in the process of becoming a closed upper low. Do not anticipate any additional precipitation chances for the rest of Saturday night. Models agree on the development of this closed upper low over the western Great Lakes on Sunday and this may lead to a few showers to pop up in the heat of the afternoon. Max temperatures on Sunday to be in the upper 60s to around 70 degrees north/lakeside, lower 70s south. Sunday night through Tuesday... This closed upper low will not be in any hurry to leave the Great Lakes early next week. A cyclonic flow and individual shortwaves rotating around the low could keep the weather a bit unsettled, especially over eastern WI through at least Monday night. A ridge of high pressure building eastward should keep most areas dry on Tuesday. Temperatures to remain slightly below normal on Monday and begin to warm on Tuesday. Tuesday night and Wednesday... Drier and warm conditions to return to the region by mid-week as the surface high pressure ridge pushes into WI. Max temperatures for Wednesday to range from the middle to upper 70s near Lake MI, lower to middle 80s inland. && .AVIATION...for 00Z TAF Issuance Issued at 631 PM CDT Wed Jun 7 2023 VFR conditions are expected through the TAF period as high pressure slides across the Great Lakes. Smoke aloft will continue times, but looks to remain pretty thin so will stick with P6SM and FEW250. Could be just enough moisture on Wednesday to touch off a few daytime cumulus, especially where the smoke is the thinnest, but coverage should be very limited. North to northeast winds will become light this evening then only gust to around 10-15 kts on Thursday. && .GRB WATCHES/WARNINGS/ADVISORIES... Frost Advisory from 2 AM to 7 AM CDT Thursday for WIZ005-010>013- 018. && $$ SHORT TERM.....Kallas LONG TERM......Kallas AVIATION.......Bersch