406 FXUS63 KGRB 221129 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 629 AM CDT Sat Jun 22 2019 Updated aviation portion for 12Z TAF issuance .SHORT TERM...Today...Tonight...and Sunday Issued at 330 AM CDT Sat Jun 22 2019 An upper level ridge remained over the western Great Lakes region early this morning, and a surface ridge was situated over Lake Superior, the Upper Peninsula and northeast WI. These features continued to prevent any precipitation formation, and only patchy mid/high level clouds were observed over the forecast area. Have continued the trend of the past few days of slowing down the arrival of precipitation, such that today's forecast is now dry. Expect similar temperatures as yesterday, with highs in the 70s inland, and upper 60s and lower 70s lakeside due to east flow. The upper ridge and surface ridge will shift east tonight into Sunday, with a couple short-wave troughs and an 850 mb warm front impacting the region. In addition, precipitable water values will increase from southwest to northeast, and reach 1.50-1.75 inches by Sunday. In addition, elevated instability will arrive tonight, with 850 mb LI's of 0 to -3 C. Precipitation chances will increase from southwest to northeast tonight, with showers and scattered thunderstorms likely over the entire forecast area on Sunday. The severe threat appears to be limited by relatively weak instability, but heavy rainfall should accompany any thunderstorms. Lows tonight will be milder, with readings in the middle 50s to lower 60s. Highs on Sunday should be a little cooler due to cloud cover and showers, with readings in the upper 60s to middle 70s, and 60s near Lake Michigan. .LONG TERM...Sunday Night Through Friday Issued at 330 AM CDT Sat Jun 22 2019 Forecast concerns continue to revolve around precip chances and potential for severe weather late in the weekend into early next week. Overall, models continue to slow down the progression of shortwave energy and associated surface low on Sunday night into Monday. Will continue to use a blend of the gfs and ecmwf. Sunday night through Monday night...Shortwave energy and a trough of low pressure will be lifting northeast across the region on Sunday night. Modest most unstable capes up to 1000 j/kg and deep layer shear 20-30 kts suggest thunderstorms are likely with a few strong storms possible, but severe storms seem unlikely at this time. More concerning is the heavy rainfall as pwats climb upwards of 1.75 inches. A stronger shortwave and associated surface low will then move across the area on Monday into Monday evening. With daytime heating, most unstable capes are forecast to exceed 500 j/kg over central WI and 1000 j/kg over east-central WI. Combined with deep layer shear of 30 to 40 kts, perhaps there is a low potential for severe weather on Monday afternoon and Monday evening, though there is considerable concerns about how much instability will be realized. Heavy rainfall will also be a threat as well. Rain chances then diminish late Monday night as the low departs. Rest of forecast...Behind this system, flattened troughing with some indications of weak shortwave energy could lead to a few showers or storms on Tuesday, but lack of moisture should generally lead to sparse coverage. Mid-level heights then gradually rebound through the rest of the week. This should lead to a warming trend, but also potential for MCS activity. Trying to time the best potential for thunderstorm complexes is next to impossible this far out. However, some indications that chances increase on next Thursday and Friday. && .AVIATION...for 12Z TAF Issuance Issued at 620 AM CDT Sat Jun 22 2019 Quiet weather and favorable flying conditions will continue through early this evening as high pressure over Lake Superior continues to feed dry air into the area on east winds. Rain chances will overspread the region from southwest to northeast tonight, with ceilings probably dropping to MVFR at AUW/CWA/RHI late. There will also be a chance of thunderstorms as elevated instability arrives, but confidence in placement and timing are too low to include a mention in the TAFs right now. LLWS will develop in central WI late this evening, then spread northeast overnight. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Kieckbusch LONG TERM......MPC AVIATION.......Kieckbusch