444 FXUS63 KGRB 151742 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1242 PM CDT Fri May 15 2020 Updated aviation portion for 18Z TAF issuance .UPDATE... Issued at 410 AM CDT Fri May 15 2020 Abundant low level moisture and light winds have allowed dense fog to form near the bay of Green Bay, the Lake Michigan shoreline and areas up to Iron Mountain. HREF model shows these low visibilities will continue through 14Z across these areas, therefore will issue a Dense Fog Advisory for these areas through 9 am. Further inland county dispatch indicated there was patchy fog, but not as widespread as near the water. The HREF model shows the dense fog dissipating around 9 am. && .SHORT TERM...Today...Tonight...and Saturday Issued at 251 AM CDT Fri May 15 2020 Abundant cloud cover and some dense fog near the lakeshore and north- central Wisconsin near Iron Mountain was observed across the area early this morning. A weak cold front will track through the area this morning, which could bring some light showers or sprinkles to portions of north-central Wisconsin as it tracks through early this morning. However radar reflectivity trends are fairly meager given the lack of deep moisture, therefore not much is expected from the cold front precipitation wise. The fog should mix out later this morning as winds turn westerly behind the front and daytime heating mixes out the fog. Once the front passes to the east and the fog mixes out a fairly decent day is in store for northeast Wisconsin as some sunshine breaks out and temperatures rise into the 60s across north- central Wisconsin and the lakeshore, with highs in the lower 70s across portions of central and east-central Wisconsin away from the lakeshore. High pressure will then track through the region tonight, keeping the weather dry as lows range from around 40 across the north, with middle 40s across central and east-central Wisconsin. The high will slowly retreat on Saturday as a low pressure system develops across the central Plains. Although previous runs brought a swath of precipitation into the region Saturday afternoon, the aforementioned high will pump in dry air, which will delay the onset of precipitation as the lowest levels remain fairly dry. The upper levels will moisten up, which will mean an increase in clouds throughout the day. Therefore pulled back POPs significantly with only a slight chance across central Wisconsin very late Saturday afternoon. Highs on Saturday with the increased clouds will be cooler than today, topping out in the 60s away from the lake and 50s near the lake. .LONG TERM...Saturday Night Through Thursday Issued at 251 AM CDT Fri May 15 2020 The upper air pattern will gradually amplify next week as closed lows becomes nearly stationary over west coast and southern Appalachians. Between these features, a mid-level ridge will amplify from the southern Plains to the western Great Lakes. As a result, temperatures will be trending upwards next week, and mostly above normal. Until this occurs, the focus of this forecast remains on the potential impacts from a low pressure system which is anticipated to move across the region on Saturday night into Sunday night. Saturday night through Sunday night...Digging shortwave energy will cause a low pressure system to lift northeast from the central Plains to northwest Illinois/eastern Iowa border on Saturday night. Ahead of the low, a low level jet will push an elevated warm front northward into Wisconsin. Increasing fgen and moisture convergence north of the warm front will lead to a large area of rain arriving in the evening before sliding across the region during the overnight into Sunday. Although instability looks very meager, strong/persistent forcing north of the low and ahead of the digging shortwave combined with pwats upwards of 1.25 inches will lead to significant rainfall across the region. The highest amounts continue to look to occur over central to east-central WI where 1-2 inches of rainfall is a distinct possibility. The precipitation is expected to diminish on Sunday night as the low heads southeast towards the Appalachians. In addition to the heavy rainfall, another aspect that will need to be monitored will be the potential for lakeshore flooding on the Bay. Forecast winds show a long duration northeast wind event in a synoptic pattern that is favorable for flooding on the bayshore. Still a little early to get into details as the track of the surface low needs to get ironed out. The top CIPS analogs show this potential as well, with several showing a storm surge into Green Bay of 1 to 1.5 ft. The most favorable time appears to be on Sunday afternoon into Sunday night. Rest of the forecast...A very dry high pressure system will then slide into the region on Monday. Although there should be plenty of sunshine, may still see gusty northeast winds linger for much of the day. Some guidance indicates that moisture will get thrown back westward around the upper low positioned to the southeast of the region on Tuesday. This looks too ambitious given the very dry air situated over the region. After the rainfall this weekend, most of the next work week is looking dry with temps in the 60s and 70s. && .AVIATION...for 18Z TAF Issuance Issued at 1242 PM CDT Fri May 15 2020 Lake-induced MVFR clouds over far northern WI being stubborn to lift, but still anticipate these clouds to lift into a VFR this afternoon as mixing persists. Otherwise, mostly sunny skies this afternoon for the rest of the region. Anticipate VFR conditions to prevail for most of the area tonight as high pressure over Ontario feeds dry air into northeast WI. The exception would be near Lake MI where onshore winds could bring fog back inland. This would impact the GRB and ATW TAF sites, but especially the MTW site closest to the water. Clouds are forecast to steadily increase over the region on Saturday with a new system over the Plains/Midwest. Cigs should remain VFR through the day with east-northeast winds gradually increasing during the afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE.........Kurimski SHORT TERM.....Kurimski LONG TERM......MPC AVIATION.......Kallas