205 FXUS63 KGRB 121137 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 637 AM CDT Fri Apr 12 2019 Updated aviation portion for 12Z TAF issuance .SHORT TERM...Today...Tonight...and Saturday Issued at 348 AM CDT Fri Apr 12 2019 Lingering winter weather headlines and precipitation trends/type will be the main forecast concerns. The main band of precipitation has weakened and pulled out of far northeast WI early this morning, leaving only patchy dz/fzdz over the region. Expect light freezing rain to redevelop over north central and far northeast WI over the next few hours, as an occluded front lifts north into the region. The freezing rain/minor icing threat will continue until temperatures warm above freezing mid to late morning. Will continue with the Winter Weather Advisory over north central and far northeast WI through 15z/Fri. Gusty southwest winds will develop after the front shifts north today. The strongest winds will occur in the Fox Valley and lakeshore areas, where gusts to 30 to 40 mph are anticipated during the afternoon. Precipitation chances will increase over the northwest half of the forecast area this afternoon and evening, as the upper low (currently over southwest MN) moves through the region. Precipitation chances will gradually diminish late tonight into early Saturday as the low departs. Expect a mix of rain/snow this afternoon, changing to light snow tonight, with up to an inch of accumulation in far north central WI. Temperatures will be well below normal through Saturday. .LONG TERM...Saturday Night Through Thursday Issued at 348 AM CDT Fri Apr 12 2019 The progressive mean flow across the CONUS is expected to persist through the middle of next week, sending two more systems into the Great Lakes. There are signs the flow will become more amplified/ blocky late next week as an upper ridge builds over the western CONUS. The focus will be on these two systems with the first one Sunday afternoon/night and the second one Wednesday through Thursday. Models have various timing/location issues that will need to be resolved in the coming days. Flooding will remain a big concern as any additional precipitation (snow or rain) will only serve to keep area rivers high with fast flows. High pressure is expected to stretch from the northern Plains to northern sections of the Great Lakes Saturday night. This should allow skies to become mostly clear to partly cloudy for most of the night. The exception would be e-central WI where clouds will be on the increase well after midnight as our next weather system begins to lift northeast from the southern Plains. Light north winds will combine with the breaks in the clouds and fresh snow cover, to allow temperatures to dip to around 20 degrees far north, but hold around 30 degrees east-central WI. The area of low pressure is forecast to move northeast up the Ohio River on Sunday with the trailing mid-level shortwave trough pushing across the mid-MS Valley. The majority of the models brush east-central WI with a rain/snow mix by Sunday afternoon, however the ECMWF insists on a more western track. That being said, the 00Z ECMWF has shifted a bit farther east than its previous couple of runs. For now, will continue to use a model blend, but will have to carefully watch how this system tracks and whether precipitation types favor snow rather than rain. Max temperatures for Sunday to range from the upper 30s near Lake MI, to the lower to middle 40s north- central WI. Any mixed precipitation would turn to all snow Sunday evening as the low pressure reaches eastern sections of the Great Lakes. A ridge of high pressure is forecast to build into the western Great Lakes later Sunday night and bring a gradual decrease in clouds from west to east. There will still be enough of a northerly boundary layer wind through the night to prevent temperatures from falling too far. Look for readings in the lower to middle 20s north-central, lower 30s east-central WI. As this surface ridge slides across WI on Monday, winds will begin to back to the southwest across central WI. Onset of WAA should bring at least some high or mid-level clouds to the area later Monday afternoon, but no precipitation is anticipated. The initial sunshine will provide a boost to temperatures (away from the lake) with readings in the middle 40s near Lake MI, upper 40s to lower 50s elsewhere. Models send a modest mid-level shortwave ridge across WI Monday night, however a more pronounced surge of WAA and increased moisture transport may bring a chance for snow or mixed rain/snow back to the forecast area after midnight. Chance for mainly light rain to carry over into Tuesday as a weak frontal boundary to be in our vicinity and a somewhat tight 8H baroclinic zone to exist over southern WI. Despite the clouds and precipitation chances, max temperatures on Tuesday to be in the upper 40s near Lake MI, lower to middle 50s north and a few upper 50s west of the Fox Valley. Headed in the middle of next week, attention will be focused on the next Pacific system that is progged to dive southeast toward the southern Plains before lifting northeast toward the Great Lakes. The GFS does not dig this system as far south as other models, therefore already has light rain spreading back into northeast WI Tuesday night and several rounds of additional rain from Wednesday through Thursday. Other models provide a brief break in the precipitation across northern WI for most of Wednesday before focusing the next wave of rain primarily over the southeast half of WI. Way too early yet for a trend as this system is still well west over the Pacific. However, IF the GFS were to verify, we would be looking at a lot of rain and this would exacerbate the flood threat over the region. Just something to watch next week. Temperatures would cool below normal once again due to all the clouds and a northeast wind. && .AVIATION...for 12Z TAF Issuance Issued at 629 AM CDT Fri Apr 12 2019 A low pressure system will bring freezing drizzle to northern WI this morning, then a mix of light rain and snow to central and north central WI this afternoon into tonight. VFR conditions are possible at times in the Fox Valley and lakeshore areas, otherwise flight conditions will remain in the MVFR/IFR categories. Winds will become southwest and increase today, with gusts to 25 mph northwest, and 30 to 40 mph southeast during the afternoon and early evening. LLWS is expected to develop over mainly the southeast half of the forecast area by early evening. && .HYDROLOGY... Issued at 348 AM CDT Fri Apr 12 2019 Runoff from recent rain and melting snow should lead to slowly rising rivers and streams in upcoming days. Numerous rivers will be above bankfull, with a few reaching minor flood stage. && .GRB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 10 AM CDT this morning for WIZ005- 010>013-018-019-021. && $$ SHORT TERM.....Kieckbusch LONG TERM......Kallas AVIATION.......Kieckbusch HYDROLOGY......Kieckbusch