901 FXUS63 KGRB 161855 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 155 PM CDT Sun Jul 16 2023 Forecast discussion for routine afternoon forecast issuance .SHORT TERM...Tonight and Monday Issued at 155 PM CDT Sun Jul 16 2023 The main concerns for the short term forecast will be: -Rain and a few storms this afternoon and evening -Lingering smoke aloft from the Canadian wildfires -Another small showers chance tomorrow Storms Today: A weak cold front will work its way across the region this afternoon and evening, bringing showers with a chance of thunder to the region. The main front is still in northwestern WI, but some of the showers and a few storms will work their way into north-central WI by the mid afternoon. Dynamics along the front will be the main driver for any thunderstorm development, with fairly impressive bulk shear around 35 knots and strong vorticity advection along the left exit region of an upper level jet. Despite the forcing however, instability remains at a premium, with more modest CAPE values around 500 to 700 J/kg and only modest mid-level lapse rates. As a result, storms will likely be fairly scattered with the frontal passage. Stronger storms will likely be relatively brief, arising only where the strongest forcing aligns with the better instability. The main thunderstorm concerns will be wind gusts mixing to the surface and small hail. Severe weather still seems unlikely at this time. Smoke: Smoke has rapidly improved over the course of the day, with surface visibility from smoke around 3 miles this morning lifting to relatively unlimited visibility at the surface. Some hazy skies and light smoke at the surface will remain through at least midnight however, especially across central to east-central Wisconsin, including the Fox Valley. There area a few hints that some haze will return Monday afternoon, but for the most part the worst of the smoke will be out of the region for now. Showers Monday: Another weak shortwave will work its away across the north on Monday, producing cloudy skies along the Upper Peninsula border. Some light precipitation will be possible out of this layer at times, but no thunder is currently expected. The rest of the area will predominantly see dry conditions. Aside from the concerns above, temperatures will be a few degrees cooler than last night, with lows in the upper 40s to middle 50s. Tomorrow, high temperatures are forecast to be in the upper 60s to upper 70s. .LONG TERM...Monday Night Through Sunday Issued at 155 PM CDT Sun Jul 16 2023 Overall, no significant changes to the long term portion of this forecast package. As far as the big picture is concerned, large-scale upper-level pattern will undergo a rapid transition as the upper-level low that has been loitering around southern Hudson Bay finally releases to the northeast by 12Z Tuesday allowing upper-level heights to rebound over the western Great Lake with flow becoming strongly zonal. Unfortunately, consensus of medium range guidance is also locking in on another pesky upper-level circulation over southern Canada that will slowly drift southeast and becoming situated somewhere just north of Lake Superior by 12Z Thursday. With the fast zonal flow in place, confidence remains low during the mid-week in terms of timing of aforementioned upper-low and any weaker impulses that may eject from this primary system into the forecast area. In response to the approaching upper-level system, broad upper- level PVA in concert with low-level WAA will increase late Wednesday over the northwest portion of the forecast area, in concert with an approaching cold front. At least initially, deeper boundary layer moisture, steep mid-level LRs and best overall instability will be somewhat limited as these will be mostly bottled up across the central plains near a strong W-E baroclinic zone that will be host to MCS activity there. Thus, it appears precipitation late Wednesday into Wednesday night will be on the lighter side and mostly confined to the Northwest half of the forecast area. On Thursday, the upper-level low pressure system and associated surface low pressure system and cold front will likely be located somewhere over Wisconsin with additional shower and thunderstorm activity probable. Whether or not any of the convective activity is able approach severe limits later in the day will largely depend on cloud cover, extent of lingering morning activity and how progressive the surface cold front will translate across the forecast area. Regardless, the period from roughly 06Z Thursday through 00Z Friday will be rather unsettled. Given the above uncertainty, stayed close to blended temperature guidance during this period. Model consensus for Friday suggests that although surface low pressure will be east of the forecast area, some E-W orientated surface troughing may persist suggesting perhaps some diurnal shower activity, especially into the afternoon. By early next weekend, it appears we will be back into a more NW flow regime with some potential for some weaker, moisture limited impulses dropping southeast across the area from time to time. && .AVIATION...for 18Z TAF Issuance Issued at 1252 PM CDT Sun Jul 16 2023 A weak cold front will pass through the region this afternoon and evening, keeping scattered mid-level clouds in place and producing some rain showers a few thunderstorms. Confidence on location was not high enough to make the prevailing group for any one site, but made a mention of vicinity precipitation for each TAF site as the cold front crosses the region. Aside from the active weather, smoke and gusty winds will also hang around into the evening before departing by late overnight. Quieter conditions are expected for Monday morning, before winds begin to increase again for portions of the region. There is some potential for an MVFR cloud deck across the far north tomorrow, which may work its way into RHI Monday afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM.....Uhlmann LONG TERM......ESB AVIATION.......Uhlmann