202 FXUS63 KGRB 251155 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 555 AM CST Thu Jan 25 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Freezing drizzle is possible over northern WI this morning and again tonight into early Friday. A combination of freezing drizzle and freezing fog may result in light icing on untreated roads, resulting in hazardous travel conditions at times. - Above normal temperatures are expected through this week and well into next week. Milder air moving over a melting snowpack will produce areas of fog and patchy dense fog today and tonight, and possibly continuing into the weekend. Dense Fog Advisories will be needed at times, especially during the nighttime and early morning hours. Poor or rapidly changing visibilities will create hazardous travel conditions. && .DISCUSSION... Issued at 409 AM CST Thu Jan 25 2024 Short Term...Today...Tonight...and Friday The main forecast concerns include precipitation type and trends, fog potential and associated travel hazards. Precipitation Trends/Type: A short-wave trough was producing a small batch of showers over northeast WI early this morning, and patchy drizzle or freezing drizzle was also likely occurring. Models have slowed down the next surge of precipitation with a more potent short-wave and coupled upper jet until late this afternoon into tonight, so expecting mainly drizzle or patchy freezing drizzle (northern WI) for most of the day. As the better forcing and deeper saturation arrive later today into tonight, a period of steady light rain is expected over the southeast part of the forecast area, with a light wintry mix of rain, freezing rain and possibly some wet snow expected farther north. The precipitation will slowly taper off from northwest to southeast as the system exits Friday into Friday evening. Low-level temperatures and thicknesses support mainly rain from central WI into the Fox Valley and lakeshore areas. The best potential for light icing will occur over northern WI this morning, and again tonight into early Friday, when air and road temperatures will hover near freezing. Fog Potential: mild air (and much above normal temperatures) will remain across the region, with a gradual increase in dew points expected. Areas of fog covered the forecast area this morning, and dense fog was reported in the Fox Valley. The current Dense Fog Advisory was not verifying well west of the Fox Valley at forecast issuance, but vsbys were starting to trend back down, so at least patchy dense fog should develop there by the time of the morning commute. Models suggest that vsbys will continue to lower across northern WI this morning, with significant fog persisting regionwide today, tonight and possibly into Friday morning. The current Dense Fog Advisory may need to be expanded farther north and potentially extended through at least tonight. If trends become obvious this morning, may make some changes before the end of my shift, otherwise will let the day shift assess the need for headline changes. Travel Concerns: Hazardous travel is expected due to poor or rapidly changing visibility regionwide, and in association with light icing and slippery roads (from freezing drizzle or freezing fog) over northern WI this morning, and again tonight into Friday morning. A Special Weather Statement will be issued to address the travel concerns. Long Term...Friday Night Through Wednesday A few areas of light rain may linger into Friday night across east-central Wisconsin and a mid-level shortwaves shifts east. The area is then forecast to remain mostly dry through the remainder of the extended period. However, areas of patchy will remain possible through this weekend with the mild moist air moving over the melting snowpack. Friday night through Sunday...Light rain may linger across east- central Wisconsin through Friday night as a mid-level shortwave works off to the east. It worth noting that while primarily rain is expected during this period probabilistic guidance does have a 5-10% for freezing rain, mainly for areas north of highway 29. While the precipitation is expected to end Friday night the patchy fog and overcast skies are progged to remain through this weekend as a mid-level thermal inversion traps evaporating moisture near the surface. Slippy roads and sidewalks will remain a potential hazard this weekend, mainly during over night hours as temperatures are forecast to dip below freezing potential refreezing melting snow or creating areas of freezing fog. If 850 mb temperatures were a few degrees colder lake effect snow off of Lake Michigan would be a possibility Saturday night into Sunday as winds turn easterly behind a low pressure system moving over the Ohio River Valley, however, with delta Ts less than 10 degrees increasing clouds will likely be the extent of the effect from this system. Monday through the rest of the extended...There is some uncertainty with the forecast for the first half of next week as recent model runs have been slowing the eastward advancement of a omega ridging pattern that is forecast to set up over the northern Rockies this weekend. Both the GEFS and ENS show this ridging pattern becoming nearly stationary next Monday and Tuesday which would allow a series of weak short-wave impulses to move through the NW flow pattern and potential bring a few rounds of light rain and/or snow, however, given that there is relatively little forcing with these systems keep the forecast area dry for now. As the upper-level ridge moves east, the middle of next week looks dry with possibly a few rays of sun returning to the area. Temperatures next week are expected to continue trending well above normal with highs 10-15 degrees warmer than normal for this time of year. Highs may reach into the low 40s as early as next Tuesday. && .AVIATION...for 12Z TAF Issuance Issued at 540 AM CST Thu Jan 25 2024 Flight conditions varied from IFR to VLIFR across the forecast area. There has been a slow downward trend in vsbys over most of the area early this morning, and suspect that conditions will remain in the LIFR to VLIFR categories for most of today and tonight. An email has been sent to our aviation customers to highlight the fog and very low ceilings, potential for flight delays and cancellations, and possible airport closures. That being said, cannot rule out some minor improvement during the daytime period, during periods of steadier rain tonight, or as NE winds increase a bit in the Fox Valley/lakeshore areas late tonight. In addition to the fog, patchy drizzle or freezing drizzle will occur at times, with steadier precipitation arriving in the southeast part of the forecast area later this afternoon into tonight. The best potential for light freezing rain/drizzle will be across northern WI this morning, and again tonight, when air and pavement road will hover near the freezing mark. && .GRB WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 9 AM CST this morning for WIZ035>040- 045-048>050. && $$ DISCUSSION.....Kieckbusch/GK AVIATION.......Kieckbusch