573 FXUS63 KGRB 200437 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1137 PM CDT Wed Mar 19 2025 Updated aviation portion for 06Z TAF issuance .KEY MESSAGES... - A potent spring storm will impact the region through late tonight, bringing heavy snow to central, north- central, and far northeast WI, and rain changing to sleet and snow elsewhere this evening. A few thunderstorms are also possible late this afternoon and evening in the Fox Valley and central WI. Winter Storm Warnings and Winter Weather Advisories have been issued across most of the forecast area. - Strong northeast to north winds gusting to 30 to 45 mph may produce pockets of blowing snow in open areas through tonight. The combination of wet, heavy snow and strong winds could cause tree damage and produce sporadic power outages as well. Hazardous travel conditions are expected region-wide. - A prolonged period of snow mixed with rain at times is expected Sunday into Monday. At this time, there is a 40 to 70% chance of 3 inches of snow from Sunday and Sunday night across the entire area, and a 30 to 50% chance of 6 inches across the north. && .DISCUSSION... Issued at 348 PM CDT Wed Mar 19 2025 Short Term...Tonight and Thursday Water vapor imagery shows a strong low pressure system moving across northern Missouri this afternoon creating widespread areas of snow, sleet, and rain across the upper Midwest. Regional radar and RAP analysis shows a band of heavy snow developing due to an area of strong mid-level frontogenesis extending from northern Iowa into central WI. Within this band of 1-hr snow rates are likely 1-2" per hour which is in like with the 12Z HREF. As the stronger forcing moves northeast expected those higher snowfall rates to develop from central to far northeast WI, where a Winter Storm Warning is in effect. RAP analysis also shows increase mid-level instability across central WI leading to some convectively enhances snow in those regions. Overall snowfall amounts remain highest (4-8")along a line from AUW to ESC. The biggest question for the remainder of the afternoon is when will rain transition to snow in the Fox Valley and along the lakeshore. With temperatures still the mid 30s in the Fox Valley it may take another hour or two to cool enough for the transition to occur. For areas in the Fox Vally and along the lakeshore snow accumulations are expected to reach 3-6" with locally higher amount possible in Door Co. Area web-cams show snow has also been slow to accumulations roads, however, once the sun begins to set may see a rapid deterioration in road conditions this evening. There is going to a sharp cut off in snow amounts across north- central WI as drier air is winning our north and west of an RRL to LNL line. Winds are also starting to increase across the region this afternoon with gusts pushing 30-40 mph. Northerly winds across the region will continue to increase late this afternoon evening. Blowing snow may cause sporadic reductions in visibility across the open areas of central WI this evening. Sporadic power outages and tree damage are also possible and winds increase and wet snow accumulations are trees and powerlines. Snow is expected to come to an end from west to east overnight with most of the region expected to turn dry by day break Thursday. Breezy west winds will linger through Thursday morning before starting to diminish during the afternoon. Long Term...Thursday Night Through Wednesday Tranquil conditions will prevail Thursday night into Friday morning as a cold front approaches from the northwest. As the front moves into the area, this feature will bring a chance of light rain during the afternoon and evening. The rain could end as light snow as temperatures fall during the evening. The main system of concern is a prolonged period of light snow mixed with rain at times Sunday into Monday. A 500mb trough is expected to close off and become negatively tilted Sunday afternoon into Monday. On Sunday, the GFS model indicated 145 knot jet streak passing south of the area, with much of the area in the favorable left exit region of the jet which will enhance lift across the area. Models did show weak 850mb warm advection of the upper level disturbance that should move across the area. Temperatures are expected to warm into the 30s, however some large temperature/dewpoint spreads in the guidance would suggest temperatures will fall back closer to freezing once the precipitation arrives. Snowfall accumulations difficult to determine this time of year due to higher sun angle, air and ground temperatures above freezing. Snowfall rates will also be a determining factor, especially during the day. Looking at the DESI, probabilities of 3 inches of snow Sunday and Sunday night is between 40-70%, highest chances across the north. There is a 30-50 of 6 inches across the north. The chances for mainly snow will continue Monday as the upper low moves across the state. Will need to watch to see if there are more significant snow shower activity with this feature that could impact visibilities for motorists. The northwest flow pattern will continue Monday night into Wednesday which results in low to medium confidence in the dry conditions as the model have small features dropping southeast into the central portion of the country during this time frame. Seasonable temperatures will continue into the middle of next week. && .AVIATION...for 06Z TAF Issuance Issued at 1136 PM CDT Wed Mar 19 2025 Snow will continue to come to an end from west to east overnight. Conditions have improved to VFR where the snow has ended, with MVFR/IFR conditions where snow is ongoing. Conditions will improve to VFR overnight as the snow ends and drier air works into the region. High pressure will then ensure VFR conditions prevail on Thursday. Surface winds will continue to be very gusty through Thursday morning, with gusts of 20 to 30 knots at times from a northerly direction. Winds will eventually back to a northwesterly direction Thursday morning as they gust to 20 to 30 knots then back further to a westerly direction Thursday afternoon with gusts around 20 knots. LLWS will continue into early Thursday morning as winds just off the surface gust to 40-50 knots, then ease Thursday morning as these winds subside. LLWS is possible again Thursday evening across central and north-central Wisconsin as southwest winds just off the surface gust to around 35 knots with a light surface wind. && .GRB WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 1 AM CDT Thursday for WIZ020-021-031- 035-036-073. Winter Storm Warning until 7 AM CDT Thursday for WIZ022. Winter Weather Advisory until 1 AM CDT Thursday for WIZ038-048. Winter Weather Advisory until 7 AM CDT Thursday for WIZ039-040- 049-050. && $$ DISCUSSION.....GK/Eckberg AVIATION.......Kurimski