***Watch WISN 12 News at 5, 6, & 10 p.m. for the latest on the Winter Storm Watch***
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Let’s start by discussing the Winter Storm Watch that is in effect for all of south central and southeast Wisconsin. The Watch takes effect Wednesday evening and will continue through Thursday(Christmas Eve). The initial band of precipitation will arrive sometime late Wednesday afternoon or into the evening. Locations near the Illinois border will see the area of precipitation first. If you have travel plans on Wednesday I think the main roads will be in good shape through the morning and for most of the afternoon in Southeast Wisconsin. If you are traveling to Minneapolis or LaCrosse on Wednesday afternoon or evening, the later we get into the day, the better the chances are of running into snow. The snow could be moderate at times, especially in the evening(after dark). The roads may be snow covered or slushy in those areas.
Now let’s focus on Southeast Wisconsin for Wednesday. Temperatures will be in the low to mid 30s for highs, so above freezing. By either late afternoon or into the evening the initial band of precipitation should reach the metro. Notice I say ‘precipitation’, because it could either be some snow, sleet, or a mixture.
The map below is from ONE model. This is the 12Z run of the NAM(North American Model). This model updates 4 times a day…so we are always getting new data in! The forecast map below is valid from 6pm Wednesday until 12am Thursday…a 6 hour window. The blue line near Milwaukee(represented by a ‘*’) on this map is VERY critical. This is the 0C (32F) line at 850mb, roughly 1500 meters above the ground. When Milwaukee is near or north of this line a good rule of thumb is that the precipitation would be snow or possibly a mix. When the line is right overhead it could be snow, sleet, or even some rain mixed in. And when the line is north of Milwaukee, the precipitation would mainly be a mix or rain. The farther north the 0C line moves from Milwaukee, the better the chance of ALL rain.
Wednesday evening and Wednesday night we will likely see slippery spots develop on the roads in Southeast Wisconsin if the initial round of precipitation produces a quick 1-3″ of snow/sleet or we see a brief period of freezing rain. The greatest chance of seeing the freezing rain would be in Fond du Lac, Sheboygan, Dodge, and northern areas of Washington and Ozaukee counties. Again, I’m not expecting a great deal of freezing rain, but a brief period could still cause some headaches on the roads especially away from Lake Michigan. Areas near and west of Madison could see 2-4″ of snow/sleet on Wednesday evening and into early Thursday.
After midnight the 0C line will continue pushing north as the surface low strengthens to our south and pumps in warmer air aloft and at the surface. By Thursday afternoon, surface temperatures will likely be around 35-41 degrees, keeping the precipitation as RAIN. If you have travel plans in Southeast Wisconsin at this time it looks like the roads would just be wet. As you travel watch out for ponding of water on the roads or even some standing water. Not only will the rain create standing water if it rains hard enough, but also the snowpack in the inland locations will be melting or even blocking some of the drainage gutters.
The rain will continue Thursday Night and temperatures will only gradually begin to fall on Christmas Day in the morning. The map below continues to show RAIN at 6am on Friday…Christmas Day. By afternoon enough cold air should be wrapping into the area that there will be a changeover to snow.
At this time it does not appear that there would be much snow accumulation. In order for Milwaukee to get a big snow we would need the surface low to move to the southeast of Milwaukee, and that just is not going to happen with this storm. Snow totals are tough to predict 3 days in advance, but an early estimate for Milwaukee would be maybe around 1″ on Friday. By the weekend, colder air and snow showers will be over the region.
Here is a quick recap, late Wednesday an initial band of precipitation will move into Southeast Wisconsin. Likely starting as snow, but changing to a mix of sleet, freezing rain, and then transitioning to all rain by Thursday morning. Rain starts the day on Friday, with a change to snow showers. I would not recommend cancelling travel plans around southern Wisconsin, but just stay updated with the latest forecast on WISN 12 News and adjust accordingly. If you are traveling to Minnesota or western Wisconsin in the coming days, those locations stand a much better chance of seeing mainly wintry precipitation from this storm.
Total liquid precipitation around Milwaukee from this storm could be over 1″. This also included any snow/sleet melted down. In other words, this is going to be a very wet storm again for many!
Thank you for stopping by the Weather Watch blog! If you have questions on this storm please post them in the comments section and Mark or myself will try to answer your question.
Have a happy and safe holiday!