Good Tuesday bloggers and thank you for stopping by the WISN weather blog. Make sure to check back here for updates on this storm and also in the future.
WeatherWatch 12 has been showing you two distinct scenarios for the past several days. The storm appears to be taking the slightly more northern track.
What does this mean? It still means that a Major Winter Storm will impact the region beginning this evening and continuing through much of Wednesday, but it also means that snow, sleet, and rain will occur over parts of the area. Before we get into the analysis, let’s breakdown the warnings that have been issued.
Blizzard Warnings are in effect for the following counties: Fond du Lac, Sheboygan, Dodge, Washington, and Jefferson.
Winter Storm Warnings are in effect for the following counties: Ozaukee, Milwaukee, Waukesha, Racine, and Kenosha, and Walworth.
An intensifying area of low pressure will move into Illinois late this evening. The low will move near the extreme southeast Wisconsin border and move over Lake Michigan moving into early Wednesday. If you follow computer models, the NAM (North American Model) and the GFS (Global Forecast System) are two of the more reliable models that we typically use. The NAM has all along had the more northern track with this storm, so I am going to show a couple of the very latest maps that are just into WeatherWatch 12.
Below is the forecast map for midnight. The first dashed blue line over south central and southeast Wisconsin is the 540 thickness line. This line is usually a good indicator of where the rain/snow line will set up. There are many other factors, such as the temperatures at 850mb in the atmosphere, and also for near shore locations the temperatures of Lake Michigan. The water temps are still in the 40s!
This map alone tells us many things, but probably the biggest thing that stands out is that areas of Milwaukee, Racine, and Kenosha counties will very likely see a change from snow to a mix and then all rain for a period. The chances of seeing all rain increase the closer you get to the lake shore.
Just as the odds of seeing a mix or rain increase as you approach the lake, the odds of all snow will increase the farther west or northwest you travel. I mentioned the lake temperature will play a role in this storm … and here’s how. With water temperatures in the 40s, the air right above the lake will be several degrees or more above freezing.
With winds ahead of the storm in an east to northeast direction, this air will be pushed over the land. This will create an area of above freezing temperatures which in turn should turn the snow over to a mix or rain closer to the lake.
Here is the temperature forecast map for Midnight from the RUC (Rapid Update Cycle).
If you have travel plans, here is a quick breakdown of the time-line. The transition close to the lake from snow to a mix to possibly all rain should occur between 9 p.m. and 3 a.m.
During this window we should also see our heaviest precipitation during the storm. Away from the lake, in areas such as Waukesha, Washington, and Walworth counties, the precipitation should stay mainly snow, with a chance of a mix for a time. Snowfall rates should approach at least 1 inch per hour from the evening into Wednesday morning.
It is also possible that a few rumbles of thunder may occur. If thundersnow does happen, snow totals could be enhanced!
Now as the low pushes just east of the area, the cold air will spill in and quickly change and mix or rain back over to snow near the lake, and keep the precipitation all snow inland. Temperatures will begin to fall on Wednesday as the winds shift to the north and northwest. Wind speeds will also increase to 20-40 mph causing blowing and drifting snow and lower visibilities, especially in the Blizzard Warning areas.
Below is the forecast map for 6 p.m. Wednesday showing the strong winds with the tightly packed isobars (black lines showing lines of equal pressure).
A complete breakdown of forecast snow totals can be found on extended coverage of WISN 12 News Tuesday afternoon, evening, and again Wednesday morning. In short, the areas under the Blizzard Warnings will see 9 to 12 inches of snow with localized higher totals.
Near the lake shore totals will drop off dramatically in Milwaukee, Racine, and Kenosha counties where totals may be around 2 to 4 inches, with totals increasing steadily farther inland.
Make sure to stay tuned to WeatherWatch 12 for complete weather updates and school and business closings!
WeatherWatch 12’s Jeremy Nelson