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Thank you for taking a few minutes to read the Weather Watch 12 blog! The past 24 hours provided many twists and turns in our weather. The end result was heavy bands of lake effect snow in fairly isolated locations. Much of Milwaukee County picked up 2″-5″ of snow in a very short period of time. In this blog we will take a look a couple of pictures from the peak of snow…and also look at why the snow wasn’t our average lake effect event.
On Wednesday I spent the 5 & 6pm newscasts at Klode Park in Whitefish Bay…right next to our snow engine…Lake Michigan. When I arrived a snow loving group of kids had just finished sledding. Here is a picture of Jonah & Hayden Nelson, Belle Patzer, & Henry Davis.
The powdery snow totaled about 4.5″ in Whitefish Bay. Most of the snow there had ended by 6pm.
In order for lake effect snow to occur we need cold air to flow over the warmer lake waters and the wind to blow off from Lake Michigan…meaning some sort of a northeast wind. Typically we look for this northeast wind at the surface. But really anywhere from the surface to about 1500 meters or about 5000 feet above the ground the wind can greatly influence or create lake effect snow.
Around 4pm on Wednesday…I arrived at Klode Park in Whitefish Bay and took this picture. The flag shown below was indicating a northwest wind. That means not a favorable wind for lake effect snow, but yet there was moderate snow falling.
The surface map from late Wednesday afternoon also showed the northwest surface winds in Milwaukee and Racine…but yet lake effect snow was occurring. Below is the surface map, Milwaukee is labeled ‘MKE’. The black line attached to the pink colored in circle by Milwaukee is the wind barb. The wind barb shows the direction and wind speed.
So if the winds in Milwaukee were out of the northwest for most of Wednesday afternoon…what was the driver of our lake effect snow? That question can be answered by looking at what is known as a sounding. Each day in select cities the National Weather Service launches a weather ballon that has instruments attached to it to measure temperature, dew point, wind speed and direction, etc. This data is then translated into upper air charts. The closest city to Milwaukee that launches a weather balloon twice a day is Green Bay.
The map that was created on Wednesday that incorporated the sounding data from across the United States holds the key to why our lake effect snow occurred in Milwaukee with a northwest surface wind.
Below is the 925mb map. If you are wondering 925mb is roughly 750 meters or 2500 feet above the ground. This map shows a due northeast wind in Green Bay at this level. The blue line with two barbs indicates a northeast wind of 20 knots or about 23 mph. This northeast wind persisted from the northern part of Lake Michigan all the way to Milwaukee.
The end result was lake effect snow bands which moved from the north-central part of Lake Michigan all the way to Milwaukee. The bands picked up lots of moisture and dumped that as a quick burst of heavy snow in Milwaukee. This isn’t the first time, and it won’t be the last that lake effect snow produces more snow than the forecast calls for. But hopefully this blog entry will help you understand why this type of forecast is very difficult to detect BEFORE the heavy snow occurs.
If you have questions or thoughts please post them to the comments section of this blog. Make sure to check out the blog on Friday…we will be issuing our long range forecast for the month of March!
Have a great day!