Most commonly, we think of snow and cold when we talk about winter weather, but winter can show itself in many ways! Let's look at the setup we need to see different types of winter precipitation.
Winter Precipitation Types
Just like the weather varies at the ground level, the weather also varies at different levels of the atmosphere. This is why it's important that we look at the profile of the atmosphere when forecasting weather events.
Starting on the left, we see the atmosphere is warm through a deep enough layer that the surface precipitation type is rain.
Next is freezing rain, where frozen precipitation falls into a layer of warm air, causing it to melt. Then, near the surface, the rain encounters a shallow layer of cold air. That results in the rain freezing on contact with cold surfaces.
Sleet has gone through the process of melting, but falls through a thicker layer of cold air near the ground, meaning it has time to fully refreeze before hitting the ground.
For snow, the temperature profile is consistently below freezing.
Lake Effect Snow
Living near the Great Lakes, we are familiar with lake effect snow. Here in southeast Wisconsin, we see lake effect snow less often than on the other side of the lake, largely due to the predominant wind direction. Weather systems tend to move from west to east in the mid-latitudes (where we live) and therefore lake effect snow events more often impact areas east of the Great Lakes. But, when the setup is right, with an easterly wind component (and other necessary factors), we can see lake effect snow in Wisconsin.
When cold air moves over the relatively warmer waters of the Great Lakes, evaporation occurs, and heat and moisture are drawn up into the atmosphere. Clouds grow and begin to produce snow, which often falls in narrow, heavy bands over the nearby land.
Snow Squalls
A snow squall is a burst of intense snow and wind. These winter storms can cause a sharp drop in visibility, posing a major hazard for motorists. Whiteout conditions can trigger chain reaction accidents on roadways. The National Weather Service can issue Snow Squall Warnings when snow squalls are imminent or occurring. These can cause cell phone Wireless Emergency Alerts (WEAs) to activate within the warning area. These warnings usually last between 30-60 minutes and are focused on a small area with the highest potential for impact. Learn more about snow squalls in this blog post.
Blizzards
Blizzards happen infrequently in southeast Wisconsin; in the last 40 years, only 6 have been recorded in Milwaukee County. But when they do occur, they are dangerous and can cause major problems. A set of specific weather requirements must be met to technically classify as a blizzard. Those include: blowing snow, winds of 35 mph or higher, a quarter-mile visibility, and those conditions last for three or more hours. Low visibility due to blowing snow can create near-whiteout conditions on the roads. Snow drifts pose another hazard for drivers.
Be sure you're ready for winter weather by checking out the other TMJ4 Weather Blog posts from this week. If you have a weather question, or an idea for a blog post, write to us at weatherteam@tmj4.com.
