Moderate Snow for Some Tuesday Afternoon

From moderate snow one minute, to sunshine the next, the weather was a bit wild Tuesday afternoon.  Moderate, to at times heavy, bursts of snow occurred for much of southern Wisconsin and northern Illinois during the day, before fading away as the sun set Tuesday evening.  Accumulations were minor, but did add up to a few inches near Chicago and northwest Indiana.

To understand why we had those bursts of snow Tuesday, we need to look at what's happening in the atmosphere several thousand feet above our heads.  Low pressure moving up the East Coast continues to bring snow and wind to parts of New England and the Northeast.  Spinning around that main low are several and smaller low pressure systems that have been moving through the Great Lakes, bringing snow showers to Wisconsin, Illinois, Indiana, Michigan and Ohio the past couple of days.  As each of those low pressure systems moves through, it pulls down a little more cold air into the Great Lakes.

Temperatures at roughly 18,000ft in the atmosphere (which is where these low pressure systems are located) had fallen to nearly 40 degrees below zero!  Sunshine during the day Tuesday was able to generate enough instability in the atmosphere, due to the quick drop in temperatures aloft, causing cumulus clouds to quickly build and grow.  That instability, when combined with the rising air associated with the low pressure system moving through, allowed the snow showers to develop.  Similar to when thunderstorms develop during the Spring and Summer months.


With the setting sun, we lose the majority of the instability in the atmosphere causing the snow showers to fade away and skies to clear.  We remain under the influence of the low pressure system out East, but high pressure moving in from the west will limit any precipitation developing during the day Wednesday.