First Warn Weather Team: The science behind our May 16th snow, plus your snowy photos

Friday, May 16, 2014

The science behind our May 16th snow, plus your snowy photos

Thank you to everyone who sent in pictures of snow on Friday morning. All of the pictures really helped to get a bigger picture of the snow that impacted the region. It was definitely a surprise snow, and even in some areas an accumulation of snow.

When thinking of weather, you have to look at the atmosphere three dimensionally. What happens up above has an impact on what we see at the surface. It was an interesting set up in the atmosphere late last night & early this morning - here's what happened.

Looking above at about 18,000 feet there was a very cold pocket of air where temperatures were in the range of -20 to -30 degrees. Below that, closer to the
surface at about 3,000 feet, there was a very narrow dry wedge of air. As the precipitation passed through the dry layer, it evaporated which caused the surrounding area to cool. This process is called evaporative cooling.

Just south of I-80, there was a strong upper level low that helped provide enough lift and strength throughout the atmosphere to sustain the snow showers through the morning. The greatest snow accumulation occurred south of Rockford where between half an inch and an inch of snow fell.

The last time Rockford saw a trace of snow was May 11th, 1966. The last observed snow that occurred in Rockford was May 2nd, 2005. The Chicago Rockford International Airport recorded 0.08" of liquid precipitation this morning. We'll have to see if we ended up with a trace of snow.

Thank you for sharing your snowy May photos with us this morning!