Saturday, February 6, 2016

A Tale of Two Years

If you were in Northern Illinois in early February of 2015, you probably remember the massive snowstorm that dumped a foot of snow on Rockford, and even more in Chicago. Our snow pack on February 6th of 2015 was roughly 12". Currently, we have a snow pack of 0" with snow piles being all that is left of our snow cover. Temperatures were subzero at times in early February of 2015, and high temperatures didn't eclipse the freezing mark until February 7th. This year has been a different story with relatively mild temperatures near or slightly above average average, with Super Bowl Weekend featuring high temperatures in the 40's.

It is something that occurs quite often in many areas. One year will feature some sort of weather while the following year features the polar opposite type of weather. The atmosphere is a fluid, so it is always in motion and changing. That is why we can experience various types of weather extremes in one location year after year, and sometimes even within the same week. The Midwest is notorious for seeing many types of weather in a 1-week span, especially during the transition seasons of autumn and spring.

So, let's review last year's blizzard.
A low pressure system moved just to our south, which allowed the Stateline to be on the cold side of the system. Plenty of arctic air was in place as that low deepened and tapped into moisture from the Eastern Pacific and Gulf of Mexico. That moisture was pumped northward and ran directly into the colder air in Northern Illinois, which resulted in massive amounts of snowfall. As the event progressed, colder air continued filtering in, which led to higher snow ratios. In other words, the snow transitioned from wet and heavy to light and fluffy, meaning higher snowfall totals began occurring as fluffy snow accumulates to higher totals. Not only was the low strong, but the Stateline was in a favored area of strong lift and instability existed in the atmosphere. These are two important variables to have to see heavy snow. We essentially crossed everything off the checklist to see a significant snowstorm. With a tightening gradient, blizzard conditions were witnessed near Chicago.

Take a look at the totals that were recorded in the region. Our lowest totals were in the 7"-8" range. Meanwhile, our friends in Rochelle, Paw Paw, DeKalb, Belvidere, and McHenry saw a foot or more of snowfall over a 2-day span. In fact, Rockford reported snow for 27 hours straight during the event as a large precipitation shield developed. That essentially means there were no breaks in the snow. It snowed at a good rate for over a day.

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