We had a blast of lake-effect snow yesterday. This happens when cold air passes over a warm lake, pulling huge volumes of moisture from the water and freezing it into snow. The air got quite a bit below freezing yesterday morning, so the northeast winds picked up a lot of vapor from the 8°C water, which it promptly dropped on the city.
Through the spring and early summer we often hear that it's "cooler by the lake." But like the idea of "global warming," that hides a lot of nuance in a simple phrase. A slightly-more-accurate telling might be that it's "less variable by the lake." And yesterday we got an example of that.
At Inner Drive Technology WHQ, which is just over 2 km from Lake Michigan, yesterday was the first day since March 2nd during which the temperature didn't get above freezing. Yesterday the temperature ranged from -3.0°C to -0.5°C, with a dip during the second round of snowfall between 8 and 10 am. On March 2nd, it ranged from -5.4°C to -0.2°C.
Contrast with Chicago's official weather station at O'Hare (23.2 km from the lake), which last had a full day below freezing on February 21st. On March 2nd it did get down to -8°C, but it got up to 3°C, after hitting 14°C on February 28th. Similarly, yesterday O'Hare was both colder (-3.9°C) and warmer (2.2°C) than IDTWHQ, warm enough for all the snow to melt just a few hours after it fell.
Today's forecast promises above-freezing temperatures everywhere in the Chicago area today, rising to 18°C by Saturday. The snow doesn't bother me, but I hope the remaining ice melts from the sidewalks today.