Last night the temperature here got down to 5°C, which feels more like early March than mid-May. Meanwhile, in San Francisco, yesterday got up to 33°C, which to them feels like the pit of hell. In fact, even in the hottest part of the year (early October), San Francisco rarely gets that warm. The Tribune explains:
The North American jet stream pattern, a key driver of the country’s weather, has taken on the same incredibly “wavy”—or, as meteorologists say —“meridional”—configuration which has so often dominated the winter and spring. This sort of pattern leads to temperature extremes across the content.
Pools of unseasonably warm air are in place on each coast while unseasonably cool air is sandwiched between and dominates Chicago and Midwestern weather.
It’s within this slow-moving pool of chilly, unstable (i.e. cloud and precip-generating) air that Chicago resides—a situation likely to continue into Saturday. This is to keep extensive cloudiness and the potential for sporadic showers going over that period of time.
In other words, the forecast for this weekend is continued March with a possibility of April by Monday.