Several factors explain the unusual cold that settled over the United States this spring. One has been the unusually heavy snow cover in Canada and the northern United States.
This year's snow cover is deeper, colder and extends farther south than last year. That's helped chill the already cold Arctic air flowing south into the country. So it has helped amplify conditions contributing to our cold spring.
The two maps above show the difference between snow cover in late April last year and this year.
The near record cold that has held sway is finally loosening up. Another cooldown is forecast within a couple of days, but it's not expected to bring the freezing temperatures that have made people miserable and delayed the onset of spring.
Other factors contributing to the unusual cold include a deeply sagging jet stream that has allowed Arctic air to drop farther south for longer than normal.
A local factor has been cloud cover during the day. In the winter, clouds hold in night-time warmth, while in the spring, clouds keep the sun's warmth from reaching the ground.
Source: National Oceanic and Atmospheric Administration/ National Satellite and Information Service and National Weather Service.