These systems cause generally light snow or flurries, but more importantly bring quick temperature changes with them. Southwest winds ahead of the storm produce a short period of moderation. Once the storm passes, colder air rushes down from the arctic north. With wind chills in the teens, there's no doubt the winter season is here. We get the details in this AccuFacts file.
Temperature records show only a small part of the country has seen temperatures below normal.
Those regions are in the West. Namely, California through to the four corners of Arizona, New Mexico, Colorado, and Utah. But from eastern Montana through to New England, temperatures have been as high as four degrees above normal. Meteorologists blame most of the temperature spike on La Nina, which is warm water in the Pacific Ocean which changed the jet stream and allowed warm air to rise up from the Gulf of Mexico and the Atlantic Ocean. The Accufacts file has the details.