The daily climate summaries make it very clear, it's been cold. Of course, we all know that, given the hard starts of our cars in the morning, the frosty windows and the furnace that won't stop. Most of us would agree that it's too early for these cold weather complaints. The overall flow in the atmosphere during the past week looked something like this:
This allowed cold air from the arctic to dig south across the eastern half of the country. Our average temperature over the last week or so has been about 8 degrees below normal! That's cold. Here was the 6 to 10 day outlook for the week of Thanksgiving, issued on the 18th of November:
It looks like it verified pretty well. Here is an analysis of the observed temperature anomaly (departure from normal) for the 23rd-27th (note: it is off by one day).
Over the next few days, the weather pattern across the U.S. will undergo a big shift. Instead of a cold northwest flow, we'll see an evolution to a southwest flow, which means our temperatures will finally warm to more normal levels. The western U.S. will turn cold, while the eastern half warms up.
Look at the new 6 to 10 day outlook for Dec 4-8, 2013. That's a dramatic shift!
Of course, this southwest flow means more moisture begins to flow north. With cold air to the west and warmer and more moist air to the east, it's time to keep an eye out for the development of big low pressure systems. This flow can be very active storm-wise and our model simulations are starting to suggest some development around the middle of next week into next weekend. There is plenty of model disagreement, so confidence on any timing or development is very low. Just keep it in mind if you have plans later next week.