As winds aloft become southwesterly, much milder air will move from the Gulf states toward the Northeast. At the same time, a northerly flow of frigid Arctic air will plunge southward into the Rockies and northern Plains. When cold air masses move south into the Plains, the Rockies often act as a barrier to any significant advance westward.
However, when the flow aloft is northerly on both sides of the Rockies and all the way to the West Coast, cold air can make it into normally protected areas from Washington to California. In San Francisco, temperatures could drop well down through the 30s tomorrow night. In 1972, San Francisco had eight record lows, including 24 on Dec. 9. That reading stands as the lowest ever for the airport location (SFO). It has never been below 30 there in February.
At Las Vegas, Nev., the temperatures will tumble into the 20s tomorrow night and again Thursday night. Record lows there in December are all in the teens and 20s. The most recent record low there in December was in 1990. In that year, six records were set, the lowest being 11 degrees on Dec. 23. There have been no new record lows set there in this century. Before making any inferences about that, I observe there has been only one record high in December set in this century (70 on Dec. 24 in 2005).
In the Chicago to Detroit area, it will become milder through tomorrow night (into Thursday in Detroit), then colder air will move in. Farther east, from Washington, D.C., to Boston, temperatures will climb to the 50s (north) to 60s (south), then not begin to turn chilly until sometime Friday. The video has more:
Looking farther ahead, one publication that ventures into climate prediction is The Browning Newsletter (www.BrowningNewsletter.com). The author, Evelyn Browning Garriss, suggests that recent volcanic eruptions contributed to the strength of last week's cold across much of the U.S. She writes that "Historically, winters with similar conditions (i.e; similar to the situation now) in the Arctic and Atlantic have been cold, especially in the Midwest and Northeast."
It is too early to be confident about any forecast for Christmas Day (or even the week before). However, the GFS model does go out 16 days, and it has a cold look for the Northeast exactly one week before Christmas.
... much greater interest is being generated on threats and rumors about tropical storms. It is worthwhile to read Dan Kottlowski's authoritative reports on this. Here is a copy of his map from this morning:
The tropical Atlantic shows signs of life in the storm development department. Dan Kottlowski's expert discussion suggests the third storm (which could be Hermine) of current concern is one that could head to the Bahamas, Florida, the Gulf or ???
A large high pressure area centered just south of Chicago will furnish a northwesterly of pleasantly cool and dry air to the eastern Great Lakes and all of the Northeast today into Tuesday.
As the trough moves through each locality, warm humid weather will be followed by showers and thunderstorms, then cooler an drier air will arrive
D actually makes up the largest part of this map and represents the large area that is sunny for the most part
The map shows three areas of more concentrated shower activity...