While the position of the jet stream will bring periods of precipitation (mostly rain) to the U.K. In parts of Scandinavia and the Baltics, cities that normally see sub-freezing high temperatures this time of year may instead have above-freezing low temperatures. This will leave most of the European continent in a zone of mild weather. While the orientation of that jet stream will change from time to time over the next 10 days, it will generally tend to snap back to a path over the United Kingdom and Scandinavia. In Europe's case, however, it is an unusually strong northward bulge in the jet stream that's to blame (or credit) for the warm spell. Most of Europe is already in the grips of exceptionally mild December weather pattern, and that is likely to continue in most areas through next week. 11, 2015, as reflected in the altitude above sea level of the 850-millibar atmospheric pressure level. EuropeĪ plot from the American GFS computer model shows an unusually warm pattern expected over the European continent on Dec. and Mexico probably won't see record-breaking warmth, but the southern branch of the jet stream may dip far enough south to keep a tropical or subtropical influence on the weather pattern over the southern U.S., allowing temperatures to at least hover a little above average for early and mid-December. Some of that warmth will spill over into the northern U.S. and Mexico.Īs a result, very mild air will sweep across Canada, bringing extremely warm temperatures (by December standards) across the entire country. One will bring mild Pacific air into Canada while the other dips into the southern U.S. West Coast before splitting into two branches. Instead, next week will feature a strong west-to-east jet stream over the eastern Pacific Ocean, aiming right at the middle of the U.S. Those north-south swings can help usher tropical air north and pull arctic air south. Winter warmth here often comes from large north-south swings in the jet stream, the ribbon of high winds about 30,000 feet above sea level that encircles the Northern Hemisphere. That won't be the case next week, the week of Dec. Typically when one part of North America is much warmer than normal, another part of the continent is much cooler.
Virtually the entire North American continent is shown with temperatures at or above average on this plot. This map shows a European ECMWF computer model forecast for temperatures next week (in degrees Celsius), relative to average for the time of year, at about 5,000 feet above sea level.
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