Since October, the overall weather pattern east of the Rockies has been above normal temperatures and very little snow for the winter so far. The Midwest has been way above normal. This is opposite of what most forecasters were looking for in the many winter outlooks issued in the fall. Accuweather even went so far as to point to Chicago as the place you would not want to be this winter. Why have the outlooks, at least through the end of the year, been so off?
What forecasters were looking at was another moderate La Nina water pattern in the equatorial Pacific, which we have. Strong volcanic activity in far north latitudes during the summer/fall to block some incoming solar radiation. The big item was an expected Greenland blocking pattern in the north Atlantic in response to above normal north Atlantic water temperatures. This is the piece of the puzzle that so far has not materialized. This is the key to why things have been mild so far. While much in meteorology is understood, there is still a considerable amount that is not well understood. With limited knowledge, computer modeling is also limited. The computer is no smarter than the humans that program it. Limited knowledge in means limited knowledge out.
The Chicago NWS office has written an excellent article (here) explaining what has occurred so far this winter. It all has to do with something called the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO). They were expected to be in what is known as the negative phase for this winter, like the past few winters. This produces a cold air and stormy long wave trough over the eastern part of the country, like in the map on the left. Instead, the AO and NAO have been in a positive phase, which in combination with the La Nina pattern, produces basically a mild west to east flow over the country which brings in milder Pacific air, the cold Arctic air is held up in Canada.
For the Chicago metro area, the week ahead looks more of the same. We will be on the north edge of a rain system mostly to our south for Monday night. Much needed moderate to heavy rain will fall in the deep south. High temperatures this week will vary from the upper 30s to lower 40s, or 5-10 degrees above normal. No significant storms are in sight into early next year, along with no prolonged cold snaps into early next year. Our winter weather paradise continues.
You can follow my articles by clicking on the “Subscribe to get instant updates” link on top.
You can also follow me at http://www.facebook.com/allfish2 and at http://www.twitter.com/allfish2
Comprehensive weather articles and discussion can be found at http://www.stormcentral1st.com