Updated Winter 2010-2011 Outlook

So far this winter, we saw a moderate to strong La Nina, which on average produces cold and snow from the NW US through the Great Lakes with a mild East. When making the winter outlooks in the fall, it appeared that this winter would at least start out differently, with an east based La Nina and a -NAO/-AO pattern persisting and leading to a colder than average East, which a moderate to strong La Nina would usually have a positive NAO/AO. That was true of December, however the pattern was much more extreme than previously thought, with the AO and NAO being very negative, locking in a very cold and dry pattern across most of the eastern and southern United States. The blizzard that the area saw last weekend shows the fact that only one storm can change the entire snow outlook, as with that single storm, parts of the area are already very close to their total winter average snowfall, with a few locations even passing their average snowfall. With the area already seeing these totals with another 2-3 months of winter left, upward adjustments are necessary for this winter's snow forecast.


January Outlook: Cold And Potentially Snowy Pattern

When making the final winter outlook, it appeared that the colder than average pattern may persist into early-mid January, with a mild pattern becoming established around mid January with the storm track going near the Great Lakes, bringing above average snow to these areas. The pattern, however, does not support this happening, as after a brief time frame which we are currently seeing, where the pattern is reloading and temperatures are warmer than average, starting on January 3rd the cold pattern will return again for the area, with the NAO and AO remaining negative through most of January, ending what was a brief and weak January thaw.

As a result, we are looking at a cold pattern for most of January, with the coldest departures in the Southeast and the Mid Atlantic regions. While January will start out dry, as other than a storm threat around January 7-9, it appears that a stormy pattern may develop after January 10, which combined with the cold may lead to several snowstorms over the Mid Atlantic and Northeast regions, including a potential storm between January 12-14. Depending on what happens in this time frame with the potential storms, it is possible that the NYC area may end up with above average snowfall for the month.

Around the third week of January, after 1/15, the AO is modeled to become strongly negative, and the GFS model has been consistent in showing some type of an extreme arctic air mass in this time frame with the ECMWF also starting to show this potential. Given the pattern, it is a possibility that we may see an arctic outbreak focus on the north central US and potentially affect the rest of the Northeast/Mid Atlantic around the third week of January, with the potential for the coldest temperatures of the winter to take place if this potential verifies. More detailed updates will be posted on this potential once it gets into the medium range, if there is still a potential.


February And March: Potential Break From Consistent Cold, Then More Cold And Snow?

By the end of January, there is more uncertainty with the long range forecast, however it is a possibility that the cold may weaken, with a milder pattern for parts of February with more cold and snow towards the Great Lakes region, though if we do see such a pattern evolve, at this time it appears to be unlikely to be as strong or as long as the final winter outlook had it, even though warmer temperatures than those of January are possible. It is possible that by late February and March, we could see a colder pattern returning with more snow threats into the Northeast, however the February and March outlooks are still uncertain, and more on these two months will be posted once we get towards the end of January.


Winter Oultook Update Summary:

Overall, with the changes in the forecast for January, including a potentially weaker warm up for February than originally expected, I am going at this time with below average temperatures in January and slightly above/above average snowfall, and if the snowy January potential verifies, the total winter snowfall may end up between 40 and 55 inches of snow for New York City, making this winter's snowfall above average, something which is quite unusual for a moderate-strong La Nina. Depending on how cold January is and the pattern that we see in February, the December-February time frame may end up with below average temperatures for the NYC area.