Winter 2011-2012 (DJF) forecast – Update

Here’s the updated forecast for this winter. I used the same six analog years, with different weights (more below).

IMPORTANT: The updated outlooks use the NEW 30-year normals (1981-2010), whereas the original forecast used the OLD normals (1971-2000). Overall, there were no drastic changes to the forecast.

Winter 2011-2012:

The monthly breakdown:

in [year (weight)] format

2010-11 (more)
1995-96 (more)
2008-09 (normal)
2000-01 (normal)
1970-71 (less)
1962-63 (less)

So what changed? Overall there was slight warming in northern California, cooler Gulf Coast and a warmer northern New England. Most, if not all, of the changes can be attributed to subtle strengthening in the blocking pattern (more negative AO/NAO) that will allow the cold to work further into the south-central and southeastern U.S. At the same time, this blocking pattern will pull slightly warmer air in off of the Atlantic into northern New England. The ridging in the western U.S. has shifted slightly further west, which is why northern California turned warmer. It is also the other contributing factor that caused Texas to turn cooler. Warm risks are in place in Texas and the Southeast as ridging could be more prevalent in these areas.

Precip/snowfall forecasts that I made previously are fairly similar to the update, so there isn’t any need to go into detail about these. There is a wet risk in the Northeast, which I decided to leave as near normal while the region is borderline normal to above normal (especially in southern New England).

From the analogs, 2010-11 was given more weight (equal to the weight of 1995), while 2008-09 and 1970-71 were given slightly less weight. I was going back and forth on whether or not to add 1955-56, but I decided that the La Niña in 1955-56 was too strong from the start of the summer through most of the winter compared to what is forecast (which will likely be a borderline weak/moderate La Niña).

I may issue an update once we’re into the season for the end of winter, but we’ll see if it’s needed.

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