So how exactly did we reach our long-term forecast of winter weather? Simple — well, sort of.
There will be a weak to moderate El Nino developing for the upcoming winter. This is where surface water temperatures are running slightly above average.
Last year we saw a weak La Nina setup, where surface water temps along the equatorial Pacific were a little below average.
Eurasian snow cover, while it had a slow start, has really picked up over the last several weeks. We now have above average snow cover across Eurasia. This helps the development of arctic air-masses. This doesn’t necessarily mean we’ll see these air-masses and that’s why we look at the NAO, which stands for North Atlantic Oscillation.
There are a couple of semi-stationary areas of pressure that sit over the north Atlantic. There’s the Icelandic Low and the Azores High. If these areas of pressure are stronger than average we’ll have a faster moving jet stream across the Atlantic. This will prevent a blocking pattern and sustained cold weather outbreaks in the east. If these areas of pressure are weaker than average than we have good chances for a blocking pattern and sustained cold.
This year we expect to start with a more positive NAO, however with more neutral and even negative tendencies later in winter.
This year’s teleconnections compare very favorably with the winter of 1994-95, which is what we based our prediction off of.