Tuesday, November 05, 2013

Warm or colder mid-November? Fun with teleconnections

I love to play with the huge palette of teleconnections at our disposal. As we transition from fall to winter, the big ones like the AO and the NAO will gradually become main drivers of cold air outbreaks across the North American continent. The PNA will give us the pressure tendencies across the west. This would signify a ridge/warmth out west or a trough/cooler out west. The opposite would occur in the east. So let take a look at what they are saying today on Election Day.

The AO
The PNA - Notice the +PNA corresponded to our cold spell in late October
This is all fine and dandy. The problem is that the GFS is showing a HUGE ridge in the east with temperatures well above normal by the 21st.

So what do we make of all this? 

First, the atmosphere is an inherently complex and chaotic system. A few teleconnections, while a good tool to use, rarely tell the complete story unless the indices are extreme to one side or the other.

Secondly, there is a distinct trend for the AO and NAO to sag into "cooler, troughy" territory. But for a colder, snowy pattern to develop, the numbers would have to go decisively negative which isn't shown here. The PNA is trending the other direction from the levels (strongly positive) during our brief lake effect snow event in late October.  PNA sharply negative indicates a ridge (milder temps) in the east NOT cooler.

So we might have to wait a few weeks for cold enough air to bring a good lake effect snow event.

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