Thursday, November 24, 2011

Teleconnections Gearing Up for Winter Pattern Change

Forecast PNA Index.
Positive Phase is Good for Snow and Cold

Forecast AO Index.
Negative Phase is Good for Snow and Cold

Forecast NAO Index.
Negative Phase is Good for Snow and Cold
The teleconnections are looking much better than they have been looking and may be hinting that this winter pattern change is closer than we think. Above are 3 important indices that are commonly tracked and do affect the weather. We have labeled what is good for snow and cold people in each image. Click on the following links for explanations of the indices:
PNA (Pacific North American Pattern) --- NAO (North Atlantic Oscillation) --- AO (Arctic Oscillation)

The PNA has recently been in a strong negative phase, leading to unfavorable chances for snow and cold. However, in the above images, we see the majority of ensemble members are trending towards at least a weak positive phase already in progress but most likely becoming prominent just before November 30 or so. If the PNA is to go positive, chances for snow and cold would rise.

The AO has been in a positive phase most recently. When it is in a positive phase, a vortex around the North Pole strengthens and literally locks in cold air, forcing it to stay up north. However, if the AO is in a negative phase, this vortex weakens and the cold air can escape south, sometimes into the US. The ensemble members forecasting for the AO indicate equal chances for repeating positive spikes or a downward trend towards negative territory. We will have to watch this closely to see what happens.

The NAO has recently also been in positive phase, not a good sign for those who like snow and cold. The ensemble members indicate there is a very substantial potential for the NAO to go negative, increasing chances for snow and cold. The AO and NAO are closely related, so if one goes negative it is possible the other will as well.

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