Sunday, December 2, 2012

ECMWF Corals Polar Vortex into North America

ECMWF 8-10 500mb height anomaly forecast

The latest 8-10 day forecast from the 0z ECMWF and Day 10 forecast from the 0z ECMWF Ensembles (EPS) shows that the Arctic will be changing its game plan in coming days, with forecasts calling for a strong ridging system of high pressure anomalies to be setting up from the Bering Sea to North Asia, North Europe and Greenland in what could be a dazzling display of flexibility as far as ability to change the entire field of the North Hemisphere goes.

If these forecasts of a horseshoe-style high pressure arrangement actually happen, there is only one option for the polar vortex (a semi-permanent low pressure system over the Arctic, the base of the Arctic Oscillation): It must be forced south into North America. If the polar vortex is forced south into North America, severe cold could flood the region.

Arctic Oscillation (AO) forecasts for the long range from the Climate Prediction Center suggest that there remains a very wide spread (range between forecasts) among the ensemble members forecasting this oscillation. However, the consensus does appear to be for the AO to stay mainly negative, although a trend towards a weaker negative phase appears to be in order.

The 12z GFS ensembles show their variance as well in the long range, suggesting that the AO will remain negative, but at a moderate negative stance and not as strongly negative as we have seen in recent weeks.

If the polar vortex does indeed come into North America, the US and Canada will be visited by many more instances of cold and snow, especially if that horseshoe blocking pattern does not dissipate for an extended period of time.



Anonymous said...

So if this blocking pattern stays, the eastern portion of the U.S. should get the wonderful winter forecast that every website's talking about?

KakHome said...

Andrew: I understand and respect that forecasts like this can be hard to iron out and that inevitably leads to a change in thought.

However - at this point - what is your relative confidence level that Northeast Ohio will get at least an *average* winter for temps/snow, all said and done?

And also how confident that either a) there will not be a stubborn eastern ridge or b) if there is, it won't be strong enough to significantly spoil mid/late December in particular for Ohio, if the PV drops into North America?

KakHome said...

If you can't answer the second question above as of yet please at least cover the first. Thanks.

All I'm asking in the second however is basically how significant do you think the risk is for an eastern ridge strong enough to spoil things in NE Ohio or if I should be far enough north/west?

ERN WX said...

Hello KakHome, I see cold and SNOW for many in the long range. The clippers and more are coming. The 18z GFS has a good idea in the long range. Esp. -NAO/+PNA. Not like last year!!!!

Anonymous said...

link to the models ERN WX please?

Anonymous said...

Today's 18z GFS and GEFS both are forecasting a negative PNA for the next two weeks.