The Power of the Polar Vortex and the PNA

It’s Monday and I said yesterday morning that I would wait until at least tonight for the final word on the storm for the end of the week.  Pretty much all of the models have lost it, as data collection continues to get better.  There are two main reasons for this, illustrated below, from the 500 mb map from the 0z European run last night:

The first is the Polar Vortex, the large blue mass centered over eastern Canada above.  When it’s this strong, and this far south, it makes it virtually impossible for the storm in the gulf above to gain lattitude and come north.  You can see how the resulting trough is broad and the upper air flow is more ENE than NE or NNE, as indicated by the dashed line, which is the ideal trough you’d like to see for an east coast storm. That dense cold air shunts the storm off the coast and out to sea.

The second is the PNA, or western ridge seen above. The forecast for the PNA has changed some just in the last 48-72 hours:

The PNA is clearly going negative.  This results in a weaker western ridge, and therefore a less amplified (or more broad) trough, again wisking the the low out to sea.

So, clearly the threat for a storm late this week has substantially diminished.  The pattern we’ve been in for the past several weeks also looks to change starting early next week, with a return to normal to above normal temperatures for at least the mid to latter portion of the month.

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One Response to The Power of the Polar Vortex and the PNA

  1. Pingback: Tweets that mention The Power of the Polar Vortex and the PNA | doctoochweather -- Topsy.com

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