Sunday, November 30, 2014

Encounter With Polar Vortex On The Horizon in Early-Mid December

It now appears much of the United States will undergo its first encounter with the polar vortex in the second week of December.

Tropical Tidbits
The image above shows 500mb height anomalies over the Western Pacific on the evening of December 1st. In this image, we see what is very likely a lobe of the polar vortex passing just north of Japan, occluding and cutting north as it does so. Minimum values here at the 500mb level in this image, off the GFS ensembles, appear to drop close to 490 dam, an indication of either an incredibly strong upper level low, or the more-likely polar vortex lobe.
This situation appears similar to the case we had last winter, where we saw a very strong upper level low crash into Japan to round out the year 2013, which then led to incredibly cold weather in the first week of the new year.
December 27, 2013
If we recall the Typhoon Rule, which states weather phenomena occurring over East Asia is reciprocated in the United States about 6-10 days later, we could expect a bout of  substantial cold here at home in the December 7-11 timeframe. Should this verify, which is becoming increasingly likely given model consistency, the Central and parts of the East US may expect a bout of intense Arctic air to hit in the middle of December.

But it doesn't end there...

Tropical Tidbits
The image above once again shows 500mb height anomalies from the GFS ensembles, now valid on December 6th. Notice that we still see below-normal heights over Japan. This means Japan has been under a strong upper level low's influence for nearly a week, and still going. Building off of the first graphic, it's quite possible that the United States may also undergo a harsh beating from cold weather for nearly a week straight. The degree of this cold air is still under examination, but if it's anything like the upper level low expected to trek north of Japan to open December, watch out.

To summarize:

- Japan looks to undergo severe cold weather to start off December, likely leading to a prolonged Arctic air intrusion in the US in the middle of December.