Tuesday, February 3, 2015

February 16-20 Potential Arctic Outbreak

There appears to be the risk of an outbreak of cold air between a February 16-20 period.

Tropical Tidbits
The image above shows 500mb geopotential height anomalies over the West Pacific, forecasted by the GFS model and valid on the morning of February 10th. In this image, we see a very strong upper level low displaced just north of Japan, with contours telling me this is a sub-500dm upper level low- a very strong storm. When we use the Typhoon Rule, which states weather phenomena occurring in Japan is reciprocated in the United States 6-10 days later, a strong upper level low could approach the United States from the north in a February 16-20 period. It's too early to tell definitively, but this could correlate to a lobe of the tropospheric polar vortex plummeting south towards the mid-latitudes. Again, it's too early to tell right now.

Long range ensemble forecasts for the middle of this timeframe are already beginning to see strong upper latitude blocking leading to a new wave of cold weather for the Central and East US, as those blue colors shown over North America. We will need to watch upcoming forecasts to see how they change.

For comparison, here's the chart of 500mb geopotential height anomalies over Japan on December 27th, 2013. We saw a very strong upper level low drop south into southern Japan, which then correlated to the infamous cold blast which originally made the phrase 'polar vortex' go viral. Forecasts above don't see the impending upper level low dropping as far south, which is why I'm thinking this upper level low will approach the region, and not necessarily induce a period of incredibly frigid temperatures, like we saw last winter.

To summarize:

- A strong upper level low looks to drop south to scrape northern Japan in the next week.
- As a result, we could see a period of below-normal, possibly well below-normal temperatures between February 16th and February 20th.