Tuesday, June 4, 2013

Long Range Winter Prospects Very Favorable

Reminder: My Preliminary 2013-2014 Winter Forecast comes out Saturday, June 15 at 12:00 PM Central Time.

Long range weather models are predicting a very favorable winter for those snow lovers and plowers who have been in a big deficit in the past two years.

Shown above are two long range forecast models, predicting 200mb heights for the month of December 2013. Areas of blue depict general lower heights and thus low pressure areas, while reds indicate high pressure systems. The contour lines are superimposed on the images to help point out areas of differing pressure. There are four regions I want to look at here, so we'll start out with North America.

Both images show a pretty favorable set-up for cold weather as far as the 200mb level goes. We have a large area of rather strong low pressure over eastern North America stretching into New England, and this is reflected by the compression of contour lines in the same region. The low pressure area over New England tells me this area would indeed be favored for at least somewhat-frequent shots of Arctic air, and the tightening of the jet stream favors this theory. The overall picture is what excites me more. If we look into the far Northern Hemisphere we see no area of low pressure- the closest persistent low pressure center is the one in North America. Now, bear with me here, the idea is pretty outland-ish. But if you were to try to place a location for the polar vortex to average out over the month of December, you would want to find the area with the lowest pressure over the general upper latitudes (including North America, northern Eurasia, and Greenland). That said, it would make sense that the polar vortex may very well have a tendency to be pushed further south towards Canada and the US.

Our second area of interest is the United States. Both models show that low pressure area trying to push into New England, but we already covered that in the above paragraph. The item I want to focus on is the West Coast into Alaska. We see a separation of the contour lines into a looser composition, as well as oranges building into those areas. This indicates the presence of high pressure, and sets up positive phase of the Pacific-North America (PNA) pattern. In the wintertime, the jet stream does exactly what is being depicted above, and this means a warm West US and cold East US. Additionally, storm systems will tend to track in a path favorable for snowfall in the Midwest, Plains and portions of the Great Lakes into the Ohio Valley. The positive PNA helps to usher in lower than normal heights across the East US, and this will deliver us into the next area of interest.

The third area of interest is the Bering Sea. Both models project strong high pressure in the vicinity of the Bering Sea region; the GFDL model (left) has high pressure square in the Bering Sea, while the NCAR model (right) has the high pressure more towards Asia but still influencing the Northern Hemisphere. In both situations, the Arctic Circle appears overcome with above normal height anomalies, indicative of high pressure in the region. High pressure in the Arctic would imply a weaker polar vortex (yes, the same vortex I discussed this previous winter), as well as tendency for cooler weather to make its way down to lower latitudes of the world. If we do have high pressure in the Bering Sea, it would be easier for instances of high pressure to overwhelm the Arctic, and this could (keyword is COULD) allow the polar vortex to be pushed further south and affect lower latitudes in significant ways.

The final area of concern is East Asia. All models I observed for December 2013 depicted a tightening of the contour lines and lowering of height anomalies in East Asia, sometimes even into the northern Pacific. I have described a few times on this blog the idea of the East Asia-East US storm correlation, where a stormy period in East Asia can mean a stormy period in the East US 6-10 days later. This would mean more chances for snow whenever East Asia got active, and if long range models are correct this active period could be quite often. If the tightened jet stream in the North Pacific and stormy East Asia evolves as predicted (combined with the possible +PNA pattern and weakened polar vortex), this winter may help those winter-loving souls damaged by the last couple of winters.

Don't forget, as the note at the top says, my Preliminary 2013-2014 Winter Forecast will be released Saturday, June 15th at 12:00 PM central time.