Monday, February 4, 2013

Winter Not Over Yet

I do not believe that winter is over just yet, although we begin to approach the final weeks of the winter season.

Pictured above is the GFS Ensemble 500 millibar forecast for the very end of the forecast period, February 20th. High pressure has built in over the North Pole, and strong low pressure is present over south central Canada, extending into the Great Lakes. This is all in response to the sudden stratospheric warming we saw earlier on last month. The warming is now dying off, but its effects will continue for at least another week or two. During this time, previous warming will continue to propagate down to the surface, leading to increased chances for cold weather. One thing I am fairly certain of is the high latitude blocking finally making it into the North Pole. This blocking high pressure is already in northern Asia in the medium range, so only a slight shove north would result in the high pressure system reaching the North Pole. This could also be another effect of the previous sudden stratospheric warmings, or SSW's. SSW's are known to provoke blocking high pressure in the higher latitudes, so such a solution is certainly plausible. I do have some concerns about that small low pressure area in the Southwest US and high pressure area in the Pacific Northwest. That is a common set-up for a Rex Block pattern, which can induce warm and dry conditions over the East US- something snow lovers are certainly fearing.

Now, you may have seen some Madden-Julian Oscillation (MJO) forecasts that were moving into Phases 1-3 during this timeframe, which decreases cold and snow chances with each increasing phase. However, it looks like those models may be on the wrong track. As several global models have also been hinting at, this forecast shown above depicts Outgoing Longwave Radiation (OLR) anomalies for the next few weeks. The images are centered over the Equatorial Pacific, where the MJO occurs. For those unfamiliar with the concept, the MJO changes phases by tropical convection moving from one part of the Equatorial Pacific to another. Cold and snow is most favored when this enhanced convection (negative OLR) is shown in the Atlantic or the Indian Ocean. The above forecast from the Roundy Waves Albany indicates that very powerful negative OLR anomalies may evolve going into the last week of February. It is plausible that the last week of February may then be very active. I would like to wait a little longer until we get closer to this timeframe, but right now, it appears that a cycling MJO in phases 8-2 may occur throughout February. Those three phases are notorious for bringing cold and snow to parts of the US in the cold season.



Anonymous said...

Andrew random question but what is a deformation zone? I know its a big area of snow in winter storms but why does it happen?

Anonymous said...

Could you answer me Andrew?

Andrew said...

The deformation zone is basically the area where snow thrives. I have not really studied up on it, and may not be able to as my time is limited in coming days and weeks.