Tuesday, July 2, 2013

QBO May Stay Positive This Winter

There are indications that the Quasi-Biennial Oscillation (QBO) may stay positive for the winter of 2013-2014.

The chart above, from the University at Albany's Mike Ventrice, shows the observed Quasi-Biennial Oscillation anomalies from July 2009 to the current time. Looking towards the far right end of the chart we see that the QBO is beginning to turn positive at this point in time. This positive turn comes after almost a year of consistent negative QBO anomalies. By just looking at the chart, you can see why an entire year had a negative QBO intact- the previous positive QBO event was very weak when compared to the strength of the two negative QBO events shown on the chart.

This image, from the Institute of Meteorology in Berlin, also shows the history of the Quasi-Biennial Oscillation over the past few years. However, this time, the positive (gray color) and negative (white color) anomalies are shown as they propagate downwards from the top of the stratosphere. If you take a look to the legend on the left side of the image, you see numbers from 10 to 100. 10 hPa is the upper stratosphere, while 100 hPa is defined as the lower stratosphere. These benchmark hPa numbers are traced in dashed lines across the entire image to show when a positive or negative QBO event reaches a certain hPa level of the stratosphere.

Take a look at the previous positive QBO event; the one we discussed earlier in this post. It shows up in the middle of 2010 and 2011 on the above image. If you look closely, you can see little contour lines that show the strength of the positive QBO event. Analyzing the 2010-2011 positive QBO event further, you can see how weak it is by how the two contoured areas with the number 10 are not connected. To me, this is a big sign that the atmosphere was not fully prepared for a positive QBO event, and this is further reflected by the atmosphere's resistance to allow any sort of positive QBO event through 2012.

Looking to the present time on the above image, we can see that the first positive QBO event in some time is working its way down the stratosphere. It is currently making its way down towards the 50 hPa dashed line after already passing the upper stratosphere layers. Once again, we see the contour number '10' within that gray swath illustrating the positive QBO. At first glance, this +QBO event looks pretty well structured at this point, meaning that contoured '10' area does not look too ragged at this point. However, if you really want a negative QBO this winter and want to over-analyze this positive QBO wave, take a look at the most recent values of the positive QBO. If you look closely, you can see how the '10' contour drops off right before the most recent observation. Could that be a sign of the +QBO weakening? We'll have to wait and see.

But, if we are going to have a positive QBO this winter, what should we expect?

This image shows precipitation anomalies from winters with a positive QBO. We see a very defined area of below normal precipitation anomalies along the Gulf Coast into the Mid-Atlantic, although slightly above-normal anomalies appear in Florida. The main story, much to the elation of those in the Midwest, Great Lakes, Ohio Valley and Northeast, above normal precipitation anomalies are shown in these areas, indicating the chance for a snowier-than-normal winter in a positive QBO scenario. The Southwest US gets in on a very wet winter during a +QBO, while the Pacific Northwest suffers a drier than normal winter.

The big story about the positive QBO is how it allows above-normal temperatures to arise. Just about everyone west of the Mississippi River is in line for above normal temperatures during a positive QBO. It appears the Northern Plains would get the warmest of the warmth. The Northeast and Mid-Atlantic wouldn't be affected too much, while the Southeast US would be the only part of the nation to get in on below-normal temperatures. Bear in mind all of this would only happen if the positive QBO was the sole factor in deciding the winter ahead, and we know that such a scenario is just not possible. Nevertheless, if we do get a positive QBO winter this winter, climatologically, these two images above could help us figure out the upcoming cold season.


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