What the QBO and the sun can tell us about the winter ahead

Take a deep breath — sit back, and relax. You are about to read our first post detailing some early thoughts for the Winter of 2017-2018. August is a bit of an odd time for it, we know. Not every year offers the opportunity to discuss the road to the winter ahead during the month of August. Some years require patience until September or October before we can start discussing early signals with confidence. This year, however, we’re seeing important signs for the cold season already as we speak.

This afternoon, we’re going to take a very early look at some of the significant changes that have occurred all around us since the end of last winter. It’s true — in the time between the day the last snowflake fell in the Northeast states and today, there have been significant changes throughout the atmosphere, in the oceans, and even in the patterns of energy emanating from the sun. All of these things will impact the winter ahead — so lets dive in to what we’re observing so far.

The first area of interest comes from the Quasi-Biennial Oscillation, or the QBO as we will refer to it in this post and many times in the months to come. The QBO are zonal winds in the stratosphere that typically oscillate between westerly (positive) and easterly (negative) phases, every 12-24 months. The QBO in an easterly phase tends to promote a weaker polar vortex in the stratosphere, resulting in a propensity for more stratospheric warming events during the winter months (allowing high latitude blocking and -NAO episodes to flourish). The QBO in a westerly phase tends to allow a stronger polar vortex to form, limiting high latitude blocking and resulting in a more positive AO and NAO phase during the winter months.

The effects that the QBO has on the stratospheric polar vortex are important. While “Stratospheric polar vortex” might seem like an intimidating term, it just refers to the polar vortex at much higher height than the weather we observe. It’s thousands and thousands of feet above our head, in the stratosphere, but it is as much of a vortex of anything else we see down here in the troposphere. The QBO’s effects on the stratospheric polar vortex are critical because often times, the winds in the stratosphere will allow the warming events to downwell into the troposphere, where we experience our sensible weather. This will break down the polar vortex and cause high latitude blocking to develop, with a negative NAO and AO developing.

ECMWF showing easterly zonal winds (negative values) descended to 30mb

The westerly phase of the QBO from the last year or two has recently flipped, with an easterly QBO developing and looking likely to maintain until the colder season on its 12 to 24 month cycle. This would suggest, from a very basic standpoint, that a weaker stratospheric polar vortex would be possible this winter, and high latitude blocking (with a -NAO and -AO) could be more likely to develop than normal.

But what about our sun?

There’s an old saying that goes something along the lines of “It’s never as simple as it seems”. The same can be said for the QBO. While we discussed the easterly and westerly phases and their importance, we also have to remember that the effects of the QBO can be heavily modulated by solar activity. That’s right — the amount of geomagnetic activity emanating from the sun towards earth can impact the effects that the QBO have on the stratosphere and troposphere.

Higher solar activity typically results in geomagnetic storms. When these impact earth, the stratospheric polar vortex tends to “tighten”. Think of it almost as (this is gross, we know) a snail going back into its shell when it is touched. The stratospheric vortex tightens up and strengthens as the geomagnetic activity from the sun begins to impact the troposphere. This can aid in the development of a strong stratospheric polar vortex, even when the QBO is in an easterly phase. But weaker solar activity can act to promote the opposite — a weaker stratospheric polar vortex overall.

Solar Cycle 24 continues to head towards a minimum as we approach the Winter of 2017-2018.

As we move towards the Winter of 2017-2018, we are entering the tail end of Solar Cycle 24. Solar Cycles are measured over a period of several years and feature peaks and valleys of solar activity. We reached a relative maximum in solar activity about 4 years ago, and have been observing diminishing solar activity ever since. Now, space weather data suggests we are heading towards a “Valley” of solar activity, with a very quiet period likely during the next 1 to 3 winter seasons during the second minimum period of Solar Cycle 24. Observed Solar Radio flux this month was at 77.58, another steady drop from month-to-month over the past year.

The combination of all of this information suggests a very key piece of information: We are likely to see weakening solar activity and an easterly-phase QBO during the Winter of 2017-2018. While not a shoe-in by any means, the development of both of these features is important. In fact, some of the strongest high latitude blocking events (-NAO, -AO) have occurred when both of these conditions existed. High latitude blocking promotes higher than normal chances of snowfall and cold air in the Northeast United States.

But, we digress. As the warm sun continues to shine down on us here during the first week of August, it is important to remember that there are many, many other features that will impact the sensible weather during the winter ahead. Over the coming weeks and months, we will begin to track this data more heavily and form a picture of how the atmosphere is evolving as we head towards the winter months. We will look to the Pacific, Atlantic, Greenland, and much more — so stay tuned for periodic posts as the winter months get closer.

Have a great Monday afternoon!