Tuesday, February 26, 2013

Sudden Stratospheric Warming Could Mean Robust Spring

The chances of a late-winter sudden stratospheric warming could mean a robust severe weather season this spring.

Shown above is an animation of temperature anomalies at the 10 millibar region in the atmosphere. To give you an idea of how high up that is, we live at the 1000 millibar mark, commonly known as surface level. 500 millibars is where storm systems are most commonly seen, and 300 millibars is where airplanes fly. So 10 millibars is quite a high position in the atmosphere. If you look at the animation, you will see it start with sudden cooling after a large sudden stratospheric warming in January. From early February to now, we have seen a very chilly Arctic, meaning the chances of anomalously cold air reaching the lower latitudes and the polar vortex becoming more unstable are lower than normal. If we look towards the Himalayan mountain range, however, we can see some oranges (and more recently, reds) bubbling up in the mountain range. This does signify that the stratosphere is warming in that area, and sudden stratospheric warmings have been known to occur off of mountain ranges, particularly the Himalayan range.

From here, I can reasonably assume that the warmth in the Himalayan mountain range will continue to increase in the upper stratospheric 10 millibar level. In the next 1-3 weeks, we should then see movement of this body of warmer than normal temperatures propagate north and likely into the Arctic. This is almost an identical set up to the sudden stratospheric warming that was experienced in January- warming bubbles up in the Himalayan mountain range for a few weeks, then propagates north into the Arctic where it blossoms into a sudden stratospheric warming event.

So what does this have to do with spring? Well, the sudden stratospheric warming phenomenon involves warm air being forced up into the stratosphere. As a result of warm air going into the stratosphere, anomalously cold air must then be pushed out of the stratosphere due to air displacement. This cold air then moves down the stratosphere and troposphere until it hits the surface. This moving down takes a good 2-4 weeks, so if the sudden stratospheric warming event did come to fruition, we would still have to wait 3-6 weeks before we see its effects. This leads us into spring, the season of severe weather. If the atmospheric pattern is able to allow this cold air to flow into the US and not other parts of the world, we would most likely see additional chances for wintry weather, including snow and cold. The increased temperature gradient in a cold front would most certainly excite severe weather potentials, and this in turn could lead to more damaging wind and general severe weather events.

This all depends on if the Himalayan warmth even propagates into the Arctic, which there's not a 100% confidence in right now. However, based on past experiences with Himalayan stratospheric warming, I think what I typed above has at least a decent chance of coming true.