If you're like me, it's not winter until it gets COLD. Last winter was one of those, mild with no real shots of cold weather. If you don't like winter or cold weather, close your eyes for a moment and savor those memories from last year... then back to reality as we look ahead. Winter is FAR from over and as far as we're concerned, it begins in about two weeks or so.
I wish I could come up with dramatic ways to say we're going to get cold, but since we're 2-3 weeks away, I have a little time to pick the best words. But it's going to get cold, plain and simple. The arctic air that's been bottled up in Alaska and Canada is about to take a trip south and make some dramatic changes to our weather here. Here's why.
In my last few blog posts, I've talk about several weather indices as well as changes that are occurring in the upper levels of the atmosphere. I'll try to piece all of that together so it make some sense.
Sudden Stratospheric Warming (SSW)
The first thing I'll discuss is the Sudden Stratospheric Warming or SSW. I talked about this in my last post and alluded to the fact that this was going to occur and would be a Major SSW, and this IS occurring right now. There is still a lot of research being done on SSW's and the study of how the upper levels of the atmosphere play an important part in what happens to our weather at the surface. But what we do know is that these type of events have direct correlations with blocking patterns and temperatures. In this case, it appears the SSW will be to be the kicker to get the cold air to start moving our direction.
As of this morning, the 10hPA temperatures have risen more than 40ºC (from ~-80C) and the zonal winds have decreased from ~80 m/sec to almost zero with a reversal expected to take place. Click this link to view the temps and winds in the stratosphere. If you click through the 10hPA images, you'll see a total split of the stratospheric polar vortex by 72 hours. This also occurs at the 30hPA level even sooner.
These changes are important and imply that this is a Major SSW and we haven't had one of those in several years. Here's an Abstract from a paper on SSW's
"The dynamics of the stratosphere sudden warming phenomenon is discussed in terms of the interaction of vertically propagating planetary waves with zonal winds. If global-scale disturbances are generated in the troposphere, they propagate upward into the stratosphere, where the waves act to decelerate the polar night jet through the induction of a meridional circulation. Thus, the distortion and the break-down of the polar vortex occur. If the disturbance is intense and persists, the westerly jet may eventually disappear and an easterly wind may replace it. Then “critical layer interaction” takes place. Further intensification of the easterly wind and rapid warming of the polar air are expected to occur as well as weakening of the disturbance. The model is verified by numerical integrations of the adiabatic-geostrophic potential vorticity equation. Computed results possess features similar to those observed in sudden warming phenomena."
One important thing to note... since the stratosphere has warmed almost 100 degrees, there is a corresponding drop in temperatures at lower levels and this has important implications for temperatures at the surface. I wanted to share this link, it shows through time-lapse animations, the process of SSW and how the polar vortex breaks down. Very cool.
The next piece is are the blocking patterns that need to be in place in order to get the cold air here. Specifically, we're looking at three patterns, the Arctic Oscillation (AO), the North American Oscillation (NAO) and the Eastern Pacific Oscillation (EPO). For us, it's a matter of having the right combination of blocking to squeeze the cold air south instead of allowing it to slide east and north.
The models have been hinting about a negative NAO and EPO for a few weeks now. One of the issues we've had so far this winter has been the active upper air pattern that has brought air that originated over the Pacific Ocean. While that was good for rainfall, it prevented any real cold air to penetrate south. That pattern had to do with a EPO+ or positive EPO. That's all getting ready to change with the EPO forecasted to go negative shortly. A EPO- brings a nice blocking ridge of high pressure over the Pacific, effectively blocking that warm moist air from moving this way, and providing a barrier that keeps the cold air channeled within the continental US.
In order to channel cold air our way, the AO and NAO need to be in a negative state, and both models are forecasting some very negative states toward the end of the month. Blocking created by NAO- will force the winter storm tracks as well as cold, south instead of the zonal (east-west) flow that we've had for most of this winter.
So what does all of this mean?
There is a lag between what happens in the stratosphere and what we see on the ground,,, roughly two weeks or so. The blocking that will accompany the effects of the SSW is also about that far off. So we're looking at about 2 weeks or so before we experience any of these changes. We will have a period of mild weather between now and then, and then the vodka cold arrives (it's been -60ºF in Russia this winter). At this point it's anyone's guess as to how cold, but meteorologist have been saying the coldest air in more than two years will be coming. Right now expect the last week or so of January, and possibly the whole month of February, to be well below normal for temperatures... and possibly above normal for winter precipitation.
Hold on to your hats! This is going to be fun!
Please remember, whenever you need weather information, please visit us at the new and improved DaculaWeather.com. You can also get the latest weather information by following us on Twitter and Facebook
DaculaWeather.com... Your Window to the Weather