So I realize I’ve been shirking my usual blogging duties lately, but to be honest, there hasn’t been a lot to talk about up to this point, particularly along the coastal plain into the I-95 corridor of the Mid-Atlantic. I’ve been lucky enough to have about 12 inches of snow collectively fall from the pre-thanksgiving storm, and a few other minor storms, up here in the foothills of the Poconos, but other than that, there hasn’t been any big threats. However, winter, after all, is just beginning – the winter solstice was just the other day. So why all the complaining?
Most of it comes from people just pining away for snow at all costs – they see the majority of meteorologists talking about how the winter is set to be another bad one, and if that call for cold and snow doesn’t start in November, and last into April, well, then winter is just not happening. A complete epic fail. Climb the bridge. It’s over. Maybe next year.
Except, winter just started, and we’re just entering it’s prime months. So, all is not lost. In fact, there are still plenty of signs out there in the short, medium, and even the long range that are favorable. There are still some question marks, but lets get to what is going right.
THE ALASKAN RIDGE, THE MEGA HIGHS, AND THE EL NINO
The first thing I’m noticing is the re-establishment of big, strong Arctic highs coming out of northwest Canada, and with them, extreme Alaskan ridging (-EPO) in the 8-10 day period. These two features were the HALLMARK of last year’s winter, trumping the lack of a -NAO and the relatively non-contributory ENSO state we saw last year. You can clearly see them on the latest run of the GFS below (surface map first, 500mb to follow):
You may think, sure, but it’s the GFS; however, these features are on all the models, and many have them very strong. I often will chastise this model when it comes for east coast storms, and for good reason, as it regularly performs horribly in the medium range for such systems. But it’s performance last year was actually pretty good against the famed european model when it came to seeing the strength of these large highs coming down out of Canada in the longer range. It’s been nice to see them appear in the 10-15 day forecast on the GFS and see them hold throughout and into the 8-10 day forecast, as well as see them on other models. In fact, I will be watching the strength of these highs on the european as we get closer in time, and it would behoove you to do the same. Last year, they actually increased in strength from run to run, and were overall weaker initially when compared to the GFS.
The importance of these highs (and the Alaskan ridging) can’t be overstated. One only has to look at the 500mb map above and if you follow the contour lines over Pennsylvania and NY state back to the west, and see the source region for these upper level winds is in fact coming from north of Alaska, the north pole, and even crossing the pole from Siberia. That’s serious cold, and that’s what this setup is capable of over the next 2 weeks, beginning around December 29-29th, and onward – and we all know you can’t get the snow without the cold, especially for our friends in the I-95 corridor.
These changes at 500mb are the result of the warm sea surface temperatures seen below in the area labeled #1, which as you’ve known from earlier facebook posts, promote ridging in Alaska and northwest Canada, which in turn allows the cold air to pour into the United States (which is well established over the pole and Siberia thanks to above normal snowpack in these areas). Additionally, also discussed earlier this year, the warmer waters off the Baja of California, and the weak west based el nino state of ENSO (labeled #2 and 3) promote an active subtropical jetstream, and the moisture source for the winter storms we all live for (well, some of us).
THE COLD PRESS AND THE SOUTHEAST RIDGE
Even with that, one can look at the relatively warmer European, and to a much lesser extent the GFS, and think, but about the southeast ridge that keeps showing up? Isn’t that an issue? The answer is, yes, in most situations, but given Arctic advance associated with the Alaskan ridging and the Highs coming with it, it actually can be beneficial. Whenever you have such extreme cold air, in this case from cross polar flow, there’s always the chance that it can overwhelm the pattern, and suppress the storm track far to the south. So, you want that SE ridge to flex its muscles, because without it, you get a lot of ‘garbage cold,’ or temperatures in the teens and 20’s and wind and flurries. Not exactly a party for snow lovers, let alone anyone who doesn’t like winter.
The question becomes, how strong is this ridge, and how much does the cold air press? Unfortunately, the answer is not apparent this far out. Will there be a “storm” on December 29th exactly as depicted above on the Euro? Probably not. But something similar to this is very possible, and in fact from right before New Year’s until well after, there may be a few of these possibilities. The question becomes how much energy comes out of the southwest US – if it’s a lot, the rain snow line is shunted northwest of the one on the map above. If it’s less, the line and precip is shunted south.
And now to the question marks….
THE NEGATIVE NAO
Most forecasts included a negative NAO this year, but we just haven’t seen much in the way of Atlantic blocking. The sea surface temperature (SST) over the north Atlantic remain favorable (see below, where we have warm waters in the Davis straits (labeled #1) and around Iceland (#2), and cold waters in the central Atlantic (#3), but we have yet to see a sustained -NAO, which as most know promotes slower, longer duration storms by blocking there quick escape into the Atlantic Ocean.
Time will tell as to whether this occurs. Typically, in my experience, such a pattern tends to become more established as we get into mid to late winter, usually late January through March. Additionally, as discussed below, the stratosphere is becoming more favorable for blocking. So while although it has yet to really come on, there are signs that it will shortly.
THE QBO AND THE PACIFIC JET
Much has been made over the Quasi-Biennial Oscillation, or QBO, over the last few days, and it’s affect on the warm Pacific jet stream that has dominated the pattern over North America over the past few weeks, starting after Thanksgiving.
So what the hell is the QBO? I don’t pretend to be an expert on it, but the best most useful I’ve found is from Dave Tolleris at wxrisk.com:
“The Quasi-Biennial Oscillation (QBO) is a BAND of wind over the equator of the globe that was discovered over 50 years ago. This band of wind exists the very top of the atmosphere about 15 miles up where the pressure is about 30mb or just 3% of its surface value. The QBO has a “ cycle” to it. It runs from east to west (the negative phase) then after reaches some sort of Max negative value … the QBO moves back towards neutral. Then the winds reverse and the QBO runs from West to east (the positive phase) . The cycle takes approximately somewhere between 18 and 27 months but sometimes it can take longer or shorter.”
The bad news so far this late Fall and first few days of Winter is that the QBO has been markedly negative, in the -20’s range, for quite some time.
This is bad because it promotes a strong Pacific jet, with it’s zonal pattern and associated milder Pacific air, to flood the continental US every time a colder pattern tries to take hold.
But, there is good news on the QBO front as well. It is after all, an oscillation, which implies that at some point these values should begin to decline. Such declining more moderate negative values promote more amplification at 500mb and more blocking. I remember discussing this with a few of the EPAWA meteorologists a few months back and wasn’t worried about the highly negative values of the QBO even back then. Why? Because one only has to look at the QBO values over the past few decades (see below) to see that after about 5-6 months, such highly negative values ALWAYS fall back toward neutral within the subsequent 2-3 months.
So I knew that as we enter the heart of the winter, things should fall into place and the Pacific jet should relax, and more blocking should be the rule.
SUDDEN STRATOSPHERIC WARMING (SSW)
I also wanted to briefly touch on the Stratosphere and its warming implications for us going forward. The behavior of the stratosphere in relation to the troposphere, or where we live, is somewhat complex, but I like to think of the SSW events themselves as kind of like a sledge hammer. They in effect split the polar vortex, which when displaced from the north pole (hence the name), can bring large chunks of arctic air along with it. A few weeks ago, quite a few people were excited about the SSW that was occurring over the northern hemisphere, but in fact on the wrong side of the globe, centered over Russia, and not over the pole or North America. If there’s one thing that I learned from the winter of 2011-2012, it was the the location of such an event is as important as the SSW event itself. It’s no wonder December has been rather blah when it comes to cold and snow from a stratospheric standpoint. The Polar Vortex has been in an unfavorable position away from North America, and there’s been a lack of arctic air this past month almost nationwide.
However, there seems to be good news here as well. As you can see below, the latest forecast from the ECMWF (courtesy of WSI) shows another SSW event, but this time directed more over the pole, rather than on the other side of the globe.
This would promote splitting of the polar vortex into a more favorable position for cold for us, and a more negative NAO (blocking) and AO (cold) as we go into mid to late January, given the 2-3 week lag time that is usually the norm for such events.
THE MADDEN JULIAN OSCILLATION(MJO)
Finally, we come to the MJO. The MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Ocean. The implications of this cyclical pattern of tropical rainfall are neatly shown in the following two graphics:
One can clearly see that the phases 8, 1, 2, and 3, and to a lesser extent 7, are favorable for cold in the eastern US. Phases 1, 2, and 3 are particularly wet as well.
Right now, the MJO impulse is currently in the eastern Indian Ocean and is forecast to be in phase 4/5 over the next few days. This is why we are seeing a southeast ridge pop up on many of the models. However, there are signs it will indeed propagate into and beyond phase 6 as we go through mid January, again, favoring cold on our side of the country.
So, with all that being said, you can see winter isn’t in fact canceled, but just getting started. The mega highs and Alaskan ridge is there, just like it was last year. This will initially cause the cold to bleed southeast, on the heels of a broad based trough, and while the MJO is in its warmer phases, the southeast ridge to fight back. The QBO is markedly negative, yes, but it WILL start to move towards neutral, promoting a relaxation of the Pacific jet, and more blocking as we head into the heart of winter. The stratosphere is forecast to warm in a more favorable location for us, also favoring more blocking and a -AO. And the MJO should propagate into more favorable phases for cold and snow as we head towards mid-January. Fun times are indeed ahead.
Watch for things to get interesting beyond December 28th/29th. More as warranted as usual.
Special thanks to Mike DeFino and Bobby Martrich of EPAWA who contributed to this discussion.