It’s been a while since I’ve done an in-depth blog on winter weather for the area, but there’s a reason for that – there hasn’t been much to talk about. That appears to be changing over the course of the next 1-2 weeks. Let’s dig into it….
First of all, there is a significant stratospheric warming event that has and is currently occurring, as discussed in my blog from yesterday. I like lots of pretty pictures, so I’ve included a few to get my point across:
The image above I posted yesterday. I think everyone can see the warming taking place on the upper left hand part of the figure. These same areas were a good 30 degrees Celsius lower just a few weeks ago. But the cine loop below has an even bigger visual impact:
You can clearly see rapid warming occurring over northeastern Siberia, the northern Pacific and Alaska, and northwestern Canada. Keep these areas in the back of your head for later in the discussion.
Let me say, this is an impressive event. There were some hints on the models back in late Noevmber of this occurring, but it took much longer than anticipated – the stratosphere started out unusually cold this year. However, it IS occurring and therefore it’s the first OBSERVED positive sign that things are truly changing. Of course, the next logical argument is – does it translate down to the troposphere, or the lower portion of the atmosphere, where we live? It doesn’t always have to happen. But given the rapid warmth that is occurring, I believe it will.
The models I believe are already starting to pick up on this. The lag time between a sudden stratospheric warming (SSW) event and changes in the troposphere can be anywhere from 1-3 weeks, depending on what you read. Now remember the location of the warmest anomalies above? Here’s another global perspective to refresh your memory:
Again, over northeast Siberia, Alaska and the northern Pacific, and northwest Canada. Remember the lag time discussed above, look at the GFS ensemble forecast for about 3 days from now:
There is a stubborn vortex over Alaska (dark blue blob) , which is is one of the reasons why Arctic air has been locked up in Canada for the past several weeks, to the dismay of snow lovers on the east coast. This combined with the vortex over northern Canada effectively blocks any true or sustained arctic air from entering the United States. The result is transient cold shots of modified Pacific air, as evidenced by the upper level winds blowing from west to east.
Now lets look at the ensemble forecast for about 2 weeks from now:
A ridge has now formed over the exact position where the stratospheric warming is taking place, as the warming effectively breaks down the vortex. This allows for a cross polar flow of Arctic air from Siberia to directly discharge into the northern United States. Although the trough axis is centered in the western US, the coldest air is actually centered farther east towards the middle of the country because of the cross polar orientation. The cold then bleeds east over time. This bleeding of cold air in conjunction with the warming southeast ridge which has been prevalent this year because of the weak La Nina, creating a gradient for storms to travel along, roughly from Texas to the Mid-Atlantic and New England states. Moisture from the southern branch of the jet stream is also a bigger contributor this year due the the relatively weaker La Nina when compared to the last. This situation is a much more wintry scenario than what we’ve seen thus far, setting the stage for overrunning snow and ice events in the coming weeks right through February. Notice I included ice, and not just snow, in the equation – these will not be the snow or no snow storms we were used to in the past. Those to the north of the storm tracks will see more frozen precipitation, while those farther southeast will see more of the sloppy variety.
Now, the models are just starting to see this change. It will play itself out over the next week to 10 days, assuming the SSW event does indeed affect the troposphere, ridging develops near Alaska, and cross polar flow develops, providing a source for cold air, which we’ve lacked for just about the entire late Fall and Winter season so far. I know there will be skeptics out there, saying they’d heard the same thing for weeks. But remember, this is the first time we have actual evidence that the stratosphere has warned SIGNIFICANTLY. This is conjunction with model solutions which correlate with what we’re seeing presently is what’s important. All the other theories on when the so-called pattern change would occur (if ever) were based upon model forecasts of the SSW event, not observed data.
So, what about the more immediate future? There appear to be two potential events on the table, one around January 8th (this Sunday), and the other around January 12th (Thursday). The first is showing up on the European, GFS, and Canadian models. The second is seen on the Euro and GFS, but out of range on the Canadian.
And then the 1/12/12 event:
And finally the GFS:
Now, I’m not big into details this far out. But both storms take a general track from the Texas and lower Mississippi valley into the Mid-Atlantic region. Both will have rain/snow line issues, and in fact one or both may indeed be too warm for I-95 for much (if any) snow at all.
Let’s look at the North Atlantic Oscillation index:
There are two relatively distinct dips toward negative to slightly neutral which roughly correspond to the time periods in question. Additionally, there is relatively good agreement among the ensemble members during this time period. This lends more credibility to the two storms in question. It also provides some hope to those along I-95, lessening the threat of a coastal hugger or inland storm, which would bring rain (although it still may not be enough).
I’m not completely sold on either storm being big snow producers for the Mid-Atlantic or New England just yet. These storms may actually precede the above described pattern change that is anticipated. Given the current SSW event, the lag time, and what has been showing up on the ensembles, the actual transition to more constant colder and more wintry weather may not happen until the second half of the month. But based on the changes discussed above, I believe it is coming.
One more thing, as I type this, the new CFSV2 weekly forecasts have dramatically flipped to a colder solution, in line with the GFS ensemble run I’ve posted above, courtesy of Joe Bastardi’s recent tweets:
You can see how this nearly matches the GFS ensembles in about 14 days:
And results in the week 3 temperatures as below:
The blue is very cold air. Take my word for it, this is much colder and a complete flip from what they were showing on the last run. This NEVER happens, and only further confirms my suspicions that the models are picking up on the change at hand.
Winter is not dead, it just took a break for the first half. I expect a change to more classic winter weather for the second half of January and into February.
More on the upcoming storms discussed above during the next few days as warranted.