Sunday, November 11, 2012

Winter To Start Off Slow, Finish Very Active

The winter of 2012-2013 is most likely going to start off on the slow side before we get into a pretty active period to finish off the winter. Let's get into why I believe this will happen.

A big reason for this likelihood is something called the Rossby Wave. A Rossby wave is a storm system that emerges from the North Pole and moves to the southwest, something not usually seen in the Northern Hemisphere. The Rossby wave can be an event, where several of these storms will form and reform over the same area, typically setting up a pattern that can last for a good 4-6 weeks at a time. Unfortunately, this Rossby wave pattern has set up over the northeast Pacific, which has led to a stormy West US, and, consequently, a warm and dry East US. That is not something we want to see heading into the opening weeks of winter.

If I extrapolate (use observations to forecast the future) this Rossby wave pattern, this bad pattern in the East will end in the first couple weeks of December, as the pattern shuts down and moves on elsewhere. I am thinking that the shut down of this pattern will happen from early December to mid December, with the latest shut down date being the week before Christmas.

(This data was originally published on November 9) Observed snow cover in Siberia during the month of October is also supporting the idea of a back-loaded winter, something many winter weather lovers out there are dreading.

Something forecasters use in the fall months to help predict the upcoming winter is indeed Siberia. In October, the anomaly of snow cover over the region has been proven to correlate with observed Arctic Oscillation anomalies in the following winter. For example, if the month of October held a very below normal snow cover situation for Siberia, the Arctic Oscillation (AO) would most likely be on the positive side (warmer weather) for the winter.

If we apply this rule to the upcoming winter, I would expect a fairly warm November and most of December before some moderation in the AO occurs. This moderation from mostly positive would most likely happen around the Christmas timeframe. From there, the first week or two of January would hold continued moderation in the AO (not too positive, not too negative). However, later on in January and in February, Siberia is encouraging the idea of a strongly negative Arctic Oscillation. If this were to verify, we could see extreme cold in much of the nation- something that winter-season farmers may not want to see.

Solar activity will also play a role in this winter. A negative correlation has been found in geomagnetic activity (as shown above) and the Pacific North American index (PNA). A negative correlation means that when Factor 'A' goes up, Factor 'B' will go down. In this case, when geomagnetic activity goes up, the PNA index tends to go more negative, and we are already seeing this and will continue to see this in coming weeks.

Extrapolating previous ups and downs of the observed geomagnetic activity values in the chart above, the PNA should be the most negative in coming weeks before pushing towards positive territory by the beginning of December. The PNA should enter the positive phase by the first week or two of December, fitting in with what I have shown with Siberia and the Rossby waves.

In conclusion:
•November, much of December will be slow for snow.
•Plains, Rockies are snow hotspots for this period.
•Gradual change in last 2 weeks of December.
•January starts off modest, ends active and cold.
•February brings brutal cold, snow to the East US.


Credit on the PNA/geomagnetic piece goes to blizzardof96 on the Accuweather Forums (see entire post here)


ERN WX said...

Hello Andrew, my area has been blw avg in temps lately, unlike last mess... I agree 100% with the backloaded winter. But the Midwest will get their snow slightly sooner. I am impressed with the storms so far. What model blend do you use for snowfall forecasts? I use an ECMWF, GFS, SREF blend, and it is very effective.

Anonymous said...


KakHome said...

Models seem to want to make the PNA positive around the 18th. That is far ahead of your prediction, but it connects with the East Asian thing. I'm starting to get a big confused on just what will be occurring.

Wally Gullang Huntley, Illinois said...

Andrew how would you explain the fact that Northern Illinois has had 15 of the last 17 day's below normal. Starting tomorrow and for most of this coming week we will once again be below normal

KakHome said...

Wally same with Northern Ohio. I would say some days will be a bit above normal. And aside from Tuesday, not really anything well below normal. But nothing like today either (high 68, low 54 at Cleveland). Of course for IL the cold front as already going though but it was a very warm weekend.

@ERN WX What is your reason for a backloaded prediction (if different from Andrew's) and do you think Northern Ohio should make out decent in the end when everything is said and done?

KakHome said...

Also @Anonymous (1) I think it's too early to say depressing. It's only November 11. And just because the pattern never changed last year doesn't mean it can't this year. As far as I know, both years shared slow snow cover in Siberis to start October (never a good sign for the beginning), but this year the cover increased more.

And while some elements of last year's pattern are showing up, the pattern is not the same. The PV is still not as stable and clearly defined as in Nov 2011. The dreaded AK vortex, at the least, is weaker. Lastly, there is not really much blowtorch weather I see in the East after tomorrow. It is not a cold and snowy pattern, but not a strong ridge either.

By contrast, November 2011 saw a very well defined surge of warmth into the East behind EVERY post-cold frontal high pressure center. (Look at the height patterns in Nov '11 and you'll see ridges popping clearly from 11/6-11/8, 11/13-11/15, 11/19-11/21 and 11/25 to 11/26, roughly.)

Sure it might be a dull winter, because ANY winter can be dull, regardless of what happened in previous winters, or even the preceding fall months, but I wouldn't say it's time to just write it off either. Just don't jump in expecting an 02-03, 09-10, or 10-11 (these were the ones where the cold hit the East most frequently).

I definitely get the idea this is Andrew's view too, though I'm in no position to state for sure it is.

Anonymous said...

I realize that most of the US's population is on the east coast and midwest, which is why nobody seems to care about the west, and some of you even wishing that there would be a permanent ridge over the west, so you guys could always have your cold and snow, but look at it this way, if we see too much ridging here in the west, then no storms can make it through to produce the snow that our mountains need to replenish the rivers and reservoirs that sustain any and all forms of life around here, the east is always wet anyways, whether you get the frozen stuff or not, so you guys don't heavily depend on winter snow like we do in the west, because summers are typically pretty dry in most of the west, so try to realize that the more you guys get your troughs of low pressure in the east, the deeper the west goes into drought and water's a vicious cycle, I don't care so much about the brutal cold, but for crying out loud, we really need our storms and our mountain snowpacks, so that we can start to gain back the very thing that you easterners are getting too much of, and are taking for granted.

Anonymous said...

R u talking about a major storm on thanksgiving for detroit

Anonymous said...

I agree with the comments about the west. I love reading about weather all over, but I have noticed that often the west gets overlooked.It's very dry here in the west and water prices have gone through the roof. We desperately need precipitation to alleviate our drought and preserve wildlife.

Anonymous said...

Agreed, with the 2 comments on the West. I live in the Southwest, New Mexico. Well, below average in precip for the second straight year. If anything I can only hope the mountains get some snow this winter. In the hopes of alleviating the fire threat. But, from an overall perspective the east has been where all the weather events have occurred to this point. Out here not much to complain about it has been well above normal temps at least until today that is. Where I live winter is hit or miss with the best chances for any snow in December and January. Even though last year it snowed in April so you never can be sure. But, we really need a solid monsoon season and that hasn't happened the last 2 years which is why the below average rainfall. From my studies, I know it will snow and be cold no matter what the whole winter will be like. At least for a couple of days.

Anonymous said...

Yeah Andrew needs to stop biasing the focus of his posts on the east and focus more on the west. He says "winter will start slow" but he's only referring to the east and the Midwest. Last year, his winter forecast didn't have anything focused on the west. In facebook, he says that he gets most of his attention from the midwest and the east coast. I wonder why. There's weather in the west to, you know.

ERN WX said...

KakHome, my reasoning is teh NAO I expect to be positive in early December. Ohio will do well in snowfall this year. Apps runners and clippers phasing with southern stream enrgy. I am glad you like wx as much as I do. I say backloaded because the MOST snow will occur then. JAn/ Feb.

Andrew said...

To those talking about the lack of West US forecasts: Frankly, it's a matter of yes, bias and knowledge of a region's weather. For instance, because I was originally from the East US, of course I will post more on the East US. As for knowledge, the mountains and other factors heavily influence the weather forecasts to the point that it would take me months to fully understand that region. And because storms generally weaken across the mountains, things don't get too interesting as far as strength of a storm system. I'm sorry you all feel so strongly about this, but I honestly do not think I will post about the West more often based on the aforementioned factors.

Anonymous said...

Andrew, I think we just all really like your blog and completely understand your reasons for an east based forcast. It's just wishful thinking that you would post more on the west.I enjoy reading about all weather so I will continue to enjoy your blog regardless of where it's focused.

Anonymous said...

If the blogger lives in the eastern half of the US, along with most of his followers, then it makes sense that he will focus more on the eastern US. There are plenty of good blogs that focus only on the western US.