The first thing you want to look at when determining what an up coming winter will bring is always the winters of the past. Let's look at the past two winters.
Winter 08-09:
Snow days: 46
Days of snow cover: 72
Amount of snow: 49.5"
I find it interesting that it snowed more days in 08-09 than it did last year, yet last year brought nearly double the season total snowfall than the previous year. Also most people would assume that last winter(09-10) was colder than (08-09) and that is wrong. In fact negatives numbers weren't even seen this past winter anywhere in the state of New Jersey, but more than half the state the previous winter saw near record cold temperatures. Including Walpack Center in Sussex which approached -20 degrees F.
February this year was just 1 degree below average but brought 48.9" inches of snow to a month in which we average just 8" inches (+40.9"). Mean while January 2009 was 6 degrees below average and brought just 12.7" inches in a month which we average 14" inches (-1.3"). This helps me make my point that the amount of snow you get doesn't always go hand in hand with the temperature. Meaning a month near average could bring TONS of snow or none, or a month with extreme cold could bring TONS of snow or none. Why you ask? Cause there are many other forces at work, and that's what we are going to take a look at.
Agenda:
1. Oscillation patterns "a look at the past to predict the future"
2. The temperatures
3. The precipitation
4. Let's make a season snow map?
5. How accurate have I been?
6. What's it all mean?
1.
The oscillation patterns whether they be atmospheric or oceanic are a predictable because they are just cycles. These cycles aren't alway equal in length. Some cycles last upward of 30 years or more while others could last just a couple months. For example the NAO is one type oscillation which could be primarily positive for 20 years then negative for anther twenty. Now while in the same time period you will have a winter where it's mostly negative while the 20 year cycle is in it's positive cycle. Then you can have monthly changes and even weekly changes. So basically the oscillations have oscillations that oscillate. If that makes any sense to you? Here is a basic example:
Alright now let's talk about these oscillations. Here are some of the ones that we will be talking about:
A. North Atlantic Oscillation(NAO):
-Forecast: Primarily negative
B. Arctic Oscillation(AO):
-Forecast: Slightly negative
C. El Nino Southern Oscillation(ENSO):
-Forecast: Strongly negative
D. Atlantic Multidecadal Oscillation(AMO):
-Forecast: Positive
E. Pacific Decadal Oscillation(PDO):
-Forecast: Negative
A. (NAO) First up is the NAO. One of the most important for our region of the country. In the images below you can see the history of the NAO from 1950-present, where for year on end could be primarily positive while other periods are mostly negative. If you take a closer look some of the negative winters are 1977-1978 / 1995-1996 / 2002-2003 / 2009-2010 which are all big snow seasons. There are some odd balls in there like 1997-1998, a year which practically no snow fell. But that's why the NAO is only part of the big picture.
We currently are in the middle of a NAO which is primarily negative and will remain there for most of the winter only coming positive for brief intervals at a time like last year. For a better understanding of the NAO check out the following site:
http://www.ldeo.columbia.edu/res/pi/NAO/
B. (AO) Next on the list is the arctic oscillation. Last year this went off the charts in the negative direction which typically signals strong blocking over the pole displacing colder air and the jet stream to lower latitudes. Remember what happened last winter?
If you look at the above chart you can see the negative phases line up with the two snowiest and coldest months. December with 22.25" inches of snow and -2.1 degrees below average. And also February which we all can't forget. But January was 0.6 below average and just 6" inches of snow fell, and mostly in the beginning of the month.
Obviously understanding how the AO affects our weather is critical, but once again we need to look at the entire picture to understand the meaning. Stratospheric temperatures do matter in forecasting, although most only really care about the tropospheric temperature at the surface. But right now we have a battle taking place.
The AO is said to be negative when the stratosphere above the arctic is warmer than normal which displaces cold air south and creates blocking in correlation with the NAO. So the warmer it is the greater the impact, and the same for negative phase just with colder than normal temps. Think of the following image as a vertical profile of the atmosphere, I made some changes to help you understand better:
Pretend your at the building in the image. The time line says its about mid August, and since the air above you is warmer than normal in the stratosphere this would mean a negative phase in the AO. Assuming you took the empire state building and brought it to the arctic. Should I have used a big igloo for this example? Anyhow this is what creates blocking patterns. This AO is going to try it's hardest to stay in the negative phase through the winter, but at the same time a strengthening La Nina will be pumping warmer than normal air aloft in the stratosphere at middle latitudes, keeping the stratosphere at the pole colder than normal. This is our battle, and one which could make or break this winter season.
C. (ENSO) The El Nino Southern Oscillation will be brawling it out with the AO, which one will win it? Remember those years where it seemed like all we ever got was freezing rain and sleet? Even if is was 20 degrees outside the prominent precipitation type would still be ice! This was caused by warmer air above the surface while cooler air was at the surface. Please excuse my third grade drawing, I'm only trying to help out with this one.
Unfortunately a strong La Nina indicates to me that warmer air aloft could and probably will help to cut down on season total snowfall by adding freezing rain and sleet to the mix. And perhaps a significant amount at that, especially over the higher terrain.
The current La Nina pattern we are in may actually last for the next several years, which will eventually lead to brutally cold winter coming up in the next 3-5 years, similar to what happened in the 1970's. But the past winter's El Nino, even though it's gone helped to give us that warm summer which will lead into our winter. Above average temperatures for most of the eastern two thirds of the country seem to be what's in store. But don't get upset! Remember what I said before? Average temperature over a winter doesn't necessarily mean everything, last winter was much warmer than the previous and we got double the snowfall!
Another bummer with La Nina seasons is they aren't really known for providing abundant moisture. So I'm looking for near average precipitation (liquid equivalent).
D. (AMO) The Atlantic Multidecadal Oscillation went into it's warm phase in the mid 1990's (positive), that warm cycle should last about 25 years. In fact it's last cold year was during the season of 1995-1996, which was not only snowy but very cold. We are well into that warm phase and we have the better part of a decade before it begins into it's cold cycles once more. This is not very helpful to us, if you want cold and snow anyhow. When this goes this cold once again we are going to have some amazing winters in store, something to look forward to I guess?
E. (PDO) The Pacific Decadal Oscillation went negative just a few years and that marked it's new 30 year cold phase which will remain that way for decades to come. This has to do with waters off the coast of Alaska and have an effect on the westerly flows that come from the west to the east which brings us most of our winter time weather. During the cold phase of the PDO increased precipitation coming in from the northern Pacific brings extreme snowfalls to Rockies and Alaskan glaciers typically begin to reclaim the land they previously occupied. During some winters depending on some other factors this could really help us out, or hurt us. This year I can see how it helps us.
That's all for the oscillations. I probably have you bored already! Let's move onto the good stuff now.
2. Below is the map for the projected temperatures for this upcoming winter season, sorry? I want to stress that while it seems extremely warm its the anomaly from the average. So there will be cold periods and there will be warm periods. By the time it's all said and done the winter could end up around 1.5 to 2.5 degrees warmer than normal.
3. The precipitation for the winter season is an important factor because it can give us an idea how much snow fall to forecast. Of course not all the precipitation during the winter will fall as snow, so we need to come up with some sort of system to figure out how much snow could fall with average precipitation while factoring everything into the equation that we talked about so far. The average winter time precipitation for north Jersey (Dec-Mar) is:
December- 3.63"
January- 3.83"
February- 2.96"
March- 3.79"
Total liquid equivalent: 14.21"
Now you have average liquid over the winter time period. After factoring in the whole picture, elevation, averages, and little bit of love you can make a good snow map. Ok, maybe love is a little much...
Below is the total snowfall per season since I started my measuring back in the day. The average snowfall for my town at 1,000 feet is 55" inches per season which means most of north Jersey averaged 50"-60" depending on elevation mostly. As you can see we have seemed to reach a "peak" season last winter, so I can only assume it's downhill from there. I would put this up coming winters snow totals at just average to slightly below.
4. The snow map!
5. Previous winter outlooks:
6. What's it all mean?
-Snowfall will be near normal to slightly below
-Temperature will be 1.5-2.5 degrees warmer than normal
-Ice and sleet may be a more common event than snowfall
-May be very dry for extended periods of time
Any questions? Comments? Suggestions? Comment below or email me at millirod@kean.edu
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