Winter 2009 - 2010

[DavidS]

From StormChaserChuck, one of the youngest weather genius' world wide. You can't come into this forum and say "I know what makes a car go! It's the gas pedal!" We all know that there are SEVERAL components that make a car go - so why do you global warming enthusasits say "CO2 makes our weather warm?"

How about doing some research? How about understanding our climate and all of the different factors that go into what makes today warm and tomorrow cold.

Here's a discussion about the upcoming winter. READ IT. RESEARCH IT.

It's never too early to start thinking and talking about the Winter. There is actually a lot to look forward to this year, and the next few months can be very fun for the people that know what they're looking for. If things line up correctly, we could go into Winter 2009-2010 with more potential for a cold/snowy season along the East Coast than any other year since 2002-2003 in the Mid-Atlantic, or 2004-2005 in New England.

Of course there are several opinions regarding long range forecasting, and it's accuracy. In an attempt to steer the discussion away from the inevitable debate regarding this, I'm asking for a different response to this thread. Personal opinions are great, and everyone has a right to one.. but sometimes this can greatly distract from the topic at hand. If you are one of the people that put no value in what I am going to discuss, fine. Just ignore this. I only want to talk science.

Weather patterns are very complex, and even in our best efforts, forecasters don't come close to taking everything into account that plays a role. but I will use this thread to cover what I feel are some of the more important factors to long range forecasting (from the time scale of 3-9 months in advance). This includes:

- ENSO projections
- State of the Sun
- QBO trends/state
- Global SST trends and projections

ENSO

El Niño-Southern Oscillation is probably the most popular and well understood Global weather event. This consists of many variables, most important being SST anomalies over the Tropical Pacific region. Since most people understand the general gist of how this works, and what it encompasses, I'm not going to spend a lot of time explaining this. Linked below is a very good description.

El Niño-Southern Oscillation - Wikipedia, the free encyclopedia

One aspect of ENSO that gets not nearly as much attention as it should is where El Nino or La Nina events are based, and how this impacts the Global pattern.

An "El Nino" or "La Nina" can produce very different conditions if the event is East-based, as opposed to being West-based. What I mean by "east and west based" is that one area of the Equilateral Tropical Pacific has a greater sea-surface temperature anomaly, when compared to another region. and while there is some tendency for these events to develop in a specific area, there are a lot of different scenarios that could occur in any one event.

The Hadley Cell circulation is responsible for transmitting Tropical Pacific conditions northward. Since the size of Hadley Cells is ~40 degrees, the strongest effect of an ENSO event are is felt at ~40N and ~40S... directly above where the greatest warm or cold SSTs are located.

Here is a very simplified image showing the general ENSO/North Pacific pattern correlation that I'm referring to, and how the location of an ENSO event could potentially impact the North Pacific:



Below is a comparison of what East-based El Nino's look like vs East-based La Nina's with regards to the North Pacific pattern (measured by Winter time 500mb anomalies):



The next image shows a comparison of what West-based El Nino's look like vs West-based La Nina's in the North Pacific:



and shown by the following image, the difference in placement of North Pacific pattern anomalies in West vs East-based ENSO events is big. This is why you can't just generalize by making a forecast solely based on "El Nino" or "La Nina". Location is just as important as the event itself.



So how does this apply to weather conditions across the US? Since the flow of the Global Jet Stream is from West -> East, the Pacific Ocean is the most important region with regards to pattern influence across the US. Because of this, those differences in the North Pacific pattern between El Nino/La Nina and East/West-based events are very important.

Just like I did with the North Pacific pattern, here are the effects and differences of ENSO on US Winter temperatures.

Below is the comparison of East-based El Nino vs East-based La Nina.. this shows just how important the location of an event is. Contrary to the presumed effects of the two ENSO states, winter time East-based La Nina's actually have a tendency to produce cooler temperatures in the Northeast, as opposed to the east-based El Nino:



West-based ENSO events are kind of our best or worst case scenario along the East coast. West-based La Nina's have accompanied some of the warmest Winter's on record, while West-based El Nino's have produced Winter's such as 1977-1978 and 2002-2003. Shown below is a comparison of what is typical in a West-based La Nina vs a West-based El Nino:



and again to reiterate how important where the event is based, here are comparisons of West vs East ENSO events:



Logic says that the strength of an El Nino event only increases the likelihood and strength of its correlating North Pacific anomaly. So with this in mind, consider the fact that a strong West-based El Nino is not bad, despite what people think. The idea that Strong El Nino's lead to warm Winter's are derived from the two strongest El Nino's on record (82-83, and 97-98) being very East-based. So again: strength of the event only enhances or decreases the probability and strength of a given pattern.

Now that we have a good understanding of what each ENSO scenario produces in terms of sensible weather, the question now becomes.. which is most likely to occur later on this Fall and Winter? I'm not going to make a guess, since the premise of this thread is just to explain different forecasting methods and what certain things could mean going forward... but I will talk about recent trends (both now and going forward in the form of "updates"), and what they could mean with regards to the future.

Over the past two months, La Nina has taken a major hit. Due in large part to a strong Kelvin wave that passed through the Tropical Pacific over the past few weeks, "Neutral" conditions are currently in place.

History says that if another strong Kelvin Wave moves across the region some time in May or early June, the odds of a developing El Nino increase significantly. A good way to monitor this is through subsurface temperatures. Equilateral Oceanic Kelvin Waves really mix up things on the subsurface. An anomalous region of warm water along the thermocline progressing east is a sign of a progressing Kelvin Wave. The CPC monitors these subsurface anomalies here:

http://www.cpc.ncep.noaa.gov/products/anal...e/wkxzteq.shtml

There seems to be a consensus on this board that a Weak to Moderate El Nino will develop later on this year.. but there is less agreement on exactly where this event will based. Here is a link to a just updated discussion and forecast regarding ENSO. This is by the CDC.

ESRL : PSD : Colorado (and Interior Southwest) forecasts

The CFS computer model is currently predicting a Winter time Weak West-based El Nino (3.4 and 4 regions are "west"; 1.2 and 3 are considered "east")
http://www.easternuswx.com/bb/index.php?ac...w_post&f=15
http://www.cpc.ncep.noaa.gov/products/anal...ino12SSTSea.gif
http://www.cpc.ncep.noaa.gov/products/anal...nino3SSTSea.gif
http://www.cpc.ncep.noaa.gov/products/anal...ino34SSTSea.gif
http://www.cpc.ncep.noaa.gov/products/anal...nino4SSTSea.gif

For those that like cold and snowy Winter's, west-based El Nino's are our best case scenario. The stronger the event the better. Obviously the opposite is true with a West-based La Nina. When we have an east-based El Nino or La Nina, things aren't nearly as black and white. Both events have certain positives and negatives.

Stratospheric state and the QBO-ENSO/Solar connection

Since it would take a very long time to go into full detail regarding everything, I am going to give somewhat of a summary for this section.

There is a very strong correlation between Stratospheric state, and conditions over the Arctic/Greenland region. This (Arctic/Greenland region) is referred to by some as the "AO or NAO". Using 10mb as a base at the 55N to 90N region, I broke every Winter since 1948 down into "warm" and "cold" seasons. Of these, the top 10 warmest produced -NAO/-AO Winter's in almost every case, and visa-versa. This is shown below.





Pretty much, warm Winter Stratosphere = good.. and cold Winter Stratosphere = bad.

ENSO events interact with the QBO state and solar cycles to dictate the Winter's Stratospheric state. The QBO plays a role because it is an upper atmosphere wind oscillation. The solar cycle plays a role because the Stratosphere is very prone to space, and ultimately the sun (being that the Stratosphere is an outer layer of the atmosphere). ENSO events play a role, because they are global phenomenon. The ENSO explanation is very complex, as this effects Mountain Torque events and other things that can influence the Stratospheric state, but all that's relevant to this is the fact the ENSO state is important.

A negative/rising phase of the QBO coinciding with El Nino correlates strongly with a warm Stratosphere throughout the majority of a Winter. This usually translates into very favorable conditions across the Arctic/Atlantic for a negative AO pattern. The combination of an El Nino-like Pacific, and a -AO could produce a amazing result for much of the CONUS in a Winter. Such a result happened in one of our best Winter's on record (1977-1978).

When La Nina is combined with the positive/falling phase of the QBO, the results are very strong in the direction of a cold Winter Stratosphere. This combination has historically produced some of the warmest Winter's on record (99-00 - the warmest Winter on record for the US was a La Nina/unfavorable QBO year).

To prove these assertions, I broke down 10mb Heights in the 55N - 90N region of the globe to define and classify "Stratospheric anomalies". Here is what that research produced for total values of each 15-day period in Winter going back to 1948:

Corrected_values.txt ( 27.61k ) Number of downloads: 2


Using my custom Stratospheric index, here are the guidelines for this research:

ONI has to be <+0.5 during a Winter month
QBO has to be very positive sometime in the Fall or Winter +10 or greater

In La Nina/+QBO conditions, here is the Stratospheric anomaly +0 in all 15-day periods during Nov - Feb:

- Negative 103/113 cases (91%)
- Neutral (0) 02/113 cases (02%)
- Positive 08/113 cases (07%)

In La Nina/+QBO conditions, here is the Stratospheric anomaly +8 or greater in all 15-day periods during Nov - Feb:

- Negative 73/73 cases (100%)
- Positive 00/00 cases (00%)

In La Nina/+QBO conditions, here is the Stratospheric anomaly +10 or greater in all 15-day periods during Nov - Feb:

- Negative 63/63 cases (100%)
- Positive 00/00 cases (02%)

In El Nino/-QBO conditions, here is the Stratospheric anomaly +0 in all 15-day periods during Nov - Feb:

- Negative 11/84 cases (14%)
- Neutral (0) 03/84 cases (03%)
- Positive 70/84 cases (83%)

In El Nino/-QBO conditions, here is the Stratospheric anomaly +8 or greater in all 15-day periods during Nov - Feb:

- Negative 02/58 cases (03%)
- Positive 56/58 cases (97%)

In El Nino/-QBO conditions, here is the Stratospheric anomaly +10 or greater in all 15-day periods during Nov - Feb:

- Negative 00/49 cases (00%)
- Positive 49/49 cases (100%)

So, while this is just one piece to the quite large picture.. and the AO-Stratosphere correlation isn't perfect, it's a huge indicator. The data posted above shows a very clear-cut correlation between ENSO and QBO state determining the Winter time Stratosphere.

Predicting the QBO

A great advantage to using the QBO as a long term forecasting index is that it runs in cycles, making it an easily predictable index. Positive and Negative phases constantly interchange on an average of about 10-18 months.

To assess what is most likely for the future, we have to first look at the past. Since 1953, 21 +QBO phases have occurred. Of these, every one ended within 18 months.. while 76% lasted only 10-14 months. The ones that ended short did so because of El Nino conditions, and the long lasting ones occurred in La Nina.

We are currently in month 13 of this +QBO, already historically ahead of most +QBO analogs. This means that at the extreme the positive phase could last through September, but since La Nina is now gone, the more likely scenario is that the phases switch sooner. However, it is possible to conclude by this that the Fall and Winter 2009-2010 will have a negative QBO.

The question now becomes.. when the phases switch, how long until the -10 threshold is reached? Historically, 20/24 (83%) -QBO events reached this point within 5 months of the phase switch. Assuming the worst case scenario happens, and September is when the phase switches, using just this, there is an 83% a negative QBO state of -10 or lower will be reached by February. but there's a twist. The atmosphere does not let the QBO trend from near neutral toward extreme negative readings in the Fall or Winter.

What time of the year the QBO change phases has a major impact on when this following -10 threshold is reached. Since 1953, the QBO has changed from positive to negative 6 times in April or May. Of these 6 times, every event was at -10 or greater within two months. June has seen a switch 5 times. Of these, there are 3 examples of it reaching -10 within 2 months, one example at 4 months, and at the extreme it didn't get there until 7 months. In the 7 month example, the QBO switched in the later half of June, which matches what comes next.. When switching phases in July or August, the average amount of time it takes for the QBO to reach -10 is over 8 months.

So basically, we need to from a +QBO to -QBO sometime before June 15th to achieve a -10 or lower anomaly by the Fall/Winter. Below is data showing the direct correlation between time of year the QBO phases switch, and how long it takes for a -10 point to be reached:

CODE
Jan - 4 (19) - 4.8
Feb - 2 (7) - 3.5
Mar - x
Apr - 4 (8) - 2.0
May - 2 (4) - 2.0
Jun - 5 (17) - 3.4
Jul - 2 (17) - 8.5
Aug - 1 (8) - 8.0
Sep - x
Oct - x
Nov - 2 (10) - 5.0
Dec - 2 (9) - 4.5


This is what 30mb Zonal Winds look like in a +QBO March/April:



Compare this to the state and trend of these Tropical Wind anomalies over the past 2 months:

Things were pretty consistent across the region until about a week ago. Now we have a very fast change underway, and are probably nearing the phase switch.

The next few weeks are very important here. Since the purpose of this thread is to describe and monitor these indexes, I had to hurry up and make this thread now. If we can get some good negative anomalies across the equator by late May, a strong -QBO by the Fall is probably a lock.. especially if an El Nino develops with it.

Solar Cycle

Another major aspect of the Winter Stratospheric state is the Solar Cycle. Increased solar activity, and more frequent solar fares correlate directly with a warm Winter Stratosphere, and visa-versa. We are currently in a stubborn long term Solar Minimum, so the sun probably won't be helping us much this Winter (at least, directly). That does not mean in any way, however, that a warm Stratosphere can not occur. Of the 3 factors I have mentioned, this has the lowest direct correlation to Winter time 10mb state over the Arctic.

On the other side of this Minimum is the fact that the Earth and Global SSTs have cooled pretty significantly over the past 2 years. With a Solar Min and La Nina in place, the Global temperature has dropped. but all this really means is that more cold air should be available if a favorable pattern does set up this Winter versus the past few years (yeah, I know that's not saying much). Historically, El Nino's that occur after La Nina's are better than your average wintertime El Nino for this reason.

Global SSTs

In April and May, this is not an issue. Even in the Summer, SSTs really aren't that important. The only time monitoring trends here makes sense is during October and November.

Although the North Pacific has a classic Nina-like -PDO now, do not worry. There is plenty of time, and if an El Nino does develop, odds are that this configuration will in fact change.

There are actually some pretty cool stats between Oct/Nov North Pacific SSTs, and the following Winter's weather, but there is no point in posting it now. Maybe sometime in September or early October.

Conclusion

What we needs to happen in the short term (next few weeks):

- QBO has to continue dropping at this rapid pace. Negative 30mb Zonal Wind anomalies in the Tropics by late May will almost secure a favorable QBO state for the coming Winter.

- Kelvin wave needs to develop and move across the ENSO regions later on in May

What we needs to happen in the Medium term (next few months):

- El Nino needs to develop, and become West-based. These events usually persist in the same regions to which they form, so watch placement of the warm anomalies going forward..

What needs to happen in the Long term (through the Fall):

- North Pacific SSTs take on a 2002-like El Nino look
- Solar Cycle 24 stakes over, and we start switching away from a Minimum (although this one isn't a big deal - we can live without Solar help this Winter)
- Positive Nino 3.4 and 4 anomalies develop and persists. The stronger the El Nino, the better

If all that can fall into place, which actually isn't very far-fetched, my top analogs for the 2009-2010 Winter will be 1977-1978 and 2002-2003.