Weather Wise - Weather Forecast
published: April 8th 2016
by: Brian Bledsoe
If you have ever heard me speak or have been reading Weather Wise for the past several years, you know I do my best to educate you on the major oceanic oscillations. It has been a while since we have chatted about the PDO (Pacific Decadal Oscillation) and the AMO (Atlantic Multidecadal Oscillation). While I don’t want to lose you in their complexities, I do want to update you on what they are doing.
First, the PDO… The PDO has been in a positive/warm state since March of 2014. While there have been other contributing factors to drought eradication in the Southern Plains, the positive/warm PDO is certainly high on the list. The graph below shows the PDO phase all the way back into the 1800’s:
It is a lot to take in, but you get the idea. Long periods of positive/warm and negative/cold phases of this particular oscillation. One of the most notable times in recent climatic history was the Great Climatic Shift from the late 1970s through the 1990s. The PDO was quite positive/warm during that time. While drought in the Southern Plains occurred during that time (especially 1996), it was much less frequent than it has been since 2005. Since roughly 2005, the PDO has been predominantly negative/cold. When the Pacific is “cold,” drought seems to be MUCH more of an issue in the Southern Plains. Currently, the PDO is still quite positive/warm, but I believe this is but a detour from the long term pattern. I believe it will revert back to a negative/cold state in the near future.
While the Pacific Ocean is a really important factor in long range weather forecasting, it isn’t just about the Pacific. The Atlantic has an oscillation too...Atlantic Multidecadal Oscillation. Since roughly 1995, it has been in a predominantly positive/warm state. During the past few years, it has been flirting with more of a negative/cold state. However, it hasn’t been able to “full on flip” phases. The graph below shows AMO phase back into the 1800s:
The difference phases of these oscillations fluctuate on about a 25-35 year cycle. Figuring out when the phase of each oscillation is going to flip is very challenging. Right now, it appears that it will be at least another 10-20 years before the PDO will flip back to its positive/warm phase. Meanwhile, it will only be another few years before the AMO flips to its negative/cold phase. Once it does, it will likely stay there for 20+ years… My point is that if a particular oscillation is not in a favorable phase for your area, that it will be quite a while before that phase flips.
In 2004, McCabe, Palecki, and Betancourt came up with a “drought frequency” map that is based on what particular phase the Pacific and Atlantic are locked into. Red means higher drought frequency while blue means lower drought frequency...see below:
For the Southern Plains, the major drought of the 1950s and the recent droughts from mid 2010-2013 essentially occurred when we were dealing with -PDO and +AMO. You can see from their map above that there is higher than normal drought frequency for Texas and the Desert Southwest when in this phase. Recently, we have detoured through +PDO -AMO which aided in breaking the drought, and are now in +PDO +AMO. However, I see us reverting back to -PDO +AMO for a while, before fully flipping to -PDO -AMO in a few years. Confused? I hope not, because that is not what I am trying to do. What I am trying to do is show you how drought frequency is expected to evolve during the next several years. For me here in Colorado, I fear the time when -PDO -AMO sets in, because higher than normal drought frequency “bullseyes” my area. I know once we enter that phase, we will be in it for quite a while. Meanwhile, drought frequency seems to lower in Texas and for parts of the Desert Southwest. That is obviously good news.
I know many of you know about this already, whether it has been through me or someone else. It is a very important topic, especially for younger farmers and ranchers that may not be familiar with the previous drought cycles. It is essential that you have a drought plan and know how to execute it. Drought is a part of our past and will be a part of our future. The more we prepare for it and know about it, the better we can deal with it. Common sense, I know but many times common sense isn’t as common as we think when it comes to drought planning.