11 August 2014
I’ve spent the weekend looking at how the coming winter may turn out, and before I go any farther, let me say that long-range forecasts can turn out to be horribly wrong. Let me repeat that: long-range forecasts can turn out to be horribly wrong. That said, there are some fascinating indications that the Eastern and Southeastern U.S. may be in for a cold and wet/icy winter, while the drought in the far west gets even worse.
The reasons have to do with El Nino, and a certain type of El Nino that may be developing. There have been indications that an El Nino was on the way for months, and while there were signs early on that it might be a big one, most meteorologists thought this was overdone, and it turns out they were probably right. The last few weeks have seen Pacific ocean waters cool somewhat and the NOAA Climate Prediction Center issued an update this last week that there is a 70% chance of seeing El Nino conditions this winter. This is still fairly high, but the more important news is that there seems to be a real possibility that we will see a type of event called a MODOKI El NIno.
Modoki type El Nino events are much different that traditional warm episodes, and this is covered well in a paper in Geophysical Research Letters: (Yu, J.-Y.,Y. Zou, S. T. Kim, and T. Lee (2012), The changing impact of El Niño on US winter temperatures, Geophys. Res. Lett., 39, L15702, doi:10.1029/2012GL052483.).
The paper looks at the effects of these Modoki type El Nino patterns on the winter temperatures over the U.S. and the associated storm track. The graphic below shows the difference between normal Eastern Pacific warm episodes and the Central Pacific (Modoki) episodes. Notice how in Modoki winters we see a very cold pattern in the SE and Mid Atlantic with warm weather in the NW U.S. This kind of pattern is called a PNA (Pacific North American) pattern and is very familiar to forecasters, because it means cold and snowy weather in the eastern U.S. and drought/warm weather for California.
It’s important to remember that EACH El Nino is different (as can be seen in the anomalies above), but if you take an average you get the following:
The last Modoki El Nino winter was 2010 and it will not soon be forgotten here in Maryland and D.C., because it was one of the snowiest in recent memory. There were some heavy snow events in the deep south as well, and 1977 was also a Modoki winter (see anomalies for 1977 above). Anyone old enough to remember that winter knows that is was one of the coldest since they read the Declaration of Independence from the balconies in Philadelphia.
There are no certainties here, but if an El Nino Modoki develops, then this coming winter looks like it will be a cold one in most areas of the East, and the news for California is even worse. The worst drought in recorded history will likely get even worse, and the desperately needed winter rains may be very sparse. In short, a strong Modoki event will be catastrophic for California, and the cost of food will rise because of it. Turn down the thermostat a bit though, and save some money for the heating bill as well.
Fellow geeks: More on the two types of El Nino here- http://journals.ametsoc.org/doi/full/10.1175/2008JCLI2309.1