Recently I have had people asking me what is in store for us this winter. Will it be like last winter with the great mountain snow cover? So far, I don’t have a definitive answer, but there has been some chatter in the professional journals about the potential of another El Nino winter just like the one we had last winter.
It’s been quite a while since I discussed the mechanism that determines what kind of winter we experience here in the Pacific Northwest. We should start with the terminology used in meteorology to describe the variables that control our fate in winter.
The first term, which I’m sure you remember is El Nino. El Nino is defined as a warm water current (shown in red/orange) that appears annually, around Christmastime, along the coasts of Ecuador and Peru. The name El Nino means the boy child and refers to the “Christ Child” who’s birthday is celebrated in December when the warm water pool extends itself closer to the South American coast. It was first discovered or noted by the fisherman who found warmer water where they usually would catch fish.
The second term is La Nina which is defined as a cold water current (shown in blue) that appears annually, around Christmastime along the coasts of Ecuador and Peru. The name La Nina means the girl child and is the opposite of El Nino and is the cool water pool that extends itself closer to the South America in December.
It seems obvious that El Nino and La Nina can’t occupy the same area along the South American coast at the same time. They tend to alternate which is dominant. That is where the third term comes into play. The ENSO or El Nino-Southern Oscillation. El Nino is often called the warm phase of ENSO while La Nina can be called the cold phase of ENSO. Often the sea surface temperatures waver between the two in the same season.
I have one more definition that is almost never mentioned. What would you call it when neither El Nino nor La Nina come to visit the West Coast of South America? I guess you could call it the “nothing” and that is just what they decided to call it. In Spanish it is La Nada.
Now that you have the key definitions we need to find out how they can make our lives more pleasant or more difficult in winter. What these currents do is deflect the Jet Stream in such a way to either bring the colder air and the Winter storms our way or to act as a barrier to protect us from the stronger wInter storms and keep us warmer.
El Nino’s warm water pool actually deflects the Jet Stream in the Winter in such a way as to set up a high pressure ridge over the Pacific Northwest. That ridge keeps the cold air and the Winter storm track to our North or South and tends keep us warmer and drier. During an El Nino year there is less tropical storm activity in the tropical Atlantic due to increased vertical wind shear over the area.
La Nina’s cold water pool has the opposite effect and deflects the Jet Stream so as to send the Winter storms right at us. Which one is controlling our weather now and what kind of Winter can we expect?
According to an ElDoradoCounty.com report issued September 14, 2017 “A majority of the models in the IrI/CPC suite of Nino-3.4 predictions favor ENSO-neutral through the Northern Hemisphere 2017-18 winter. However, the most recent predictions from the NCEP Climate Forecast System (CFSV2) and the North American Multi-Model Ensemble (NMME) indicate the formation of La Nina as soon as the Northern Hemisphere Fall 2017. Forecasters favor these predictions in part because of the recent cooling of the surface and sub-surface temperature anomalies, and also because of the higher degree of forecast skill at this time of year. In summary, there is an increasing chance (55-60%) of La Nina during the Northern Hemisphere Fall and winter 2017-18.”
It is a bit early in the season to make a solid prediction for Winter. The best time is mid-November (that is more than a month away) when the sea surface temperatures are set up for the Winter months. That prediction would be for the actual Winter months of December, January, and February. So for the predictions seem to be for a small chance of above normal temperatures and precipitation. Now we just have to believe that this winter should be a lot like last winter, until proven otherwise, with plenty of snow in the Cascades producing a bountiful snow pack for the spring thaw producing plenty of water for the reservoirs and area rivers.
Let me know what you would like me to talk about or explain. You can email me at: firstname.lastname@example.org.