You might remember that I wrote past column articles about what causes winter weather patterns over the Pacific Northwest. In 2013 the article was titled ” Whose Fault Is It? El Nino, La Nina, Or Even La Nada?” Those three terms give meteorologists the tools to determine what kind of winter we will have and whether the current winter weather pattern will continue as is or change to another one.
Let’s review the three terms and what they mean. 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. 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 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.
Vertical wind shear is the change of wind direction with height. In order to build the storm clouds it takes to produce a hurricane there must be steadily rising columns of air and the change of wind direction as the air is rising tends to stop the development of the storm clouds. 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.
It seems obvious that El Nino and La Nina can’t occupy exactly the same area along the South American coast at the same time. That is where another 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. When neither El Nino nor La Nina come to visit the West Coast of South America it is called La Nada which in Spanish translates as nothing. That means the current is stable, neither warm or cold.
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. So what’s been going on these last few months? A USA Today article posted February 9, 2018 and written by Doyle Rice touts that the LaNina has ended and now we are being controlled by La Nada. That’s according to climate scientists interviewed for the story. The short-lived La Nina did bring unusually cold air in December and January to Alaska, western Canada, and the Northern plains. La Nina usually brings more precipitation to the Pacific Northwest and Northern California, but that did not happen.
Historically we have had La Nina winters in the Pacific Northwest which were more on the dry side and even warmer than expected. Instead the rain hit Central and Southern California ending in a declaration by Southern California that the drought was officially over.
The ski areas in the central part of Oregon have been suffering from a serious lack of snow cover while the Sierra in California have been experiencing one of their snowiest winters ever recorded. That shows that the deflection of the jet stream is such that the areas receiving significant snowfall were to the south and north of the southern Willamette Valley. That suggests that the Jet Stream was deflected, but the Pacific Northwest was protected from the storms by having a high pressure ridge over the Eastern Pacific and a parade of upper level Low Pressure Troughs which brought us some rain, but also kept temperatures above normal for quite some time. For some reason the Jet Stream set up to being the cold Arctic air down through Canada into the Midwest and as far south as the Gulf Coast states. Snow and record temperatures punched well into the Deep South, but nothing for us.
The National Weather Service Temperature and Precipitation outlooks for February through April give us a look into our possible weather future. The temperature graphic shows about a 40% chance of below average temperatures and the precipitation graphic shows about a 40% chance of above normal precipitation. Does this give us a handle on what the rest of our winter will be like? Not really. The potential is still there for the intrusion of much colder air moving down through Canada (this past weekend) and if there is sufficient moisture available from the South and West at the same time we could still see significant snowfall in the mountains and possible valley snow if the conditions are right.
At this point in time I’d say a flip of a coin could predict the snow chances for the rest of our winter about as accurately as the combination of the sea surface temperatures and the exact position of the jet stream over the Eastern Pacific Ocean and the Pacific Northwest. Hang on it will still be an interesting ride.
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