(This article first appeared in the Jackson Hole News & Guide, Nov. 23rd, 2016 issue.)

About a week or so ago, NOAA’s Climate Prediction Center announced that, “La Nina conditions were present and favored to persist through the winter 2016-17”. This caused local skiers and boarders to rejoice with primal screams of joy and dreams of a HUGE powder season. Why? Because they have been told over the years that: La Nina is good for snow and El Nino is not.

I hate to be the one to scrape the wax off your boards, but you need to slow down a minute and understand what exactly La Nina is, and what it MIGHT mean for snowfall around Jackson Hole in the winter. That is what I will attempt to bring to this week’s column

What is it?

La Nina & El Nino are conditions that occur in the Equatorial Pacific when there is a departure from “normal” Sea Surface Temperatures. We call it an El Nino when these temperatures are warmer than normal, and La Nina they are cooler than normal.

During an El Nino, there is a weakening pressure gradient between the eastern Pacific & western Pacific, and weaker easterly trade winds develop, allowing warmer surface water to surge eastward, replacing normal cooler water off the coast of South America. This leaves a belt of warm water along the Equator in the Pacific.

La Nina conditions occur when those easterly trade winds are stronger, causing cooler water in the eastern Pacific, near the coast of South America, to spread westward. That leaves a belt of cool water along the Equator.

How much warmer or cooler those water temperatures are, determines how strong or weak the El Nino or La Nina is. Since temperature and pressure are directly related, El Nino or La Nina will have an affect on the pressure patterns (weather patterns) and the jet stream (storm track) across the northern Pacific Ocean during the winter months.

Typically, during El Nino winters, the Southwestern U.S is cooler and snowier, while the Northwestern U.S. is warmer with less snowfall.

Typically, during La Nina winters, the Northwestern U.S. is cooler with above normal snowfall, while the Southwestern U.S is warm and dry.

How Big is it?

Calling for a “La Nina Winter” is not a slam-dunk that we will have above average snowfall. At this point, we have what is considered a weak La Nina, and the Climate Prediction Center is only giving it a 55-percent probability of persisting during the December, January and February time-frame. That probability drops to a 43-percent for the 3-month period, January though March.

During our most recent strong La Nina winters (2010-11 and 2007-08), we had way above normal snowfall. These were banner winters for powder. However, during the latest two weaker La Nina’s (2000-01 and 2011-12) Jackson Hole experienced below normal snowfall.

The same comparisons could be made for El Nino Winters. Remember last year? The Super El Nino, the Godzilla of all El Ninos, it was called. We were supposed to be drier than normal. We were not, snowfall in town was right at average, and the mountains were just above average.

The weather is never as cut-and-dried or as simple as you might believe. It’s complicated, has lots of moving parts, and La Nina is just one of those parts. A small shift in the weather pattern out in the Pacific, at any given time during the winter, can have a major effect on where storms track across the Western United States. Thus, the variability we see from one El Nino or La Nina year, to another.

I like to say, “The reality of the weather is not always as described in the forecast”.

All that said, I will still guarantee you, that every time we get a good snowstorm this winter, people will say, “How about that La Nina, pretty good, huh?” And, every time we go through a week without any snow, they will ask, “What happened to that La Nina? Where did it go?”
Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for 25 years.

(This article originally appeared in the Jackson Hole News & Guide on Oct. 26, 2016)

At the very end of August, in this column, I gave you the early, early winter outlook for 2016-17. That was ridiculously early to be talking about winter. Now that we are deep into October, have some snow on the ground, and some among us have already been skiing, I thought it might be a good time to update what was said back in August.

Some predictions will not change, like the Farmer’s Almanacs, but an update from NOAA and the El Nino/La Nina situation might provide better insight, as we get closer to the actual winter months.

The Outlooks

As you may recall from that August column, the two most prominent Farmer’s Almanacs were basically at odds with each other, as to what sort of winter this part of the country would have. One painted a picture of “Mild and Dry” conditions across the State of Wyoming, the other depicted “Freezing Cold with Average Snowfall” for this part of the country. That was neither helpful nor definitive.

Back in August of this year, the Climate Prediction Center (CPC), which produces three-month outlooks of temperatures and precipitation, was telling a slightly different story than the Almanacs. The CPC had us right on the line for a 50/50 chance of being warmer than normal in December-January-February. For precipitation, Northwest Wyoming looked to have a slightly better than a 50-percent chance of having above normal precipitation this winter.

The latest predictions from the CPC, made at the end of last week, show that we now have a little better than a 50-percent chance of being warmer than normal, and are closer to a 55-percent chance of having above normal precipitation, in the December-January-February time period.

If you look at the next three-month prediction, for January-February-March of 2017, then we drop into the “Equal Chances” category for temperatures; that is, it could be above or below normal, temperature-wise, for these three months. For precipitation, Northwest Wyoming hangs closer to that 55-percent chance of above normal precipitation.

Trend-wise, I would say that might result in something closer to normal temperature-wise for Jackson Hole this winter, and our odds of having above normal snowfall this winter in Jackson Hole are solidly better than 50/50, through the winter months.

Now, let’s see how the projected La Nina situation is developing first.

El Nino/La Nina

To review: El Nino is one phase of what is known as the El Nino Southern Oscillation (ENSO), which is tied to the fluctuations in sea-surface temperatures in the Equatorial Pacific. During an El Nino, those water temperatures are warmer than normal. During a La Nina, they are cooler than normal.

El Nino winters generally bring warmer and drier conditions across the northern Rockies. Note: we had a strong El Nino last winter and yet we ended up with a winter that had average temperatures and just above normal snowfall.

La Nina winters typically bring and cooler and wetter weather to the Pacific Northwest and the northern tier of the United States. Like the strong La Nina winter we had in 2010-11.

At present, conditions in the Equatorial Pacific are near neutral or slightly cooler than normal. Therefore, water temps will have to start diving before they will call it a full-fledged La Nina. The prediction is that a weak La Nina will develop (70-percent chance) and may persist (55-percent chance) through the winter months.

For the latest updated info on La Nina, Click Here>>

If actually we end up with more of a “Neutral”, or No-Nino winter, then our odds of an above normal winter could drop. Part of what goes into those CPC forecasts depends on these ENSO predictions for the winter.

One last thing, which I personally like to look at, is what the water temperatures are doing in the northern Pacific. This is related to what is known as the Pacific Decadal Oscillation, or PDO. During the last two winters (2014-15 and 2015-16) the temperatures in that part of the Pacific have been warmer than normal, unusually warm at times.

Since June of 2016 those temps have been in a steady decline, and were almost back to normal by the end of September. My hypothesis is: whenever the PDO is near or cooler than normal, Jackson Hole has a bigger winter.

Let’s root for that northern Pacific Ocean to keep on cooling down over the next few months. That could make for a very “powder-full” winter here.

Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for the last 25 years.