A man walks his dog around Washington park as an autumn storm sweeps over the intermountain West on Tuesday, Oct. 29, 2019, in Denver. David Zalubowski / AP Photo

News Is Colorado Expected to Have a Big Winter? October saw record-breaking snowfall and cold temperatures. But does this indicate we’ll have a solid winter season? Well, it’s complicated. • November 11, 2019

Ah, Colorado. The state that prides itself on its beautiful landscape and its drastic array of climate regions. The state that casually boasts 300 days of sunshine per year. But what about those 60 days where the sun isn’t shining? That’s when Colorado really shows off.

Those 60 days come with days of intense weather extremes—from blizzards to tornados, flash flooding to raging wildfires, extreme temperature changes to grapefruit-sized hailstones falling from the sky. Yeah, Colorado is intense and unpredictable at times but that’s part of why we love it.

So, when my editor asked about the upcoming winter season and what to expect in terms of temperatures and snowfall, I grinned and almost chuckled to myself. Colorado is one of the most difficult areas in the country to forecast—and especially when you’re looking three months out. But there are some trustworthy ways to get an idea of what winter holds. I looked over them all to determine what the season will bring. Long story short: It’s complicated.

First, Some Background on Weather Forecasting

When forecasting for the upcoming winter, there are a few weather phenomena we can rely on, and still plenty of others that can ultimately be dismissed. Here are some variables we should look at:

El Niño Southern Oscillation (ENSO)

Madden-Julian Oscillation (MJO)

Arctic Oscillation (AO)

Local extremes in early season cold and snow

What’s ENSO?

According to the National Oceanic and Atmospheric Administration, “The El Niño-Southern Oscillation is a recurring climate pattern involving changes in the temperature of waters in the central and eastern Pacific Ocean. El Niño and La Niña are the extreme phases of the ENSO cycle; between these two phases is a third phase called ENSO Neutral.”

The three phases of ENSO have rather large differences in regard to the impacts that will be felt in the United States. This year, we have ENSO-Neutral conditions, which means that there is not a significant enough warming or cooling pattern in water temperatures across the central and eastern Pacific Ocean to strongly impact large-scale weather patterns. Because of this, I took a look at what the smaller-scale weather patterns are doing.

The MJO and AO

The MJO (Madden-Julian Oscillation) is essentially a tropical cycle of dry and wet masses of air that move from west to east across the planet. Depending on which of the eight phases the MJO is in, there are different repercussions across the U.S. The MJO typically circles the globe every 30–60 days, making this a good cycle to look at for forecasts that extend out approximately one to three weeks. We tend to look at the different phases of the MJO for impacts on how much tropical or semi-tropical moisture is in place. If cold air meets up with tropical moisture, that’s a recipe for some type of frozen precipitation.

The AO (Arctic Oscillation) is basically a ring of air that circles the polar regions and fluctuates based on pressure changes in and around those areas. Large landmasses also help to disrupt this flow of air, which could allow cold air to sink southward. This winter, forecasters are watching the AO closely, because this phenomenon may have the most impact on our storm systems. The AO can be viewed on a daily, weekly, seasonal, and annual timescale, but there is no consistency in this cycle, so you can’t use it to predict what will happen three months or three weeks out.

With that said, we sometimes know impacts close to a week out depending on whether the AO is in a negative or positive phase. A positive AO (+AO) generally means that high pressure is in control over the mid-latitudes (like North America), which keeps a lot of the cold air and storminess off to the north and allows for drier and hotter air to impact the Western U.S. The opposite is felt when there is a negative AO (-AO), meaning there is typically an influx of cold air.

What Does This Mean for Our Winter Forecast?

Ultimately, this winter is tough to forecast long-term because we are relying on short-term weather cycles to bring us active weather rather than larger and longer-term weather patterns.

But what we can do is look at years when the ENSO cycle was neutral to see if there is any correlation that we can apply to this upcoming season. The NWS in Boulder tweeted the below image out by NOAA and the Climate Prediction Center (CPC) that showed what the winter outlook is for December to February, based on several of the aforementioned parameters.

The Winter Outlook favors warmer than average for many, wetter in the northern U.S. #cowx pic.twitter.com/uahlmVkNzX — NWS Boulder (@NWSBoulder) November 2, 2019

The first map shows that the majority of the country has the chance of seeing above-average temperatures. Colorado, you’ll notice, has a chance for warmer than normal temperatures.

The second map shows the chances of seeing above or below normal precipitation through February. Colorado has an equal chance of seeing a wetter than normal or drier than normal winter.

If you’re thinking that these maps don’t bode well for a snowy season on the slopes, you’re correct. What I largely gather from this is that we are going to have a semi-mild winter this year, with a near-normal amount of precipitation. I leave it vague because we are going to have to continue to watch the MJO and AO cycles to determine storminess and blasts of cold air, which is better for a forecast within the one- to three-week timescale, rather than the one- to three-month timescale.

It’s important to remember that the forecast is calling for the possibility of higher than normal temperatures—that would be an overall average for the winter. We will still have plenty of cold air at times.

But It Seems Like Winter Is Off to a Solid Start Already!

Yep, we started our snowy season with record snow and cold in October. But does that have any implication on what the upcoming winter will be like? This is something that meteorologists have been diving into across the state.

At Denver International Airport, where officials weather records for Denver have been kept since 1995, the weather station reported 12.5 inches of snow through the month of October. That made last month the 12th snowiest October on record.

At the Denver/Stapleton reporting station, where official weather records for Denver were kept from 1950–95 (they continue to take weather observations to this day), there was a total of 15.7 inches of snow last month, making this year the third snowiest October since 1950. This total is more representative of what downtown Denver actually received.

Denver usually averages 57.1 inches of snow per season. Since 1882, there have been 27 Octobers in which more than 5 inches of snow was produced. Of those, there have been 17 seasons that reported above normal snowfall. Historically speaking, that means we have a 63 percent chance of seeing above-normal snowfall for the season following an October with more than 5 inches of snow.

Since Denver saw more than that, I looked at how many Octobers had more than 10 inches of snow—there were 14 (not including this year). Eleven of those years were followed by an above-average snow season for Denver. This means that 78.6 percent of the time that Denver receives more than 10 inches of snow in October, we experience a snowier than normal season.

So that means if we compare this snowy October to ones in the past, we have more than a 75 percent chance of seeing above-average snowfall this year, or a 25 percent chance of season a below-average season. Take those odds as you will.

So, You’re Saying There’s a Chance?

Despite what some models are showing, we still have a decent chance of seeing above-average snow this winter. Remember, there are a lot of variables and nuances in Colorado’s topography. On top of that, there are many local climates around us, and that will have an effect on snowfall. We are anticipating some warmer than normal temperatures, and that could impact snow totals, too. In fact, when looking at years in which Denver picked up either 5 or 10 inches of snow in October but did not see an above-average season (there are 12 instances), five of those years featured above-average temperatures.

Keep an eye on the sky and make sure that you are getting weather information from verified sources. There’s nothing quite like hoping and wishing for something to happen (or not happen) and then being completely disappointed by the outcome. With forecasts going out months in advance, there is a good chance that things will change. But the good thing is that we had a snowy October, and there’s already a base of powder at many of your favorite resorts—plus plenty of bluebird days ahead.