Denver Winter Outlook
Colorado. The Centennial State. The state that prides itself on its beautiful landscape and its drastic array of climate regions found from east to west. The state that boasts casually 300 days of sunshine per year.
But what about those 60 days where there isn't sunshine? That's when Colorado just starts to show off.
Those 60 days where there is a lack of sunshine come with days of intense weather extremes. From blizzards to tornado outbreaks, 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 hey, that's why we love it here.
So, when asked about the upcoming winter season and what to expect in terms of temperatures and snowfall, I grin and almost chuckle to myself. Little do people realize, forecasting in Colorado is one of the most difficult areas in the country to have to forecast for.
So, it's tough to forecast in Colorado. Got it.
Alright, let's talk about the upcoming winter forecast and what we can rely on when looking that far ahead into the future. There are many parameters to look at when forecasting winter outlooks - a lot of which can ultimately just be dismissed - but there are certain ones that truly do have an implication of what the upcoming winter may hold or at least will tell us what else we should be looking at.
~ El Niño Southern Oscillation (ENSO)
~ Madden-Julian Oscillation (MJO)
~ Arctic Oscillation (AO)
~ Local extremes in early season cold and snow
There are other things we could look at but these are what I will be referencing going forward.
Let's talk about ENSO. What is it? "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" as defined by climate.gov.
The three different phases of ENSO have rather large differences in regards to the impacts that will be felt in the United States.
This year, we have ENSO-Neutral conditions. Neutral, as you can gather, means that there isn't a significant enough warming or cooling pattern in water temperatures across the central and eastern pacific ocean to strongly impact large scale weather patterns this upcoming winter.
Then what else can we look at to forecast this upcoming winter? Well, since our very large-scale weather influencer (ENSO) is pretty average this year, we should look at what the smaller-scale weather patterns are doing.
MJO and AO
So many abbreviations but it's worth it. The MJO is a tropical cycle of dry and wet blobs of air that move from west to east over time across the planet. Depending on which phase the MJO is in (there are 8 phases), there are different repercussions felt across the United States. The MJO typically circles the globes every 30-60 days making this a good cycle to look at for forecasts that extend out ~1-3 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 across the U.S.
The AO is basically a ring of air that is circling the polar regions and fluctuates based on pressure changes. Large landmasses help to disrupt this flow of air as well which allows cold air to sink south. This winter, the AO is something that is going to have to be watched because it's likely that this is the phenomenon that may have the most impact on our storm systems and cold air that move through. The unfortunate thing is that the AO can be viewed on a daily, weekly, seasonal and annual timescale with no consistency meaning that there's no real predictive possibility when forecasting the AO.
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 US. The opposite is felt when there is a negative AO (-AO). There is typically an influx of cold air across the mid-latitudes when the AO phase is negative.
Ultimately, this winter is going be tough to forecast long-term for because we are really relying on short term weather cycles to bring us active weather rather than larger and longer-term weather patterns.
Now, we can look at years when the ENSO cycle was neutral to see if there is any correlation we can apply to this upcoming season. The NWS in Boulder tweeted the image put out by NOAA (National Oceanic and Atmospheric Administration) and the CPC (Climate Prediction Center) that showed what the winter outlook is for this December to February.
https://twitter.com/NWSBoulder/status/1190419435502350337
What this shows is that the majority of the country has the chance of seeing above-average temperatures and in areas where there is no color, there is an equal chance of seeing above or below normal temperatures during the period. Colorado is firmly in the chance for warmer than normal temperatures.
This also shows the chances of seeing above or below normal moisture during the winter months. Colorado has an equal chance of seeing a wetter than normal or drier than normal period from December to February with the northern US being favored for above-normal precipitation.
What I largely gather from this is that we are going to have a more 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 storm cycles and blasts of cold air which is better within the 1-3 week timescale rather than the 1-3 months timescale.
Even though the forecast is calling for the *possibility* of higher than normal temperatures - that would be an overall average of the winter. What you should realize is even though the average as a whole may be higher than the normal, it will be winter and we will have plenty of cold air at times.
SOMETHING OF NOTE
We started our snow season in a very shocking manner. With record snow and cold in October. Does that have any implication on what the upcoming winter will be like? This is rather interesting and something that meteorologists have been diving into across the state.
October 2019, at Denver International Airport - where officials weather records for Denver have been kept since 1995 - the weather reporting station reported 12.5" of snow through the month. That made October 2019 the 12th snowiest October on record.
October 2019, at the Denver/Stapleton reporting station where official weather records for Denver were kept from 1950-1995 (they continue to take weather observations to this day) there was a total of 15.7" of snow that fell during the month of October this year making it the 3rd snowiest month since 1950 there. This is more representative of what Downtown Denver actually received. Before 1950, Denver's weather records we reported from the Downtown City Office.
Since 1882 - there have been 27 October's that produced more than 5" of snow.
Denver averages 57.1" of snow per season - so how many of those 27 years did Denver end up getting above average snowfall for the season? 17 years (or 63% of the time).
There have been 14 years where Denver picked up more than 10" of snow in October (not including this year).
And of those 14 years, 11 of them were followed by an above-average snow season for Denver - or about 78.6% of the time Denver receives more than 10" of snow in October, we experience a snowier than normal season.
That's a lot of numbers but the takeaway here is that if we compare this snowy October to one's of the past - we have more than a 75% chance of seeing above-average snowfall this year. That also means that we have a 25% chance of season a below-average season so take those odds as you will.
SUMMARY
If you're a snow lover, we have a decent chance of seeing an above-average season this winter! Remember, there are a lot of variables and a lot of nuances in Colorado's topography and the many local climates we have that will have an effect on actual snow that falls.
It's Colorado, it's nearly winter, just be prepared. Remember that we are anticipating some warmer than normal temperatures this season. That could have an impact on snow totals.
In fact, when looking at the years where Denver picked up either 5" or 10" of snow in October but didn't see an above-average season (which there are 12 years total) - 5 of those years featured above-average temperatures. We do have that chance of seeing too warm of weather impact our snow season. Time will tell.
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.
But what about those 60 days where there isn't sunshine? That's when Colorado just starts to show off.
Those 60 days where there is a lack of sunshine come with days of intense weather extremes. From blizzards to tornado outbreaks, 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 hey, that's why we love it here.
So, when asked about the upcoming winter season and what to expect in terms of temperatures and snowfall, I grin and almost chuckle to myself. Little do people realize, forecasting in Colorado is one of the most difficult areas in the country to have to forecast for.
So, it's tough to forecast in Colorado. Got it.
Alright, let's talk about the upcoming winter forecast and what we can rely on when looking that far ahead into the future. There are many parameters to look at when forecasting winter outlooks - a lot of which can ultimately just be dismissed - but there are certain ones that truly do have an implication of what the upcoming winter may hold or at least will tell us what else we should be looking at.
~ El Niño Southern Oscillation (ENSO)
~ Madden-Julian Oscillation (MJO)
~ Arctic Oscillation (AO)
~ Local extremes in early season cold and snow
There are other things we could look at but these are what I will be referencing going forward.
Let's talk about ENSO. What is it? "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" as defined by climate.gov.
The three different phases of ENSO have rather large differences in regards to the impacts that will be felt in the United States.
This year, we have ENSO-Neutral conditions. Neutral, as you can gather, means that there isn't a significant enough warming or cooling pattern in water temperatures across the central and eastern pacific ocean to strongly impact large scale weather patterns this upcoming winter.
Then what else can we look at to forecast this upcoming winter? Well, since our very large-scale weather influencer (ENSO) is pretty average this year, we should look at what the smaller-scale weather patterns are doing.
MJO and AO
So many abbreviations but it's worth it. The MJO is a tropical cycle of dry and wet blobs of air that move from west to east over time across the planet. Depending on which phase the MJO is in (there are 8 phases), there are different repercussions felt across the United States. The MJO typically circles the globes every 30-60 days making this a good cycle to look at for forecasts that extend out ~1-3 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 across the U.S.
The AO is basically a ring of air that is circling the polar regions and fluctuates based on pressure changes. Large landmasses help to disrupt this flow of air as well which allows cold air to sink south. This winter, the AO is something that is going to have to be watched because it's likely that this is the phenomenon that may have the most impact on our storm systems and cold air that move through. The unfortunate thing is that the AO can be viewed on a daily, weekly, seasonal and annual timescale with no consistency meaning that there's no real predictive possibility when forecasting the AO.
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 US. The opposite is felt when there is a negative AO (-AO). There is typically an influx of cold air across the mid-latitudes when the AO phase is negative.
Ultimately, this winter is going be tough to forecast long-term for because we are really relying on short term weather cycles to bring us active weather rather than larger and longer-term weather patterns.
Now, we can look at years when the ENSO cycle was neutral to see if there is any correlation we can apply to this upcoming season. The NWS in Boulder tweeted the image put out by NOAA (National Oceanic and Atmospheric Administration) and the CPC (Climate Prediction Center) that showed what the winter outlook is for this December to February.
https://twitter.com/NWSBoulder/status/1190419435502350337
What this shows is that the majority of the country has the chance of seeing above-average temperatures and in areas where there is no color, there is an equal chance of seeing above or below normal temperatures during the period. Colorado is firmly in the chance for warmer than normal temperatures.
This also shows the chances of seeing above or below normal moisture during the winter months. Colorado has an equal chance of seeing a wetter than normal or drier than normal period from December to February with the northern US being favored for above-normal precipitation.
What I largely gather from this is that we are going to have a more 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 storm cycles and blasts of cold air which is better within the 1-3 week timescale rather than the 1-3 months timescale.
Even though the forecast is calling for the *possibility* of higher than normal temperatures - that would be an overall average of the winter. What you should realize is even though the average as a whole may be higher than the normal, it will be winter and we will have plenty of cold air at times.
SOMETHING OF NOTE
We started our snow season in a very shocking manner. With record snow and cold in October. Does that have any implication on what the upcoming winter will be like? This is rather interesting and something that meteorologists have been diving into across the state.
October 2019, at Denver International Airport - where officials weather records for Denver have been kept since 1995 - the weather reporting station reported 12.5" of snow through the month. That made October 2019 the 12th snowiest October on record.
October 2019, at the Denver/Stapleton reporting station where official weather records for Denver were kept from 1950-1995 (they continue to take weather observations to this day) there was a total of 15.7" of snow that fell during the month of October this year making it the 3rd snowiest month since 1950 there. This is more representative of what Downtown Denver actually received. Before 1950, Denver's weather records we reported from the Downtown City Office.
Since 1882 - there have been 27 October's that produced more than 5" of snow.
Denver averages 57.1" of snow per season - so how many of those 27 years did Denver end up getting above average snowfall for the season? 17 years (or 63% of the time).
There have been 14 years where Denver picked up more than 10" of snow in October (not including this year).
And of those 14 years, 11 of them were followed by an above-average snow season for Denver - or about 78.6% of the time Denver receives more than 10" of snow in October, we experience a snowier than normal season.
That's a lot of numbers but the takeaway here is that if we compare this snowy October to one's of the past - we have more than a 75% chance of seeing above-average snowfall this year. That also means that we have a 25% chance of season a below-average season so take those odds as you will.
SUMMARY
If you're a snow lover, we have a decent chance of seeing an above-average season this winter! Remember, there are a lot of variables and a lot of nuances in Colorado's topography and the many local climates we have that will have an effect on actual snow that falls.
It's Colorado, it's nearly winter, just be prepared. Remember that we are anticipating some warmer than normal temperatures this season. That could have an impact on snow totals.
In fact, when looking at the years where Denver picked up either 5" or 10" of snow in October but didn't see an above-average season (which there are 12 years total) - 5 of those years featured above-average temperatures. We do have that chance of seeing too warm of weather impact our snow season. Time will tell.
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.
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