We take a broad look at White Christmas occurrences in Boulder’s historical record and discuss why Christmas Day, out of all days, has the highest probability of snow on the ground. We also give our White Christmas forecast for this year.
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here are two acceptable meteorological definitions for the occurrence of a “White Christmas.”
- 1″ of snow present on the ground at any point during Christmas Day (this is the “official” definition as denoted by the National Climatic Data Center).
- At least 0.1″ of snow must fall and accumulate on Christmas Day.
Surely we all prefer the second option, with actual snow flying as you open your gifts and stuff your face with holiday food! Old, disgusting brown snow on the ground doesn’t really tend to spread the holiday cheer, now does it?
The climatology map below from the NCDC paints the Front Range at about 40% chances of having 1″ of snow on the ground on December 25th, with near 100% odds in the western Mountains of Colorado.
Percentage chance of having snowfall on the ground on Christmas (Credit: NOAA). This is a climatology, not the forecast or specific odds for 2020.
When just considering the last 30 years, Boulder has a 23% chance of recording snowfall on Christmas Day, but a much higher 57% chance of having some snow on the ground. The graphic below compares all chances of snow on Christmas and surrounding days since 1990. The longer-term averages dating back to the 1940’s for Boulder (17% snowfall and 37% snow on ground) suggest we have been relatively more fortunate in the last few decades.
Christday Day snow occurrences by year are shown in the graphic below. Click to zoom!
Here are some additional Santa Day tidbits for Boulder…
Top 5 Snow Depths on Christmas Day Since 1948:
- ~15″(1982, unofficial)
- 13″ (2006)
- 11″ (2011)
- 9″ (2007)
- 7″ (1983)
Top 5 Snowfalls on Christmas Day Since 1948:
- 6.7″ (2012)
- 5.9″ (2007)
- 2.9″ (1997)
- 2.5″ (1964)
- 2.2″ (2014)
How the Last 5 Christmas Days Played Out in Boulder:
- 2019: December 2019 was one of the least snowy December’s in Boulder history with only 3.4″ for the entire month. Christmas Day was no exception with no snow falling or present on the ground. There were quiet conditions in Boulder and partly sunny skies. The high was 50 degrees.
- 2018: No snow fell in Boulder for nearly three weeks leading up to Christmas 2018 and the day itself was rather mundane. The high was 44°F with mostly sunny skies and light winds.
- 2017: Two quick-moving light snow events dropped 7″ of new snow in Boulder in the few days leading up to Christmas 2017. With temperatures largely staying below 40 degrees, this snow persisted to Christmas Day with a depth of 4″ reported on the ground. No snow fell in Boulder on Christmas, though a favorable northwest flow pattern produced widespread accumulating snow in the Mountains this day. The high in Boulder was a cold 26°F after a morning low of 11°F.
- 2016: A strong storm system was pushing across Colorado/Wyoming this year, but the track was too far north and the Front Range got downsloped. A few convective rain/snow showers were reported in eastern Colorado, including brief thundersnow at DIA (no accumulation) which resided in the warm sector in the morning. However, it was dry and extremely windy in Boulder with gusts up to 80MPH around the area Christmas evening! The 4″ of snow that fell about a week before Christmas 2016 was long gone so there was no snow on the ground this year either.
- 2015: Light snow fell on the evening of Christmas 2015 and spilled over into the 26th totaling 2.6″. However, since Boulder’s record-keeping for the date ends at 6PM local time, there was no snow “officially” reported for the day. There was snow on the ground though as nearly a foot of snow pummeled Boulder on December 15th and due to seasonally chilly conditions leading up the holiday, 2″ of that nasty snow remained on the ground in Boulder for Christmas.
Christmas Day has the best odds of snow on the ground?
With closer examination, it became evident that over the last 30 years, Christmas Day, at 57%, has racked up the highest chance of measurable snow depth out of any day in the entire year (well, tied with January 4th).
Why is there a spike in snow depth on Christmas Day? Well, it’s certainly not because it snows preferentially more around the holidays. The chances of new snowfall greater than 0.1″ peaks in February and early March, and then again in early April. There is a slight uptick in snow chances in the weak leading up to Christmas, but this is still lower than other times of the year.
We do note that December is technically Boulder’s second snowiest month of the year with an average of 14.5″ (based on 1988-2017 data).
How much snow is on the ground doesn’t just depend on newly falling snow. It also depends on old snow sticking around for longer once it has fallen. Thus, both soil and air temperature are also key factors influencing snow depth as both contribute to melting. As it turns out, the few days leading up to Christmas have in fact been the coldest in Boulder’s climatology. Both daily high and daily low temperatures show this same pattern.
The coldest days of the year occurring in December is something observed only over a small portion of the United States. Just about everywhere east of Boulder and in the Mountains will normally see their most frigid temperatures in January or early February. The map below is from the NCDC.
In addition to the week before Christmas being the coldest of the year in Boulder, it’s also when the Winter Solstice occurs annually. This is the time of the year with the lowest sun angle and shortest days, both of which are good for preventing drooping of any lingering snowmen. Denver’s climatology shows a marginal uptick in total sun hours in December relative to November due to slightly less clouds despite the shorter days, but it’s not much. December is still a very sun-lacking time of year.
To summarize, Christmas Day having the highest chance of snow on the ground in Boulder is no surprise at all. New snowfall is relatively common during this period. It’s also the coldest part of year and the time when the powerful melting capability of the sun is most reduced. In addition, over the years there may have also been a bias among weather observers to report 1″ of snow depth specifically on Christmas when it didn’t quite measure up. Gauging the depth of old, patchy lingering snowfall can be quite arbitrary as it is. We jokingly wouldn’t blame anyone for fulfilling the hopes of the local community with an official “White Christmas” report!
2020 White Christmas Outlook
As of Monday evening, Boulder’s 10-day streak of reporting snow on the ground came to an end.
Given the forecast for the rest of the week, lingering old snow on the ground was our only chance of a White Christmas this year. Since that hope has clearly been obliterated, we solemnly declare that it will be a “Brown Christmas” in Boulder and Denver for 2020. The latest snowfall analysis from across the country shows that you will need to head into the Mountains in order to find appreciable snowfall on the ground, or to the Northeast US where a recent nor’easter dumped anywhere from 1 to 4 feet of snow last week.
We’ll continue to monitor the weather through the week ahead with hopes that Mother Nature can pull a snowy rabbit out of the hat for us on Christmas Day. As of now, though, we’re not expecting any Yuletide magic tricks with dry weather and seasonal temperatures expected for both Christmas Eve and Day for the Denver Metro area.
From all of us at BoulderCAST,
we wish you a Happy Holidays!
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