Why does it always seem to snow on Wednesdays? We asked the National Weather Service

DENVER — Another midweek snowstorm is on the way for Denver, and it had some folks online wondering: Is it snowing an awful lot on Wednesdays lately?

The National Weather Service office in Boulder looked into it, and it turns out that answer is yes – but it’s not much more than a meteorological coincidence.

First, a look the data:

For the last four winters in Denver, Wednesday has been the snowiest day of the week.

The NWS compiled daily cumulative snowfall data from October of 2019 to present day at Denver International Airport, the weather station of record for Denver. In that time, nearly 50 inches of snow have fallen on Wednesdays.

Tuesday and Thursday have been the next snowiest days, with 43.5 and 41.1 inches falling on those days, respectively.

Weather data recorded in Boulder shows the most daily snowfall on Thursdays, but with one important caveat: Weather observations there are done once per day, at 6 p.m., according to NWS meteorologist Zach Hiris.

The Thursday totals are those recorded from 6 p.m. Wednesday to 6 p.m. Thursday. DIA, by contrast, takes observations every six hours.

“I think a lot of that is those storms that start up Wednesday afternoon, Wednesday evening, and continue overnight,” Hiris said, acknowledging that comparing the different data sets is an imperfect science. “That's where it's kind of shifted into Thursday for Boulder.”

So, to Coloradans out there curious about these “weather Wednesdays” – worry not, it isn’t just you.

The folks pining for a meteorological explanation for this phenomenon, however, shouldn’t hold their breath.

“It really is just kind of a random coincidence,” Hiris said. “To have it a couple of years in a row is kind of fun, but there's no real statistical meaning there. And in fact, if you go back and look through all the data going back till about 1900, that signal really gets muted out.”

That doesn’t mean every seemingly random weather trend is mere happenstance, though.

For instance, March has been Denver’s snowiest month on average, not just over the last several years but over the 30-year climate normal period, Hiris said. The longer-term data is more indicative of a true meteorological trend.

To get more specific, high precipitation totals at night across the Central Plains are not a coincidence, either. Hiris said that’s a result of what’s known as the low level jet, or “a region of relatively strong winds in the lower part of the atmosphere,” according to the NWS.

The low level jet is more common in the summer, which leads to more thunderstorms at night, which in turn leads to higher nighttime precipitation.

“There are things like that that are linked,” Hiris said.

What we also know is that it’s been a snowy winter in Denver.

DIA has already recorded 40.5 inches of snow, with another 4-6 inches expected this week and the snowy month of March still ahead.

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