A strong late season storm is bearing down on eastern Colorado, with people tossing around words like "blizzard," "cyclone" and "bombogenesis." But the worst of the worst, by whatever name, will likely not apply to Boulder County.
"My general sense is this is one of those where the blizzard-type conditions will be much worse as you go out on the plains," said Bob Henson, a meteorologist and blogger for Weather Underground, which is part of IBM. "The (Interstate) 25 corridor could be the dividing line, with stark differences within just a few miles."
As of Tuesday afternoon, the National Weather Service had Denver and much of Colorado east of I-25 under a blizzard warning, with Colorado west of I-25 issued a winter storm warning, with rain most likely changing over entirely to snow after 11 a.m. Wednesday.
On Tuesday, the National Weather Service issued an advisory suggesting that people cancel any travel plans, especially east of I-25, for Wednesday afternoon and evening.
Colorado State Climatologist Russ Schumacher said, "There's going to be problems" Wednesday, and in fact, flight cancellations at Denver International Airport were already being announced on Tuesday afternoon.
On Tuesday, well before the storm struck, a significant number of closures were already announced locally; Boulder and Longmont courts will be shut down at noon Wednesday, as will all Boulder County offices. Boulder Valley, St. Vrain Valley and Adams 12 school districts also announced schools will be closed on Wednesday.
Nezette Rydell, National Weather Service meteorologist in charge for Boulder, on Tuesday said she expected Boulder County to see 4 to 6 inches of snow across the area, with those figures trending higher — to perhaps more than 10 inches east of I-25. Snow totals also will be higher into the foothills, she said, with 6 to 8 inches in the Nederland area, and greater totals in higher mountain locations.
"The story tomorrow for us is winds," Rydell said. "The winds will be increasing as you move east from Boulder, where they will be 40 to 50 mph, and by the time you get to the airport, 60 to 80, and that's because the low (pressure) is so very deep."
The greatest uncertainty in Wednesday's forecast is for I-25 westward, she said.
"The last few model runs have sort of trended toward worsening conditions to the west (of I-25), but not a great deal. Our best guess (for Boulder) is 4 to 6 inches, with quite a bit of wind, starting around noon and going right through the afternoon into the night."
Bombogenesis 'a bit bombastic'
Garnering much of the attention is a low pressure system developing that could be a record breaker with readings in the 970-millibar range. Schumacher tweeted early on Tuesday that Colorado doesn't keep an official low sea-level -adjusted pressure record, due to there being very few stations with long and reliable data. However, the lowest he could find, he tweeted subsequently, was 975.0 mb at the Lamar airport March 14, 1973.
Henson said that wind typically circulates counterclockwise around a low pressure system, which is what creates the upslope conditions typically associated with the heavier snows in Boulder County and the rest of the Front Range.
However, he said, an extreme low pressure situation is accompanied by isallobaric winds, or, winds blowing very strongly toward the low pressure, "basically trying to fill the cavity created" by the low pressure system.
"That is going to help produce some downslope component over Boulder County that kind of works against the upslope," Henson said.
Klaus Wolter, a climatologist recently retired from the University of Colorado's Cooperative Institute for Research in Environmental Sciences, said the last storm he could find locally that is analogous to this week's blast occurred March 8-9, 1992.
"There was a tornado touching down in Limon, 2 feet of snow in Gunbarrel," Wolter recalled of that event. "This is not what I'm predicting. But this is in the realm of possibility. If you look at the models, there is a very wide range of outcomes. What is very clear is that this is going to be an exceptional storm."
He observed that a significant influence on our weather pattern of late is a return of El Niño conditions, a warming of the equatorial surface waters of the east-central Pacific Ocean.
"This is important, since March is best correlated with El Niño (i.e., wet). Notable examples of wet Niño Marches since 1990: 1992, '98, '03 (yes, that was one big storm), '10, and '16," he said in an email.
"So, if we end up getting 'whacked', it would fit that mold of increased probability (no guarantees in this business, alas).
Wolter laughed, when asked about the "bombogenesis" aspect of this week's storm.
"There are certain terms that come up that to me, it's almost like 'Snowmaggedon,'" he said, referencing the nickname given a snowstorm that blasted the northeast United States Feb. 5-6, 2010.
"It seems they have to come up with a new term each time. To me, we've always had 'synoptic bomb.' But 'bombogenesis' is a bit bombastic. I personally wouldn't use the term."
March is 'our time'
Schumacher, the Colorado state climatologist, in looking at comparable storm from the past, mentioned the storm that savaged the Front Range March 23, 2016, when Boulder was hit with 16.4 inches of snow. That broke the one-day record for the date, set three years before. He also invoked the Front Range storm of March 17-20, 2003, when 2 feet fell in the Boulder area, with 87.5 inches falling in Nederland and 63 inches in Jamestown.
"That storm was a lot slower moving," Schumacher said. 'That was the one that dumped 30-plus inches up and down the Front Range. This one is going to move out more quickly, so we are not going to see those huge snow totals."
The common thread between Wednesday's storm, and the 2016, 2003, and 1992 onslaughts, of course, is one word: March.
"It's our time," Schumacher said. "That's when we get these sorts of big storms, where there's the calm beforehand, it's in the 60s, pretty warm, and then pretty rapidly it shifts over to a very intense storm."
The detailed discussion of Wednesday's forecast posted on the National Weather Service site Tuesday noted that important to the precise development of the storm was a secondary trough that on Tuesday was still off the coast of Oregon. That system carries with it an injection of cold air expected to deepen and amplify the main trough that is originating from the Baja, Calif., further strengthening the Colorado storm.
"It is also important, in that it (the secondary trough) will be the key factor in changing the precip type over northeast Colorado from rain to snow during the day Wednesday," the forecast stated. "One of the biggest question marks with this system is the timing, location and strength of this low to mid-level air."
Boulder meteorologist Matt Kelsch, who saw the potential for as little as an inch in Boulder, on Tuesday in a blog post noted that it was a good occasion to point out that a blizzard is not simply a big snowstorm.
"We can have blizzards with relatively small accumulations," he wrote. "A blizzard is when the combination of snow and wind causes dangerous blowing snow conditions that could be life threatening if caught out in the open. Blizzard warnings are issued when visibility in snow and blowing snow is expected to drop below 1/4 mile for several hours."
There will be calm, on the other side of this storm.
While Boulder County should remain cloudy and breezy on Thursday with a high near 35, sunny skies should return Friday, with a high of 42.