From The Fort Collins Coloradoan (Miles Blumhardt):
This is mostly because of the influence of terrain, including the mountains, but also because of more subtle influencers such as the Palmer Divide and Cheyenne Ridge and the Denver Convergence Vorticity Zone, which played a role in our most recent storm.
There are many TV and private business meteorologists in Colorado. But let’s take a look at the accuracy and lead time of the National Weather Service’s snow total forecast for the biggest snowstorm this season for the Interstate 25 corridor.
You might be surprised how accurate the forecast was.
Fort Collins forecast accuracy
Fort Collins received 9 inches of snow during the two-day storm, with 1.2 inches on Tuesday and 7.8 inches Wednesday, according to the Colorado Climate Center. Reports from around the city varied from 7.5 inches to just more than 10 inches.
On Monday, the National Weather Service forecast for Fort Collins was 4 to 6 inches, but the weather service doubled its forecast to 8 to 12 inches Monday evening as the storm approached.
The weather service also has a feature called a probabilistic snowfall forecast that is a percentages-based model of varying snow totals for various cities in Colorado.
The low-end forecast for Fort Collins was 5 inches, the high-end forecast was 12 inches and the expected amount was 10 inches.
That forecast indicated Fort Collins had a 100% chance of seeing more than 2 inches of snow, 97% chance of more than 4 inches, 72% chance of more than 6 inches, 54% chance of more than 8 inches and 14% chance of more than 12 inches.
Predicting heavy snow isn't always based on just upslope! An area of convergence (similar to the Denver Convergence Vorticity Zone, or DCVZ), played a huge role last night – see radar loop between 9 pm and 630 am, showing evolution of heaviest snow (dark green). #COwx (1/4) pic.twitter.com/axIR9lGRbj
— NWS Boulder (@NWSBoulder) February 2, 2022
Greeley, Boulder, Denver forecast accuracy
The National Weather Service forecast for Greeley predicted 6 to 8 inches of snow, and reports from the city ranged mostly from 5 to 8 inches.
The weather service forecast for Boulder was 8 to 12 inches, and reported totals ranged from 8.3 to 10.5 inches.
Like with Fort Collins, by Monday night the weather service doubled Denver’s expected snowfall from its morning forecast, making the city’s forecast total 8 to 12 inches. Reported totals ranged from 6.3 inches in Denver to 10.5 inches in Aurora, with many stations reporting 8 to 9 inches.
Heavy snow bands formed from the Denver Convergence Vorticity Zone that rolled over Boulder, Denver and Aurora.
Sometimes referred to as the Denver Cyclone, this condition forms east of Denver when a low-level moist, southeasterly flowing air mass meets the Palmer Divide, a ridge that extends east of the Front Range between Denver and Colorado Springs.
The convergence of this air mass and winds coming off the foothills creates what’s called an enhanced cyclonic vorticity. The effect is most noticeable in warmer months and plays a role in creating tornadoes.
Colorado Springs area sees biggest snow totals
The Monday night forecast for the Colorado Springs area was 8 to 12 inches. Many of the reporting stations in the city measured 7 to 10 inches.
However, three sites southwest of the city reported 24, 18 and 22 inches, the highest totals from the storm. Even then, the weather service forecast called for 12 to 18 inches of snow for a small pocket in that area.