Colorado Weather Discussion #136: Oct. 20, 2021

Snow totals from yesterday, a look at the warm weekend, updates on snow potential next week.

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Updated Wed Oct 20, 2021 1:30pm MST | Published Wed Oct 20, 2021

By Thomas Horner

This is an update for our current valid forecast, please consult that article for any other details about the future weather forecast.

Snow Totals 10/18-10/20

A weak wave impacted Colorado and brought a few inches of snow to the mountains.

In Summit County and the peaks of the Front Range, most observations showed a couple inches of snow at best (our forecast: T-4”). A-Basin recorded 2” of snow, and the automated Berthoud Pass SNOTEL recorded an inch. Decent sunshine interspersed with the snowfall and quickly melted and compacted much of this snow.

In the western mountains and Park Range, totals were a bit higher, mostly in our forecasted 2-5” range. The Tower SNOTEL near Buffalo Pass recorded about 4” of snow, most of which is gone as of this morning.

The biggest “bust” was some frontogenesis that occurred east of the Divide, near the Cheyenne ridge. This produced some decent, widespread rain in northern Colorado. A pocket of instability southwest of the Denver metro also allowed a weak thunderstorm to jump over the Divide and bring some measurable rainfall to southwest Denver – we weren’t expecting much precipitation at all east of the Divide.

Much of the observed precipitation from the past 48 hours was virga, which is precipitation that did not reach the ground. It still shows up on this map, though:

(via NSSL/NOAA)
(via NSSL/NOAA)

The Weekend

The weekend continues to look decent, but ensembles have started to agree that a very weak disturbance will impact Colorado on Saturday night.

(via WeatherBell)
(via WeatherBell)

At most, this could bring a couple inches of snow to the Colorado high country (maybe up to 4-5” north of I-70) by Sunday morning – but most models have significantly lower totals than that. This would at least advect slightly cooler air into state, though the forecast for both Saturday and Sunday still features mild, mostly sunny conditions during the daytime.

In general, the next few days feature a strengthening mid-atmospheric ridge which will advect dry, warm air into Colorado from the desert, and conditions will be predominantly mild.

Snow 10/26-10/27

Weather models still agree on a storm in the Tuesday-Wednesday timeframe next week, but more and more guidance is pointing towards this being a weak event. Deterministic models are showing a center of low pressure ejecting from flow aloft, which puts the potential for an upslope Front Range storm in play…but ensembles are overwhelmingly on the side of this being a weak event for the mountans, with a low potential for light rain east of the Divide. Even if precipitation does fall in the Front Range, there would need to be a much stronger push of cold air than we’re seeing on models when considering the warm airmass that will be in place on Tuesday.

(via WeatherBell)
(via WeatherBell)

Consider the median of model guidance, which is barely more than a dusting:

The 75th percentile is looking a little more likely to us right now…This would be another weak wave like we saw yesterday.

The most optimistic (and unlikely) solutions show a bit more exciting of an event, but still fall short of bringing a more powerful winter storm:

Overall, the probability of this storm providing a decent refill of snow for Colorado’s mountains has been on the downtick.

There’s 6-12” of snow on the ground for many mountains across the state right now, which is a bit better than average for this time of year.

If we look west, we can see that the Sierra Nevadas in California are expected to pick up a couple feet of snow or more thanks to deep troughing over the Pacific Northwest, which is the system that is spitting weak disturbances out at us.

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