Colorado Weather Discussion #128: Sep. 30, 2021

Snow totals, current snow depth, and updates on additional snow for southern and central Colorado.

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Updated Thu Sep 30, 2021 11:00am MST | Published Thu Sep 30, 2021

By Thomas Horner

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

Precipitation associated with a trough entering our region has largely wrapped up this morning, with a dusting (or more) up high and plenty of liquid precipitation down low. Some webcams around northern Colorado show areas near treeline still holding on to snow this morning.

Loveland Ski Area
Loveland Ski Area
Breckenridge Ski Resort (via Breckenridge Associates Real Estate)
Breckenridge Ski Resort (via Breckenridge Associates Real Estate)

The rain has been a nice change of pace – drought is slowly creeping back into Colorado as we’ve been anomalously dry for over a month now.

(via Pivotal Weather)
(via Pivotal Weather)

Many mountain ranges of Colorado picked up a few inches of snow from this storm – but due to warm air temperatures, warm surface temperatures, and periods of sun between snow events, the actual snow depth on the ground this morning is a few inches less than what actually fell. In general, the first few inches of snow did not meaningfully accumulate except on certain surfaces or at the highest elevations.

This is a common issue for shoulder season storms, or for instance, warm spring storms down in Denver where some surfaces pick up a couple inches of snow and other surfaces accumulate no snow at all. In winter proper, the forecasted snow amount is much closer to the final snow depth change due to snow already being on the ground, air temperatures being cold, and snow-liquid ratios being higher.

It’s a double edged sword: while forecasting the actual snow depth change may be more practical for skiers and boarders, a forecast for “trace to an inch” for large parts of the northern mountains with this storm would have been quite unhelpful if you were actually having to hike or drive through the repeated periods of heavy snowfall!

Anyways, the SNODAS model captures this phenomena pretty nicely: their driving snowfall accumulation data is several inches higher than the model’s actual snow depth as of this morning.

Northern Colorado:

Central Colorado:

Southern Colorado:

These estimates are a little inaccurate in some areas – for instance, radar and gauge sensors indicate that parts of RMNP likely did not get as much snow as the accumulation as SNODAS estimated over the past 48 hours, but other areas corroborate pretty nicely, such as 3-4” via MRMS for the James Peak Wilderness area. In generally this model is usually off by a few inches in places, which doesn’t matter too much as we get into the season, but is notable when we’re discussing final totals of only 1-5”.

As low pressure closes off and wanders into New Mexico, we’re still on track for a decent hit of snow in the higher elevations of southern Colorado, and models have converged on a decently wet solution for the San Juans and Sangres, with 3-7” possible above treeline (remember though – the actual snow on the ground by the weekend will be several inches less than what falls).

The Blend looks most realistic to us:

(via Pivotal Weather)
(via Pivotal Weather)

Interestingly, the recent run of the HRRR high resolution model has some very impressive totals, with 60” of snow forecasted for the mountains near Taos(!!!)

(via WeatherBell)
(via WeatherBell)

The HRRR is completely on its own with that forecast, as even the overzealous NAM is calling for substantially lower totals.

Still, probablistic guidance looks very decent for New Mexico and southern Colorado, though totals drop off sharply below 12,000ft. Thus, most of the actual Taos Ski Valley likely wont end up with much snow on the ground.

(via Highpoint Weather)
(via Highpoint Weather)

The largest consideration is the impact on the alpine climbing and mountaineering season for the high peaks of the San Juans and such – this is a fairly considerable forecast which could have lasting impacts at the higher elevations.

(via Highpoint Weather)
(via Highpoint Weather)

Snow or not, it’s nice to see some healthy precipitation in the forecast for southern Colorado, and on radar, we can see it moving in now.

(via Pivotal Weather)
(via Pivotal Weather)

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