Colorado Weather Forecast #138: Oct. 28 - Nov. 4, 2021

A lull in the action through Saturday, then a cold front kicks off several days of cold, unsettled weather for northern and eastern Colorado.

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Updated Thu Oct 28, 2021 5:30pm MST | Published Thu Oct 28, 2021

By Thomas Horner

Summary

  • Tuesday to Wednesday’s storm had some very productive northwest flow which bumped some areas well above our forecast range.

  • Some light snow has continued in the high country, though only adding an inch or two in spots.

  • Colorado warms up into Saturday and stays dry.

  • Cold front late Saturday / early Sunday kicks off several days of colder temperatures and snow chances, mainly in northern and eastern Colorado.

  • Large amounts of uncertainty for this pattern. In general, several days of light snow in the northern mountains which may add up to something decent.

  • In Denver, the best snow chances have shifted to Wednesday morning, but both temperatures and precipitation probability are a concern.

  • Model uncertainty hasn’t improved significantly in the past 24 hours, may not be until Saturday when we have a much better idea of what may happen.

Retrospective: Tuesday to Wednesday’s Storm

A powerful piece of the atmospheric river that hit California impacted our state from Tuesday morning and into Wednesday. Some residual moist flow has kept snow going in the northern mountains and along the Divide since then, but with fairly minimal accumulations.

Here are some estimated snow totals:

In the day leading up to the storm, models began to really converge on higher totals (actually, pretty close to what fell in a lot of areas). We were hesitant to bump our forecast up as we’ve seen this occur in the last 24 hours prior to a storm only for the 2-3 day forecasts to verify a little better. That said, we posted this social media update the night before:

… We do see some more consistent data where it’s probably a safe bet to raise our forecasted snow totals (in our current forecast article) for the San Juans, Park Range, Elk Range, and other western ranges (Flat Tops, Grand Mesa, north Sawatch / near and west of Vail Pass) by a couple inches. Other areas, like most of Summit County, will still struggle to see decent accumulations from this storm.

Lots and lots of moisture – we continue to think that the crux is the warm temperatures at the start of the storm and quite a hefty amount of precipitation will fall early on with SLRs well below 10:1. Looking for colder northwest flow to later on Tuesday to really deliver, if this is the case.

Overall, several areas busted high compared to our forecast, and hardly any busted low. Our expectations for a warm, disappointing initial phase of the storm were on the money, but northwest flow ended up really delivering.

Euro vs. GFS, and Model Guidance Issues

If we look at model trends before the storm, it’s obvious what happened. Check out this blue tendril reach further into Colorado – this is the Euro model forecasting increasingly favorable conditions for snowfall in each model run up to the start of the event:

(via Pivotal Weather)
(via Pivotal Weather)

The GFS handled this storm better and more consistently than the Euro model, which was unfortunate as we leaned heavier on the Euro model’s guidance.

Many Euro model runs a few days before the storm showed a closed low near the surface of south Colorado / northern New Mexico, with cyclogenesis over the Texas panhandle impairing the productivity of NW flow over Colorado into Wednesday. Its last few runs before the storm switched to a markedly different solution – a deeper, open wave. This meant warmer temperatures at the start of the storm (especially in southern Colorado), but more robust NW flow (with a more westerly component) from Tuesday afternoon and onwards in the absence of stronger lee cyclogenesis into Wednesday.

Here was the Euro’s Wednesday morning expectations from its run on Saturday:

(via Pivotal Weather)
(via Pivotal Weather)

And what it actually thought was happening on Wednesday morning:

(via Pivotal Weather)
(via Pivotal Weather)

This may not look like much at a glance, but check out the absence of those closed ovals over north Texas.

Totals and Timings

In the San Juans, Red Mountain Pass picked up over a foot of snow. Telluride’s social media told tale of 20 inches of snow, which was not the same story as told by their snow stake camera, but either way, they picked up quite a decent amount of snow from Tuesday afternoon into Wednesday. Buffalo Pass’s nearby SNOTEL site is reporting a foot of fresh snow since Tuesday morning, and Vail and Beaver Creek offered some big surprises with 9-10” of snow!

Here’s how it all went down.

Heavy precipitation moved into western Colorado on Tuesday morning, with some embedded lightning.

(via Pivotal Weather)
(via Pivotal Weather)

Temperatures a few thousand feet above the surface were at near record highs, which made snow production very difficult. Some SNOTEL sites in the San Juans, even those as high as 10,000ft., reported 0.5”+ of precipitation (that’s a decent amount, especially in a few hours), with only an inch or two of snow to show for it (making the snow-liquid ratio like 5:1 or worse – 15:1 is more typical with cold winter storms). Clearing skies followed this initial push of snow and further compacted what was received.

In central and northern Colorado, temperatures were a little better, and the high elevation ski resorts started off a little better than expected (2-3” at Loveland, for instance).

By the evening, flow had become more northerly, though like we said, it ended up being a bit more westerly than guidance had suggested from a few days before, which really helped bump up totals for the western San Juans and Beaver Creek / Vail / Vail Pass / Copper areas among others. It was around this time that a strong cold front had pushed down the Front Range and brought a briefly upsloping surge of moisture, producing rain, hail, and lightning across the urban corridor with some snow on the higher reaches of the Palmer Divide.

Wind Observations

Winds increased into Wednesday as a strong jet core moved overhead. Here are some reports:

  • Eagle (San Juans): 90mph
  • Wolf Creek Pass: 78mph
  • Telluride SA: 75mph
  • Cinnamon Mountain: 69mph
  • Loveland Pass: 63mph
  • Storm Peak Observatory (near Steamboat): 58mph

Forecast Verification

How did our forecast do?

  • Park Range: 5-10” (3-7” for lower elevations like Steamboat, even less for Steamboat Springs)

Forecast was a couple inches too low (Steamboat: 8”, Buffalo Pass: 12”), though not if you consider our final update about raising totals by a couple inches. :)

  • North Front Range (Cameron Pass, Berthoud Pass, RMNP, IPW): 2-6”

This looked to verify. 6” near Cameron Pass, less at Berthoud Pass and Winter Park (3-4”).

  • Summit County resorts (Loveland, A-Basin, Breck, Keystone, Copper): 1-5”

Forecast range was a couple inches too low. 4” Keystone, 5” Loveland, 6” A-Basin, 7” Copper.

  • Vail and Beaver Creek: 2-6”. Vail Pass maybe 4-8”.

Oops, even with our last update about bumping totals up, Vail and BC were just shy of 10”.

  • Elk Range: 4-8”, maybe a bit lower at the lower elevation resorts (Buttermilk and Aspen Mtn).

4” at the Aspen resorts, with higher totals further into the range.

  • San Juans, south of Red Mountain Pass and west of Wolf Creek: 5-10”.

Our forecast was a couple inches too low.

  • San Juans, north of Red Mountain Pass: 4-8”.

Our forecast was a couple inches too low.

  • Flat Tops: 4-9”.

Again, a couple inches too low.

  • Wolf Creek: 3-7”.

6-7” on the Wolf Creek SNOTEL.

  • Sangres: T-3”.

This verified, with 1-2” on a few SNOTEL stations.

  • Sawatch Range: 1-4”.

A few inches too low at Monarch (6” - wind direction was optimal for them), but 2-3” at other sites we checked.

  • Foothills east of the Divide, 7,000ft-9,000ft.: T-1”.

This ended up being like 0-T.

  • Urban corridor: 0”.

Yep. Some parts of the Palmer Divide got accumulating snow – do we count that?

Current Conditions and Short Range Forecast

As we mentioned in the past forecast, some lingering showers would likely continue over parts of northern and central Colorado, and these have brought another inch or two to some areas into this morning, though snow is generally not falling faster than the snowpack beneath it is compacting.

(via NOAA/STAR)
(via NOAA/STAR)

You can see some clouds near the eastern edge of the imagery which are associated with the system that just impacted us. Strong cyclogenesis has brought strong winds, heavy precipitation, and tornadoes to parts of the midwest and south.

Ridging is taking hold over our region as we progress into the weekend:

(via Pivotal Weather)
(via Pivotal Weather)

Notice how strong that system is to our east!

Warmer air will advect into Colorado, with the highest temperatures on Saturday.

(via Pivotal Weather)
(via Pivotal Weather)

Perhaps a little mild, but a nice day with mostly sunny skies expected in the afternoon.

(via Pivotal Weather)
(via Pivotal Weather)

Forecast Discussion: Cold and Unsettled from Oct. 31 Onwards

High temperatures on Sunday look a little different, particularly on the Front Range.

(via Pivotal Weather)
(via Pivotal Weather)

This is due to a cold front which is expected to move through the Front Range later on Saturday or early Sunday, depending on what model you look at. This shouldn’t impact Saturday’s high temperatures, though these tend to come in a little faster than models expect – still, we think the buffer is long enough where this is more of a Saturday evening/night consideration.

(via WeatherBell)
(via WeatherBell)

This cold front kicks off several days of colder temperatures and snow chances across much of the state, including the urban corridor. Impacts are more limited in southern and western Colorado.

Weather models have been incredibly erratic with their guidance through Thursday. A few days ago, snow looked to be a near-certainty for Denver and the foothills, particularly on Monday morning. Models then pushed that back several days, but continue to flirt with the idea of it occurring on Monday…or maybe not at all.

The National Weather Service’s recent discussions sum a lot of our feelings up nicely:

…models struggle to resolve details…plethora of poorly resolved short waves…no agreement or consistency…flip-flopping…

Feebly drifting…Nevermind about that snow, says the 00z GFS.

…maybe half of them aren’t cold enough for snow in Denver…a nice snow event…but even if it happens, which day?

…All that to say that there’s a lot of uncertainty on everything but “cooler.”

Indeed, if we’re thinking about snow in the Front Range, the spread is still considerable and guidance continues to be less than helpful. On a meteogram, we can see that the members of the Euro ensemble continue to disagree about totals, timings, and even the possibility of snow even happening in Denver at all:

(via WeatherBell)
(via WeatherBell)

The GFS is looking even worse, abandoning its very snowy wishcast from a few days ago:

(via WeatherBell)
(via WeatherBell)

We are basically relying on some weak shortwaves to graze us just enough to bring sufficiently cold temperatures and strong enough lift or upslope to drive snow in the Front Range – and this not confidence-inspiring.

(via WeatherBell)
(via WeatherBell)

The current Euro deterministic run does eventually bring a decent snow event to the urban corridor on Tuesday night (along with up to two feet of snow in the northern mountains)…but its previous run didn’t. The overall pattern suggests that Tuesday night / Wednesday morning is the best chance for Denver to pick up some snow.

Until the models get a better idea about the upper atmospheric pattern over the next few days, we can’t do much more than explore the statistical likelihood of certain situations.

For Denver International Airport, there’s a fighting chance for snow accumulations from Monday to Wednesday:

(via ESRL)
(via ESRL)

Precipitation chances are slightly better (though not likely), which points to temperatures as being the potentially limiting factor (with the snow level possibly staying above 5,500ft.). It’s a little disappointing to watch another Front Range storm start to slip through our fingers, for sure.

In the mountains, snow is much more likely, but the spread of potential impacts remain almost uselessly large. The Blend’s 25th Percentile of snow accumulations has little more than a dusting:

And why not? There are still several ensemble members out there with no more than a few flurries in the forecast.

Even the 75th Percentile suggests that at least one of the shortwaves showing up on deterministic models may actually miss us…

…and the spread of totals between the 25th and 75th percentiles is 5-10”+ in places. The 90th Percentile suggests that even the best case scenario from this pattern likely wont blow the doors off the start of ski season, but a decent event nonetheless:

If we can start eliminating the stingy ensemble members then we’ll see these numbers start bumping up, but we haven’t seen that happen yet. We’ll continue to wait and see if any consensus begins to develop over the next few days. For now, expect Sunday through Thursday to be chilly and unsettled, with periods of snow in northern Colorado. It’s possible that a few weak events each day over the course of the week could result in some decent accumulations by next weekend, at least somewhere in northern Colorado.

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