Colorado Weather Forecast #133: Oct. 11 - Oct. 17, 2021

Storm Tuesday to Wednesday (decent snow in the mountains, none for the Plains/Denver), Thursday to Friday (not much snow in the mountains, but likely some flakes in Denver). Increasingly cold into Friday. Drier, sunny, warmer weekend.

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Updated Mon Oct 11, 2021 10:30am MST | Published Mon Oct 11, 2021

By Thomas Horner

Summary

Our stormier pattern continues into the end of the week. Temperatures will drop through Friday as two systems impact us. A storm from Tuesday-Wednesday should bring decent totals to the mountains (7-14” for the southern San Juans, 3-7” for most other ranges, 5-12” in the far northern Colorado ranges), but little to no precipitation much east of the Divide (no snow in Denver).

Another system behind that storm should bring even colder temperatures and snow from Thursday to Friday, with Denver having a ~50% chance of seeing a little bit of snow on Thursday night. This system wont bring much snow to the mountains, with 0-6” expected for most mountain ranges, slightly higher totals possible near the Divide. See below for more details on our snow expectations.

The weekend should be warmer, dry, and mostly sunny.

Retrospective

A system is departing the region which brought snow, rain, wind, and cooler temperatures to Colorado from Friday to Sunday. A cooler airmass has advected into Colorado, at least west of the Divide.

(via WeatherBell)
(via WeatherBell)

This will erode a bit today, but a colder, more winter-esque airmass will be arriving with our next system tomorrow. More on that later.

(via WeatherBell)
(via WeatherBell)

The moisture and cooler air associated with our departing system allowed the Arapahoe Basin and Keystone ski areas to start making snow on Saturday night.

(via Arapahoe Basin)
(via Arapahoe Basin)

Snow totals were about as expected, and for most areas, final accumulations came in a little over the 50th percentile snow accumulation guidance provided by the Blend a few days before the storm, which we anticipated. Some areas, like the San Juans, got very little snow, which was more in line with that guidance.

The initial wave of precipitation with the storm came before the cooler air, which was expected. Precip totals were pretty decent for some areas of western and central Colorado.

(via Pivotal Weather)
(via Pivotal Weather)

We were perhaps more interested in the potential for strong wind gusts as a jet maximum set up over southwestern Colorado. These certainly delivered, as we detailed in our forecast discussion on Saturday.

On Sunday, we were expecting a final wave of light precipitation in the afternoon, and that never really materialized except in far southern Colorado.

Current Conditions

As mentioned, cooler air is locked up west of the Divide, but temperatures are recovering quickly and today looks to be a nice autumn day across much of the state, if just a touch on the chilly side.

(via Pivotal Weather)
(via Pivotal Weather)

Colorado is under some mild ridging between this weekend’s system and the approaching system which will impact us tomorrow.

(via WeatherBell)
(via WeatherBell)

It’s sunny out this morning, with fresh snow visible on the peaks, though moisture ahead of the next system is leading to the formation of upper-level clouds across the region.

(via NOAA)
(via NOAA)

In the Front Range, it’s obvious how warm this storm was as there are very little accumulations below treeline. We also notice that Loveland is making snow this morning:

(via Loveland Ski Area)
(via Loveland Ski Area)

Forecast Discussion: Storm Tues - Weds

A trough over the Pacific Northwest is poised to drop into the Intermountain West today. A center of low pressure is expected to close off over Utah on Tuesday morning before lifting northeast over northern Colorado into Wednesday morning.

(via WeatherBell)
(via WeatherBell)

This storm certainly looked a lot more exciting last week, and we were closely monitoring uncertainty in the weather models. For much of last week, a decent upslope event for the Front Range looked possible, with the potential for a more southerly track and some decent lee cyclogenesis on Wednesday morning. Unfortunately, the past couple days saw model guidance converging on forecasting a weaker system with a more northerly track. This track reduces the impacts across Colorado both in terms of precipitation and cold air – though this will still be the coldest system we’ve seen this season.

We can see that snow potential with this storm has been completely eliminated for the Front Range urban corridor – though there’s actually still a decent chance for snow this week with the wave behind this system. We’ll discuss that in a bit.

The storm’s more northerly track puts Colorado in a less favorable region of the jet, which means less lift and thus less snow production over our area.

(via WeatherBell)
(via WeatherBell)

The San Juans are most favored for the highest snow totals in Colorado as they have best window of lift and moisture. The should see moderate to heavy snow from Tuesday morning until about midnight, with a good upslope from the southwest. The rest of Colorado’s high country will see only more moderate snowfall, mostly on Tuesday afternoon and tapering off into Wednesday morning.

On Tuesday night, lee cyclogenesis over the Nebraska panhandle will probably drive some enhanced snow production in far northern Colorado – the northern Front Range, Medicine Bow Mountans, and Park Range. Overall, the best snow totals will be from central Wyoming north to southern Montana. Snow wraps up for most of Colorado by Wednesday morning, with som snow potential lingering into mid-day Wednesday for far northern Colorado.

(via WeatherBell)
(via WeatherBell)

Snow Forecast

We’re expecting 7-14” of snow in the southern San Juans, but most of the rest of Colorado’s high country should only see 3-7” or so. If lee cyclogenesis ends up being particularly strong on Tuesday night, the far northern Colorado ranges could pick up just over double digits of accumulation. The latest run of the Euro model is calling for that scenario, so expect totals in the Medicine Bow Mountains, northern Front Range, and Park Range to be more in the 50th-75th percentile range.

Parts of Wyoming could see 12-24” of snow!

Here’s how the spread of potential snow totals in Colorado looks, with the totals very likely to not fall outside of this range:

25th Percentile

50th Percentile

75th Percentile

Temperatures

For temperatures, a cold air mass will reach the southern San Juans by noon on Tuesday. By Tuesday night, cold air will have worked its way into most of western and central Colorado. Lee cyclogenesis to the northeast of the Front Range should prevent the urban corridor from experiencing much of a serious cool down. In Denver, temperatures will likely bottom out in the mid 30s on Tuesday night and just above freezing on Wednesday night – but if you have plants outside or haven’t blown out your sprinklers, you should consider dealing with the potential for freezing overnight temperatures starting on Wednesday night. Otherwise, highs in the Denver metro area look to be in the high 50s or low 60s on Tuesday and Wednesday.

Denver International Airport temperature ranges (via ESRL)
Denver International Airport temperature ranges (via ESRL)

In the mountains, temperatures look confined to the teens and 20s for much of the rest of the week, at least above 10,000ft., with lows bottoming out in the single digits at the higher elevations. The snow level will drop to about 6,000ft., so precipitaton will fall entirely as snow across the mountains and foothills, which is a change of pace from the past couple weeks. The snow liquid ratio should get up to about 15:1, which is decently cold and light for this time of year.

Forecast Discussion: Storm Thurs - Fri

As Tuesday’s system lifts out of the region on Wednesday, an open trough moves in directly behind it, impacting the state on Thursday.

(via WeatherBell)
(via WeatherBell)

This provides a reinforcing shot of cold air (Friday should be the coldest day of the season so far across the state). Another round of snow should arrive in northwestern Colorado on Thursday morning, with light to moderate snowfall occurring for the rest of Colorado’s high country later in the morning and into the evening, with precipitation mostly wrapping up (from west to east) by late Thursday night. The last bit of precipitation looks to hold on into early Friday morning in the Front Range and southern Colorado plains, with perhaps some pockets of light snowfall in some of the higher subranges of Colorado.

(via WeatherBell)
(via WeatherBell)

Snow in Denver

This system will finally manage to work much colder air into the Front Range via a cold front on Wednesday evening. As the cold air mass advects further into Colorado on Thursday, the snow level should finally drop below 5,000ft. on Thursday night, which should coincide with a shallow upslope and precipitation in the Front Range. The Blend currently has Denver with a 57% chance of seeing “accumulating” snow that night – though it will have a hard time sticking due to warm ground temperatures. The 50th Percentile snow product shows snow accumulating in Denver (less than an inch), which means at this point it’s more likely than not. We don’t think temperatures will be a problem, we just need precipitation to occur – and that’s not a sure bet, given the lack of lift and moisture with this wave.

Snow Forecast

Despite the cold air, snowfall across the state will be greatly limited by a lack of lift, as we’re stuck in the left entrance region of the jet for much of the storm. Available moisture is also less than ideal, so snowfall rates will be modest and final totals across the state look pretty disappointing, despite the 8-12 hour duration of this storm.

For the San Juans and Sangres, we’re thinking 0-3” of snow. The central mountains should see 1-5”, except for the Elks and Gore Range which could see 2-6”, in addition to the Front Range. A few higher peaks on the Continental Divide could see up to 8” of snow, but we think most totals will come in under 6”.

Here’s how the spread of potential snow totals in Colorado looks, with the totals very likely to not fall outside of this range:

25th Percentile

50th Percentile

75th Percentile

Forecast Discussion: The Weekend

Friday will be our coldest day before we quickly warm up for the weekend as broad ridging returns to the region.

(via WeatherBell)
(via WeatherBell)

Temperatures will warm to the 60s on the plains and above freezing in the mountains, at least below treeline and in the southern Colorado mountains. For the northern Colorado mountains, areas near treeline may not get above freezing until Sunday. It will be mostly sunny, with only some mild gustiness along the Divide.

Long Range

A weak wave could move through early next week – but there isn’t a strong signal in the ensembles. Guidance leans towards next week being warmer and drier, but we do see some potential for a weak storm or two into next weekend.

(via WeatherBell)
(via WeatherBell)
(via WeatherBell)
(via WeatherBell)

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