Colorado Weather Forecast | Apr. 19–25, 2021
Storm later Mon., hard freeze on Mon. and Tues. nights (lows likely in the teens for the urban corridor), unsettled pattern Weds.— Fri., warm weekend.
Today features a short respite from the unsettled and cold weather pattern of the past week.
Satellite imagery shows the mountain snowpack, along with snow on the Palmer Divide, in the foothills, and west of I-25, all of which is melting rapidly.
Over the past two days, we’ve seen some decent snow accumulations in central and southern Colorado.
On Saturday, snow primarily fell in the San Juans during the day, and before that, parts of the Continental Divide picked up some decent totals on Friday evening / night. Here are a few reports over the past 48 hours, both from ski resorts and estimated from SNOTEL sites:
- South Colony Lakes: ~12"
- Taos: ~10"
- Wolf Creek: ~8"
- Monarch Pass: ~7"
- Breck: 5" on Saturday morning (16" in past 5 days)
- Red Mountain Pass: ~4"
- Eldora: 1" this morning, 4" Saturday morning, 17" in past 5 days
- Cooper: 3" on Saturday morning (8" in past 5 days)
- Loveland: 3" on Saturday morning (11" in past 5 days)
- Aspen Snowmass: 3" on Saturday morning (12" in past 5 days)
This has finally been sufficient enough to stop the melt in many parts of the high country.
The impacts differ across Colorado mountain ranges. In the Front Range, these frequent, frigid upslope storms have propelled the snowpack up to another peak.
In southern Colorado, the lower snow totals and warmer temperatures have done very little to inhibit the melt.
Dr. Becky Bolinger, Colorado’s Assistant State Climatologist, has some predictions about how long snow will hang on in the higher elevations as we progress towards summer:
For now, conditions are almost winter-like across the Divide. Thomas Horner snapped some shots on a ski mountaineering jaunt yesterday of hoar development and riming at around 12,000ft., and enjoyed some very silky turns.
Even with fresh snow and cold temperatures, the high angle April sun really does a number on the snowpack, so despite another week of unsettled weather ahead of us, we’ll need consistently decent snow accumulations, low temperatures, and strong cloud cover to keep things adequately soft. We’re sure the sun today is already blasting the new snow.
Oh yeah, here are the resorts that closed on Sunday:
- Aspen Mountain
- Echo Mountain
- Purgatory (was open weekends only, now closed)
- Ski Cooper
This leaves A-Basin, Breck, Copper (closes next Sunday), Loveland, Aspen Snowmass (closes next Sunday), and Winter Park as the only resorts still open in Colorado.
Forecast Overview: Next Week and Weekend
From Monday evening to Tuesday morning, we see a storm that generally impacts northern Colorado and the Front Range. After a short break into Wednesday afternoon, a series of weak systems move through the area and keep snow and cold temperatures in the forecast, though northern Colorado is most favored in the Blend.
We’re not seeing strong support for particularly impressive snow accumulations over the next seven days. The median of snow accumulations through next weekend is fairly disappointing:
Again, we see the high terrain near and east of the Divide as the likeliest candidates for highest snow totals, and note how most accumulations come by Tuesday morning, with only trace amounts of snow falling during the “active” end of week pattern.
However, the 75th percentile (optimistic, but not unlikely) snow forecast is considerably higher, revealing the uncertainty in next week’s forecast.
Regardless, southern Colorado looks to struggle to get much out of this pattern, with double digit totals confined entirely to northern Colorado. Let’s get into the details and expectations for these events.
Forecast: Monday to Tuesday
Brief ridging today gives way to broad, positively-tilted trough which sweeps through the state on Tuesday morning.
Accompanying this trough is frigid air, in fact, colder air than we’ve seen over the past week.
This cold air hangs on into the end of the week, but is strongest on Tuesday and Wednesday morning. We see lows dipping into the single digits in parts of northern Colorado tomorrow night, with low temperatures in the teens likely for the Front Range, even along the urban corridor.
The temperatures below may be a bit too high, as decent snow coverage on the ground would result in even lower temperatures than forecasted:
This would be a hard freeze, so take action if you have plants outdoors or sprinkler systems prepped.
This trough does provide a period of dynamic lift and an associated band of precipitable water values of 0.25–0.5". As such, widespread snow will push through northern and central Colorado starting Monday afternoon (in far northern Colorado) until just after midnight/early Tuesday A.M. (in the Front Range east of the Divide).
The arrival of snow will preceded by a strong cold front, which will push down the Front Range on Monday afternoon.
This will help generate an easterly upslope which will enhance snowfall east of the Divide on Monday evening.
The winds are considerable on Monday, with strong winds along the Divide all day (thanks to the jet stream) and under the heavier bands of snowfall, perhaps even putting a snow squall or two in the forecast.
You can expect gusts of 50mph+ in the high country, especially along the Divide, and especially as we get into the afternoon and evening hours.
This animation from the HRRR model shows snow falling on Monday night:
This model currently expects snow totals to be highest east of the Divide, with the foothills picking up 7–12" of snow and the urban corridor getting in on the action with a decent 4–8" event. The mountains, even along the Divide, only see 3–6" or less.
However, this model may be underpredicting northwest flow. The NAM3km model has lower totals east of the Divide (5–10" in the foothills, 2–6" on the urban corridor) but a more consistent 4–8" snow accumulation forecast for many of the mountains near the Divide.
There are three factors driving snowfall: lift from the jet stream, frontogenesis (both of these would produce strongly banded snowfall similar to our last storm on the Front Range), and orographic lift (northwest flow for the mountains, easterly upslope on the Front Range).
Even though these factors will all work in tandem, the dynamics only last for 6–12 hours, with the best moisture lasting even more briefly than that, so many areas will have to rely on consistent snowfall rates of 1–2"/hour if decent accumulations are to be expected by Tuesday morning.
This might not be too hard to achieve with the snow-liquid ratios (SLRs) expected from this event. Even along the urban corridor, model guidance has decent 10:1–15:1 SLRs during the heart of this event!
Despite that, some global models are fairly unenthused about the veracity of this storm, and the Blend has pretty lame totals across much of northern Colorado:
However, the HRRR outperformed the Blend with this much lead time for our past storm, so is this too conservative? We can take a look at probabilistic guidance for an idea of the likelihood of busting higher than the above forecast map.
…and for the high country:
Double digit totals certainly look to be in reach for some of the high terrain east of the Divide, but perhaps not as easily as some would like. With all that in mind, here’s what we’re thinking for final totals by noon on Tuesday:
- A-Basin: 4–9"
- Aspen Snowmass: 0–4"
- Berthoud Pass: 5–10"
- Bierstadt & Evans: 4–9"
- Boulder: 4–8"
- Boulder County, 6,000–9,000ft: 4–10"
- Breckenridge S.A.: 3–8"
- Buff Pass: 3–8"
- Cameron Pass: 5–10"
- Castle Rock: 3–7"
- Colorado Springs: 1–5"
- Copper: 3–8"
- Denver metro: 2–6"
- East of the Divide, 9,000–11,000ft.: 5–12"
- Eldora: 5–10"
- Fort Collins: 3–7"
- Grays & Torreys: 5–10"
- Hidden Valley: 6–11"
- Hoosier Pass: 3–8"
- Jefferson County, 6,000–9,000ft: 3–8"
- Longs Peak: 6–11"
- Loveland S.A.: 4–9"
- Quandary Peak: 3–8"
- Vail Pass: 3–7"
- Winter Park: 5–10"
We’ll update these expectations tomorrow morning as more data comes in.
Tuesday remains cold, with high temperatures in the mid 30s at best for the urban corridor and another night of lows in the 20s or even teens for much of the high plains. We don’t look to break into the 40s in Denver until Thursday.
Forecast: Wednesday to Friday
Precipitation chances increase as we progress into the middle and end of the week, as a complex but weak series of disturbances keep clouds and light precipitation in the forecast.
We see snow chances on Wednesday, Thursday, and Friday, but models generally have only a dusting as the most likely scenario each day.
If we look at the more optimistic scenarios, we can see that most of the snow is forecast for Wednesday night, and even then, it’s not much.
Probabilistic guidance doesn’t completely rule out conditions staying fairly soft into the end of the week, but it’s sort of a long shot.
Still, more consistent cloud cover and significantly colder temperatures than average should help our snowpack hang on, at least in northern Colorado. Skiing conditions will be suboptimal for any areas that don’t have a decent of new or wind-loaded snow on top, except for higher north-facing terrain.
Due to the complexity of the pattern and the large model uncertainty surrounding it, we wont go into much details about the actual components driving snow — but we are seeing that another easterly upslope is likely Wednesday night for the Front Range.
It’s likely than a decent amount of snow will be convective in nature, and rumbles of thunder aren’t out of the question, particularly on Thursday and Friday afternoon.
The Euro ensemble has better snow potential, especially outside of northern Colorado, so let’s not write the end of the week pattern off just yet. We’ll dive into in detail early next week.
Forecast: Next Weekend
Despite the disagreement across models for our pattern into Friday, we do see decent agreement that ridging will return to Colorado for the weekend, though it may not last long.
Warm air quickly advects back into Colorado from the southwest on Saturday, with temperatures reaching a maximum on Sunday evening.
With most or all of the new snow melted, it will be right back to climbing and biking in t-shirts…or outrageous brunches on patios. Or both? Whatever suits your fancy.
The warmth could last into Monday, depending on the speed of our next system, which is a decently strong signal across ensemble members — stay tuned.
Thomas Horner (Twitter: @thomaschorner)
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