Apr 9, 2021
Colorado Weather Forecast | Apr. 9–18, 2021
Very weak system on Sunday before a much snowier pattern next week.
Synopsis
- Pretty nice day on Saturday, if not particularly warm.
- “Cool” front pushes through northern Colorado on Sunday morning. Only low chances for light precipitation on Sunday night. Colder temperatures (40s and low 50s on the Plains, freezing in the mountains). Much of Colorado south of the Palmer Divide, south of Leadville, and/or west of Vail Pass is unaffected.
- Cold air pushes through the rest of the state on Sunday night, with overnight temperatures in the 20s/30s on the Plains and single digits / teens in the mountains.
- Chillier day on Monday, except in southwestern Colorado. Strong winds in the central and southern Colorado mountains.
- Unsettled, chilly, and likely productive pattern begins late Monday/Tuesday as a large trough develops over the Great Basin and stalls. Decent amounts of snow likely through the week and into the weekend.
Nowcast / Retrospective
Winter weather and fire weather! We’ve been treated to both this month which is fairly common this time of year.
On Tuesday and into Wednesday, we had a system that brought a few inches of snow to the central and northern Colorado ski resorts (0–4", as forecasted). This has pushed east and intensified into a full-on cyclone over the Mississippi River. Another weak system moved through last night / this morning, which brought only trace amounts of snow.(
In the animation above, you can see a cyclone (Tuesday/Wednesday’s storm) bearing down on the Great Lakes and the clouds associated with yesterday’s system pushing southeast down the High Plains.
Though last night’s winter weather wasn’t significant, yesterday’s fire weather was. The US Wildfire Activity Web was lit up in Red Flag Warnings (pink) and Fire Weather Watches (yellow).
Humidity across the plains and lower terrain dipped into the single digits and teens, and strong winds associated with the strong pressure gradients from our passing system amplified fire danger. Gusts on the plains were recorded as high as 55mph, just shy of being considered a downslope wind storm (60mph).
Today, despite a bit of moisture and precipitation in the northern mountains and in the northeastern Colorado plains, we continue to see elevated fire concerns due to the strong winds and low humidity, though both factors are not quite at the level needed for widespread Red Flag warnings.
Meanwhile, our unsettled weather hasn’t done much to quell the rapid meltoff of our snowpack, but we should have a chance next week to reverse that trend at least briefly.
Forecast: This Weekend
A look at the mid-atmosphere provides a general overview of what to expect this weekend. As last night’s system departs, weak ridging returns to the state on Saturday, before a stronger system drops into the region on Sunday.
Gusts will settle down on Saturday a bit as strong upper-level winds move out from over Colorado, but some warm air advection will keep gusts on the Divide elevated, with gusts of 20–40mph on the nearby mountains (like Winter Park) and around 60mph on the actual peaks of the Divide (such as Longs Peak).
We also rebound to more seasonal temperatures on Saturday, with the foothills hitting the 50s to 60s, the plains hitting the mid/high 60s to mid 70s, and the mountains seeing temperatures above freezing at elevations at/below treeline.
The past week of freeze-thaw has continued to heal the snowpack, and despite persistent slabs still lurking on northern aspects, we’re seeing big ski mountaineering lines start to open up across the state, though timing actually decently skiable snow has been a bit tricky due to the cloud cover and frequent systems.
On Saturday night, winds increase across northern Colorado as our next system begins to push towards the state. Earlier this week, we discussed that models had a chance to come around on this system delivering a bit of measurable snow to the northern Colorado mountains, but that’s not the case, and this look like another fairly dry event with some gusty conditions and a cooldown — another “cool front” like last last night.
Models show only trace amounts of snow on Sunday evening with this storm, with perhaps an inch of snow possible for some very lucky areas of the Park Range and northern Divide. The foothills could also see some unsettled weather and light precipitation as an upslope from the east as low pressure at the surface pushes south down the Front Range on Sunday.
Since the coldest air is locked up east of the Divide, this system wont be felt all that strongly in the mountains west of the Divide. The cooldown will be noticeable in the foothills and on the Plains, however, especially into Monday.
Forecast: Next Week
Some big changes are in store as we see a more favorable, prolonged pattern which should bring precipitation to Colorado more days than not.
In general, flow aloft will turn westerly as we start the week and then southwesterly as we progress later into the week. Lower in the atmosphere, flow becomes cyclonic around an intensifying low over the Great Basin, which means upslope winds will evolve into something more like southwesterly winds in southern Colorado, southerly winds in central Colorado, and southeasterly winds in northern Colorado. The system could (though may not) eject eastward before or by the weekend, which sets up the (small)potential for an upslope snow storm for the Front Range.
Due to the relative complexity of this setup, there is a lot of disagreement between models, so it’s hard to pin down the timing and intensity of snow events. From a general standpoint, the snow machine turns on around Tuesday, and doesn’t seem to turn back off until the weekend or even after.
Models have been trading blows in regards to impacts, with the previously-stingy Euro model now putting down some impressive totals by next weekend, even as the previously-optimistic GFS model has backed off. The Canadian model sits somewhere in the middle. Regardless, those three models, and their ensembles, agree on significant snow by the end of the week.
The current Euro run has a couple feet of snow for the central/northern mountains and foothills, and significant totals on the Plains. The latest GFS run has the highest totals confined to the foothills, though the mountains will still get a nice refresher.
The current run of the Blend — which takes into account model ensembles — seems pretty realistic to us, with a good chance of double digit totals in the mountains (at least the Front Range, Summit County, Sawatch, and Elks) and foothills and only marginal chances for good snow down on the plains, but this is certainly subject to change.
If we look at some cross-sections, we can visualize the uncertainty as well as some of the timings. This chart for Berthoud Pass has pretty steady accumulations from Tuesday to Friday, with snow chances diminishing by the weekend. There does seem to be a decrease in snow intensity around Wednesday as a pocket of drier air moves overhead.
Otherwise, each day brings about 3–6" of snow, so there may not be a singular event that puts down an awesome powder day, but conditions will be quite soft across the mountains as we get towards the end of the week. We also can’t ignore those powder day possibilities creeping up as we get closer to the event and model uncertainty decreases. Right now, many days are sitting around a 10–20% chance of >6" of snow in 24 hours.
However, the medians continue to sit at 2–4" of snow for each day, so lets not get our hopes up too high yet.
Despite southwest flow aloft, southwestern Colorado doesn’t seem to get a good piece of the action, with many mountains in the 4–10" range by Saturday. This is due to the better mid and low-level dynamics being located in central and northern Colorado as the system evolves to our west.
We have to wonder how much models may be overdoing this snow. For one, wind direction in northern Colorado is not ideal, with generally southerly or southeasterly upslope winds as we get later into the week. Models traditionally overdo the snowfall from these wind directions for the northern ski areas. We aren’t inclined to believe any solutions that have much more than 10–16" of snow for the mountains right now, until we see some better consensus on supporting dynamics, e.g. moisture convergence or deformation, which would overcome the lack of a good upslope.
As for the urban corridor, though we’ve seen models put down some big totals in Denver and Fort Collins from time to time, the ensembles aren’t showing a strong signal for that to happen. We think that’s fair — just using our gut, the pattern doesn’t look like it would swing through in a particularly powerful way based on how it forms and what else is going on in the atmosphere.
If low pressure even does end up in southeastern Colorado, it will probably be pretty weak. However, since disagreement is so large by this point, there’s plenty that could change to more realistically raise the prospects of a stronger snow event. For now, that’s not the likely way things will trend, but it shows up as a slight signal in the Blend:
What we do know for sure is that we wont see spring-like temperatures next week, with a pronounced and prolonged cold signal.
Definitely an exciting week ahead of us, and in a couple days, we can take a look at more specific timings and impacts, perhaps breaking out our big grid of forecasts and custom maps again (we enjoyed the break from having to fill that out every day!). Until then, enjoy the drier and warmer weather.
Forecast by
Thomas Horner (Twitter: @thomaschorner)
Laura Smith (Twitter: @Hurricane_Laura)
Website and app with automated, high-resolution forecasts for mountains, climbing areas, and ski resorts (+ backcountry) with elevation switcher, uncertainty visualization, and more:
https://highpointwx.com
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