Colorado Weather Forecast | May. 1–5, 2021
Little to no freeze this weekend, snow, lightning, and rain from Sunday to Tuesday.
Synopsis
- Little to no freeze for the snowpack this weekend, even at high altitude. Considerable wet avalanche danger.
- Storm (not particularly cold) from Sunday afternoon to Tuesday morning. Soft conditions on Monday morning (storm skiing), powder on Tuesday morning. Fairly heavy/wet snow.
- Snow levels at 10,000ft. initially, ~8,000ft. on Monday, and 6,500ft. on Monday night.
- Widespread thunderstorms Sunday afternoon, severe storms and supercells possible on the Plains.
- Consistent rain and snow in the Front Range, Mosquito/Tenmile Range, and Sawatch Range through Tuesday morning, and decent precipitation elsewhere.
- Over a foot of snow possible for many mountains in the above mentioned ranges.
It’s hot out there! The last day of April has featured some of the warmest temperatures in months, with 80s on the Western Slope and across much of the High Plains.
Even above 13,000ft., temperatures are over 40 degrees. With the continued warmth and some cloud cover overnight (cutting down on outgoing longwave radiation), the snowpack will struggle to refreeze, even at high elevation. This has caused the CAIC to issue a Considerable Danger avalanche forecast across the Colorado Rocky Mountains.
In particular, the north-facing high altitude slopes that haven’t shed their drier snow surface are likely to be dangerous this weekend, even early in the morning, as water percolates through the newer snow. A solid release on these slopes would result in a large wet slab avalanche, instead of the more manageable loose wet slides we’ve seen over the past few weeks. Keep that in mind if you have popular Front Range lines like the Tuning Forks, Quandary Couloir, Democrat North Face, etc. as objectives this weekend.
Tomorrow features even warmer temperatures, with the 90s possible on parts of the High Plains.
That’s about 20 degrees warmer than average for May 1st.
We do see some modest thunderstorm potential tomorrow — maybe an isolated cell or two across large regions of the state. Nothing to be concerned about, but it’s worth keeping an eye on the sky.
Storm Overview: Sunday Afternoon to Tuesday Morning
Changes are on the way by the end of the weekend. Though Sunday starts off warmer than average, the weather will quickly deteriorate by the afternoon as a broad trough sweeps across western North America.
The animation above shows strong ridging (dark reds — which is responsible for our warmth) overhead weakening and giving way to a large but fairly shallow trough on Sunday morning. There’s also a closed low over Mexico that pushes through Texas, which wont directly effect us, but will influence the dynamics and evolution of the trough.
With this trough comes colder temperatures and moisture. Though the mountains and foothills will see snow again, this isn’t a particularly cold shot of air.
Precipitation increases on Sunday evening, but likely falls as rain below 10,000ft. The snow level quickly drops by sunset, and continues to lower to about 8,000ft by sunrise on Monday, finally reaching as low as 6,500ft by the end of the storm on Monday night.
This means the urban corridor and metro area will be seeing entirely rain (and thunderstorms) for this event. Many communities in the foothills will struggle to pick up considerable snow totals, as even when it does switch over to snow, it will be a wet and sloppy affair with snow-liquid ratios of 7:1–10:1.
Snow totals quickly increase as you get higher in altitude and temperatures become less of an issue. Unlike some of our previous storms from the past few weeks, we do have some jet dynamics in play, which gives us a better chance at more consistent and productive snowfall, beyond our usual (and often fussy) ingredients of convective instability and upslope.
Regardless of rain or snow, the next few days look like another win for the Front Range, with 1–2" of liquid precip in store for much of Colorado’s higher terrain east of the Divide, and some healthy totals elsewhere (hopefully the Flat Tops — the Western Slope needs water!).
For backcountry skiers, another refresh for northern Colorado and central Colorado is in store, even if the fresh snow is fairly wet and heavy.
The above table has trended higher and higher over the past couple days as certainty grows across models and ensembles in regards to a decent precipitation event. Of note, a foot of snow or more near the Divide seems more easily attainable than the past couple storms. In fact, the current “most likely” scenario for St. Mary’s Glacier cracks into the double digits!
Those totals are even nicer when we consider how dense the fresh snow might be. Snow-liquid ratios barely crack 10:1 during the hours of heaviest precipitation (during the day on Monday).
The current Blend deterministic is in good agreement with the probabilistic and ensemble products used in the tables above.
Timings: Sunday Afternoon to Tuesday Morning
Our first noticeable change in weather will be the leading edge of a cold front that pushes through on Sunday morning.
The significantly colder air takes some time to work into northern Colorado, so in general, Sunday morning will feel similar to Saturday morning, though perhaps a few degrees cooler in northeastern and far northern Colorado, particularly in the mountains. As colder air pushes into the state over the course of the day, we’ll struggle to warm up, with high temperatures considerably lower than Saturday.
Before we get into the precipitation details, here’s an overview:
If you’re looking to ski fresh snow, you should experience soft conditions (and legitimate storm skiing) on Monday morning, with a full blown (but not blower) powder day in store for Tuesday at many locations.
On Sunday afternoon, we’ll likely see widespread thunderstorm activity, though in far northern Colorado, we could have some lightning-producing cells in place as early as 8 or 9am. For the rest of Colorado, storms don’t look to mature until noonish, with fairly minimal activity in the San Juans and southern Sangres.
East of the Divide, a line of severe thunderstorms should develop and push east in the afternoon, with an environment that is fairly conducive for supercell formation, particularly along the Palmer Divide. A forecast sounding for the Palmer Divide at 1pm doesn’t look too boring at all.
Here’s how the storm development currently looks on the NAM3km model:
By the later afternoon and evening, widespread precipitation can be found across Colorado as the location of the jet stream increase large-scale lift over the state.
A northeasterly upslope also gets going, and looks to be pretty deep!
This will enhance precipitation over the foothills, urban corridor, and Palmer Divide, regardless of rain or snow, and looks to be strongest late Sunday night and into Monday morning.
This strong upslope continues well into Monday, keeping consistent rain and snow chances in play for most everywhere along and east of the Continental Divide and north of the Palmer Divide. Thanks to the easterly component of these winds, the Divide resorts (Loveland, A-Basin, Winter Park) should score a decent piece of the action.
Flow near the surface also looks to be oriented correctly to bring decent snow totals to the Sawatch Range and Mosquito Range, as moderate northeasterly winds work their way through South Park and onto the highest terrain in the state.
The upslope finally loses its grip on Monday night as the trough exits our area and drier air moves back into Colorado, which quickly shuts precipitation off by the early morning hours of Tuesday. West of the Divide, the trough axis passing overhead on Monday flips flow aloft around to come from the west, which could get some northwesterly and westerly flow going and increase snow potential that evening and night.
Besides the upslope, enhanced lift from the jet stream will help bring several inches of snow to most mountains in northern and central Colorado, with the biggest issues being in the Park Range and west of Vail due to lower elevations and the lack of cold air. They’ll still get a decent amount of moisture, but accumulating snow will difficult to produce.
Models are putting down some pretty good snow totals in places most impacted by the prolonged upslope event. The Euro model’s 10:1 output (which is actually a pretty reasonable SLR for this storm) isn’t shabby at all, with over a foot of snow at the Divide resorts, almost two feet of snow in the foothills (seems unlikely, due to SLRs lower than 10:1), and over a foot of snow in the Sawatch Range, Mosquito Range, Flat Tops, and West Elks.
Here is a rough forecast of how much snow we think will fall from Sunday at noon to Tuesday at 6am:
- Arapahoe Basin, Loveland: 7–15"
- Berthoud Pass: 10–18"
- Bierstadt / Evans: 10–18"
- Breck S.A.: 5–10"
- Buffalo Pass: 4–9"
- Cameron Pass: 7–15"
- Cottonwood Pass: 5–10"
- Grays / Torreys: 8–16"
- Hidden Valley: 6–12"
- Hoosier Pass: 6–12"
- Independence Pass: 4–9"
- Indian Peaks Wilderness: 10–20"
- Longs Peak: 10–20"
- Monarch Pass: 5–10"
- Pikes Peak: 8–16"
- Mt. Sherman: 8–16"
- Vail Pass: 5–10"
- Winter Park: 8–16"
We look to warm back up for the rest of the week, with thunderstorm chances on Tuesday and Wednesday evening.
Forecast by
Thomas Horner (Twitter: @thomaschorner)
Website and app with automated, high-resolution forecasts for mountains, climbing areas, and ski resorts (+ backcountry) with elevation switcher, uncertainty visualization, and more:
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