Colorado Weather Forecast | Storm Mar. 16–17, 2021
Snow this afternoon/evening as another cutoff low wanders through the desert southwest.
Header image: Golden from S. Table Mountain (via Thomas Horner)
This will be a quickie since we’re running behind and this storm doesn’t look that exciting. Here’s the snow forecast:
Another cutoff low has come ashore and is making its way from California eastward across the desert southwest. This low fairly weak and is traversing well to our south.
In terms of large scale dynamics, the San Juans, particularly Wolf Creek, are under the left exit region of the jet until the afternoon, but this doesn’t really coincide with moisture availability, so that wont really be a snow producer (it’s currently sunny in Wolf Creek, as of 11am).
However, this will at least keep large-scale subsidence out of the state until later into the night, allowing orographic flow to do its work as moisture becomes more readily available in the afternoon and evening.
The Wolf Creek webcam shows some snow showers in the distance as deeper moisture begins to infiltrate the Colorado Rocky Mountains.
By this evening, the 700mb low will be in New Mexico and flow near the surface will be northerly, specifically NNW west of the low (driving snow in Telluride, Silverton, and Powderhorn) and northeasterly to the east of the low (bringing snow to the east facing slopes of the Sangres, which should have the best totals due to more plentiful moisture). This is in part due to another weak low over the Dakotas, which is helping to veer winds into our state.
We are seeing pretty good support for moisture convergence along a north-south boundary in central Colorado where the cyclonic flow around the low in New Mexico meets these upper level northerly winds.
This would potentially greatly enhance snowfall at the Aspen resorts, Vail, and Beaver Creek, with resorts to the east (Cooper and Copper) possibly picking up a piece of the action. Some models have this as a fairly narrow swath of double digit totals, which could be a nice surprise, though not the Euro and HRRR. Check out the obvious band of much higher totals west of Summit County:
If the GFSv15 (being retired in a few days) is to be trusted, these high totals could be seen throughout Summit County in addition to the Winter Park area, but it is the only model suggesting that possibility, though its upgraded version still has better totals there that could bust the 1–5" forecast.
By early Wednesday morning, large scale subsidence in the jet left entrance region brings snowfall to a halt (maybe some pockets of light snow in places) despite moisture still being available. This could, perhaps, bring an inch or two with northwest flow to the northern mountains as we get into Wednesday.
We have adjusted some totals in regards to model guidance. Purgatory’s forecast looked too high considering they will have downsloping winds for much of this storm, but the HRRR does bring them 3–6" in just a few hours, so maybe we’re being cynical. Powderhorn’s forecast looked too low, and the Summit County resorts seemed a bit high in general due to the GFS’s insistence on higher totals, though the Berthoud Pass area could come away with 4–7" if they’re lucky, but we don’t think that’s a likely scenario.
Resorts near Summit County will be of interest— with the HRRR and Euro calling for only a couple inches of snow, and the GFS calling for 6"+, it will be another test of their respective reliabilities. We’ve gone for the conservative estimate, especially seeing the dynamics for this storm.
The I-25 corridor and foothills will also pick up a bit of snow due to a window of weak upslope, but overall, a westerly component to the northerly flow will be prevalent which will cause downsloping. We’re not seeing any serious potential for appreciable totals until you get down towards Pueblo.
If you want to compare our expectations to a model blend, check it out:
The only real area of serious disagreement appears to be in Purgatory. Also, look at those nice totals in the Sangres! They don’t show up on our forecasts (except Taos in the far southern Sangres) but these kinds of lows are usually good to them.
A Glimpse Ahead
Despite this bump in the road, we continue our path towards more seasonal temperatures to end the week.
By Friday, warm air will be locked west of the Divide and temperatures will start getting above freezing in the mountains, except perhaps above treeline. The Plains will stay cooler, with temperatures not reaching the 50s in Denver until Friday. This looks to be due to anticyclonic flow around high pressure over Minnesota transporting colder air in from the passing storm systems that will be well to our east.
Despite the cooler air temperatures east of the Divide, the high angle March sun will be out, and winds wont be a factor besides some blustery conditions on the high ridgelines on Wednesday afternoon as warm air advects into the state with the approaching ridge.
We then wait for our next storm at the end of the weekend (likely Sunday afternoon), which will likely come as an open wave that pulls far south. In that case, the most snow will focus on the San Juans (especially Wolf Creek) and western Colorado. There looks to be some complexity in the wave which could embed some energy in northwest flow aloft — we’ll see as we get closer.
An alternative solution that is obvious in the ensembles is that troughing over the Pacific Northwest prevents the wave from propagating east, and instead low pressure digs further south over California and doesn’t lift east to impact Colorado until Wednesday, possibly as a closed low. Significant snow on Sunday is thus not a certainty, but we’ll likely know which scenario is more likely tomorrow.
Forecast by
Thomas Horner (Twitter: @thomaschorner)
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