ForecastAnother Strong System Impacts Colorado; Denver Area to Experience Springlike Snow StormA rare March/April-esque storm for January -- big totals in the San Juans, northern mountains more questionable. Denver area is staring down heavy snow from Tuesday PM to Wednesday AM.
- Another system is impacting Colorado tonight through Wednesday.
- Southwest flow: big totals are expected in the San Juans -- lower as you look further north.
- Robust (unusual for January) cyclogenesis should bring heavy snow to parts of the I-25 corridor (particularly the Denver metro area) by Wednesday morning.
Alright, take two. Was rushing to get this article out at a reasonable hour, and by "rushing" we mean "not autosaving" and also "hitting the key combo that resets everything." So this one is going to be a little more...loose.
Anyways, hello there. It's been a pretty exciting couple weeks and we have another system impacting us right now that will close out a period of record atmospheric river activity. And in interesting fashion too!
Eastern Colorado is looking at a historically unusual storm. This system isn't unusual in general -- it's the common March/April springtime kind of event. But this system's well-developed structure, which is more common in March and April, is highly unusual for January. In fact, it's so unusual that model guidance suggests that these sorts of conditions have never been forecasted for the few weeks around the forecast date.
Before we get to that though, let's take a look at how the storm will impact Colorado initially. Southwest flow with fairly deep moisture will impact the San Juans, favoring Wolf Creek. The best moisture wont quite make it into Colorado, but that doesn't matter too much considering how robust dynamics look. Astute readers will note that this clashes with our previous forecast (on social media), where we didn't think this system would be as strong as the previous one. Well, the track changed.
This particular track should mean that a bulk of snowfall (for Colorado's mountains) will be accompanied by southwest flow, with the jet having to do some serious work to bring some better bands of snow to the I-70 ski areas and northern Colorado. With little wraparound moisture and disappointing NW flow expected behind the system, forecast totals drop off as you move away from the San Juans. This is visualized nicely on our comparison charts:
It's pretty clear on a map as well though take some of the totals here with a grain of salt.
In general though most areas have the potential for some decent snow accumulations if not a powder day, with the obvious exception being parts of the San Juans, which could be measuring final totals in feet.
In the San Juans, double digits are pretty likely for almost all popular ski areas...
...and though totals could be pretty nice near Summit County, one should not discount the low-end of 3-4":
As mentioned, this is a fairly springlike storm and if you recall, many of these systems end up dumping more snow on Denver than in the mountains immediately to the west (i.e. Summit County). That's certainly a possibility here.
So what is interesting about this system? Well, as the upper-level trough swings over the region, it traverses over the Continental Divide and compresses vertically. Once it descends eastwards from the Divide, it stretches vertically which causes it to spin faster in a process known as lee cyclogenesis.
The center of low pressure associated with this system needs to end up over southeastern Colorado in order for cyclonic flow to set up a northeasterly upslope for the Denver metro area. This setup typically isn't productive for areas south of the Palmer Divide (Colorado Springs) or south of the Cheyenne Ridge (Fort Collins) as the northerly winds downslope off those features.
So while these sorts of storms aren't uncommon in spring, it's certainly unusual for Denver to end up in the northwest quadrant of fully developed cyclone in January. Looking at cross-sections, we also see the potential for very fluffy snow (high snow liquid-ratios) and thus snowfall rates in excess of 1" per hour at times on Tuesday.
These maps look decent but may be underselling the fluffiness of the snow over the I-25 corridor:
So while there's a lot to like with the track and smaller-scale dynamics of the system, there are a few models showing a less-than-impressive event (4-6" in Denver) -- the main issue being the system should be lifting out of the region, which could limit jet dynamics lessen snow intensity, at least for Colorado. Despite that, a healthy upper end is about a foot of snow, and then some. One may consider recreationally looking at the HiresW-FV3 model for some real fun, though that model has some issues.
Looking at a model comparison, definitely some duds, but more recent consensus has converged on about 4-10":
...which again may be a bit low. It's looking like our custom forecast is about 5-12" right now. A large spread, but with some serious outliers still in play our model is trying its best. Speaking of huge spreads, this 7-30" forecast for Wolf Creek by Tuesday night is ridiculous:
That's the kind of stuff we're talking about when we struggle with getting reasonable forecasts out to you all when model uncertainty is high, and what we've been working on for many weeks now with our custom forecasting system (which has 12-24" for Wolf Creek).
Timings are a bit fluid as the storm still has an opportunity to stall out and delay things by several hours...or vice versa.
Right now snow is already falling in parts of the southern and central mountains, with some areas of the northern mountains seeing some snow tonight. A stronger push of moisture comes on Tuesday morning (after 5am), which should bring a period of more consistently heavier snow to the San Juans (particularly Wolf Creek).
The warm moisture plume is making the heaviest snow a bit spotty thanks to some instability, but the sheer amount of it and duration of better snowfall should hopefully even things out.
By Tuesday evening cyclonic flow will start developing, with snow filling in for the northern and eastern mountain ranges and over the Front Range / northeastern plains. The upslope for the I-25 corridor wont really get going til early Wednesday morning though -- snow will be heaviest and most consistent during this time. The northerly and northwesterly flow further to the west of the Front Range will favor more productive snowfall in the northern mountains.
As the system moves eastwards, winds will become more northwesterly and snow in the Front Range should clear up by noon on Wednesday. Some lingering snow showers may persist into the afternoon in the northern mountains.
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