ForecastWinter Storm Likely Saturday PM to Monday; Impacts Highly UncertainModels are in good agreement that a winter storm will kick off the start of next week -- let's take a look at some possible scenarios.
- Warmer and dry this week.
- Winter storm system impacts Colorado from Saturday night to Monday.
- Exact timing and duration depends on the track and nature of the storm system. Models have very different forecasts at this point.
- Right now, 6-12" of snow at higher elevations seems like a reasonable guess, especially for the western mountain ranges. Plenty of scenarios where significantly more snow could fall, but still plenty of bust scenarios in play too.
- Snow east of the Divide is quite unlikely, but there will still be a strong cool down.
Eastern Colorado finally saw some freezing temperatures this morning behind our latest cold front.
There will be another chance for frost tonight, but the rest of the week looks pretty warm.
In the mountains, we're starting to face the prospects of some of the latest opening dates for Front Range ski areas in the past 10 years. There have only been two seasons since the 2010-2011 season where A-Basin opened after October 19th. With overnight wet bulb temperatures climbing back into the 20s this week, it seems like there will be a lot of work cut out for the snowmaking crews -- nevermind the lack of natural snow.
All of that is looking to finally change by Sunday as a big-time upper level trough drops into the western United States.
To be completely realistic, if you're looking for an accurate forecast for this coming storm, the above sentence is about the only thing we can state with any certainty. There will be some snow in the mountains, and a significant cooldown across much of the state. There's not nearly enough agreement in model guidance to forecast anything more specific.
...but we can speculate.
Right now, model guidance has generally been split between two scenarios.
The first scenario is a more progressive, open trough, with an initial salvo of southwesterly flow (San Juans are favored) followed by northwesterly flow (northern Colorado is favored).
The second scenario is a closed low barreling through Arizona and New Mexico. The San Juans would be heavily favored, and the I-25 corridor would have better chances of seeing measurable snow.
The Euro Model
The Euro has been more consistently calling for the first scenario.
On Saturday night, southwesterly flow in the jet left exit region would bring heavy snow to the San Juans.
By Sunday evening, a strong jet max overhead would bring snow to the rest of the high country with more westerly/northwesterly flow.
Strong downsloping off the Divide would make it very difficult for the Front Range to see any significant snowfall, though freezing temperatures on Monday morning would be likely.
We can see that the Euro ensemble members lean mostly towards the "open trough" scenario as northern Colorado is slightly favored.
In generally this would be a safe bet for 6-12" of snow for many mountain ranges, particularly in western Colorado (the San Juans, Elk Mountains, and Park Range).
The Canadian Model
The Canadian model's guidance has consistently shown a rather different solution, with a strong closed low barreling through the desert southwest.
This solution is less progressive, with snow falling from Sunday AM to Tuesday. This storm would heavily favor the San Juans thanks to consistent southwesterly flow under the jet left exit region.
There would only be a brief hit of northwesterly flow and large scale lift on Monday, bringing just a couple inches of snow to much of the rest of Colorado's mountains, compared to up to a couple feet in parts of the San Juans.
If this system does end up tracking through the area as a closed low, then it just needs to end up a bit further north than what the Canadian is currently showing to put measurable snowfall along the I-25 corridor in play.
The Canadian ensemble is leaning towards this scenario, overall.
The GFS Model
The GFS has been all over the board, generally showing a closed low tracking across the desert southwest, but occasionally leaning towards a more progressive open wave. The very latest 00Z run shows something in the middle...
This scenario would bring heavy snow to the San Juans or Elk Mountains [Aspen] (depending on where the moisture plume ends up -- could be north of the San Juans) on Saturday night (again, southwesterly flow under the jet left exit region) and a bit better shot of northwesterly flow on Sunday.
Looking at the very latest ensemble, the GFS seems to be trending away from a closed low scenario.
If we were to construct an atmospheric profile based off all the above solutions, the final snow totals would look something like this:
Overall, the western mountain ranges should do well no matter how this plays out. Plenty of scenarios deliver heavy snow to the San Juans, and the Elk Mountains are also in a decent spot to pick up some of the better dynamics and moisture.
We think the above map is slightly conservative as it takes into account plenty of scenarios where the system is even more progressive or otherwise fails to tap into decent moisture and provide enough large-scale lift over Colorado. Those scenarios would result in snow totals more like this:
Somewhat concerningly, this percentile hasn't budged in the past 36 hours, suggesting that there's still a good chance this storm could really bust as we get closer to the weekend.
A more optimistic scenario has 6-12" across most of the higher elevations, and 10-16" in the San Juans.
Until the models get their act together, there's not much else to say. It's just an odds game at this point.
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