Colorado Weather Forecast | Aug. 17–22, 2021
Big pattern change on the way: significant cooldown, snow at higher elevations, heavy precipitation in parts of Colorado.
Well, well, well…look what has made a return:
Air quality has kicked up into the “Unhealthy for Sensitive Groups” category across the Front Range this evening as easterly flow pushes smoke up against the higher terrain. Air quality is also marginal on the Western Slope, with the clearest air in central Colorado.
Smoke will stick around for most of the state through Wednesday, and possibly into Thursday for the Front Range. We don’t think the PM2.5 Air Quality Index will ever really exceed 150 (Unhealthy), but smoke will be noticeable and possibly irritating over the next couple days. The culprit is our subtropical high which is currently located over California, having retrograded west across the Intermountain West over the course of the weekend.
A ridiculous amount of smoke has been dumped into the atmosphere from hundreds and hundreds of fires across the northern Rockies and Pacific Northwest, and it is slowly being advected over Colorado. The current uncertainty in regards to just how bad our air quality will get is in regards to how much of the lofted smoke will mix down to the surface — there is a ton of it higher up in the atmosphere, but we look to continue to get decent surface-level flow that will inhibit it from effectively mixing down.
Just look at how much smoke there is:
…produced by a large quantity of intense wildfires (look for orange and red dots):
Luckily, Colorado and Utah have not had to deal with too many fires of their own lately, though the past two weeks have been on the dry side.
That will change by the end of the week. A pattern change is coming in the form of a proper mid-latitude storm which is dropping into the Pacific Northwest tomorrow and then lifting across the northern Rockies into Saturday, with a bit of negative tilt.
These are the sort of storms that bring us heavy snowfall in fall, winter, and spring, but in the middle of August, we’ll see some heavy rain, widespread thunderstorms, cooler temperatures, and a bit of snow above 12,000ft.
Importantly, this storm (and some follow up disturbances behind it) should cool things down over Canada and the Pacific Northwest, with decent chances for rain over areas that experiencing large wildfire outbreaks. This will be important as it has a large bearing on our eventual return to a more monsoonal weather pattern by the end of the week, and thus potentially smokier conditions.
For this coming weekend, the major system rolling through now looks to dig far enough south, then lift far enough north, to clear smoke out of Colorado. That’s good news! Check out the attached video showing the smoke forecast into Saturday:
The cooldown into the weekend should be fairly pronounced and widespread:
There is still a decent amount of disagreement in regards to weather impacts further south down into Colorado. Many of you east of the Divide (i.e. in the Front Range urban corridor) may not experience much more than a 10 degree cooldown and an uptick in thunderstorm activity, with the potential for severe weather out on the plains.
Better agreement surrounds precipitation chances for the Western Slope and Utah, which are running a moisture deficit — they are expected to get a decent amount of rain by the weekend.
With the current timing of the system, we see a big uptick in precipitation chances on Wednesday afternoon in western and central Colorado, with precipitation potential finally dropping as we progress into Friday and Saturday:
You’ll also notice the blue colored bars, which indicate snow (this chart is for 14,425ft.). With the cooler temperatures, the snow level looks to drop to about 12,000ft. by Friday.
Some of Colorado’s highest peaks could pick up a couple inches of snow through Saturday at their highest elevations:
For timings, western Colorado’s best chance for precipitation comes Wednesday evening, while eastern Colorado’s best chances come Thursday evening.
The significant instability associated with this system will mean much of this precipitation falls as part of widespread thunderstorm activity. In fact, parts of western Colorado and the mountains see chances for lightning in the mornings.
We’ll update you on that tomorrow when the convection-allowing models are more in range.
For Denver, we’re currently expecting highs to remain in the 90s through Wednesday, before they drop into the the 70s or low 80s for Thursday, with a slow recovery into the weekend.
Wednesday should feature some thunderstorm activity before more widespread rain and thunder on Thursday, with precipitation chances quickly backing off by Friday.
We’ll give you a more in-depth scoop on precipitation potential and outdoor recreation for the rest of the week and weekend either tomorrow or Wednesday. This weekend looks to be quite pleasant!
After that, we look to get another weaker system on Monday or Tuesday, before we return to a warmer, more monsoonal weather pattern by next weekend.
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