Aug 20, 2021
Colorado Weather Forecast | Aug. 20–25, 2021
Cooler weekend, warmer and fairly dry next week, smoke concerns.
An exciting couple days of weather in Colorado, though perhaps you have a different way to describe it if your car got destroyed by one of the tornado-warned cells in the Denver metro area on Thursday.
The system we’ve been forecasting for the past week is finally lifting out of the area. Western Colorado saw a couple days of heavy rain, including some severe storms, then eastern Colorado saw severe weather on Thursday, including several tornado warnings. Late last night, a final wave of precipitation pushed across the state, which fell as snow at higher elevations.
Here’s the total accumulations over the past three days:
This lines up nicely with model predictions — quite a decent amount of rain on the Western Slope, dry in southeastern Colorado, and thunderstorm activity for the north Front Range with the signature of a very heavy severe storm outbreak near the CO / NE border.
On Thursday, we (Thomas Horner and Seth Linden) chased storms near Keenesburg on I-76, with support from Laura Smith. Storms were reluctant to organize, with the best action happening back in town (a tornado warning was issued for a storm near Arvada / Westminster / Broomfield, then later, another tornado warning was issued for a storm near Parker). None of these storms ended up dropping a tornado, with the only serious action out near Nebraska.
On the last intercept of the day near Hoyt, CO, we did manage to catch a small cell right at the peak of its cycle — it was barely rotating and didn’t want to drop anything, but looked mean and was accompanied by fierce cloud-to-ground lightning. Here are a couple shots:
Laura helpfully labeled what some of these features are:
We took these pictures from north of the storm, looking south. To escape, we went west and skimmed the edge of the forward flank downdraft, where the hail core was.
A final band of precipitation moved through early in the AM as advertised. Some lightning and hail woke up people in the northern urban corridor around 3am.
This band had pushed most of the way across Colorado and dropped snow above 10,000ft — a bit lower elevation than we were forecasting!
As the system traversed over Colorado, winds aloft intensified, which were felt along the Divide. By later this morning, it was estimated that winds on parts of the Divide were 60–80mph!
Here are the estimated snow totals from last night.
And here’s how the Maroon Bells and Pyramid Peak looked from the Aspen Highlands Roundshot Cam this morning:
A lot of this snow has already melted off, and only areas that received more than a dusting and/or have shaded areas at high elevation will be holding on to snow by the start of the weekend.
You can also see some smoke in the background — our passing system sucked in some smoke from the California wildfires. This will be advected out today, with our weekend forecast still looking nice and relatively smoke-free.
Notice a direct shot of smoke go into Wyoming — this was what we were worried about earlier in the week, but luckily the system which impacted us tracked favorably to redirect the worst of the smoke to the north of Colorado.
Still, there will be some lingering light smoke on Saturday morning, and some smoke concerns along the very northern edge of Colorado on Sunday as heavy smoke enters Wyoming. A weak cold front on Monday morning will likely push a noticeable amount of this smoke down the Front Range.
Why the cold front? We have another disturbance aloft on the heels of our previous system:
This wave is weaker and doesn’t dig as far south, so it wont have a major impact on our weather. It should enhance precipitation in northern Colorado later on Saturday, in addition to kicking out the aforementioned weak cold front down the Front Range on Monday morning. By weak, we mean that high temperatures in Denver will probably be in the high 80s instead of the low 90s.
So let’s take a look at the weekend: Sunday is looking less stormy than our previous forecast indicated, with most of the thunderstorm concerns being relegated to Saturday. On Saturday, the highest thunderstorm chances are in the Front Range thanks to the next disturbance — though the best chances come later in the afternoon.
On Sunday, isolated thunderstorm chances are relegated to the Divide and the Sangres, with very limited lightning potential elsewhere. Winds will be fairly gusty, especially along the Divide, with large swaths of 30–60mph gusts possible.
However, temperatures will be seasonable, perhaps slightly warmer than average east of the Divide.
By Tuesday the Subtropical High begins to rebuild and flow turns mostly zonal over the western United States.
We’ll need to watch out for some disturbances aloft in that flow, but otherwise, we are looking at a fairly typical late summer weather pattern. Unfortunately, it appears as though the tropical storm activity to our south will disrupt consistent monsoonal moisture flow into the state. The outlook is looking fairly dry into next weekend.
With that pattern in mind, we’ll be keeping our eye out for isolated thunderstorm potential in the mountains next week along with the potential for a return of heavier smoke. Have a great weekend and let’s reconvene on Monday.
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