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Colorado Weather Forecast | Aug. 8–15, 2021

Smoke remains a concern, as heat and rain chances ramp up into the week.

Yesterday (and this morning) was a tough day to breath in Colorado as a direct shot of smoke from California’s Dixie Fire was advected into the state behind a passing shortwave, which was also responsible for the storm activity on Friday. The Dixie Fire is California’s second largest blaze on record (463,000 acres), behind the August Complex Fire (2020, 1+ million acres), in addition to the largest single fire on record.

Most AQI sensors in the Colorado — regardless of whether they were in mountain towns or urban areas — topped out out a PM2.5 AQI of 180–200. An intense gradient of smoke pushed from northwest to southeast in the nighttime hours on Friday, with areas like Grand Junction and Rangely jumping from AQIs of 20–30 to almost 200 in less than an hour. Most areas of the state spent a considerable amount of time in the “unhealthy” or even “hazardous” air quality categories.

(via PurpleAir)

Smoke is finally clearing out a bit on the urban corridor, though it was still thick this morning due a surface temperature inversion. Some mountain valleys are still having trouble mixing the smoke out due to their topology. On a large scale, cleaner air from higher in the atmosphere is working its way back into Colorado, which is mixing some of the smoke out, but unfortunately this improvement will be short-lived.

(via WeatherBell)

As we make a brief return to zonal flow, a system traverses over Montana, which helps redirect some smoke-filled low-level flow back into Colorado. This is older, more dispersed smoke, not a direct shot like we saw on Saturday, but this still promises to be about as bad, or worse, than anything we saw last week.

(via WeatherBell)

This system should also kick a weak cold front down the Front Range early Tuesday morning, which blow some surface smoke back into the urban corridor.

(via WeatherBell)

In Denver, this should keep temperatures from reaching the mid to upper 90s on Tuesday. Otherwise, those temperatures will be commonplace through the week. This front is not associated with an uptick of moisture, so no significant storms are expected.

As we progress into the week, the subtropical high associated with the monsoon begins to reestablish itself over the western United States. We transition away from zonal flow and back into a pattern that we saw last week, with broad anticyclonic flow rotating around broad high pressure centered in the western United States.

On Wednesday, we see ridging establishing itself over the west, with high pressure over the desert southwest:

(via WeatherBell)

The ridge builds through the weekend, with a center of high pressure moving into the Great Basin:

(via WeatherBell)

We’ll discuss what this means for temperatures and precipitation before looking at smoke concerns for the week.

Like we said, this pattern is more similar to what we saw last week, and it opens the door for pulses of monsoonal moisture into the desert southwest. Unfortunately, guidance doesn’t suggest these pulses will be particularly strong, with only a weak precipitation signal in Colorado by the end of the weekend. Still, this steadily bumps up probability of precipitation as we get into the week.

Despite the increased chance for afternoon thunderstorms, it doesn’t look like we’ll get enough moisture to tip the balance from the next week being a bit drier than normal.

(via WeatherBell)

One thing will have plenty of is warm air. We start the week with another heatwave roasting the Pacific Northwest.

(via WeatherBell)

This is relevant, as it means firefighters are unlikely to continue making significant progress on fighting fires in northern California, Oregon, and Canada, so we continue to think about smoke concerns.

The heat then pushes east, with most of Colorado seeing anomalously warm temperatures into the weekend. Southern Colorado may see more average temperatures, thanks to a cooling influence from pulses of monsoonal moisture.

In Denver, the mid to high 90s are on the table most days, except for Tuesday, thanks to the aforementioned “cold” front.

In the mountains, we see highs in the low to mid 70s at 10,000ft, with lows in the low to mid 40s…

…and at 14,000ft., temperatures remain above freezing, with highs in the low 50s and lows in the mid 30 to high 30s.

Precipitation chances will be highest next weekend, which should moderate high temperatures a good amount. 12 hour thunderstorm chances in the mountains look to top out at 70–75% (in southern Colorado, and 60% in northern Colorado) on Saturday and Sunday, compared with 15–20% on Monday and Tuesday. Be prepared for scattered afternoon thunderstorm activity next weekend after a much calmer start of the week.

That brings us to smoke. Let’s break it down day by day:

Monday

Expected worst AQI for the metro area: 110–130.

Smoke returns with zonal flow, not as thick as Saturday, but noticeable.

Tuesday

Expected worst AQI for the metro area: 100–140.

Backwards trajectories indicate that smoke will likely continue to advect into the state. We don’t think it will get too much worse than Monday, but we’re thinking that air quality may continue to deteriorate somewhat, especially during the day time.

(via NOAA HYSPLIT)

Wednesday

Expected worst AQI for the metro area: 120–170.

Smoke transportation looks to get particularly problematic, as we start tapping into some of the denser smoke from the Dixie Fire smoke plume, in addition to whatever is lingering in the Intermountain West.

(via WeatherBell)
(via NOAA HYSPLIT)

Depending on the exact placement of the high (roughly over New Mexico), we could be getting set up for a more direct shot of smoke like we saw on Saturday — though it doesn’t look like a sure bet. Otherwise things may not get much worse than they were on Tuesday.

Thursday

Expected worst AQI for the metro area: 80–120.

By Thursday, a strong center of high pressure has established itself to the west of British Columbia, which redirects flow over the Pacific Northwest to be easterly. This will have cut off the supply of smoke into our region, as we start drawing in cleaner air from our north.

(via NOAA HYSPLIT)

Still, we may be tapping into lingering smoke in the northern Rockies, and looking at the vertical cross-sections above, we may not be effectively mixing out the existing smoke unless we can draw in more air from the upper atmosphere.

Friday

Expected worst AQI for the metro area: 70–100.

Thanks to broadening anticyclonic rotation we still aren’t likely to be drawing in too much smoke in the region.

(via WeatherBell)

However, we are setting the stage to eventually loop some wildfire smoke up through the northern United States and down into Colorado, like we saw last week.

The Weekend

Expected worst AQI for the metro area: 70–100.

This is satellite imagery from last week, and it may be similar to what we see this coming weekend:

(via College of DuPage)

That said, guidance is showing fairly robust low level flow into Colorado from the Gulf of Mexico, which could keep any lofted smoke from effectively mixing down to the surface. We’ll see — but we’re optimistic that the weekend may only be a bit hazy.

We’ll send out another update before the middle of next week.

Cover image: Aspen Highlands Roundshot

Forecast by
Thomas Horner (Twitter: @thomaschorner)

Website and app with automated, high-resolution forecasts for mountains, climbing areas, and ski resorts (+ backcountry) with elevation switcher, uncertainty visualization, and more:
https://highpointwx.com

Frequent updates, graphics, and general stoke:
Twitter / Instagram / Facebook: @highpointwx

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Weather forecasts and articles for the recreating in the Colorado high country — mountains, ski resorts, and crags.

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Highpoint Weather Forecasting Team

Highpoint Weather Forecasting Team

The Highpoint Weather forecasting team — weather nerds who like to play outside.

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