Colorado Weather Forecast #125: Sep. 27 - Oct. 3, 2021

Widespread moisture and a notable cooldown in store for the rest of the week, with decent snow potential at elevation. The weekend looks to be mostly dry and a bit warmer.

This forecast is no longer valid. Please return to our list of forecast articles to find more recent posts.

Updated Mon Sep 27, 2021 10:00pm MST | Published Mon Sep 27, 2021

By Thomas Horner

Hello and welcome to the new blog that we built. We have moved off of Medium permanently, and all our content will be located here from now on. Let us know what you think!

Summary

We transition to a more seasonal weather pattern, with a cold front on Wednesday and snow forecasted at higher elevations. Decent precipitation chances for most of the mountains until a period of slightly warmer, drier weather this weekend.

Tuesday

  • Widespread thunderstorm activity in the mountains.
  • Cooler than today.
  • Snow above 12,000ft. Some mountains could pick up a few inches of snow.
  • Modest thunderstorm chances for the urban corridor, mostly confined to west of I-25.
  • Precipitation will likely remain fairly consistent in parts of western and central Colorado into the late hours of the night.

Wednesday

  • Cold front pushes through from west to east on early Wednesday morning (or late Tuesday night, for western Colorado), with some precipitation at the leading edge.
  • Gusty winds in the morning, last until the afternoon.
  • Cold front should reach the urban corridor before sunrise.
  • Parts of western Colorado will see ongoing precipitation through the morning, before most of the high country sees isolated to scattered afternoon storm coverage.
  • The snow level falls to about 10,000ft.
  • By the late afternoon or evening, the urban corridor could see some thunderstorm activity, especially near Colorado Springs.
  • Another push of colder air from north to south by the evening or night, mostly impacting the Front Range.
  • High temperatures will be noticeably lower than Tuesday.

Thursday

  • There’s a slight chance that some mountains could have picked up several inches of snow at higher elevation – the Blend has reasonable ranges of 2-12”.
  • Colder than Wednesday.
  • Afternoon storms for the Colorado mountains, favoring the San Juans and central ranges.

Friday

  • Decent snow potential in the San Juans and Sangres early on Friday morning.
  • Isolated afternoon storms across most of the high country, with some slight chances down on the Plains.
  • Wet in southeast Colorado.

Saturday

  • Isolated afternoon storm potential along the Divide, lower chances elsewhere. Some storms could push into the urban corridor.
  • Warming.

Sunday

  • Warming.
  • Some minimal afternoon storm chances near the Divide.

Current Conditions

A low pressure system is currently located south of the Four Corners region of the United States.

This system is pushing wildfire smoke westward and has entrained a large amount of moisture which is beginning to work its way into Colorado. This has led to widespread thunderstorm production this afternoon across the San Juan and Sangre de Cristo mountain ranges of Colorado, with some storm activity in the central mountains as well. Due to clockwise (cyclonic) flow around the center of low pressure, storms have been moving from southeast to northwest.

(via Wolf Creek)
(via Wolf Creek)

Temperatures are above average across the state, except in southern Colorado which is being impacted by the low pressure system.

Denver International Airport officially topped out at 89 degrees yesterday, which is one degree shy of the record high for September 26th. The airport hit 89 degrees again today.

For the Front Range urban corridor, late September is usually the start of a much drier period that typically lasts until March. In the mountains, September tends to be a bit drier than other months, with monthly precipitation gradually increasing into spring as the state starts to get impacted by winter storms. Regardless, the past two weeks have been exceptionally dry, with most of the state receiving no precipitation whatsoever.

(via WeatherBell)
(via WeatherBell)

Forecast Discussion

Over the next 24 hours, the closed low to our south will deepen and move north. This advect a large amount of moisture into Colorado, though the best moisture availability will be locked up to the west of the Divide.

Tonight, a stronger push of moisture and a weak boundary will work its way from southern Colorado into central Colorado. This will set up a band of light to moderate precipitation that will impact the Sangres, central mountains, and central/south urban corridor (Denver to Pueblo) overnight and into the early morning hours, with perhaps some lingering showers by 5-7am across the Denver metro area tomorrow.

(via WeatherBell)
(via WeatherBell)

On Tuesday, better moisture availability across the state (except eastern Colorado) along with warm temperatures puts widespread thunderstorms in the forecast for most Colorado mountains and the Front Range urban corridor, though storms are much more likely west of I-25 than east of it. Storm motion should be fairly slow and generally from west to east, with precipitation falling as snow above 12,000ft.

In some parts of the mountains, the widespread and prolonged nature of precipitation could result in quite the dusting at elevation. For instance, the Blend has 1-4” of snow in the forecast for the higher reaches of Mt. Elbert, thanks to a snow-liquid ratio of around 10:1.

At the same time, a trough is dropping into the Pacific Northwest and a decent shortwave associated with it will impact our region by Wednesday, with part of the jet stream dropping down into Colorado before the wave becomes cutoff and forms a closed low over the Four Corners region by Friday.

(via WeatherBell)
(via WeatherBell)

Wednesday’s Cold Front

A cold front will push through Colorado on Wednesday morning, with high temperatures taking a big hit on the Plains. By Thursday, highs will be 20-30 degrees lower than what was experienced today.

The mountains wont experience as strong of an impact, with temperatures falling by around 10 degrees. Wednesday morning will be gusty.

This will be enough to make snow a consideration below treeline. Right now, the Blend has been holding steady with a rain/snow level of about 10,000ft. by Thursday, but we’ve seen other models bringing snow down to 8-9,000ft at least briefly.

Let’s not get ahead of ourselves. The widespread thunderstorms on Tuesday evening will likely continue unabated late into the night across western Colorado as the leading edge of the cold front begins to impact Colorado. Rain and snow will push eastward across Colorado early on Wednesday morning, though precipitation will become much lighter as it crosses east of the Divide around 6am on Wednesday.

Precipitation Probabilities

Here’s an overview of some precipitation chances for the week across the state before we break it down a bit:

Isolated thunderstorms/thundersnow will then pop up across the mountains on Wednesday afternoon, though parts of western Colorado may never really see a break from precipitation. Later in the afternoon and into Wednesday evening, stronger storms could start to fire off the higher terrain to the west of the urban corridor, particularly south of the Palmer Divide, which would impact Colorado Springs.

Storm coverage decreases on Wednesday night (earlier in western Colorado as drier air enters the region), though precipitation looks to still linger near and east of the Divide and across parts of the central and southern Colorado plains on Thursday morning. On Thursday, another round of afternoon storm activity puts decent probabilities of precipitation at play across most of the Colorado high country, with impacts highest west of the Divide and in the San Juans.

This again dies down overnight, but a strong push of moisture into southern Colorado puts the San Juans and southern Sangres at risk of picking up some significant snow accumulations into Friday. In fact, the upper reasonable bounds of the Blend have the higher elevations of the Chicago Basin 14ers picking up 6”+ of snow from Thursday to Saturday morning.

Snow

In fact, the higher ends of probablistic guidance are fairly impressive, with even the somewhat reasonable 75th percentile forecasting almost a foot of snow for some peaks.

However, most of this is expected to come on Tuesday and Wednesday evenings/nights.

The Weekend

By the weekend some slightly warmer, drier air works its way into the state, along with a bit of subsidence. This should keep precipitation chances much lower than the week, though isolated afternoon storms look to remain a possibility, especially near the Divide. Some of these storms could push onto the urban corridor.

Long Term

You’ll notice that high temperatures never really recover from the cold front on Wednesday. The long term forecast does not show any strong ridging signal, which is the weather pattern that has brought us such unseasonably warm weather over the past few days. In fact, next week’s pattern looks weird for lack of a better term.

The Front Range may experience another cold front early Monday morning, but the ensembles generally lean towards a slightly warmer and drier pattern overall, but nothing too unseasonable. Decent precipitation chances remain in western and southern Colorado throghout the week.

Otherwise, ensemble members are all over the board in terms of the precipitation and temperature forecast, with spreads of 10+ degrees and no agreement on the existence of a decent storm in the future. The only thing we have our eye on right now is a growing troughing signal around October 12-13 which may suggest the potential for a winter storm.

We’ll update you later this week in regards to the weekend and the ongoing precipitation this week.

--

More frequent updates on Twitter, Instagram, and Facebook: @highpointwx


💙 Supported By 💙

  • Kim H.
  • Briana K.
  • Kevin M.
  • Cullen O.
  • Tal W.

We love doing this and making our work available for free! But it does take a ton of time to put these forecasts together, develop our custom graphics, and keep our servers running. Consider throwing some beer or coffee money our way: Support us on Patreon!


Shout out to our friends: Weather5280, Seth's Weather Report