Forecast for the approaching fall storm system that will impact the state from 2pm Mon through 11pm Tue

09/22/25 8:15am: Happy first day of astronomical fall! In fitting fall fashion we have a stronger fall storm system on tap for the state from this afternoon through tomorrow afternoon. Some rain showers are already pushing into parts of northwest CO now with a few weak rain showers on the front-range. The forecast remains on track with just a few small changes.

Main impacts from the storm will be from 2pm today through 11pm Tue, coming in two pieces.

Overall models show the low tracking a bit farther south and west and thus the heaviest precip along the northern front-range will be a bit further south.

It now appears the heaviest precip will really be in the upslope notch: southwest of a line from Boulder to Parker, with overall heaviest precip expected in the foothills west of Denver and along the Palmer Divide.

In the mountains the heaviest rain/snow will be in areas closer to Winter Park, Berthoud / Jones Passes, IPW, southern RMNP and maybe Cameron Pass areas (that area will be on the northern edge now).

As I mentioned the storm system will come in two parts with maybe a break in-between: first part as the jet-stream pushes in from the northwest will be from 2pm today through 12am Tue.

Second, colder part of the storm system will be when the main upper-level low moves into CO and a strong surface low will setup in southeast CO with impacts expected from 3am Tue to 11pm Tue. This will be the time-frame with the heaviest precip along the front-range, including Den/Bou (as the cold northeast upslope flow devlops).

For the north-central and front-range mountains: rain and thunderstorms develop after 1pm today, then a round of rain through about 11pm (snow-level initially above 11k). Then as the colder air moves in (with the low) rain/snow expected Tue morning through the afternoon and the snow-level will drop to around 9k ft by Tue am.

In terms of snowfall for the mountains, still expecting 2-8" for parts of the north-central mountains, mostly from Summit Co east and favoring the Front Range mountains (Loveland ski area, Grays/Torreys, Jones/Berthoud Passes, IPW, RMNP, Cameron Pass).... maybe up 10: few spots up high.

Mountain Valleys like Silverthorne/Dillon, Frisco, Winter Park/Fraser may get 1/2" to 2" in spots, it will be close.

It will be chilly on Tue with highs only in the 30s/40s in the mountains.

For Den/Bou and the front-range: rain showers and weak thunderstorms primarily from 2pm-10pm today, then maybe a break. Then cold rain from about 5am Tue through 11pm Tue (that will be the main event). Still looks like much of Den/Bou will pick up 1-2" of rainfall. It will be chilly on Tue with high in the 50s.

Snow level in the foothills will likely drop to around 9k ft by Tue am (so some snow for areas near Nederland to Allenspark to upper Estes Park areas: 1-3" in spots).

The storm system clears out after 12am Wed.

First image loop shows forecast radar over the next 48hrs (6am this morning through 6am Wed) from latest HRRR. Images 2 and 3 show forecast total liquid precip and total snowfall from now through 6am Wed from latest HRRR, take with grain of salt but high-res models get the terrain. Images 4 and 5 show equivalent for latest ECMWF model (which is typically good with the precip, maybe a bit off for snowfall, so take with grain of salt).

This is going to be fun!