Increasing thunderstorm chances Tue, then a more fall like storm system for Thu to Sat

09/08/25 8am: Morning its Monday. We do have some weather to talk about this week. It will be summer like for the first part of the week with some afternoon thunderstorms, especially in the mountains. But then I'm tracking a more fall like system for Thu to Sat which will bring better rain (and snow chances above 12k ft) across much of the state, especially to the southern mountains.

For today (Mon), just some isolated to scattered thunderstorms over parts of north-central mountains and front-range.

Deeper moisture starts to move in ahead of a west-coast trough tomorrow, so better thunderstorm chances especially in the mountains tomorrow (but also a chance for front-rang as well)

For Den/Bou and the front-range:

• For today: A chance for isolated, high-based storms from 2pm-8pm, best chances in the foothills and near the PD. Most areas stay dry

• For tomorrow: scattered storms (maybe a couple rounds) from 2pm-9pm (best chances around the edges: foothills, PD, along/east of I-25 later, eastern plains)

• For Wed, drier, just very isolated storms after 2pm again, most areas stay dry

  
  

For the north-central and south-central mountains:

• For today: isolated to scattered thunderstorms mostly from Leadville north from 2pm-9pm, best coverage near/east of the Cont. Divide (Front Range mountains will be favored)

• For tomorrow a better chance for scattered thunderstorms from 12pm-10pm, likely multiple rounds, best chances after 2pm, best coverage from Monarch Pass north (central mountains will be favored)

• There could be a few rain showers late Tue night into Wed am over southern / south-central CO

• On Wed mostly isolated storms for southern CO / San Juans from 1pm-8pm, further north very isolated activity

  
  

Then a disorganized upper-level low will approach the state on Thu into Fri, but it is not clear exactly how this will evolve and how far north and east the main wave(s) will track (looks like CO will be on the southeastern edge of the best lift and moisture).

Given that the trough is just to our west, with strong southwest flow forecast over the state Thu to Sat, southwest CO and the San Juans up to the Elks will be favored for heaviest precip for this upcoming weekend.

Most of the impacts from this large trough will be from 3pm Thu through 3pm Sat, with rounds of afternoon rain and thunderstorms and some snow mostly above 12,500ft. Its not a particularly cold storm system.

Wettest and coolest conditions expected across the mountains from 12pm Fri trough 12pm Sat (Fri night will have best chances for a little bit of snow up high)

But overall better rain and thunderstorm chances for most of the mountains starting Thu afternoon, break Fri am, again Fri afternoon into Sat am, break Sat am, then more rain showers likely Sat afternoon into Sun (so you can see most of the precip will be in the afternoons each day).

Den/Bou and the front-range will also have better rain and thunderstorms chances especially Fri and Sat afternoons but its unclear how much rain (may not be that much for front-range urban corridor with this setup).

First image loop shows forecast radar over the next 48hrs (6am this morning through 6am Wed) from latest HRRR. Second image loop shows the evolution of the large west-coast trough / upper-level low via 500mb vorticity / wind from latest ECMWF (from Tue through Sat). Third image shows forecast total liquid precip from now through Sun am from latest ECMWF and I circled the area that has best chances for heavier rain (and snow above 12,500ft) this weekend.