Our post from over the weekend highlighted the first round of heavy rainfall and flooding in southwest Colorado. There was a break in the rain on Sunday, October 12, and then a second round of heavy rain on Monday the 13th associated with moisture from remnant Tropical Storm Raymond. That’s right, a one-two punch of tropical moisture from the larger Priscilla and then from Raymond a couple days later. Here are some observations of the total precipitation over the entire event.

With soils already saturated and rivers and creeks running high, the Monday rainfall led to even more flooding in La Plata and Archuleta Counties. The San Juan River at Pagosa Springs actually peaked slightly higher on Tuesday morning than it did on Saturday, once again reaching major flood stage.

The high elevations of the San Juan mountains received another 3-4″ of precipitation on Monday (a bit of it as snow on the higher peaks), with 1-3 additional inches at lower elevations around Pagosa Springs, Bayfield, and Durango. This brought the 7-day total precipitation to a remarkable 10.2 inches at the Upper San Juan SNOTEL station, with over 9″ at several other sites.

Volunteer observers from the Community Collaborative Rain, Hail, and Snow network (CoCoRaHS) recorded over 7 inches of rainfall in 7 days north of Bayfield and northwest of Pagosa Springs. These are huge rainfall totals for this part of the state!

Updating the table from the previous post to show seven-day precipitation accumulations at the Upper San Juan SNOTEL station, we see that the 10.2″ from the recent storm is surrounded only by huge winter snowstorm cycles. In the years since that station was established in 1978, there aren’t any fall rainstorms that come anywhere close to rivaling it.

The hurricane and flood of October 1911

Looking back farther in history, however, there is one event that surpassed this one in terms of the level of flooding in the southwestern US (including Colorado): the “Sonora hurricane” of October 1911. This caused the flood of record on many rivers in southern Colorado, including the San Juan at Pagosa Springs (the 17.8 feet shown on the graph at the beginning). Jonathan Thompson of the Land Desk had a great summary a few years ago about that flood along with other historic floods in the region. (h/t John Orr for pointing me to this).

The track of the 1911 hurricane appears to be somewhat similar to what happened with Priscilla this year, with tropical moisture streaming ahead of the decaying circulation. (Animations below are from this year, the map below that is the track of the 1911 hurricane.)

There are a lot more rainfall observations available now than there were during the 1911 storm (thank you, CoCoRaHS observers and SNOTEL network, among others!), but from the available data, the rainfall totals over 1-2 days in the 1911 storm were greater than those in the 2025 event, but the fact that there were *two* tropical cyclone remnants in 2025 made the total precipitation over 5-7 days much greater. The break in the rainfall on Sunday in between the two waves of heavy rain was certainly important, or the flooding could have been closer to what happened in 1911.

And it turns out there was a particularly controversial rainfall observation in October 1911 — I was not really aware of this previously, but my predecessor Nolan Doesken was involved in many of the debates surrounding the chart shown here.

This is the observation form from Gladstone, Colorado, north of Silverton, at around 10,500 feet elevation. It shows 8.05″ on October 5, 1911. There’s no question that a lot of rain fell in southwestern Colorado during that storm based on the floods that happened, but if it’s possible for over 8″ of rain to fall in one day at 10,500 feet, that has major implications for the robustness of infrastructure that is needed. A later study of the flooding near Gladstone by Pruess, Wohl, and Jarrett found that it was not consistent with such large rainfall accumulations (or at least not within 24 hours), and the Gladstone observation is now generally deemed to be unreliable. (Thanks to Jeff Lukas for pointing this paper out.) Even so, Silverton recorded 4.05″ on October 5, 1911, and flooding on the Animas and San Juan Rivers reached record levels (at least since measurements have been in place)

The good news: improvements in drought conditions

The flooding in southwestern Colorado led to the destruction of multiple homes and to major disruptions around the region. But the flip side is that all the rain will help to ameliorate the lingering drought in the area. Everyone would prefer that the water arrive more steadily rather than in a huge burst like this, but as noted in this Colorado Sun story, small reservoirs like Vallecito saw big boosts in their storage from the storm. On this week’s US Drought Monitor, there were widespread two-category improvements in southwestern Colorado, going either from D2 (severe drought) to D0 (abnormally dry), or from D1 (moderate drought) to nothing on the map. Two-category improvements in one week are very rare for the Drought Monitor, typically only applied when there are major rain events associated with tropical systems.

Both the Animas and Rio Grande Rivers saw huge increases in streamflow, with 7-day average flows near record levels for the fall, and close to the average early-summer peak from snowmelt runoff. On the Rio Grande, only the peak from October 1911 is higher than the current average flow for the period between October and April. [Daily data is missing for the Animas in October 1911, but it surely peaked even much higher than shown on the graph.]

Other than around the San Juan Mountains, this event didn’t end the drought that goes back to last winter (or even longer, depending on how you define it) across western Colorado, but did put a nice dent into the precipitation deficits that had mounted over that period. Now it’s time to look ahead to the snow accumulation season and see what arrives in the usual source of water in western Colorado: the mountain snowpack.

We got pulled in to analyzing this major storm, along with some other activities this week, but we will be finalizing and releasing our recap of Water Year 2025 within the next week or so, so please stay tuned for that! [Subscribe here if you want to get it delivered straight to your inbox. And use the ‘subscribe’ box here on the blog if you like these posts and want to get them in your email — it’s a different mailing list.]