Click the link to read the discussion on the CBRFC website:

The Colorado Basin River Forecast Center (CBRFC) geographic forecast area includes the Upper Colorado River Basin (UCRB), Lower Colorado River Basin (LCRB), and Eastern Great Basin (GB).

Water Supply Forecasts

January 1 water supply forecasts are generally well below normal and summarized in the figure and table below. Snowpack and soil moisture are the primary hydrologic conditions that impact the water supply outlook, while future weather is the primary source of forecast uncertainty.

Water Year Weather

The 2025–26 winter season has thus far featured record-setting warmth and limited precipitation, driven

by a persistent high-pressure ridge over the CBRFC area. Most of the major climate sites in and around the CBRFC area experienced their warmest (e.g. Salt Lake City, Phoenix, Tucson, Las Vegas, Pocatello) — or second warmest (e.g. Flagstaff, Grand Junction, Denver) — December on record. An active northern stream riding over the ridge has delivered above average precipitation to the northern fringes of the UCRB and GB, but given the warm maritime influence, snow accumulation has remained unimpressive.

The water year as a whole tells a different story. In October, several rounds of heavy rain tied to decaying tropical storms brought record flooding to portions of AZ, southern UT, and southwest CO — making it one of the wettest Octobers on record. November brought continued above average precipitation to the LCRB, but well below average precipitation was observed elsewhere. Water year 2026 precipitation is summarized in the figure and table below.

Snowpack Conditions

UCRB January 1 snow water equivalent (SWE) conditions are highly variable and range between 35–100% of normal. Storm systems this winter have been warmer than normal with high snow levels resulting in much of the precipitation falling as rain rather than snow. SWE conditions are very poor across most of the UCRB, with numerous SNOTEL stations across western CO reporting January 1 SWE values at or near record low. The exception is the Upper Green headwaters, where SWE is near to above normal. UCRB January 1 snow covered area is around 28% of the 2001–2025 median, which is the lowest on record dating back to 2001. ¹ LCRB January 1 SWE conditions are at or near record low across much of southwest UT, central AZ, and west-central NM.

GB January 1 SWE conditions are also very poor, ranging between 25–65% of normal. SWE at the majority of SNOTEL stations across UT are below the 10th percentile, with several stations reporting record low January 1 SWE. January 1 snow covered area across UT is record low at just 15% of the 2001-2025 median.¹ SWE conditions are summarized in the figure and table below.

Soil Moisture

CBRFC hydrologic model fall (antecedent) soil moisture conditions impact water supply forecasts and the efficiency of spring runoff. Basins with above average soil moisture conditions can be expected to experience more efficient runoff from rainfall or snowmelt while basins with below average soil moisture conditions can be expected to have lower runoff efficiency until soil moisture deficits are fulfilled. The timing and magnitude of spring runoff is impacted by snowpack conditions, spring weather, and soil moisture conditions.

Soil moisture conditions heading into the 2026 spring runoff season are below normal across most areas as a result of warmer and drier than normal weather during the 2025 water year. Water year 2025 precipitation was around 80% of average across the UCRB and GB and around 60% of average across the LCRB. The least favorable soil moisture conditions exist across central UT and the Colorado River headwaters. Soil moisture conditions across southwest CO and central AZ are exceptions, where very wet October–November weather led to improved soil moisture that is near or above average. CBRFC hydrologic model soil moisture conditions are shown in the figures below.

Upcoming Weather

After a cold and somewhat snowy system sweeps through the CBRFC area this week, high pressure looks to dominate the region for the foreseeable future, which will suppress any chances for significant precipitation. The 7-day precipitation forecast and the Climate Prediction Center (CPC) 8–14 day temperature and precipitation outlooks are shown in the figures below.

References

1. Rittger, K., Lenard, S.J.P., Palomaki, R.T., Stephenson, L. (2026). Snow Today. Boulder, Colorado USA. National Snow and Ice Data Center. Data source: MODIS/Terra/SPIRES.

Click the link to view my posts on Twitter(X).

From the report Colorado River Insights, 2025: Dancing With Deadpool (Jonathan Overpeck and Bradley Udall):

• Jonathan Overpeck is a climate scientist and Dean of the School for Environment and Sustainability at the University of Michigan; prior to moving to Michigan, he lived and worked in Colorado and Arizona for over 25 years.
• Bradley Udall is a Senior Water and Climate Research Scientist/Scholar, Colorado Water Center, Colorado State University.

Basin status update

Back in 2017, we published a peer-reviewed research paper (Udall and Overpeck, 2017) asserting that climate warming was a principal cause of the then eighteen-year Colorado River drought, a drought that had already seen a 17% reduction in natural flows of the river. We expressed confidence that warming would continue to eat away at these flows until the warming (due to greenhouse gas emissions, high confidence) ceased and suggested that increases in precipitation would likely not be able to compensate for the long-term impact of rising temperatures. We used the term “Hot Drought” to distinguish this period from the “Dry Droughts in the 20th century. This important concept continues to be researched and confirmed (King et al, 2024, Zhuang et al, 2024). Now, eight years later, as the warming has continued unabated and may be accelerating (Hansen et al, 2025, Ripple et al., 2025), it has become clearer than ever that precipitation declines have also played an important role in causing the worst drought in at least 1200 years (Williams et al., 2022). More troubling, however, is new evidence that human caused climate change is not only driving a steady increase in temperature but is also the main culprit behind the precipitation declines as well.

This is clearly bad news, but there is a silver-lining. But first, let’s review where we are with respect to the unprecedented 21st century Colorado River drought, and the new evidence suggesting the situation is worse than we first thought.

Each year one of us updates a figure³ that was first published in our 2017 paper showing the status of the Colorado River drought and its climate drivers. We’ve included this figure here, updated through the September 30th end of the 2024-25 water year (Figure 1). The combined volume of water stored in Lakes Mead and Powell has continued its decline to less than 15 maf (million acre-feet), the 26-year average naturalized flow of the Colorado River at Lees Ferry is now 12.2 maf, well below the 16.5 maf mainstem apportionments assigned to the seven Colorado River Basin states and Mexico. Critically, the 6 years since 2020 have averaged 10.8 maf/year, the same as the then-unprecedented low flows during 2000-05 at the start of this record-setting drought.

Matching the long slow decline in naturalized flows over the last century has been a similar long slow decline in precipitation in the Upper Basin of the Colorado (Figure 1, Panel C). Superimposed on this long trend are two notable drought periods with lower-than-average precipitation: one in the 1950’s-60’s and now the on-going current drought, at 26-years and counting, a multidecadal “megadrought” and the longest drought in the Colorado River Basin instrumental record. Mirroring the century-long declines in precipitation and naturalized flows is a long-term warming trend that started to accelerate in the 1970’s and that is clearly linked to on-going global warming (Williams et al., 2020, Masson-Delmotte et al., 2021). Whereas the former drought of record, in the 1950’s and 60’s, was defined almost entirely by precipitation deficit (Figure 1, left gray shaded area), the current megadrought is being driven by a precipitation deficit compounded by relentless warming (Figure 1, right gray shaded area).

The impact of a warming climate

As we highlighted in earlier peer-reviewed papers (e.g., Vano et al., 2014, Udall and Overpeck, 2017), warming exacerbates drought in multiple ways. A warming atmosphere can hold progressively more water, and thus as the atmosphere warms it can evaporate more water. At the same time, a warmer atmosphere can cause soils and vegetation to lose more water to the atmosphere via evapotranspiration, especially as the warming atmosphere also causes the growing season in the Upper Basin of the Colorado to become longer (Das et al., 2011; Udall and Overpeck, 2017). Hot, dry springs in the basin bring on early melt and green-up (Hogan and Lundquist, 2024, Lin et al., 2022). Drier soils and vegetation thus mean less water that can eventually end up in the river, and incidentally also explains why the West I experiencing more wildfire (Abatzoglou and Williams, 2016). Atmospheric warming also leads to snow loss, a shorter snow-cover season, and an associated loss of solar radiation reflectivity – this drives further warming and yet more evapotranspiration (Milly and Dunne, 2020; Ban et al., 2023).

Large changes in groundwater supplies in both the Upper and Lower Colorado River Basins have been noted from soil moisture to deeper layers since 2002 (Abdelmohsen et al., 2025, Chandanpurkar et al., 2025). It is becoming increasingly clear that dry summer soils can persist into the fall and winter soaking up snowmelt the following spring thereby reducing runoff (Das et al., 2011, Lapides et al, 2022).

Precipitation declining

Estimates vary, but it appears that up to half of the observed roughly 20% reduction in Colorado flows are likely related to the steadily warming temperatures of the Colorado River headwaters region (Udall and Overpeck, 2017; Xiao et al., 2018; Milly and Dunne, 2020, Bass et al, 2023). Moreover, since 2017 it has become increasingly clear that the other major cause of the flow reductions is a sustained decrease in precipitation (Figure 1, Panel C). Until recently, the big question is whether the observed 7% post-1999 decrease in precipitation relative to the 20th century average was due primarily to natural multidecadal climate variability or human-caused climate change.  We now have good reasons to suspect the latter, and this translates to mostly bad news.

Megadrought country

It is now more clear than ever that the southwest United States, including the headwater regions of the Colorado River, is megadrought country. Tree-ring and other paleoclimatic sources reveal that multiple droughts lasting two or more decades took place over the last 2000 years (Meko et al, 2007; Gangopadhyay et al., 2022), and a good case has now been made for the current drought being among the most severe in at least 1200 years in large part because of the unprecedented amplifying effect of warming temperatures during the current sustained period of reduced precipitation (Williams et al., 2020; 2022).

However, there is another important lesson to be gleaned from the rich paleoclimatic record of pre-20th Century droughts and megadroughts. Given that global temperatures were likely significantly cooler prior to the last 50 years then they are now (PAGES 2k Consortium, 2019), it follows that themany long Upper Colorado Basin droughts that took place over the last 2000 years preceding the current drought were likely due much more to precipitation deficits alone. This means that we have good evidence that precipitation deficits exceeding those of the current on-going drought in both magnitude and duration are not rare, and that the current drought could see not just warmer temperatures in the future (a sure bet), but also even larger and longer precipitation deficits. It is thus critical that we consider what is presently causing the precipitation decline in the headwaters region of the Colorado River, and from that get a better sense of what’s most likely ahead. And for motivation, since we wrote our 2017 paper, new evidence has emerged that drought-dominated periods – likely driven mostly by precipitation declines for the reason noted above – as long as 80 years have occurred in the last 2000 years in the Upper Basin of the Colorado River (Gangopadhyay et al., 2022).

The cause of precipitation decline

Could we be in for an even longer period of reduced precipitation than the last quarter. century in the years to decades ahead? The answer depends on knowing the cause of the on-going precipitation decline, and there are two primary possibilities. The first is natural climate variability in the climate system, which can cause periods of lower precipitation to oscillate irregularly with periods of higher precipitation. Thus, if the recent period of low precipitation is due to natural climate variability, there could be periods of greater precipitation returning to the Colorado headwaters, although these wet periods would be increasingly unlikely to offset the drying impact of the steadily increasing temperatures. The second potential cause of on-going precipitation deficit is an anthropogenically-forced trend in precipitation decline due to increasing human emissions of greenhouse gases and reductions in Asian, mostly Chinese, aerosols to the atmosphere.5 Such an anthropogenic trend would likely portend continued low precipitation into the future, in synch with continued warming.

One well-known source of natural variability in precipitation in the Colorado River Basin is decadal and longer variation in the sea-surface temperature patterns of the North and tropical Pacific Ocean, giving rise to what is called the Pacific Decadal Oscillation (PDO). A peer-reviewed research paper just published (Klavans et al., 2025) reviews the scientific literature and notes that decadal and longer variability in the PDO has long been thought to have arisen from atmosphere-ocean interactions internal to the natural climate system and has in turn caused decadal and longer precipitation variability downstream over western North America. The PDO is strongly correlated with La Nina, and both are known to be associated with a dry Southwest US (Seager and Ting, 2017; Lehner et al., 2018; Hoerling et al., 2023, Seager et al., 2023). Klavans et al., 2025 also presents convincing new evidence that anthropogenic forcing in the form of human emissions of greenhouse gases and reductions in atmospheric aerosols is now the primary driver of the same elevated sea-surface temperatures and this forcing is thus the primary cause behind the precipitation decline that has been observed since the start of the on-going Colorado River megadrought. In other words, human-driven climate change has caused the PDO oscillation to lock into its negative dry phase and this situation is likely to persist into the future.

A second new paper (Todd et al., 2025) highlights that higher Northern Hemisphere temperatures from about 11,000 to 6,000 years ago, in this case due to well-understood changes in the Earth’s orbit, caused a negative PDO-like Pacific warming that in turn forced western U.S. precipitation to lock into a multi-millennia-long dry phase. This new research thus provides yet more confidence that the odds will favor lowered precipitation in the Colorado River headwaters for as long as human-caused warming persists. Both new research papers (Todd et al., 2025; Klavans et al., 2025) also note that state-of-the-art climate models underestimate the role of human-caused climate change in driving persistent drought in the region containing the headwaters of the Colorado River. Natural decadal and longer climate variability clearly caused the many droughts and megadroughts of the last 2000 years, but looking ahead today, it appears that human-caused climate change is likely to exert a stronger influence, and this will mean a higher likelihood of continued lower precipitation in the headwaters of the Colorado River into the future.

Conclusion: bad news, good news

To sum it up, since 2017 we now know quite a bit more about how climate change is altering the flows of the Colorado River. Whereas eight years ago we were able to confidently anticipate that human-caused atmospheric warming alone would continue to reduce flows in the river, we now have a better, though still emerging, understanding of how human emissions of greenhouse gases are likely to also cause a continued reduction in precipitation in the headwaters of the Colorado River. Whereas we have known since 2017 that additional future climate warming will cause continued and even larger flow reductions, two new carefully crafted studies strongly suggest we are in for extended dry periods in the Colorado headwaters in the decades ahead.

As we hinted earlier, is important to recognize that the news is not all bad, and there is indeed a silver-lining to our improved understanding of why the natural flows of the Colorado are declining, and what this means for the future. We can say with confidence that human-caused emissions of greenhouse gases are having an increasingly negative impact on the flows of the Colorado River, a river that serves over forty million people and region that has an annual economy in excess of $1.4 trillion (James et al., 2014). This climate change impact will continue to worsen, but because humans cause it, humans can halt it. This is good to know as we work to reduce the greenhouse gas emissions to the atmosphere that are causing the climate change. The Colorado River will benefit. 

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Footnotes

³ https://coloradoriverscience.org/Current_conditions#The_Colorado_River_.274-panel_plot.27

⁴ NOAA’s nClimGrid dataset indicates that over the Upper Colorado River Basin there has been a 7% annual precipitation reduction during 2000-26 compared to 1897-1999. This reduction is not evenly spread over the seasons, however; reductions in the fall (SON), winter (DJF), spring (MAM) and summer (JJA) are 3%, 0%, 11% and 12%, respectively. Fall and winter precipitation for snowpack has thus been close to normal while spring and summer has been much reduced.

⁵ Sulfate aerosols are emitted in large quantities when sulfur in fossil fuels is burned. These shiny particles can end up high in the atmosphere where they reduce anthropogenic warming by reflecting sunlight. But near the surface their sulfur-based precursors cause serious human health problems and thus many countries in the last few decades have tried and succeeded in reducing these emissions. China, notably, has made great strides in reducing these emissions but the unfortunate side effect is increased warming, especially in the Pacific Ocean downwind. It is believed that this aerosol cleanup (also underway in ocean shipping) is causing at least some of the accelerated global heating now underway including the additional heating in the northern Pacific contributing to precipitation reductions in the Southwest US.

Click the link to read the briefing on the Western Water Assessment website:

December 8, 2025 – CO, UT, WY

A hot and dry November left the Intermountain West with much below average snowpack conditions. November temperatures were four degrees above average region-wide and much of Utah and Wyoming baked under mean temperatures that were six to ten degrees above average. High temperatures coupled with mostly below normal precipitation caused low snow water equivalent (SWE) and worsening drought conditions.

November precipitation was much below average for much of the region, especially in Wyoming, northern Colorado and northern Utah, which received less than half of normal precipitation. Much above average November precipitation was observed in southern Utah and eastern Colorado. Record dry Novembers were observed at thirteen locations in Wyoming, ten locations in Colorado and five locations in Utah. Despite dry November conditions, regional water year precipitation is near to above average except for eastern Colorado and southeastern Wyoming.

November was an extremely warm month, especially in western Wyoming, where monthly temperatures were more than eight degrees above average. The entire region observed November temperatures that were at least four degrees above average, with all of Utah, nearly all of Wyoming and western Colorado experiencing temperatures that exceeded six degrees above average. Record warm October conditions were observed in western Colorado, southwestern Wyoming and throughout Utah.

Record low SWE conditions exist at many locations in Colorado, Utah and Wyoming. A hot and dry November left most regional river basins with SWE conditions at less than 50% of average, with the least snow in the Six Creeks near Salt Lake City, where December 1st SWE is 22% of median. Slightly better SWE conditions exist in southern Colorado and southern Utah.

Regional drought coverage expanded slightly during November, increasing from 51% five weeks ago to 54% on December 2. Eastern Colorado and eastern Wyoming remain drought-free, but drought emerged along the northern Front Range and adjacent plains. Coverage of drought in Utah dropped below 100% for the first time in five months. Utah and Colorado were last free from drought six years ago, while the current drought in Wyoming began five years ago.

A NOAA La Niña Advisory is still in effect as eastern Pacific Ocean temperatures are below average. Weak La Niña conditions are expected to transition (60% probability) to neutral conditions by early 2026. The NOAA December Precipitation Outlook suggests above average precipitation for most of Wyoming. For the winter months (Dec-Feb), there is an increased probability for above average temperatures in Utah and southwestern Colorado. In Wyoming, there is an increased probability for above average precipitation and below average temperatures.

Record high temperatures drive record low snowpack. On December 1, record low SWE conditions were present at 52 regional Snotel sites in northern Colorado, northern Utah, and across Wyoming. Despite very low snowpack conditions, water year precipitation is above average for the region, except in northern Colorado. During early October, daily precipitation records were set in Utah and Colorado, including widespread flooding in southwest Colorado. Due to the tropical origin of those storms, nearly all precipitation fell as rain. Contrasting precipitation, water year temperatures are much above average with record high temperatures observed in parts of western Colorado, eastern Utah, and southwestern Wyoming. Consequently, the current snow drought is primarily the result of high temperatures rather than low precipitation. While October precipitation generally fell as rain in regional mountains, above average precipitation has increased soil moisture, which could help to bolster the efficiency of runoff in 2026.