Predicting California River Flows for Rafting

Posted February 1, 2023 by Gregg Armstrong, Co-Founder
Co-authored by Lenka Bostian

All it took was that first rafting trip on the Stanislaus River in 1962. Moments after we floated off from shore, we became hooked on white water rafting and therefore hooked on rivers. As a result, we also became interested in learning how snowpack levels and rain totals received each winter affect California river flows for the upcoming white water rafting season.

Rain and Snow Make Rivers Go

All rivers are connected to rain and/or snow. If you want to know what most rivers will be doing during each of The 4 “Seasons” of the California Rafting Season, you need to know what happened in the Sierra Nevada mountains during the “wet season” – from October through April. Ever since that first rafting trip, we have become students of rain totals and snowpack levels in California because what flows in the river comes from higher elevations above.

California river flows

Accessing Snow and Water Data over the Years

At first, we got our precipitation “facts” from the puddles in the backyard of our Walnut Creek home. We looked at their size, their number, and how many times they occurred. We later started to take note of the snow depth at our family cabin in the Sierra. It was a primitive start to our river flow predictions.

As time went on, we became more refined. We got to know key folks in the California Department of Water Resources in Sacramento on a first name basis. They graciously spent time educating us about interpreting rainfall and snowpack reports, as well as water reservoir storage data. Over time, we learned how to use these to predict river flows in the future.

With the birth of the internet, even more information became readily available. Today we no longer rely on the puddles in our backyard or the snow on the deck of our cabin. Instead, we have multiple sophisticated resources at our fingertips that along with our 60+ years of experience help us estimate how rivers will run in the next rafting season. (See the list at the end of this post).

bomb cyclone winter storm builds snowpack for California river flows come spring

Wintertime: Watch and Wait

Two things are certain when it comes to predicting California river flows for the coming rafting season: it is a very dynamic process and no two years are ever the same. As mentioned earlier, California’s “wet season” goes from October to April. The first couple of months (October and November) and the last month (April) usually have little impact on the California snowpack levels and rain totals because they are typically warmer and drier. The middle part (December through March) has the greatest impact since most precipitation takes place in these four months.

Over the years we have witnessed all kinds of possible scenarios unfold: early series of atmospheric rivers followed by months of dry weather, late season storms after months of nothing but sunshine, and everything in between. We’ve learned that following the weather patterns and snowpack reports carefully during the wet season is  important. However, we really don’t know for sure how the rafting season will play out until we get to late March.

Sierra Snowpack

Putting It All Together Into a Flows Forecast Each Spring

Once we get to the early spring months, we compile all the rainfall and snowpack data available. We then compare it with six decades of past rafting seasons. Looking for years with similar patterns, we come up with season predictions for each of the 10 California rivers we run.

A summary of our rafting season predictions is presented each spring on our River Flows page. This helpful resource features real-time river flow graphs and is updated regularly during the rafting season with the latest water flow forecasts.

Our efforts over the years have resulted in forecasts that have been relatively accurate, and have given our company and our guests the ability to plan ahead and enjoy amazing rivers and rafting in California!

California River Flows on the Tuolumne in Spring

California Snowpack Resources Today

Here is a peek at some of the resources we utilize each winter to determine how high and long and well our 10 California rivers will be running in the coming rafting season:

CA Department of Water Resources – Snow Water Equivalent Daily Report
This page is updated daily during the wet months, generally October to May, with snow water equivalent data from a collection of snow survey stations across the state. Snow water equivalent means the amount of water stored in the snow.

CA Department of Water Resources – Snow Water Content Chart
The chart shows the percent of April 1 average snow water content (water stored in the snow) for the three regions of our state (North, Central, South) with comparisons to other past years. The shape of the bell curve indicates how close or how far the season is from the 50-year average snowpack.

National Weather Service – Regional Snow Analyses, Sierra Nevada
This interactive panel shows a variety of precipitation related data for the Central and Southern region of Sierra Nevada. Static and animated maps going back nearly two decades allow us to review the rates of accumulation and melt of snow in different years, helping us make predictions for the next rafting season.

CA Department of Water Resources – Twitter Feed
During the wet season and springtime we come here for the most up-to-date information related to the official monthly snow surveys and other water related data.

UC Berkeley Central Sierra Snow Lab – Twitter Feed
The university laboratory which is located at nearly 7000 ft elevation posts and shares some great insights and information about the Sierra snowpack.

National Weather Service Sacramento – Twitter Feed
The Sacramento regional station is a good general go-to source for everything weather related year-round. During the wet months it’s a great resource for storm and snowpack information for the Central Sierra region.

Author Bio

Gregg Armstrong

Gregg is the middle child of George and Dolores Armstrong's five children. He has been working with All-Outdoors since it was founded. He guided and set up early operations on California rivers in the 70's and 80's before making marketing for AO and reservations his main responsibilities. One of his claims to fame is that he and his wife Marion had triplets, who grew up to enjoy rafting and outdoor activities as much as he does. When not doing AO and family life he loves to ski, garden, and spend time with people.


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