We have a history of floods in California. In 1861-1862 there was a Great Flood that created a lake 300 miles long. It killed 25% of the cattle in the state. It is said that a total 9 feet of rain fell on Nevada city in California. What would happen today if that much rain fell on the state? We are probably in the start of the worst El Nino since 1877. The rain melts the snow in the mountains causing floods.

 You've got the history right, and your instinct about the snowmelt mechanism is exactly what makes this scenario so dangerous. Let me walk through what happened then versus what would happen now—and where the current El Niño fits in.

The 1861–62 Flood: What Actually HappenedYour figures check out. A 43-day storm beginning December 1861 dumped roughly 9 feet of rain on Nevada City over 60 days (with a Sierra snowpack equivalent to ~115 inches of rain), and it turned the Sacramento and San Joaquin Valleys into an inland sea nearly 300 miles long that persisted for months

San Francisco recorded 34 inches and Sacramento 37 inches over two months; roughly 4,000 lives were lost, and the damage was 50–100million—about∗∗50–100million—about∗∗3 billion in today's dollars** 3

 Critically, warm rain melted the Sierra snowpack and sent that water surging into the valleys, exactly as you describe 

Geologic evidence suggests rainfall-driven megafloods like this recur every 100 to 200 years 

 What Would It Mean Today? This is the sobering part. In 1862, California had maybe 380,000 people and no major cities in the Central Valley floodplain. Today:

Population in harm's way. The Central Valley alone holds roughly 7 million people, and projections call for another 5 million by 2060

Sacramento—the state capital—sits in a bowl protected by levees, with a metro population over 2 million, and has been described as the second most flood-at-risk city in the U.S. behind New Orleans  

Much of downtown Sacramento and the Natomas basin sit below sea level, kept dry only by the levee system 

 Infrastructure vulnerability. California has 13,800 miles of levees, many over a century old, graded D+ by the American Society of Civil Engineers

Many levees built decades ago are simply too small for present-day storms, and failures on the Pajaro and Cosumnes rivers in 2022–23 showed how fragile the system is 

Addressing statewide flood risk would require an estimated $59 billion in capital investment 

The economic stakes. USGS modeled a hypothetical modern "ARkStorm"—an atmospheric river sequence resembling 1862 but somewhat less extreme—and estimated damages around $725 billion, making it the costliest natural disaster in U.S. history, with weeks-long inundation across the Central Valley and Southern California

A true repeat of 1862 could plausibly exceed even that figure. Beyond buildings, you'd lose:

The Central Valley agricultural engine (8% of U.S. farmland value), submerged for months

Interstate 5 and 80, the state's freight spine, underwater

Water supply infrastructure—reservoirs, pumps, and the State Water Project would be overwhelmed or shut down

Mass displacement of millions, likely exceeding any evacuation in U.S. history

The compounding factors you mentioned. Warm rain melting snow is worse today than in 1862 because a warming climate means more precipitation falls as rain rather than snow at mid-elevations, so the snowpack that used to act as a natural reservoir releases all at once instead of slowly through spring

Add El Niño-elevated coastal sea levels (15–30 cm higher), which slow the drainage of floodwater out of the Delta, and you get a genuine "triple threat" 

 The Current El Niño (2026–27)You're right that this is historic. As of October 2026, NOAA puts greater than 83% odds that this becomes the strongest El Niño on record by October–December, and the WMO classifies it already as a "very strong" or Super El Niño peaking in November–December and lasting into early 2027

Model ensembles show Niño 3.4 heat peaking around 3.6°C above normal, which would beat the 2015–16 record by ~0.8°C—a margin rarely seen when records fall 

Yale Climate Connections notes roughly a 77% chance it becomes unprecedented going back to 1877 

 So your "worst since 1877" framing matches the published forecasts closely.

One important caveat, though: as we discussed earlier, atmospheric rivers don't reliably follow the El Niño script—they're often the "disruptor" of canonical forecasts. A super El Niño raises the odds of landfalling ARs and intense coastal storms, but it doesn't guarantee a megaflood. The 1862 event required a specific, persistent train of atmospheric rivers hitting the same regions for weeks.

Bottom Line If 1862-scale rain fell today, it wouldn't be a $3 billion disaster—it would be a multi-hundred-billion-dollar national emergency threatening millions of residents, the state capital, and a large share of the nation's food and freight system. That's precisely why researchers like those at Scripps' Center for Western Weather and Water Extremes track AR forecasts so intensely during El Niño winters like this one. Given the forecast strength, staying alert to local flood and landslide warnings this winter—especially if you're near burn scars, foothill communities, or unimproved levee districts—is genuinely worthwhile.

 (THIS IS FROM 2 QUESTIONS PLUS ONE CLARIFICATION I ASKED MY BRAVE BROWSER FREE AI )

 What Are Atmospheric Rivers? An atmospheric river (AR) is a narrow corridor of intense moisture in the lower atmosphere—typically 100–200 miles wide—that transports enormous amounts of water vapor, often from the tropics. When these moisture-laden streams hit land (most notably the U.S. West Coast), they can dump heavy rain or snow. They're responsible for roughly 30–50% of annual precipitation on the West Coast and play a critical role in water supply, but also in flooding and landslides.

The AR Severity Scale (AR 1–5)Developed by researchers at Scripps Institution of Oceanography and the National Weather Service, the scale rates atmospheric rivers from 1 (Weak) to 5 (Exceptional) based on two factors: the amount of water vapor transported (measured as vertically integrated water vapor transport, or IVT) and how long the AR lingers over a location'

 Category  Name                          IVT Threshold                                         Description

 AR 1        Weak                           ≥250 kg m⁻¹ s⁻¹                                        Primarily beneficial; modest rain, good for water supply

 AR 2        Moderate                     ≥500                                                        Mostly beneficial but somewhat hazardous; can cause river flooding

AR 3         Strong                          ≥750                                                        Balance of beneficial and hazardous; significant rain possible

AR 4          Extreme                      ≥1,000                                                     Mostly hazardous; heavy flooding, landslides likely

AR 5          Exceptional                  ≥1,250                                                    Primarily hazardous; extreme flooding, widespread damage

  (THIS IS THE CLARIFICATION)

 Please translate the following in the above into normal English. ≥250 kg m⁻¹ s⁻¹ Thanks. I need to be sure I understand what that means. Thanks.

 That formula is a unit of measurement for Vertical Integrated Water Vapor Transport (IVT)—basically, how much water vapor is being pushed through a column of air every second across a one-meter width.

Here's the plain-English breakdown:

kg = kilograms (weight)

m⁻¹ = per meter (width of the "stream")

s⁻¹ = per second (time)

So it literally means: kilograms of water vapor moving per meter of width, per second.

In simpler terms: it's a measure of how dense and how fast moisture is flowing through the atmosphere. Think of it like measuring how much water is flowing through a pipe—the higher the number, the more moisture is packed into that atmospheric river, and the more rain or snow it can dump once it hits land.

For context on the AR scale:

≥250 = the minimum threshold to even be classified as an atmospheric river (AR 1)

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Frequency The typical frequency of landfalling atmospheric rivers along the U.S. West Coast is roughly 10–15 per winter season (November–March), though this varies from year to year

Most are AR 1 or 2 events, which are common and generally beneficial. AR 3–4 events happen less frequently—perhaps a few per winter—while AR 5 events are rare, occurring perhaps once every few years or less at any given location. However, the exact frequency depends on geography and year-to-year climate variability.

Are They Stronger in El Niño Years? The relationship between El Niño and atmospheric rivers is complex and nuanced, not a simple "yes":

El Niño tends to increase overall storm activity and precipitation along the California coast. Storm tracks shift, bringing more westerly winds across the Pacific and generating higher surf, elevated sea levels, and potentially above-normal rainfall 

The 1982–83 El Niño was one of the most destructive in California history, with repeated powerful storms causing hundreds of millions in damage 

The 2015–16 El Niño also produced record-breaking waves—individual waves exceeding 66 feet along the coast 

 However, researchers note that atmospheric rivers are often the "disruptor" of El Niño's canonical precipitation patterns 

 In other words, while El Niño sets up conditions favorable for more intense storms, atmospheric rivers don't always follow the expected pattern—they can make or break seasonal forecasts 

 El Niño can create a "triple threat" for coastal hazards: increased rainfall (triggering landslides), powerful storm waves (accelerating erosion), and elevated sea levels (amplifying coastal flooding) 

 So yes—El Niño years tend to produce stronger and more impactful atmospheric rivers, especially along the California coast, but the relationship is not perfectly predictable, and individual AR events can vary significantly from the general pattern

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I SHOULD EXPLAIN. WATER COMES FROM THE PACIFIC. WHEN THE ATMOSPHERIC RIVER HITS THE SIERRA NEVADA MOUNTSINS, THE AIR IS FORCED TO AN ELEVATION WHICH IS HIGHER AND  TEMP IS COLDER. THIS CAUSES THE LOSS OF MOISTURE WHICH AT THIS POINT CAN FALL AS SNOW IN THE WINTER. THE SNOW PACK IS MELTED IN THE SPRING WITH A HEAVY RAINFALL OR SERIES OF HEAVY RAINS. IN 1861-2 THAT RAINFALL TOTALED 9 FEET!! AND THAT WAS ON TOP OF THE SNOW PACK WHICH WAS THE EQUIVALENT OF 115 INCHES OF RAIN. 

I am thinking that California could be hit by 300 mile long floods before the Cascade Megaquake destroys Oregon, Washington and in BC Canada.

That 1862 flood flooded Oregon, Nevada, Utah and Arizona and New Mexico as well.

Most likely is that we get major flooding this winter. To be followed by a Cascades Megaquake. That Megaquake would trigger the San Andreas fault.

Studies estimate that a 1862 type flood would actually do more damage than an 8.0 earthquake in California. 

The End of the Age is Nigh.