The Pacific Northwest was soaked by a prolonged chain of atmospheric rivers that dropped almost 5 trillion gallons (19 trillion liters) of rain over the past seven days, centered on Washington state and raising the risk of record floods, officials said. The heaviest, most persistent downpours were expected to linger through late Thursday into early Friday before the main plume of moisture shifts, though forecasters warned that the West Coast may face repeated “fire hose” moisture events into the week of Christmas. Meteorologists trace the exceptional runoff to unusually warm ocean and air temperatures and a sequence of weather drivers stretching back to tropical cyclone flooding near Indonesia.
- Rainfall volume: Nearly 5 trillion gallons (19 trillion liters) fell across the affected region in the past seven days, based on rain gauge and station estimates.
- Local extremes: One Mount Rainier station recorded 21 inches (53 cm) of rain since Thursday, officials reported.
- Flood risk: Forecasts show potential record-level flooding on the Skagit River in northern Washington, which drains to Puget Sound.
- Duration: The worst rains were forecast to continue through late Thursday and into early Friday, with the broader West Coast pattern remaining active into the week of December 21 (week of Christmas).
- Drivers: Warmer-than-normal Pacific waters north of Hawaii, an unusually strong Madden–Julian Oscillation and a high-pressure ridge off California combined to funnel and intensify the atmospheric rivers.
- Climate context: Analyses and modeling indicate atmospheric river events in the region have grown slightly larger, more frequent and wetter since 1980; human-caused warming increases the likelihood of warmer ocean and air conditions fueling such storms.
Background
Atmospheric rivers (ARs) are narrow corridors of concentrated water vapor that form over the ocean and transport tropical moisture poleward. The Pacific Northwest typically receives a couple dozen ARs each year—more than some other West Coast regions—but this episode has been larger and more persistent than usual, meteorologists said. The extra intensity reflects both the immediate weather setup and a background of warmer ocean and atmospheric temperatures.
Forecasters link the moisture to a broad source region a few hundred miles north of Hawaii, where sea-surface temperatures were several degrees above the seasonal average. That warmer ocean surface can load more water vapor into the air; when that moist air is steered into the Northwest by atmospheric patterns, heavy rainfall concentrates over the same river basins repeatedly. Local topography then converts rainfall into rapid runoff and elevated river stages.
Main Event
The most intense band of precipitation stalled over parts of western Washington, producing prolonged heavy rain on Monday and again on Wednesday, compounding impacts. State and federal weather officials issued flood watches and warnings for rivers including the Skagit, and emergency responders carried out rescues in low-lying communities. Officials said the persistent repetition of ARs—what some forecasters described as the atmosphere ‘‘reloading’’—is a key reason flood risk escalated.
Using gauge-based sums and station reports, meteorologist Ryan Maue estimated nearly 5 trillion gallons of rain in the weeklong period, a quantity he compared to filling large natural or man-made landmarks. Washington State Climatologist Guillaume Mauger highlighted forecasts that show record-setting flood stages on the Skagit River as the combined result of high rainfall totals and saturated catchments.
National Weather Service acting western region science chief Matt Jeglum said the worst rainfall was expected to taper around late Thursday and early Friday morning as the main river of moisture shifts. At the same time, he cautioned that additional atmospheric rivers could follow, keeping the region on alert into the coming week. Localized totals varied widely: while Mount Rainier saw about 21 inches (53 cm) at one station, lower-elevation totals and basin responses determined where rivers and towns faced the greatest danger.
Analysis & Implications
This episode illustrates how multiple climate and weather factors can align to produce extreme precipitation. Warmer sea-surface temperatures increase the atmosphere’s moisture capacity, so an AR tapping a warmer Pacific can carry more water than a cooler counterpart. Combined with atmospheric steering patterns such as a persistent high-pressure ridge and a strong Madden–Julian Oscillation phase, that moisture can be funneled into a narrow region repeatedly, increasing flood potential.
Hydrologically, repeated heavy rain on saturated soils shortens the time between peak rainfall and peak river stages, creating flashier and higher floods than isolated storms. Urban drainage systems, levees and floodplain infrastructure that were designed to historical baselines can be quickly overwhelmed by multi-day totals like those observed this week, raising concerns about longer recovery times and greater economic damage.
Climate attribution studies indicate that ARs in the Pacific Northwest have expanded in areal extent by roughly 6%–9% and increased in frequency by a few percent since 1980, and observational analyses show the ocean and air temperatures beneath recent ARs are more often warmer than average. That does not mean each event is driven solely by climate change—short-term tropical cyclones, MJO pulses and regional pressure patterns played clear roles here—but a warmer planet increases the odds of more intense, rain-dominant ARs.
Comparison & Data
| Location/Measure | Reported Total |
|---|---|
| Regional 7‑day rainfall (estimated) | ~5 trillion gallons (19 trillion liters) |
| Mount Rainier station | 21 inches (53 cm) since Thursday |
| Relative examples | Enough to fill Oregon’s Crater Lake or over 18,000 Empire State Buildings (illustrative) |
The table above synthesizes publicly reported gauge-based totals and station observations from the week. While point measurements vary by elevation and exposure, basin-scale aggregations show very large integrated volumes of rainfall; hydrologists use both point and basin-integrated gauges to estimate runoff and peak river flows for flood forecasting.
Reactions & Quotes
“The atmospheric rivers are continually reloading; the three-week rainfall could reach 20 to 30 inches (51 to 76 cm) in places—that’s quite extreme,”
Ryan Maue, private meteorologist (former NOAA chief scientist)
Maue emphasized the repeated nature of the plume and the unusually large integrated totals, warning residents in the hardest-hit areas about safety. His comment reflects real concern among forecasters about compound rainfall impacts on rivers and infrastructure.
“Those numbers are big, but are not unheard of,”
Guillaume Mauger, Washington State Climatologist
Mauger noted that while the totals are exceptional, the Pacific Northwest’s climate and topography make it susceptible to large AR-driven rainfall events, and he pointed to model forecasts showing record flood potential on the Skagit.
“Because it’s so warm, a lot more of that moisture is falling as rain than snow,”
Jeff Masters, meteorologist, Yale Climate Connections
Masters highlighted the role of above-average air temperatures in shifting precipitation from snow to rain, which increases runoff and raises river levels more quickly than if the same moisture fell as snow at higher elevations.
Unconfirmed
- The precise causal chain connecting the Indonesia tropical cyclone flooding to the Pacific Northwest’s ARs involves complex atmospheric teleconnections that remain an active research topic and cannot be definitively proven in a single event-summary.
- Outlook projections that the West Coast pattern will remain active through the week of Christmas depend on model runs that can change; late-model updates could shorten or lengthen the active period.
- Estimates that attribute exact fractions of the event’s intensity to human-caused climate change vary by method; attribution statements reported here reflect broader findings but not a single quantified attribution for this specific episode.
Bottom Line
This multi-day deluge in Washington reflects a convergence of short-term weather drivers and a warmer baseline atmosphere and ocean that can supercharge atmospheric rivers. The immediate priority is emergency response and flood protection as rivers rise and communities face evacuations and infrastructure impacts. Over the medium term, planners and water managers must account for the growing likelihood of heavier, rain-dominant ARs when reassessing floodplain maps, stormwater systems and regional resilience investments.
For residents: stay updated with local emergency management and National Weather Service bulletins, avoid flooded roads and follow official evacuation guidance. For policymakers and technical managers: this episode underscores the need to accelerate adaptation planning that addresses compound and repeated extremes rather than treating such storms as isolated incidents.
Sources
- Associated Press — news report summarizing meteorological analysis and field reporting (journalism)
- National Weather Service — regional forecasts and science leadership (official forecast agency)
- NOAA — climate and oceanographic context (official agency)
- Climate Central — rapid analysis of ocean and air temperature anomalies and human influence (research/analysis)
- Yale Climate Connections — expert commentary on atmospheric river behavior and temperature effects (science communication)