Since Jan. 31, NOAA satellites have been closely monitoring a series of strong atmospheric rivers bringing heavy rain and mountain snow from central California to the Pacific Northwest, the Sierra, southern Cascades, and northern Rocky mountains.
Atmospheric rivers are long, narrow bands of concentrated water vapor that transport moisture from warm tropical oceans to higher latitudes. In these regions, heat from the sun causes large amounts of water to evaporate into the atmosphere. When this humid air meets the mountains along the West Coast, the winds blow uphill, and the air cools, condenses, and precipitates, forming a torrent of rain and wind.
These systems vary in size and strength, but on average, they carry as much water vapor as the Mississippi River discharges at its mouth—and some can even transport up to 15 times that amount. When they make landfall, they unleash heavy rain or snow, accounting for roughly 30 to 50 percent of annual precipitation in the West Coast states.
NOAA and its partners utilize advanced satellite observations to study atmospheric rivers. Satellite data, combined with land-based observations, helps refine forecast models, improving predictions of atmospheric river intensity and duration to support water resource management and public safety.
Geostationary satellites, such as NOAA’s GOES East (GOES-16) and GOES West (GOES-18), provide continuous monitoring of atmospheric rivers, capturing their structure and movement in near real-time. The Advanced Baseline Imager (ABI), onboard these satellites measures water vapor in the atmosphere. The “mid-level troposphere” water vapor channel is particularly useful for observing air mass interactions and jet streaks (localized areas of very fast winds within the jet stream). In addition to valuable information about atmospheric moisture, GOES satellites also provide critical data about the movement of clouds and water vapor patterns that help to forecast heavy rain and flash flooding events.
Additionally, NOAA’s Joint Polar Satellite System (JPSS) satellites—including the NOAA/NASA Suomi NPP, NOAA-20, and NOAA-21—provide critical high-resolution atmospheric data that enhance weather models. These satellites use microwave sensors to measure the total amount of water vapor in the atmosphere, known as Total Precipitable Water (TPW). This information is crucial for tracking the movement of moisture and predicting rainfall, supporting more accurate weather forecasts.
When an atmospheric river makes landfall, satellite observations are supplemented by additional data sources to provide a more complete assessment of their impacts. NOAA has developed atmospheric river observatories, which use ground-based instruments to measure key atmospheric variables like water vapor, snow levels, and wind profiles. When combined with satellite imagery, these observations help forecasters establish thresholds for landfalling atmospheric rivers and monitor evolving conditions.
Enhanced satellite-derived datasets also support NOAA’s National Weather Service in issuing early warnings for heavy rainfall and potential flooding, often five to seven days in advance. These forecasts provide critical information for emergency managers, reservoir operators, and other decision-makers responsible for water resource planning. Additionally, NOAA’s Modeling, Analysis, Predictions, and Projections (MAPP) and Climate Variability and Predictability (CVP) Programs support research to improve long-term forecasting of atmospheric rivers, extending prediction capabilities from weeks to months.
Beyond satellite and ground-based observations, reconnaissance aircraft missions further enhance atmospheric river observations and predictions. These missions deploy dropsondes—small instruments that gather real-time atmospheric measurements— which are then integrated into global weather prediction systems.
A dropsonde is released from a NOAA Gulfstream IV-SP jet. [Credit: NOAA’s Office of Marine and Aviation Operations]
NOAA satellites play a pivotal role in monitoring atmospheric rivers and assessing potential long-term shifts in their behavior. By combining satellite data with Earth-based measurements, NOAA provides critical insights to help communities prepare for future changes in water availability and extreme weather events.