Glossary#

The acronyms and terms used across these docs, grouped by what they name. Data providers first, because most product names are built from them.

Agencies and data providers#

NOAA#: The U.S. National Oceanic and Atmospheric Administration. Three of its offices publish the climate-mode indices in esd.climate.indices: CPC, NCEI and PSL.
CPC#: NOAA’s Climate Prediction Center, part of the National Weather Service’s National Centers for Environmental Prediction (NCEP). It issues the official ENSO advisories and maintains the operational RONI, ONI, Niño 3.4, AO, NAO and PNA series. https://www.cpc.ncep.noaa.gov
NCEI#: NOAA’s National Centers for Environmental Information, the agency’s data archive. It maintains the ERSST sea-surface-temperature record and the PDO and AMO indices computed from it. https://www.ncei.noaa.gov
PSL#: NOAA’s Physical Sciences Laboratory, a research lab in Boulder, Colorado (formerly the Earth System Research Laboratory’s Physical Sciences Division). It maintains MEI.v2 and a “climate indices correlation page” that republishes many indices in one file format; source="psl" in esd.climate.indices reads those copies. https://psl.noaa.gov
NOHRSC#: The National Weather Service’s National Operational Hydrologic Remote Sensing Center, which produces SNODAS.
NRCS#: The USDA Natural Resources Conservation Service. Its National Water and Climate Center runs SNOTEL, SCAN and the western snow-course program, and serves them through AWDB.
AWDB#: The NRCS Air and Water Database and its REST API, the source for esd.stations products from SNOTEL, SCAN and snow courses.
SNOTEL#: Snow Telemetry, the NRCS network of automated snow stations in the western US and Alaska, most with a snow pillow (SWE), snow depth, precipitation and temperature. Daily records at most sites begin around 1980.
SCAN#: The NRCS Soil Climate Analysis Network, automated soil-moisture and weather stations, some of which measure snow.
CDEC#: The California Data Exchange Center, run by the California Department of Water Resources, which serves California’s snow pillows and snow courses.
DataBC#: The Government of British Columbia’s open-data service, which serves the province’s automated snow weather stations and manual snow surveys.
NVE#: The Norwegian Water Resources and Energy Directorate, whose HydAPI serves Norway’s snow stations (it needs a free API key).
ECMWF#: The European Centre for Medium-Range Weather Forecasts, which produces ERA5.

Climate modes#

ENSO#: The El Niño-Southern Oscillation: the coupled warming (El Niño) and cooling (La Niña) of the tropical Pacific, and the atmospheric response. The largest single source of year-to-year variation in western-US snowpack.
Niño 3.4#: The region of the tropical Pacific (5°N-5°S, 170°W-120°W) whose sea-surface-temperature anomaly defines most ENSO indices.
ONI#: The Oceanic Niño Index: the 3-month running mean of the Niño 3.4 anomaly. CPC’s official ENSO index until February 2026.
RONI#: The Relative Oceanic Niño Index: like the ONI, but with the tropical-mean sea-surface-temperature anomaly subtracted first, so that a warming ocean does not read as a permanent El Niño. CPC’s official ENSO index since February 2026.
MEI.v2#: The Multivariate ENSO Index, version 2, from PSL: ENSO measured from five variables (sea level pressure, sea-surface temperature, surface winds and outgoing longwave radiation) rather than from temperature alone.
PDO#: The Pacific Decadal Oscillation, the leading pattern of North Pacific sea-surface temperature. It changes phase on a scale of decades, unlike ENSO.
AO#: The Arctic Oscillation, the leading pattern of Northern Hemisphere sea-level pressure north of 20°N.
NAO#: The North Atlantic Oscillation, the pressure seesaw between Iceland and the Azores.
PNA#: The Pacific/North American pattern, a wave train of pressure anomalies from the central Pacific over North America; the main route by which ENSO reaches the western US.
AMO#: The Atlantic Multidecadal Oscillation, the multidecadal swing in North Atlantic sea-surface temperature.
ERSST#: NCEI’s Extended Reconstructed Sea Surface Temperature record (version 5 for the PDO and AMO; CPC’s ENSO indices moved to version 6 in 2026).

Snow and hydrology#

SWE#: Snow water equivalent: the depth of water the snowpack would make if it melted. Station SWE comes back in centimetres; every variable carries its units in its units attribute.
April 1 SWE#: SWE on April 1, the traditional index of a western-US winter’s snowpack, close to the date of peak accumulation at many stations.
water year#: The 12 months that hold one snow season, named for the year they end in. In the northern hemisphere water year 2024 runs from 1 October 2023 to 30 September 2024. See esd.processing.wateryear.
SNODAS#: The Snow Data Assimilation System, NOHRSC’s daily 1 km model of SWE and snow depth over the conterminous US.
HUC#: A Hydrologic Unit Code, the USGS identifier for a watershed in the Watershed Boundary Dataset (WBD); more digits mean a smaller basin.

Remote sensing and geospatial#

RTC#: Radiometric terrain correction: SAR backscatter corrected for the brightening and darkening that topography causes, so pixels are comparable across slopes.
HLS#: Harmonized Landsat and Sentinel-2, NASA’s surface reflectance from both missions on one 30 m grid.
DEM#: A digital elevation model.
NLCD#: The USGS National Land Cover Database for the United States.
ERA5#: ECMWF’s fifth-generation global atmospheric reanalysis, hourly from 1940.
RGI#: The Randolph Glacier Inventory, the global inventory of glacier outlines.
GMBA#: The Global Mountain Biodiversity Assessment, whose Mountain Inventory v2 supplies the mountain-range outlines in esd.boundaries.mountains.
AOI#: Area of interest: the first argument of every loader. See Concepts.
STAC#: The SpatioTemporal Asset Catalog specification, which Planetary Computer, Earth Search and NASA’s CMR use to describe imagery; easysnowdata searches it for most image products.
COG#: A Cloud-Optimized GeoTIFF: a GeoTIFF laid out so a reader can fetch only the tiles it needs over HTTP.
Zarr#: A chunked array format for cloud storage, read lazily by xarray.