Glossary

Short definitions for terms this site actually uses. They are for reading the gauges and the Story chapters, not a water-law textbook. Links from first use on Story, Trends, and the notes under live numbers come here.

Acre-foot: A volume of water: one acre of land covered one foot deep, about 326,000 gallons. Reservoirs and water rights on this page are often counted in acre-feet, not gallons.
AFY (acre-feet per year): How much water a use takes over a year, measured in acre-feet. It is an annual rate, not the water sitting in a reservoir right now.
ARkStorm: A USGS research scenario for a month-long sequence of atmospheric rivers, on the scale of California's 1861-62 floods. DRI later downscaled it to this Sierra Front. It is a standing worst-case study, not a forecast for this winter.
ASR (aquifer storage and recovery): Treated river water is injected into wells when demand is low, held in the aquifer, and pumped back later. TMWA has run a version of this since 1993. It is a bank, not a new water right.
Atmospheric river: A long, narrow plume of water vapor in the atmosphere that can drop heavy rain or snow when it hits the Sierra. ARkStorm is a research picture of many of these in a row.
cfs (cubic feet per second): How much water passes a river gauge each second. One cfs is about 7.5 gallons moving by every second, roughly a large cooler's worth.
Closed basin: A watershed whose water does not reach the ocean. Precipitation here evaporates, sinks underground, or collects in lakes such as Pyramid. The hydrographic Great Basin is closed in that sense.
CPC (Climate Prediction Center): A NOAA office that issues monthly ENSO discussions. This site's El Niño dates follow CPC's bulletin, not a live gauge.
CNRFC: The California-Nevada River Forecast Center. It publishes the official Truckee ensembles and stage guidance this site links out to, including Farad (FARC1).
Cui-ui: An endangered sucker that lives only in Pyramid Lake. Adults wait at the mouth each spring for enough Truckee flow to spawn.
Derby Dam / Newlands Project: Reclamation's diversion on the lower Truckee that sends water toward Lahontan Reservoir and the Newlands irrigation project. It is downstream of Reno, not a Tahoe outlet.
U.S. Drought Monitor: A weekly map of drought categories from D0 (abnormally dry) through D4 (exceptional drought). This site shows the worst category among Reno, Tahoe, and Pyramid Lake for that week, not a live soil probe.
El Niño / ENSO: A warming of the equatorial Pacific that can shift winter storm tracks. ENSO is the whole El Niño Southern Oscillation cycle. A strong ocean forecast is not, by itself, a Tahoe snow forecast.
Ensemble: A fan of many model traces, not one official number. Width on CNRFC's Farad plot is their spread. This site does not redraw that fan.
FNU: Formazin nephelometric units, a live measure of how cloudy the river is at a USGS turbidity meter. It is not the same lab method as NTU in a drinking-water report.
HAB (harmful algal bloom): A posted swim risk in a lake or lagoon, usually from cyanobacteria. On this site HAB lines are recreational notices, not a claim about Reno and Sparks tap water.
IRI: The International Research Institute for Climate and Society at Columbia. Its ENSO forecast is cited next to CPC on the outlook, as a second ocean bulletin, not a local snow number.
Natural rim: Lake Tahoe's outlet elevation, 6,223 feet. Only above that line can the lake feed the Truckee through the dam at Tahoe City. The legal ceiling is higher, 6,229.1 feet.
NIFC: The National Interagency Fire Center. This site's fire perimeters come from NIFC's WFIGS current-interagency layer, not from a local dispatcher radio.
NWPS: NOAA's National Water Prediction Service. The Truckee-at-Reno flow forecast on Story is an NWPS point forecast, a single expected number, not a range.
OCAP: Operating Criteria and Procedures for the Newlands Project, in federal regulation (43 CFR part 418). They govern how diverted Truckee water is supposed to be used, not TMWA's tap plants.
Orr Ditch Decree: The 1944 federal decree that still governs Truckee River water rights. No new rights on this river have been created since. What changes is who holds a right, and what it is used for.
Percent of typical: Snowpack here is compared with the historical median for that calendar date at the same pillows, not with a single "normal" year. A median is the middle of the record, not the average of extremes.
Public Law 101-618: The 1990 Truckee-Carson-Pyramid Lake Water Rights Settlement Act. It is the federal statute behind later operating rules, including TROA. This site states that history; it does not argue the settlement's fairness.
Point forecast: A single expected number from the River Forecast Center, such as a peak flow in cfs. It is not an ensemble range. Trace spread for this river is on CNRFC's Farad plot.
SNOTEL: NRCS snow telemetry stations: automated pillows that weigh the snowpack. The six Story stations sit on ridges that melt into Tahoe and the Truckee.
SWE (snow water equivalent): The depth of water you would get if that snow melted. SNOTEL reports it in inches. Percent of typical on this site is SWE versus that date's median, not snow depth in inches of fluff.
TMWA: The Truckee Meadows Water Authority, the municipal supplier for Reno and Sparks. It treats Truckee River water and runs wells. Storey County's industrial park is on a different district, TRIGID.
TROA: The Truckee River Operating Agreement. It was signed in 2008 and took effect in 2015. It is how reservoirs and the Tahoe outlet are operated among the parties, not a live gauge reading.
USGS: The U.S. Geological Survey. River flow, lake stage, and the quake catalog on this site come from USGS feeds. Those readings are provisional until USGS reviews them.
Water year: October 1 through September 30, labeled by the calendar year of that September. Trends charts follow this year, not January–December.