## Glossary of Terms and Acronyms

AHPS
  Advanced Hydrologic Prediction Services

Bias
  An error (difference between forecast and actual) that favors a particular tendency

CFSv2
  Climate Forecast System version 2

CHPS
  Community Hydrologic Prediction System

Ensemble forecast
  a set of single-valued forecast for the same location and times

Ensemble member
  one of the single-valued forecasts in an ensemble

Ensemble spread
  a measure of the average deviation between the individual ensemble members and the ensemble mean

EnsPost
  Ensemble Post Processor (a function of the HEFS)

Exceedance probability
  the probability of exceeding a given threshold; for example, a 0.25 exceedance probability implies that the threshold is (predicted to be) exceeded on 25% of occasions

EVS
  Ensemble Verification System (a function of the HEFS)

GEFS
  Global Ensemble Forecast System

HEFS
  Hydrologic Ensemble Forecast Service

MEFP
  Meteorological Ensemble Forecast Processor (a function of the HEFS)

NOAA
  National Oceanic and Atmospheric Administration

NWS
  National Weather Service (part of NOAA)

QPF
  Quantitative Precipitation Forecast (part of NOAA

RFC
  River Forecast Center

Single-valued forecast
  A forecast with only one value for a given time and location

Uncertainty
  In general terms, a lack of confidence about the "true" state of some environmental system (e.g. river stage at time X and location Y). This may be represented with a set of possible outcomes (possible "true" states) and their associated probabilities (as in the HEFS).

WPC
  Weather Prediction Center (part of NOAA)