Several climate indicators are used to monitor drought in the United States. These indicators include:

• the Palmer Z Index, Palmer Drought Severity Index, and Palmer Hydrological Drought Index

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• the one-month, two-month, three-month, six-month, nine-month, 12-month, and 24-month Standardized Precipitation Index

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• maps showing the percent of normal precipitation for airport stations for the current month, last three months, and year-to-date

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• the statewide precipitation ranks for current month (short-term) and 3-months, 6-months, and 12 months (longer-term)

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• the percent of normal precipitation maps, based on Cooperative Network and other station reports, provided by the NOAA Regional Climate Centers (HPRCC)

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• the short-term surface wetness anomaly map computed by the National Climatic Data Center from the Special Sensor Microwave Imager (SSMI), a polar orbiting satellite with global coverage. During the cold season, the presence of snow cover complicates the SSMI analyses. SSMI-based temperature anomalies cannot be computed over a snow-covered area. Above-normal precipitation that falls largely as snow may be reflected as above-normal snow cover but below-normal liquid wetness. Snow-covered areas that are warmer and drier than normal may show below-normal snow cover but above-normal liquid wetness as the snow melts more than normal.

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• modeled runoff, evaporation, and soil moisture conditions as calculated by the National Weather Service

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• modeled soil moisture conditions in the top and deeper soil layers as calculated by the Midwest Regional Climate Center

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• the percent of average precipitation map for the water year to date for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center

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• the percent of average snow water content map for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center

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• the January 1 mountain snow course snowpack observations made by the USDA Natural Resources Conservation Service

• the USGS December daily streamflow and monthly mean streamflow maps