This experimental, station-based drought tracker uses near-real time data from several precipitation monitoring networks to estimate a drought index value at each location at several different timescales. Total precipitation for the past 30, 90, 180, and 365 days is summed up at each station with less than 10% missing observations and compared to a distribution of historical estimates at that location derived from a long-term gridded precipitation dataset (PRISM, 1895-2020). A drought index called the Standardized Precipitation Index or SPI (more info here) is calculated for the current observation in relation to the distribution of historical estimates. SPI values are simply standard deviation units so values close to 0 are near-average while negative values indicate dry conditions and positive ones wet.
Each tab contains a map representing precipitation information summarized over different timescales ranging from the last 30 days to as long as 365 days. Each map displays precipitation observations from the Rainlog.org network, the NOAA Global Historical Climate Network (NOAA-GHCN), and numerous other meteorological mesonets available through the SynopticData API. The NOAA-GHCN includes data from several other networks including NOAA Cooperative Observers, WBAN/ASOS at airport, SNOTEL sites, and the CoCoRAHS volunteer observer network. The SynopticData API pulls data together from numerous other networks including county-level flood control gauges, the Citizen Weather Observer Program, and Remote Automated Weather Stations. Use caution when interpreting observations from the Synoptic networks. Many of these observations come from automated stations with limited error checking. The Rainlog, NOAA-GHCN, and MesoWest sites can be toggled on or off by using the checkboxes at the upper right hand corner of the map. The latest U.S. Drought Monitor (USDM) map also is plotted on each map and is updated each Thursday. A reference grid that matches the PRISM Climate dataset which is used for the historical estimates at each location can also be toggled on using the map controls in the upper right hand corner.
|Observed Precip||Total precipitation observed at station over select time period (inches)|
|PRISM Avg||Estimated long-term average (1895-2020) precipitation for location from gridded PRISM dataset (inches)|
|Diff from Avg||Observed minus long-term average (1895-2020) precipitation (inches)|
|SPI||Observed precipitation expressed as Standardized Precipitation Index value|
|% rank||Observed precipitation expressed as percentile rank value with 100% being wettest value on record (1895-2020)|
|Max 1-day Precip||Maximum daily precipitation amount observed during select time period (inches)|
|Days missing||Number of missing days during select time period|
|Gauge||Gauge name or number|
|Network||Name of gauge’s network|