Global Drought Prediction Tool: NMME Multi-Model Ensemble SPI Forecast

This tool displays maps of probabilistic forecasts of the Standardized Precipitation Index (SPI, for 3, 6, 9, or 12-month accumulation periods) for the globe based on monthly precipitation predictions from 6 NMME models and the initial observed condition. For locations and seasons where NMME does not show demonstrable skill, the SPI forecasts are based on a persistence methodology.

The forecast Start Time denotes the end of the latest full month of observations available to make the forecast. use the Map Type menu to display either the forecast Probability of a user-selected SPI Threshold value or the SPI Value associated with a user-specified Probability of Non-Exceedance. Users can also select a desired Lead Time for the forecast.

The "Probability" map shows the probability (on a fractional scale between 0 and 1) that the SPI in a future month will have a value equal to or less than the SPI value chosen in the "SPI Threshold" drop-down menu. Alternatively, the "SPI Value" map shows the SPI value in a future month that is forecast not to be exceeded at the probability level chosen from the "Probability of Non-Exceedance" drop-down menu. The color shown next to the "SPI Threshold" or "Probability of Non-Exceedance" drop-down menu is the same as the color legend below the forecast maps generated. Click and drag on any of the forecast maps to zoom in to a specific region of interest. To select which administrative boundaries to display on the map, mouse over the map and select the "Layers" icon. Then use the check boxes that appear above the map to select the corresponding administrative boundaries.

The color scale used in the SPI forecast maps is the same as in the U.S. Drought Monitor, with negative values corresponding to the percentiles associated with the D0 (30%tile) to D4 (2%tile) drought intensity categories.


Lyon, B., M. A. Bell, M. K. Tippett, A. Kumar, M. P. Hoerling, X. Quan, H. Wang, 2012: Baseline probabilities for the seasonal prediction of meteorological drought. J. Appl. Meteor. Climatol., 51, 1222-1237. doi:

Quan, X. W., M. P. Hoerling, B. Lyon, A. Kumar, M. A. Bell, M. K. Tippett, H. Wang, 2012: Prospects for dynamical prediction of meteorological drought. J. Appl. Meteor. Climatol., 51, 1238-1252. doi:

Dataset Documentation

Model Forecast Data: The NMME multi-model ensemble forecast precipitation used in this analysis includes data from the following subset of models:

Observational Data: CPC GOB Combined Retrospective and Real-Time Blended Daily Precipitation Data Accumulated to Monthly and Regridded to 1.0 deg. lat/lon, U. S. Climate Prediction Center (U. S. Climate Prediction Center GOB Daily Blended Precipitation)



Contact with any questions about or problems with this Map Room.