U.S. Climate Divisons Drought Prediction Tool: SPI Multi-Model Ensemble Forecast

This tool displays maps of probabilistic forecasts of drought in U.S. Climate Divisions using a forecast of the Standardized Precipitation Index (SPI; 3, 6, 9, or 12-month accumulation periods) in future months based upon forecast precipitation from the IRI Multi-Model Ensemble and the SPI Persistence methods. These maps provide quantifiable, probabilistic drought predictions for the United States over the next few months.

Here, forecasts of SPI are based upon precipitation from the IRI Multi-Model Ensemble where the hindcast correlation skill exceeds the correlation skill of the SPI Persistence method. For starting months, leads, and locations where the correlation skill of the IRI Multi-Model Ensemble is lower than that associated with the SPI Persistence method, the SPI Persistence forecast is used. The forecast start time shown denotes the end of the last available month of observations (e.g., Sep), or, essentially, 00Z on the first day of the following month (e.g., 00Z 01 Oct), which is the issue time of the IRI Multi-Model Ensemble Forecast.

Use the "Map Type" menu to choose a map of forecast probabilities or SPI. The "Probability" map shows the probability (on a fractional scale between 0 and 1) that 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 for the marginal probability chosen from the "Probability of Non-Exceedance" drop-down menu. Other menus select the SPI accumulation period (3, 6, 9, or 12-month SPI) and forecast lead time (in months) of interest. Click and drag on the map to zoom in. To select which administrative boundaries to display on the map (including U.S. counties), 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 SPI maps provide an indication of short-term to longer-term wet (green, positive SPI) or dry (yellow to red, negative SPI) conditions based upon precipitation alone. The negative half of the color scale uses the same colors and thresholds of SPI corresponding to the percentiles associated with the D0 (30%tile) to D4 (2%tile) drought intensity categories used in the U. S. Drought Monitor.


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: http://dx.doi.org/10.1175/JAMC-D-11-0132.1

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: http://dx.doi.org/10.1175/JAMC-D-11-0194.1

Dataset Documentation

Model Forecast Data: IRI Multi-Model Ensemble Forecast
Observational Data: Monthly precipitation totals from U.S. nClimDiv Version 1 climate divisions, U. S. National Climatic Data Center (U. S. nClimDiv Version 1 Climate Divisions monthly data)



Contact help@iri.columbia.edu with any questions about or problems with this Map Room.