Shading on this map identifies regions where there has been below-normal or above-normal precipitation during the previous 3 months AND where the IRI seasonal precipitation forecast for the next 3 months indicates an enhanced likelihood of a reversal of these precipitation conditions.
NCEP gridded monthly precipitation data for a 30-year period are used as the observational data reference, and CAMS-OPI monthly gridded precipitation is used for the observations for the past 3 months. Observed precipitation over the past 3 months at each grid point is ranked on a scale from 0 to 1, with 0 as the driest event for the same 3-month period of the year as compared to the 30-year observational reference period, and 1 as the wettest event. A value of 0.333 and less is considered dry (below normal), and a value of 0.667 and greater is considered wet (above normal). Secondly, the forecast for the next 3-month season is examined for the same location. A forecast with a 40% or greater probability for the below-normal category is considered an "enhanced" likelihood of dry forecast, and a forecast of 40% or greater for the above-normal category is considered an "enhanced" likelihood of wet forecast.
Based upon the observed and forecast precipitation, green areas on the map indicate where precipitation for the past 3 months has been below normal AND where the IRI seasonal forecast for the next 3 months indicates an enhanced probability of above-normal precipitation. Yellow areas on the map indicate where precipitation for the past 3 months has been above normal AND where the IRI seasonal forecast for the next 3 months indicates an enhanced probability of below-normal precipitation.
The date shown on the map is the calendar month in which the forecast was issued. The 3-month period of observed precipitation ends in the calendar month before the month in which the forecast was issued. The three-month seasonal forecast period begins in the calendar month after the month in which the forecast was issued.
Contact help@iri.columbia.edu with any technical questions or problems with this Map Room.