The "Monthly-Average Streamflow" map upgrades and replaces the "National Water Conditions" map. The new monthly map shows the average streamflow conditions in hydrologic units of the United States and Puerto Rico for the past calendar month. The colors represent monthly average streamflow compared to percentiles of historical streamflow for the calendar month. Thus, the map represents conditions adjusted for this time of the year. Only stations having at least 30 years of record are used. Subregions shaded gray indicate that insufficient data were available to compute a reliable monthly average. During winter months, this situation frequently arises due to ice effects. The data used to produce this map are provisional and have not been reviewed or edited. They may be subject to significant change.