Retirement Notice: This item is in mature support as of November 2024 and will be retired in December 2026. A new version of this item is available for your use. Esri recommends updating your maps and apps to use the new version.The National Water Model (NWM) is a new product from the National Weather Service that forecasts streamflow volume and velocity over the entire continental United States. It is a hydrologic model that predicts the flow in every river reach of the National Hydrography Dataset, mathematically modeling physical processes like snowmelt, infiltration and the movement of water through soil layers in order to determine how much of the NWS precipitation forecast becomes runoff, then routing that runoff through the river network. This is the short term forecast, which is run every hour, predicting streamflow over the next eighteen hours at one hour intervals. Rivers are symbolized according to how the streamflow differs from the monthly normal.What Can You Do With This Layer?This map service is designed for fast data visualization. Identify features by clicking on the map to reveal the pre-configured pop-ups. View forecast  data sequentially using the time slider, which is set to one hour intervals by default, by Enabling Time Animation. This layer type is not recommended for use in analysis. RevisionsSep 23, 2020: Updated 'qout' field values for Water Bodies. Null values are now being replaced with '-9999' in order to correct an identify issue at small scales. Also updated Pop-Up to reflect that the 'qout' value is Not Available (N/A).Nov 18, 2021: Updated Feature set to v2.1 of the NWM data. Added 'qnormal' field to provide expected monthly flow for given forecast.