Understanding Precipitation Data
This guide provides a simplified overview of how precipitation data is gathered and processed to inform the public about weather trends and patterns across the United States.
To explore detailed precipitation data and analysis, visit the official National Weather Service's Precipitation Analysis website.
Recent Rainfall Precipitation
The "Recent Rainfall Totals" precipitation data is a compilation of information from the National Weather Service's operations at 12 River Forecast Centers. These centers create gridded precipitation fields with a 4x4 km spatial resolution. Data is collected over a 24-hour period, ending at 1200 UTC, which corresponds with the "hydrologic day" used in river modeling and coincides with most cooperative observers' reporting times.
Average Precipitation
"Average Historical Rainfall" precipitation data represents long-term averages derived from the PRISM climate data sets. Data avergaes are from the periods 1981-2010. This information is critical for establishing a baseline to compare current precipitation against historical averages, providing insight into trends and anomalies in rainfall patterns.
Derived Precipitation Products
Derived products, such as "Rainfall Variation Totals" offer a straightforward way to visualize how current precipitation measures up against historical averages. Showing if the area is above or below normal rainfall amounts in inches
If "Data not available"
If the data is not available, it could be due to a variety of reasons, including the area not being covered by the National Weather Service, especially outside of the United States, or the river forecast center not having submitted their data for that area. If the river forecast centers have not submitted their data, you can return and check at a later date to see if it has been submitted.
Observation Methods
Multisensor techniques are employed to gather "Observed" data, utilizing inputs from radar, ground gauges, and satellite observations. This approach provides a more accurate estimation of precipitation then a single sensor approach, although it's important to note that there can be discrepancies due to factors like radar calibration, gauge siting, geography (mountains, etc.) and the nature of precipitation itself.
Note: The data provided here and on the National Weather Service's website is for informational purposes and should not be used as the sole resource for decision-making in critical situations. Always consult with local weather service advisories for the most current and accurate information.
For more in-depth information on the methodologies, data quality, and applications of this precipitation data, please refer to the additional resources available on the NWS Precipitation Analysis website.