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ESTIMATED PRECIPITATION AND LIGHTNING MAP
Observation Methods
East of the Continental Divide, RFCs derive the "Observed" precipitation field using a multisensor approach. Hourly precipitation estimates from WSR-88D NEXRAD are compared to ground rainfall gauge reports, and a bias (correction factor) is calculated and applied to the radar field. The radar and gauge fields are combined into a "multisensor field", which is quality controlled on an hourly basis. In areas where there is limited or no radar coverage, satellite precipitation estimates (SPE) can be incorporated into this multisensor field. The SPE can also be biased against rain gauge reports.
The following links provide additional information about the programs
used to derive these multisensor fields:
In mountainous areas west of the Continental Divide, a different method is used to derive the "Observed" data. Gauge reports are plotted against long term climatologic precipitation (PRISM data), and derived amounts are interpolated between gauge locations. The following link provides more information about the process and program used to derive observed precipitation for the western U.S.
Quality of Data
"Observed" data, and by extension the derived data, is vulnerable to inaccuracies that can be caused by either radar or precipitation gages. For radar, problems would include freezing or frozen precipitation, low topped convection, bright banding, the reflectivity/rainfall relationship in use, calibration of the radar, radar location and elevation, range degradation, and the radar's effective coverage. For precipitation gages, problems come from freezing precipitation, windy conditions, gage siting, undermeasurement by tipping bucket gages in high intensity rainfall, and gage maintenance.
Production / Update Times
The precipitation analysis pages are routinely update three times per day, at approximately 9:30am, 12:30pm and 4:30pm Eastern Standard Time. Data for the western U.S. are usually available by the second update. The data for the first two updates are preliminary and subject to change. While the data in the final update are much less likely to change, they are neither official nor certified. Please contact the National Climatic Data Center for certified past weather information.