Updates to Precipitation and Sample Data

Precipitation Data Adjustments

In the past year, NADP has been making updates to how the electronic precipitation gauges are configured. Previously, almost all gauges were set to report precipitation data using Greenwich Mean Time (GMT). NADP, via Environmental Engineering and Measurement Services, Inc. (EEMS), is resetting these electronic gauge clocks to report precipitation data using the local standard time (LST) for each specific site.

During these efforts, NADP has discovered multiple sites where the precipitation gauge clock was using LST, but NADP was unaware of this. In these cases, the precipitation data is offset between 4 to 10 hours from the actual precipitation events. When this is discovered, NADP makes adjustments to the precipitation records so the data is aligned correctly.

In conjunction with the adjustments to the precipitation data, NADP also updates the specific NTN and MDN samples, as well as any published aggregate data, that is associated with the precipitation adjustments. These sample updates are documented in the Change Log for either network, using phrases like “…incorrect precip datalogger time offset” or, “Updated precipitation values from time offset error”.

Other Precipitation Adjustments

Occasionally, a site will not provide precipitation data that correspond to specific samples. In those cases, the NADP will try to use the sample volume as an estimate for the precipitation. If electronic gauge precipitation data is later found and sent to NADP, we may update sample data, and their published aggregate data, to include the newly received gauge data. In those cases, the Change Log may reflect a reference to new egauge data, or may have a note in the values fields of “based on svol est” and “based on act ppt”.

In most cases, these do not affect the validity of the sample. In the cases where the validity is affected, we have tried to note this.