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Provisional Rainfall Data

Data from rain gages that provide real-time data are relayed to the USGS, Oregon Water Science Center office in Portland through telephone lines, radio telemetry, or the Geostationary Operational Environmental Satellite (GOES) data-collection system. Data are transmitted from each station at intervals of 1 to 8 hours and are loaded onto the USGS computer system.

Real-time data available on the Oregon Water Science Center web pages are provisional data that have not been reviewed or edited. City of Portland and National Weather Service (NWS) data available on the USGS pages have not been verified to be correct and as such are provisional and subject to revision. The data are released on the condition that neither the USGS, the City of Portland, nor the NWS may be held liable for any damages resulting from their use.

These data may contain significant errors and are not citeable until reviewed and approved by the U.S. Geological Survey. For example, precipitation data may have errors due to a malfunction of the sensing or recording equipment. Precipitation data collected at standard rain gages during cold weather can be affected by the accumulation of snow in the funnel of the gage. The snow is not recorded as precipitation until temperatures rise and the snow melts. The timing and volume of snow-affected data are subjected to appreciable errors and should not be used in modeling. Gages noted with heating elements melt snow upon falling in the funnel, giving a more accurately timed water equivalent of the snow amount. Errors in the water-equivalent snow data can still result, and therefore, the data should be used with caution.

Data users are cautioned to consider carefully the provisional nature of the data before basing decisions utilizing the data that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Data are reviewed and corrected periodically to ensure accuracy. All data from the station record are considered provisional until the data are published.

Water Year

A water year is defined as the 12-month period beginning October 1 of any year and continuing through September 30 of the following year. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the water year ending September 30, 2010 is called the 2010 water year.