DATA SOURCE: River Forecast Centers ~5000 stations per day, including ~1500 stations from the Hydrologic Automated Data System, and Climate Anomaly Data Base ~several hundred stations per day

RESOLUTION: 0.5 degree x 0.5 degree

DOMAIN: 20N - 60N; 140W - 60W

FORMAT: The format is sequential 32-bit IEEE floating point created on a big_endian platform (e.g. cray, sun, sgi and hp). The undefined (missing) value is 9999.

WINDOW: Day 1 analysis is valid for the window from 12Z on day 0 to 12Z on day 1; because of report receipt timing, daily minima are available 1 day earlier than the maxima and the means.

ANALYSIS SCHEME: Modified Cressman (1959) scheme (Glahn et al. 1985; Charba et al. 1992). Minimum stations for analysis: 350. If the number of stations is fewer than the minimum, the analysis is not performed for that day.

QUALITY CONTROL: Climatological standard deviation check. If a reported value is more than 4 standard deviations removed from the historical distribution, the value is omitted from the analysis.