There are 4 selectable options that help you pinpoint the Water Year data you need:
After the selections have been made, the table shows the station name, precipitation totals by month, the annual total of these months, the 30-year normal (see Normal below for an explanation), the percentage of the annual sum of the 30-year normal, and the number of years included in the normal calculation following the 3/5 Rule. A definition of the 3/5 Rule is contained in the second paragraph of the Months section below.
For each station for a selected state or country, the Water Years table provides monthly totals for the selected year and month period. COOP measures precipitation in inches and GHCN records precipitation in millimeters.
Stations with a month with an “M” indicate that the month fell short of the requirements of the 3/5 Rule. As defined by the World Meteorological Organization (WMO), the month is to be marked as missing if there were more than 3 consecutive days or more than 5 days total in the month that had missing precipitation amounts. If all months have missing values based on this rule for a given Water Year, the Water Year record for the station will not be included in the table. If the annual total precipitation has an asterisk next to it, this symbolizes a partial total. This asterisk indicates that there was at least one month that was not missing and at least one month was marked as missing.
Stations with a month marked with a “T” show that a least one daily, immeasurable precipitation amount and no other recordable amounts occurred within the month. If only monthly trace amounts were recorded for months in a given Water Year including months with zero precipitation, a “T” is marked in the annual total.
The Normal is a 30-year average which is used as an average basis for the annual precipitation totals for the Water Years in the decade following it. For example, the 2005-2006 Water Year would use the 1971-2000 Normal and 1969-1970 would refer to the 1931-1960 Normal. Each Normal column heading in the table includes the 30-year Normal period for selected Water Year.
The percentage of normal (% of norm) column shows the percentage of the Water Year total divided by the 30-year Normal. This number is multiplied by 100 and given as a full percent in the table.
The 30-year Normal is calculated using the 3/5 Rule (see the Month section above, second paragraph, for a definition of the 3/5 Rule). The Good Years of Normal column in the table indicates the years within the 30-year Normal period that kept in line with the 3/5 Rule. Each 30-year normal for each station in the table has a superscript that rates the amount of years that were not missing and included in the calculation of the 30-year Normal. The amount of years included in the Normal calculation are represented by the superscript as follows: