Precipitation Summary and Historical Context

Description:

This program produces a summary of precipitation amounts over a specified interval of months. The size of the interval can be anywhere between 1 and 12 months. For example, if the user is interested in winter precipitation, the starting month could be 12 (December) and the ending month could be 2 (February).

The product produces a listing of the monthly precipitation totals for this range of months. Flags indicate the number of missing days in each month. If there are at least 20 years of historical record, the monthly averages for the period of record are also displayed. The number of missing months in each historical monthly average is indicated by a flag (see Notes).

The second portion of the product is simply the total precipitation for the period of interest and the historical average for the same period. The requested interval and historical interval used for the averages are included in the product header. Again, at least 20 years of historical data are required to produce a historical interval average.

The third section lists the 5 wettest such intervals in the historical record and the 5 driest intervals on record and their years of occurrence. An item in the "Notes" section indicates the number of years that were considered in the rankings. A minimum of 10 years of record is required to complete this section.

The final section gives the probability of receiving certain amounts of precipitation during the interval. These probabilities range from 0.01 (on the average 1 year in 100 will receive this amount of precipitation or less) to 0.99 (on the averge 99 years out of 100 will receive this amount or less). The probabilities are computed by fitting a Pearson Type III distribution to the historical data. Again, an item in the "Notes" section indicates the number of years that were used in constructing the distribution. A minimum of 30 years of data are required to fit the distribution.


Price

The price for this product is $0.50/summary.

Sample

Precipitation Summary and Historical Context

Station: CHARLESTON YEAGER ARPT State: WV ID: 461570
Latitude: 38.38 Longitude: -81.59 Elevation: 1016 feet
Station period of record: 8/1/1948-10/12/2000

Requested Interval:
01/01/1999- 08/01/1999  
Historical Interval:
08/01/1948- 10/12/2000  
Product Creation Date:
10/13/2000 14:46 EDT

Monthly Precipitation Totals (inches)
Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1999 4.81 2.67 3.70 2.20 1.90 1.30 5.37 2.97 - - - -
Ave 3.42a 3.24a 3.99a 3.33a 3.97a 3.73a 5.03a 3.96 - - - -

Interval Sum: 24.92 inches
Interval Average:   30.67 inches

Interval Precipitation Rankings (08/01/1948- 10/12/2000)
Rank High Beginning Year Low Beginning Year
1 44.46 1958 18.39 1988
2 42.12 1950 21.39 1966
3 41.90 1989 23.77 1964
4 41.81 1994 23.93 1970
5 39.68 1961 24.19 1963

Pearson Type III Frequency Analysis (08/01/1948- 10/12/2000)
Frequency 0.01 0.05 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.95 0.99
Amount 19.06 21.86 23.50 25.64 27.29 28.77 30.21 31.72 33.39 35.44 38.45 41.08 46.37

Notes:
  1. Precipitation values are given in inches.
  2. Missing days in monthly sums: a=1, b=2, c=3, etc.
  3. Missing months in period of record averages: a=1, b=2, c=3, etc.
  4. Historical averages calculated from daily data.
  5. Ranking analysis based on 52 of 53 data intervals.
  6. Frequency analysis based on 52 of 53 data intervals.

For additional assistance, you can contact the HPRCC.