HOMS COMPONENT

MEAN AREAL PRECIPITATION (NWSRFS-MAP)

1.   Purpose and objectives

     The program contains techniques and procedures for computing basin-wide estimates of mean areal precipitation from time series of observed hourly and daily point precipitation data.

2.   Description

     The program is designed to prepare times series of mean areal precipitation for input to the NWS River Forecast System lumped rainfall- runoff models, such as the Sacramento Soil Moisture Accounting model (NWSRFS-SAC-SMA). Included are methods for estimating missing precipitation 
amounts, distributing estimated or accumulated precipitation into hourly amounts, adjusting precipitation data for orographic and/or other effects, and creating synthetic (dummy) hourly or daily stations for which all data are estimated.

     Options are included to compute grid point or Thiessen weights for each station, or input predetermined station weights; compute MAP in a 1, 3, or 6 hour interval; input a maximum of 9 changes in observation time for each daily station; input a maximum of 10 precipitation correction factors for each station; make consistency plots of a station's precipitation data without computing or printing MAP; and make consistency plots of a station's precipitation data without including that station in the group base.

3.   Input

     ASCII files of time series of daily and hourly observed precipitation are required in a specific format: OH Datacard Format.

4.   Output

     ASCII time series of mean areal precipitation values are printed or written to a disk file. Consistency plots of station input data and a MAP summary are printed.

5.   Operational requirements and restrictions

     a) One person with knowledge and experience in analysing precipitation
        data and familiarity with computers and software can run the program.

     b) One day of training is required.

     c) The program was written in FORTRAN 77 for use on an HP workstations.
        It runs in 615 kbytes. Note: The MAP program creates a very large
        scratch work file, depending on the number of stations and period
        of analysis. 

     d) Input file sizes are not restricted.

     e) Program limitations: at least one time series of hourly data is
        needed.

6.   Form of presentation

     Program available as part of the National Weather Service River Forecast System (NWSRFS); documentation is included. 

7.   Operational experience

     Has been used extensively in the USA with good results.

8.   Technical support

     Dr. Michael Smith
     National Weather Service
     Hydrologic Research Lab

9.   Availability

     From the HOMS National Reference Centre for USA.

10.  Conditions on use

     Free.

Last updated: 01 DEC 99)
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