Weather Wizard – A Method to Refine Weather Data for Your Location

Chapter 10-Economics and Application, No. 6, Winter 1988

Don Wysocki

Few growers have long-term weather records for their farms or for land that they rent. Occasionally some farms have precipitation records that date back several decades or more, but these cases are rare. It is even more rare for individual farms to have records of daily temperature. Most growers probably keep some record of crop year precipitation but these are not cataloged to produce any long-term record.

Keeping long-term records is tedious and requires a commitment for many years. Some growers have not been established for that long or may not have the time to devote to such record keeping. However, long-term records may be beneficial in making management decisions. Weather records can be used to supplement your experience and other information when making management decisions such as: (1) seeding dates, (2) seeding rates, (3) fertilizer rates, (4) top dressing rates and dates and (5) fallow vs. recropping or single fallow vs. double fallow. You can obtain records from nearby weather stations, but these may not necessarily fit the conditions for your location, and these records can be cumbersome to use,

To fine tune weather records at a particular location, John Zuzel, hydrologist with the USDA-ARS at the Columbia Plateau Conservation Research Center near Pendleton, is developing a computer software package that can generate weather records for locations in northeastern Oregon.

Weather Wizard

The software package, which has been tentatively entitled “Weather Wizard,” uses weather information from 30-year records at 18 weather stations in Baker, Gilliam, Grant, Morrow, Sherman, Umatilla, Union, Wasco and Wheeler counties in Oregon and Walla Walla County in Washington (Table 1). The software will produce average weather data for any of the 18 weather stations. In addition the program will generate average data for any location that lies within the perimeter defined by the 18 stations. For locations other than weather stations, the program generates a record by interpolating information from the three nearest stations. The interpolation is weighted by proximity of the location to the respective weather stations. Thus, closer stations are given greater emphasis. Locations are entered into the program by speci~ing their latitude and longitude. These can be obtained from state highway maps, USGS topographic maps or other sources.

Table 1. Weather station locations used in ''Weather Wizard" software.

Weather Data

The program determines the average precipitation, air temperature and growing degree days for any period of time from 2 weeks to 1 year. For example, with a time window of September 1 to August 31, the following data were obtained for Helix, OR:

• Average rainfall = 14.08 inches
• Average temperature = 52 ‘F
• Degree day > 32 ^oF = 7,278
• (degree days are a measure of accumulated heat)

Secondly, the program generates, for the time specified, 10 traces or weather scenarios for the location given. Table 2 shows traces that were generated for Helix, OR. The 10 traces represent a distribution of possible weather scenarios around the average. Thus, a user can evaluate a situation for below average, average and above average conditions.

Table 2. Ten traces generated for Helix, OR, time window = 9/1 to 8/31.

Any or all of these traces can be evaluated. After selecting the trace or weather scenario desired, the program will generate daily information on: (1) precipitation, (2) maximum and minimum air temperature and (3) solar radiation (Table 3). Daily weather data given by the program are not forecasts, but rather statistically average representations of past weather events. In other words, given past information about the weather, the daily values are a likely way the trace might take place.

Table 3. Partial print out of daily values for Helix, OR, time window = 911 to 8131.