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CHAPTER 9. DROUGHT <br />9-5 <br /> <br />Figure 9-4. Palmer Hydrological Drought Index for July 2018 <br /> <br />9.2.3 Frequency <br />Meteorological drought is the result of many causes, including global weather patterns that produce <br />persistent, upper-level high-pressure systems along the West Coast resulting in less precipitation. Scientists <br />do not know how to predict drought more than a month in advance for most locations. Predicting drought <br />depends on the ability to forecast precipitation and temperature. Weather anomalies may last from several <br />months to several decades. How long they last depends on interactions between the atmosphere and the <br />oceans, soil moisture and land surface processes, topography, internal dynamics, and the accumulated <br />influence of weather systems on the global scale. In temperate regions such as Washington, long-range <br />forecasts of drought have limited reliability. Meteorologists do not believe that reliable forecasts are <br />attainable at this time a season or more in advance for temperate regions. <br />Based on Washington’s history with drought from 1895 to 1995, the state as a whole can expect severe or <br />extreme drought at least 5 percent of the time. All of Eastern Washington, except for the Cascade <br />Mountain’s eastern foothills, can expect severe or extreme drought 10 to 15 percent of the time. The east <br />slopes of the Cascades can expect severe or extreme drought from 5 to 10 percent of the time. <br />The Washington State Hazard Mitigation Plan determined that from 1895 to 1995, Kittitas County <br />experienced serious or extreme drought at least 10 to 15 percent of the time. Thus it can be predicted that <br />Kittitas County may experience the effects of drought at least once every decade. This may be changing, <br />however. For the period from 1985 to 1995, Kittitas County experienced the effects of drought at least 30 <br />percent of the time, and during the 1977 drought, the county experienced its effect 30 to 40 percent of the <br />time. There are no data available regarding of how much effect the 2001 drought had on the county.