The Short-Term Influence of the Mount St. Helens Volcanic Eruption on Surface Temperature in the Northwest United States

Abstract The surface temperature effects of the 18 May 1980 eruption of the Mount St. Helens volcano were examined for the two days immediately following the eruption. The volcanic signal was investigated by examining regional maps of surface temperature, 24 h surface temperature differences and Model Output Statistics (MOS) errors, as well as the detailed temporal evolution of surface temperature and MOS errors at selected stations. The analysis was simplified by the presence of a large anticyclone which dominated the synoptic situation both before and after the eruption. During the daytime hours immediately after the eruption; temperatures in eastern Washington State were up to 8°C colder because of the volcanic plume. That night, because of low-level volcanic dust, temperatures were up to 8°C warmer in Idaho and Montana. These effects, caused by large aerosols in the troposphere, quickly diminished the following day as the volcanic dust cloud dissipated and moved toward the east. This is believed to be...