Spectacular sunrises and sunsets -- and perhaps some dirty rain -- are likely to follow the dust from the Mt. St. Helens eruption in Washington State. As the dust drifts around the globe, however, there should be no significant impact on the world's weather.
When the volcano exploded at 8:39 a.m. May 18, it sent dust high into the air. Some of it penetrated the stratosphere. This stratospheric dust, catching the sun rays, should give an unusual luminous quality to sunrises and sunsets as happened after Mt. Agung erupted on Bali in 1963. The effect could last for several months.
More immediately, dust in the lower atmosphere could be brought down by precipitation over parts of the United States. This could yield what may appear to be dirty rain, according to the (US) National Weather Service.
The stratospheric dust also can cut down on incoming sunshine a bit. Some climatologists believe that such action by volcanic dust has caused a cooling of climate in the past, although some other experts doubt that such a link has been proved. However, in this case, there does not appear to be enough dust to cause any significant climatic effect, even if the dust-climate relationship is valid.