The USGS provides forecasts of expected ash dispersion (ash clouds) and deposition (ash fall) from volcanic eruptions using Ash3D. It is a three-dimensional simulation of volcanic-ash dispersion that uses time-varying wind fields and other meteorological properties to calculate where airborne ash is transported under current or historical atmospheric conditions. It was developed by USGS scientists specifically to forcast the location of volcanic plumes to provide situational awareness to the aviation industry.
USGS Volcano Observatories run Ash3D for any US volcano at elevated alert level (excepting effusive Hawaiian volcanoes) assuming a reasonable hypothetical eruption. Should an eruption occur, the responsible volcano observatory updates the forecast with actual observations (eruption start time and duration, plume height) as they become available. Model results are posted on Observatory websites, as well as provided to the National Weather Service for use in its public Ashfall Advisories.