  A new multispectral Geostationary Operational Environmental Satellite (GOES)
imager product has been developed to assess downburst potential over the
western United States employing brightness temperature differences (BTD)
between band 3 (upper level water vapor), band 4 (longwave infrared window),
and split window band 5. Band 3 is intended to indicate mid to upper-level
moisture content and advection while band 5 indicates low-level moisture
content. Large BTDs between bands 3 and 5 imply a large relative humidity
gradient between the mid-troposphere and the surface, a condition favorable for
strong convective downdraft generation due to evaporational cooling of
precipitation in the deep sub-cloud layer. In addition, small BTDs between
bands 4 and 5 indicate a relatively dry surface layer with solar heating in
progress. This paper will outline the development of the GOES-West imager
microburst product and present case studies that feature example images,
outline potential operational use and assess performance of the algorithm.
