RAMMB Satellite Case Studies

What the GOES imagery shows us over Colorado & Kansas

The 6.7 micron channel on the GOES imager is sensitive to water vapor in the middle and upper levels of the troposphere. Frequently, atmospheric disturbances (such as shortwaves or jet streaks) can be tracked using this channel, because the zones of upward and downward motion associated with these features remain quasi-steady in a storm-relative sense. Note, for example, the comma-shaped feature moving across southern Colorado. This is a shortwave trough that played a role in aiding developing convection. Notice how much easier it is to see this feature on the 6.7 micron channel compared with the 10.7 micron channel.

Lower tropospheric boundaries are important to the development and evolution of deep convection. One of the more important boundaries on this day was an east-west oriented outflow boundary situated in central Kansas at the time of convective development. Look at both the 10.7 micron and fog product imagery (AREA's 6908-6944) from overnight. This derived-product is made by differencing the 3.9 micron and 10.7 micron channels, because the brightness temperature at 10.7 micron is greater than that at 3.9 micron for water clouds. Notice the line of stratiform cloudiness to the south and west of the squall line traveling through Nebraska and South Dakota. These clouds are along the outflow boundary being produced by the storms, and can be easily identified using the fog product. The boundary is not nearly as easy to see on the 10.7 micron channel, since the actual temperature of the cold ground and stratiform clouds are similar.

The outflow boundary, once identified, can be followed into the daylight hours. Construct an animated sequence of visible images to follow this feature, and see how late you can track it. HINT: look for differences in cloud type on either side of the feature.

For those with RAMSDIS units, compute cloud motions for the smaller cumulus clouds in central Kansas. These cloud motions reveal the location of a moderately strong convergence zone that may play a role in later convective development. Stratiform clouds in southeast Colorado can also be used to track the circulation around the low in the early part of the morning. Be careful, though, because dissipation later in the period can make cloud-derived motions deceiving.