04 October 1999 | Lake Effect Rain Band Over Lake Michigan
|
|
|
|
|
NOAA GOES-8 visible imagery (above) showed a lake effect cloud plume over Lake Michigan during the morning hours on 04 October 1999. This cloud plume was producing light rain in some of the Chicago suburbs prior to 16:00 UTC. Rapid Scan Operations (RSO) was activated to allow the development of this cloud band to be monitored at 5 to 10 minute intervals (versus the standard 15 minute image interval). As the lake cloud plume became less well-defined, mesoscale cyclonic eddy circulations could be seen along the axis of the cloud band. This RSO imagery was also helpful to monitor the dissipation of valley fog over portions of the Mississippi River and central Wisconsin.
One factor that is important in forecasting the occurrence of lake effect cloud bands is the difference in temperature between the relatively warm lake water and the cold air within the lowest 1-2 km of the troposphere. As seen from the Green Bay WI rawinsonde (below left) and the Lake Michigan water temperatures, the lake water (+15 to +17 C) minus 850 hPa (-4.5 C) "Delta-T" in this case was on the order of 20 degrees C. An example of a GOES-8 Sounder IR temperature difference product is shown (below right) which can help to estimate the magnitude of the Delta-T over cloud-free portions of the Great Lakes. Calculating the difference between Sounder channel 8 (longwave IR window channel, 11.0 micron wavelength) and Sounder channel 5 (longwave IR, 13.4 micron wavelength) brightness temperatures generates an estimate of the Delta-T; Channel 8 senses the greatest amount of upwelling thermal radiation from near the surface, while Channel 5 senses less thermal radiation from the surface and more from the lower layers of the troposphere.
|
|
