Impact of snow cover on NGM forecast temperature

This report was written in response to a memo from Jim Kaplan at the WSFO in Denver in which he brought to our attention an NGM forecast with significant low level temperature errors in the western U.S. Jim suggested that there may have been too much radiational cooling in the model. After looking into the situation it was determined that there may have been too much snow cover in the Rockies which could lead to excessive radiational cooling in the lowest layers of the models To test this hypothesis two reruns of the NGM were made: first with the snow cover removed under the 'C1 grid and then with the physics package turned off. Turning off the physics package will result in the M3M reverting to the version run prior to 23 July 1986.