Figure 3.7 36-h forecasts of the 950-mb vertical motion fields valid at 00Z on 5 May 2001 from runs using the Eta 10-km central nest are shown for the operational control (left) and the new grid-scale microphysics (right). The vertical motion is expressed in 10*Pa/s, which is roughly equivalent to units of cm/s, such that a value of 1.0 in the figure is associated with 0.1 Pa/s. Negative values denote upward motion. Spurious gravity waves in the operational control run are forced by three areas of intense precipitation, one in the Texas panhandle along the border with New Mexico, the second over northern Missouri, and the third along the line of precipitation over central Illinois and Indiana (see Fig. 3.6). The waves are produced by periodic updates of temperature by cloud processes in the operational control run, and they are absent in the new model because temperature is continuously updated every time step.