Further details on this change can be found here. The model is now run at a horizontal resolution of 22 km with 50 levels in the vertical. The domain has been expanded slightly, and the 3DVAR initialization has been improved. The convective scheme has been modified to reduce the dry bias in the western U.S. and the moist bias along the Gulf and southeast U.S. coast. VAD winds are now being used again with a new quality control code, and balloon drift is now accounted for in the processing of radiosonde data.
More info is available here .
Tests of the new 3DVAR analysis produced much higher forecast accuracy. The 03 Nov 98 change to the Eta post processor involving computing RH has been removed. RH will now always be computed with respect to water saturation. Expect to see, as before 3 Nov, the same lower RH values at upper levels or wherever cloud ice is found. This is done to prevent unphysical values such as negative cloud base heights, for example.