Increasing the height of the Altai-Sayan mountains shifts the region of stationary eddy momentum flux convergence equatorward, which shifts the stormtracks equatorward as well. The equatorward shift of the stormtracks reduces the storminess over the Altai-Sayan region, which in turn reduces the intensity and frequency of eddies entering into the North Pacific.
The equatorward shift of the stormtracks also decreases the local baroclinicity in the North Pacific, and thereby weakens the local storm development. Even though the baroclinicity in the subtropical North Pacific increases, the latitudinally constrained sharp-narrow subtropical jet seems to suppress the storm development. The high barotropic conversion rate might also be a suppression factor.