Hi John,

That's a good question! With the observations, I did try setting a higher La Nina amplitude threshold (DJF Nino 3.4 SST anomaly amplitude greater than 1 deg. C) and did not see any substantial differences than when I considered all La Nina episodes. So, I did not see any obviously linear effect of La Nina amplitude in the observational analysis. 

In the SPEAR simulations, I examined the relationship between the ensemble mean Southwest U.S. precipitation anomalies and the La Nina SST anomalies. Surprisingly to me, the SST correlation pattern did not project strongly onto the mean La Nina SST anomaly pattern, as one might expect if the dominant effect was a linear amplitude effect. Instead, the pattern looked a bit more like the positive phase of the Pacific Meridional Mode. 

So, the bottom line is that the relationship between La Nina amplitude and Southwest U.S. precipitation does not appear as simple as one (or at least I) would expect based on this analysis, and it's something I would like to understand better.