If a weather pattern persists over several years you might expect similar crops but in our particular case we had two years without El Nino and now we apparently have a strong El Nino event.  The  thing about El Nino is that it takes some time for it to really get going.  We might not feel the full effects of  this El Nino until later in the summer or even this fall.
  You are correct that there have been periods of several years when yields followed the trendline quite closely only to be interrupted by periods of substantial year to year variation.   Only time will tell which period we're in.