The above are from the CPC showing forecasts from the fully-coupled, global CFSv2 numerical forecast model. The forecasts are for monthly rainfall anomalies during July, August, and September 2014. The model forecasts each of these months to to be wetter than normal over most of the Southwest and also over northwest Mexico. These numerical forecasts are what led to the headline we saw on the front page of last Saturday's (June 14th) Arizona Daily Star - "Dig umbrella out of closet - monsoon could be a wet one."
Below are outlooks from Art for the same months. These are based on Art's analog identification procedures and his years identified as analogs are indicated. Art's outlook indicates a drier than normal summer for most of the Southwest, although there is some recovery during August.
So different procedures and different models produce widely varying forecasts. Here in southern Arizona El Nino summers tend to be near normal or dry. El Nino July's tend to be quite dry but an August rebound can sometimes bring the summer rainfall back to near normal. I tend to consider September a "wild card" month, since there are so many features in play - how long does the summer pattern continue into the month; how do middle-level, westerly short-waves interact with residual subtropical moisture in low-levels (so called "transition events"); do westerly short-waves pick up decaying tropical storms and bring significant rains into the Southwest? So, it's a complicated mess - especially since across southern Arizona several heavy thunderstorms hitting the same measurement site can determine the character of a month or even of the season's rainfall.
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