One of climatologists’ predictors of whether or not we’re going to have a big monsoon is the date of onset. Early onset generally means a wetter monsoon. We’ve got no crisp definition here in Albuquerque (and, in fact, the monsoon onset isn’t very crisp here), but in Tucson they’ve developed a very precise definition based on dewpoints. Their start was June 28, nearly a week early. Compare that to the onset since 2001, when they had a late start all five years and a lousy monsoon four out of five years. I’m comparing apples to organges by using the Tucson start date, because that isn’t the definition used in the paper I cite below. And the actual correlations between Tucson’s onset date and total monsoon rainfall, either there or here, are so weak as to render the above discussion irrelevant. So it’s not science, just blind optimism.
Last year we had a false start in late June, and then things dried up. But we’ve got rain in the forecast for the next week.
 Interannual Variability of the U.S. Summer Precipitation Regime with Emphasis on the Southwestern Monsoon, R. W. Higgins and K. C. Mo, Journal of Climate: Vol. 11, No. 10, pp. 2582–2606