Chuck Doswell Asks:

Chuck Doswell asked: Any idea of the history of "failed" AZ monsoon rainy seasons? Is this something of historic proportions or is it something that happens every so often?

Paul I. of Phoenix replied: At least from the Phoenix database, my single point analysis shows there have been other years worse than this one. Can't provide a "why", or how often, but it appears that this does happen every once in a while.

David B. of Flagstaff replied:

Farther north, Flagstaff rainfall for the period July 4 through August 15 is the driest on record (1898-2009). Here are the driest 10:

1. 0.80 2009
2. 0.86 1900
3. 1.21 1960
4. 1.25 1960
5. 1.27 1995
6. 1.42 1940
7. 1.60 1996
8. 1.71 1939
9. 1.74 1978
10. 1.75 1991

Normal for this period is 3.88".

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I snipped the above graphic for southeastern Arizona from the Tucson NWS web page. It shows summer 2009 rainfall from June 15 to August 17 versus a 30-year normal for the same period. So, several locations are having what I've been calling a failed monsoon with small percentages of typical rainfall at this date (Organ Pipe NM 16%; Safford 22%; Tucson 53%; Douglas 53%). Even though I've been moaning about things here at the house, it's been much worse at Organ Pipe and Safford.

In contrast, Willcox, Picacho Peak, and Ft. Thomas have been having a fairly typical summer so far. This illustrates the patchwork character of summer rainfall down here - not surprising for a region of complex terrain during a mostly convective regime.

As for the four stations having a dry monsoon to date, the long period monsoon data show:

Tucson Ave. 6.06" Wettest 13.84" (1964) Driest 1.59" (1924)

Douglas Ave. 8.28" Wettest 15.90" (1964) Driest 2.76" (1956)

Safford Ave. 4.60" Wettest 9.05" (1966) Driest 1.49" (2003)

Organ P. Ave. 4.42" Wettest 11.93" (1984) Driest 0.69" (1975)

These data are for a subjectively determined monsoon period and are thus not directly comparable with the data in the table. But, it does appear that Safford and Organ Pipe NM have some chance of experiencing their driest ever summer/monsoon period during the period of records.

The convective character of the summer here is again illustrated by the fact the 8 years of record rainfall amounts have only one repeat year.