The monsoon has arrived! It hasn’t really, but the government says it is here so who am I to argue?
When I first arrived in Phoenix and heard people talking about “The Monsoon”, I thought they were joking. Monsoons drench the jungles of India and such places. This is the Sonoran Desert. I remember seeing Richard Burton & Lana Turner in “The Rains of Ranchipur” but, to my knowledge, no one ever filmed The Rains of Ahwatukee. I have since learned, however. that the term correctly describes our summer weather. Somehow, that knowledge is not really all that comforting.
As I’ve come to understand, the term monsoon applies to regular seasonal changes in wind patterns. Worldwide, this is usually associated with heavy rains but it is the wind and not the rain that is the defining characteristic.
For a Midwesterner, the monsoon presents a collection of odd and unfamiliar weather conditions. Every afternoon the valley becomes sounded by heavy clouds. It is often cloudless all day but by 4:00 PM the clouds will come over the hills and into the valley from every direction. As the evening progresses the heavier moist air in the clouds starts to sink. As the clouds collapse they generate wind. It will usually rain, somewhere, but it falls in small localized pockets. It may be completely dry at Casa de Harper when folks living 5 miles away will get an inch of rain. The rains give rise to flash floods. Interestingly, because of the topography, the flooding often occurs some distance from where the rain fell.
We rarely have tornadoes in this part of the country but we do have dust storms called Haboobs. They are actually less frightening than one might imagine, assuming one is not trying to travel. The wind can be damaging but mostly they just make everything very, very dirty. Unlike tornadoes, they are not quick events. The 2011 storm in this photo moved about 30 mph. I was driving on the expressway, away from it thank goodness, so I was able to get a good view of it in my rear-view mirror and still get home before it arrived.
Thunderstorms occur frequently in monsoon season. In many ways they are like the thunderstorms with which I was familiar growing up in the Midwest; thunder, lightning, high winds and the sky changing color. The remarkable difference, however, is that it often does not rain. Maybe it’s the unfamiliarity but I find thunderstorms without rain to be much more disturbing than the wetter variety.
Historically the monsoons in this part of the world; it affects Arizona, New Mexico and a large part of Mexico; have begun in early July and ended in September. The warmer summer temperatures heat up the desert. The warm air rises creating wind. The winds pull moister air from the Pacific. We get about one third of our 8-9 inch annual rainfall in the summer months. More often than rain, however, we just get the wind and thunderstorms.
Prior to 2008, the official beginning of the monsoon was the first date when the Dew Point rose above 55*F and stayed there for three consecutive days. It was a little confusing to track because the monsoon official begins on the FIRST of those three days but, of course, one doesn’t know until Day 3 that the Dew Point stayed high enough. With our average temperatures, the relative humidity needs to rise above 30% to result in a 55* Dew Point. Using the old definition, in the years I’ve lived in Arizona, the monsoon has begun as early as June 30th and as late as July 18th.
In 2008 the National Weather Service decided that, henceforth, the Southwest monsoon would officially begin on June 15th and end on September 30th. Their thinking was that people would take storm safety more seriously if the uncertainty about season were removed. I don’t understand that. Were there really that many people who stood by watching their roof tiles fly away as the Haboob enveloped their house thinking; “thank goodness the monsoon hasn’t arrived yet”. Maybe there were. In any case, thanks to the government’s clarification, the next gust of wind will be officially a monsoon wind. Well O.K. then.