By Reginald Stanley. Posted August 25, 2019, 10:34 PM.

The summer of 2019 has thus far been a quiet one across Southern California weather-wise, with almost no monsoon or thunderstorm activity occurring even in the deserts since the summer's beginning.

Since June, summer for Southern California has been largely defined by a number of cooler-than-average periods, unusual marine layer intrusions, a smaller number of minor heat spells, and only one notable monsoon-related event on July 23. From 2010 through 2018, every summer featured some level of monsoon-related activity in Southern California, with some years more active than others, however all of those years were more active on average than the summer of 2019 has been so far. The last summers to feature very little to no monsoon-related activity in the region occurred in both 2008 and 2009.

While summer is typically dry across Southern California, it is not usually devoid of any activity in the region - monsoon-related influence from the east, particularly from centers of high pressure near the Four Corners region, often spills over into Southern California's inland regions a number of times each summer. The lack of monsoon activity this summer has been noted by the National Weather Service offices in Tucson, Arizona as well as Flagstaff, Arizona. In Arizona, the monsoon season is officially measured between June 15 and September 30 of each year. Although no thunderstorms are currently forecast, the possibility of significant or otherwise notable activity during the month of September remains possible.

The potential causes behind the lack of monsoon-related activity in 2019 are not clear. Unusually persistent troughing off the coast of the Pacific Northwest might be related, which may be hindering the development of monsoon-inducing high pressure even as far away as the Four Corners region. It should also be noted that monsoon activity in the deserts and convective activity over Southern California can and have occurred independent of each other.