“Trough luck” for southern California?

As a person who grew up in the Midwest, and spent a lot of time living in the Great Plains, it took a while for me to get used to forecasting in southern California.

My first summer out here, a wise Lead Forecaster at the NWS in San Diego advised me, “troughs in the summer are a good thing”. And he was right.

The low pressure troughs aloft bring a stronger onshore flow of cooler air, which for us, is modified by the cool currents of the Pacific. They are also associated with a deeper marine layer, bringing higher humidities, and more nighttime and morning cloudiness.

But unlike troughs moving across the central and eastern parts of the US, the troughs over the vast cool waters of the north Pacific often are dry just a bit above the surface.

This helps to bring us that “Chamber of Commerce” weather combination to the area. Cloudy and cool with some moisture in the air in the late nights and mornings…sunny, mild, and a bit drier in the afternoon.

Sorry to say…it won’t last forever. Long range models are indicating around the 11th of June a warm high pressure ridge will build in the upper parts of the atmosphere over the southwestern US, and possibly bring more moisture after the 13th…although it is still a bit early for the monsoon season.

Jim Purpura
Certified Consulting Meteorologist
Director, Weather Forecasting