Tuesday, November 29, 2016
Fog Returning to the Great Valley...Maybe
The Tule fog is a radiation fog, caused when heat from the ground radiates into the atmosphere at night, cooling the ground and causing condensation to take place. The fog persists as long as the temperature doesn't rise, and in the Great Valley, ringed is it is by high mountains, the conditions may persist for weeks at a time. Stable motionless air develops an inversion layer that can be difficult to break up unless a large storm blows in.
I was not prepared for the fogs when I made the valley my home nearly 30 years ago. I hated the gloomy days that seemed to never let up for weeks at a time. I had frightening near-misses on the highways. I even got lost a few times in the pre-GPS days, getting disoriented on backroads that were poor in signage. I was known to drop important projects and drive into the Sierra Nevada foothills for the sole purpose of getting into the sunshine. I hated descending back into the soupy mess.
The drought in California has caused a drop in the number of foggy days, since wet ground is a major requirement for forming the hated mist. Global warming plays a role, as warmer conditions are less likely to result in foggy conditions. Temperatures in some parts of the Great Valley are up by 3 to 4 degrees Fahrenheit. According to one report, the number of foggy days in Fresno declined from an average of 37 in 1980 to 22 in 2014. This has been a two-edged sword: besides the reality of the drought itself, the lack of cold wet conditions have caused a drop in agricultural production, as a number of fruit trees like cherries and peaches require the cold dark days to help the trees go dormant in winter.