Diablo wind
From Wikipedia, the free encyclopedia
Diablo wind is a modern term for the hot, dry offshore wind from the northeast that typically occurs in the San Francisco Bay Area of Northern California during the Spring and Fall. The term came into contemporary usage by local news media in the aftermath of the 1991 Oakland firestorm, to distinguish it from the comparable, but more familiar hot dry wind in Southern California known as the Santa Ana wind. In fact, in decades previous to the 1991 fire, the term "Santa Ana" was occasionally used as well for the Bay Area dry northeasterly wind, such as the one that caused the 1923 Berkeley Fire. [1] The name "Diablo wind" may have been coined from the observation that the wind blows into the inner Bay Area from the direction of the Diablo Valley in adjacent Contra Costa County, and mindful of the fiery, sensationalist connotation inherent in "devil wind".
The Diablo winds are created by a strong high pressure area over Nevada and lower pressures west of San Francisco and Monterey. The air descending from the mountains compresses at sea level where it warms as much as 20 °F, and loses humidity. [2]
Unlike the Santa Ana wind which is a downslope wind ("föhn") draining air off the high deserts, the so-called Diablo wind originates from areas of strongly sinking air aloft, associated with the development of high atmospheric pressure inland following the passage of storms just north of California. As the air sinks, it heats up by compression and its humidity drops. This heat is in addition to heat picked up by the wind as it crosses the Central Valley and the Diablo Valley. This is the reverse of the normal summertime weather pattern in which a trough of low rather than high pressure lies east of the Bay Area, drawing in cooler, more humid air from the ocean. If the pressure gradient is large enough, the dry offshore wind can become quite strong with gusts reaching speeds of 40 mph, particularly along and in the lee of the ridges of the Coast Range where the air stream is forced to squeeze over them.
While the Diablo occurs in both the Spring and Fall, it is most dangerous in the Fall when vegetation is at its driest.
[edit] See Also
[edit] References
- ^ extract from the Report on the Berkeley, California Conflagration of September 17, 1923, issued by the National Board of Fire Underwriters’ Committee on Fire Prevention and Engineering Standards, reprinted in the Virtual Museum of the City of San Francisco
- ^ WEATHER CORNER, San Jose Mercury News, Jan Null, October 26, 1999
 |
This California-related article is a stub. You can help Wikipedia by expanding it. |
