The Pt. Reyes fire, which destroyed about four dozen homes as well as more than 11,000 acres of forest, burned out of control for several days, whipped by dry, gusty northeast winds of the sort not uncommon in California in the fall. At the time of the fire, low dew point temperatures (from the thirties down to the high teens in degrees Fahrenheit) as well as relatively strong surface winds (30 knots and more) were reported around much of Northern California.
This North American sea-level pressure map, superimposed on a visible satellite image, shows a region of relatively high pressure (greater than 1024 millibars) across the Pacific Northwest. Northern California lies within a strong pressure gradient (where isobars pack relatively closely together) south of the high, where the pressure drops off rapidly toward the south. A large sea-level pressure gradient implies a strong pressure-gradient force driving surface winds, in this case from the north and northeast.
Note the smoke plume emanating from Pt. Reyes and blowing offshore to the southwest, barely visible on this North American-scale visible satellite image. (A companion image in our special-image archive shows a closer view of the smoke plume with surface weather observations superimposed, and a summary of information on the close-up image provides more information about the image. A second companion image shows a high-resolution view from much closer to the earth, recorded by a polar-orbiting NOAA satellite.)
Similar weather conditions contributed greatly to the most damaging fire in U.S. history, in the East Bay hills of Oakland and Berkeley along the east side of San Francisco Bay, in October of 1991.
(Also on the North American sea-level pressure map, note the "bull's eye" sea-level pressure signature of hurricane Opal making landfall on the Gulf Coast, where it was already dark and therefore not visible on this composite visible satellite image.)
