San Francisco Bay Area
The most microclimate-dense ground in North America, and a gap in the Coast Ranges that explains it.
The Coast Ranges run unbroken for hundreds of miles and then, at the Golden Gate, they simply stop — one sea-level gap between the cold ocean and a Central Valley that in summer is 40°F warmer. That pressure difference pulls marine air through the gap like a nozzle, and everything downwind of it is cold, grey and windy while a ridge two miles away is in full sun. San Francisco and Walnut Creek can differ by 25°F on the same July afternoon; that is not a quirk, it is the gap doing exactly what a gap does.
- Elevation range
- 0 ft → 4,360 ftHigh point: Mount Hamilton
- Relief
- 4,360 ftTop to bottom, inside this region
- Span
- 109 × 117 miEast–west by north–south
- Annual rainfall
- 13–50″Driest to wettest ground here
- Köppen types
- CsbCsa9 counties
Map of San Francisco Bay Area within California.
The four seasons here
NOT A GENERIC SEASON WITH THE PLACE NAME SWAPPED INWinter
Wet and mild. Frontal rain, occasional atmospheric rivers, and the season the hills go green.
Spring
The transition month is April; by May the marine layer is running most nights.
Summer
Rainless. Fog and wind on the west side, heat on the east side, and the two are the same weather.
Autumn
The dangerous season. The marine layer breaks down, and the first offshore Diablo events arrive before the first rain does.
Places in this region
6 PLACES, LOWEST FIRST| Place | Elevation | Jan high | Jan low | Jul high | Jul low | Annual precip | Snow |
|---|---|---|---|---|---|---|---|
| Oakland | 43 | 60° | 45° | 72° | 57° | 22.6″ | — |
| San Francisco | 52 | 58° | 47° | 66° | 54° | 22.9″ | — |
| Half Moon Bay | 69 | 59° | 43° | 65° | 53° | 26.0″ | — |
| San Jose | 82 | 59° | 43° | 82° | 59° | 16.1″ | — |
| Santa Rosa | 167 | 60° | 38° | 82° | 52° | 31.5″ | — |
| Livermore | 486 | 57° | 39° | 89° | 57° | 14.6″ | — |
National Parks in this weather region
FIELD NOTES FROM THE PARK TRANSECTTerrain and gradients
WHAT THE ELEVATION ACTUALLY DOESRanges and passes
A PASS IS A WIND FEATURE FIRSTWho forecasts it
OFFICIAL FORECASTS AND WARNINGS COME FROM HEREGolden State Weather is not a source of watches or warnings. For those, go to the offices above.