Golden State WeatherRegionsSacramento–San Joaquin Delta

Sacramento–San Joaquin Delta

The only sea-level break in the Coast Ranges, and California's air conditioner.

The Delta breezeCarquinez Strait windBelow-sea-level islands

Every drop of water leaving the Sierra reaches the sea through one gap, and so does every bit of marine air going the other way. When the Central Valley heats up, the pressure difference between it and the coast draws cool air through Carquinez Strait and up both rivers — the Delta breeze, which is why a 105°F Sacramento afternoon becomes a 60°F night. When the breeze fails, the valley's heat waves turn dangerous, because the overnight recovery that people rely on simply does not come.

Elevation range: 15 ft below sea level → 100 ftHigh point: below sea level on many islands
Relief: 115 ftTop to bottom, inside this region
Span: 49 × 45 miEast–west by north–south
Annual rainfall: 12–18″Driest to wettest ground here
Köppen types: Csa4 counties

Open climate division

Map of Sacramento–San Joaquin Delta within California.

Where it is. The highlighted frame is this region's viewport; the others are its neighbours.

The four seasons here

NOT A GENERIC SEASON WITH THE PLACE NAME SWAPPED IN

Winter

Fog, and the highest flood risk in the state when a warm atmospheric river melts low-elevation snow upstream.

Spring

Windy. The gradient between a warming valley and a cold ocean is at its strongest.

Summer

The breeze runs almost nightly, and the days it does not are the dangerous ones.

Autumn

Winds relax; the first tule fog of the season usually forms in the Delta before anywhere else.

Places in this region

1 PLACE, LOWEST FIRST

NOAA/NCEI 1991–2020 monthly normals, from the nearest publishing station at a comparable elevation. Full twelve-month tables are on each place's own page.
Place	Elevation	Jan high	Jan low	Jul high	Jul low	Annual precip	Snow
Antioch	46	56°	40°	91°	61°	12.6″	—

Terrain and gradients

WHAT THE ELEVATION ACTUALLY DOES

Too few reporting stations to regress a terrain gradient.

Ranges and passes

A PASS IS A WIND FEATURE FIRST

Carquinez StraitSecond gate inland. Marine air accelerates through it toward the Central Valley almost every summer evening.PASSAltamont PassWhere the Delta breeze crosses the Diablo Range — and where California's first big wind farm went in.PASS

Who forecasts it

OFFICIAL FORECASTS AND WARNINGS COME FROM HERE

NWS SacramentoSacramento Valley, northern Sierra, DeltaNWS STOWEATHER.GOV NWS Bay AreaBay Area and the central coastNWS MTRWEATHER.GOV

Golden State Weather is not a source of watches or warnings. For those, go to the offices above.

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