THE WIND REGIMES
Every named California wind, and the gap or slope that makes it.
California names its winds, and the names are geography. A Santa Ana is not "a strong easterly" — it is desert air being forced through specific canyons in the Transverse Ranges and heating as it descends. A Sundowner is the same physics through a different range, forty miles away, arriving in the evening. The Delta breeze is the reverse direction through the state's only sea-level gap.
Which means all seven come down to two questions: which way is the pressure gradient pointing, and what is in the way. Everything below is one answer to that pair.
Offshore — downslope, warming, drying
HIGH PRESSURE INLAND, LOW OFFSHOREThe dangerous direction. Air sinking from the Great Basin compresses as it descends — roughly 5.5°F per 1,000 feet — so it arrives hot, and because warming air holds more moisture than it carries, its relative humidity collapses. Single digits are routine. This is the combination behind nearly every catastrophic California fire.
Santa Ana
SOUTHERN CALIFORNIA · SEP–MAR · PEAK OCT–DEC- Trigger
- Great Basin high, coastal trough
- Conduits
- Cajon, Soledad, Santa Ana Canyon
- Typical gusts
- 45–70 mph in the canyons
- Humidity
- Often under 10%
High pressure builds over Nevada and Utah while a trough sits off the coast. The gradient points from desert to ocean — the opposite of the normal onshore flow — and the Transverse Ranges stand in the way. Air cannot go over a wall that long without help, so it goes through: down Cajon Pass into the Inland Empire, down Soledad Canyon into the San Fernando Valley, out the Santa Ana Canyon into Orange County.
Two things happen on the way down. The air compresses and warms, which is why Los Angeles records its hottest days of the year in September and October on a wind blowing from the desert. And the canyons act as nozzles, so the wind is not uniform — it is a set of jets with quiet ground between them, which is why one neighbourhood is destroyed and the next is untouched.
Diablo
SAN FRANCISCO BAY AREA · SEP–NOV- Trigger
- Great Basin high, offshore gradient
- Conduits
- Diablo Range gaps and ridgelines
- Typical gusts
- 40–70 mph on the ridges
- Timing
- Overnight into early morning
The Bay Area's version, named for the range it comes over. The same synoptic setup as a Santa Ana, but the terrain is different: instead of long canyons through one big wall, northern California has ridgelines, so the strongest wind is on the tops and the lee slopes rather than in a canyon mouth.
Its timing is the thing to know. A Diablo event usually peaks between midnight and sunrise, when the marine layer has drained away and the gradient is strongest — which is the worst possible hour for a fire start, because it is the hour when the fewest people are awake to notice one.
Sundowner
SANTA BARBARA · YEAR-ROUND · PEAK MAY–SEP- Trigger
- Offshore gradient across the Santa Ynez range
- Conduit
- The Santa Ynez Mountains' south face
- Typical gusts
- 35–60 mph at the coast
- Timing
- Late afternoon into evening — hence the name
A local speciality, and geometrically strange. Santa Barbara sits on a south-facing coast with an east–west range immediately behind it, so when air spills over the Santa Ynez Mountains it descends straight onto the city and the beach. Temperatures at the coast can climb 20°F in an hour while the sun is going down.
It is the one offshore regime that runs through summer, and it is the reason the Santa Barbara front country burns in months when the rest of Southern California is under a marine layer.
Onshore — the cooling machine
A HOT INTERIOR PULLING COLD OCEAN AIR INLANDThe everyday direction, and the one that makes California's summers survivable. The Central Valley heats to 100°F while the ocean stays near 55°F; that temperature difference is a pressure difference, and air moves down it. The only question is where it can get through.
The Golden Gate sea-breeze jet
BAY AREA · MAY–SEP · DAILY- Trigger
- Valley heating against a 55°F ocean
- Conduit
- The Golden Gate — sea level, ~1 mi wide
- Typical speeds
- 20–35 mph, gusting higher
- Timing
- Afternoon into evening
The Coast Ranges run unbroken for hundreds of miles and then, at one point, stop. Every bit of marine air heading for the Central Valley is funnelled through that gap, and a nozzle accelerates what passes through it. This is why San Francisco is windy, why the fog pours through the Gate as a visible river, and why the city's warmest month is September — once the interior cools in autumn, the pump switches off.
It is also why the Bay Area has the sharpest microclimate gradients in North America. Downwind of the Gate is cold and grey; two miles behind a ridge is 25°F warmer and sunny. Both are the same weather event.
The Delta breeze
CENTRAL VALLEY · MAY–SEP · EVENINGS- Trigger
- Valley heat; the same gradient, further inland
- Conduit
- Carquinez Strait and the Delta channels
- Typical speeds
- 15–30 mph
- Timing
- Evening, strongest after dark
The same marine air, having made it past the Gate, continues inland through Carquinez Strait and up both rivers. This is California's air conditioner: it is the reason a 105°F Sacramento afternoon becomes a 60°F night, and it is why the Central Valley is habitable in August.
The important thing about the Delta breeze is what happens when it fails. In the heat waves that kill people, the breeze does not arrive — usually because a ridge has built far enough west to shut the gradient down — and the overnight recovery everyone's houses and bodies depend on simply does not come. A Central Valley heat wave is measured by its night-time minimum, not its afternoon maximum.
San Gorgonio Pass wind
BANNING PASS · YEAR-ROUND · PEAK APR–JUN- Trigger
- Coastal basin against the Coachella Valley
- Conduit
- A 2,600 ft pass between two 11,000 ft peaks
- Typical speeds
- 25–50 mph, near-continuous
- Why it matters
- Thousands of turbines stand in it
The most consistently windy place in California, and the geometry explains itself: San Jacinto Peak on one side, San Gorgonio Mountain on the other, both above 10,800 feet, with a 2,600-foot notch between them connecting the Los Angeles Basin to the desert. Air crossing from the cool coastal side to the hot desert side has exactly one route, and it takes it at speed for most of the year.
Unlike a Santa Ana this is usually the onshore direction and it does not need a special synoptic setup. It is simply what happens when a desert and an ocean are connected by one gap.
Mountain waves
WHAT HAPPENS DOWNWIND OF A 10,000-FOOT WALLThe Sierra Wave
OWENS VALLEY · YEAR-ROUND · PEAK SPRING- Trigger
- Strong westerlies across the Sierra crest
- Conduit
- The 10,000 ft eastern escarpment
- Signature
- Lenticular clouds, lee rotors
- Hazard
- Severe turbulence; dust off Owens Lake
When a strong westerly flow crosses the Sierra crest, the air does not simply come down the other side and stop. It oscillates — a standing wave that can extend into the stratosphere, marked by the smooth lens-shaped lenticular clouds that sit motionless above the Owens Valley while the wind roars through them.
Underneath the wave, a rotor can form: a horizontal roll of air near the ground with violent turbulence inside it. The Sierra Wave Project of the 1950s flew gliders into it deliberately and it remains one of the best-studied mountain-wave systems anywhere. On dry years it also lifts dust off the exposed bed of Owens Lake, producing some of the worst particulate events in the United States.
Wind warnings come from the National Weather Service
This page explains mechanisms. It is not a forecast and it is not a warning. For active Red Flag Warnings, High Wind Warnings and Wind Advisories, go to weather.gov and your regional office — every region page on this site links its own. Fire information is at CAL FIRE. All of that is free here, permanently, and always will be.