CALIFORNIA CLIMATES OUTLINE

VICKI DRAKE

EARTH SIENCE DEPARTMENT

SANTA MONICA COLLEGE

I. Climate vs. Weather

II. Climate Determination Factors

  1. Average annual temperatures
  2. Total annual precipitation
  1. California’s precipitation seasons:
  2. Northern California: October to April
  3. Southern California: December to March

III. California’s Seasons

  1. Two season year

1. 6-7 month cool to cold, wet season

2. 5-6 month warm to hot, dry season

  1. Two principal climate regimes

1. Subtropical: mild wet winters, warm dry summers, long growing season, latitude range – 250-400

2. Midlatitude: colder ‘snowy’ and wet winters, warm dry summers, shorter growing season, latitude range: north of 400

  1. Moisture levels: humid, semi-humid, semi-arid and arid
  2. Subtropical Climates

1. desert: Colorado Desert, Mojave Desert, Death Valley, SW San Joaquin Valley

2. interior semi-arid: Central San Joaquin Valley

3. coastal semi-arid: San Diego county to Mexico

4. Mediterranean: Coastal ranges to central valleys (found exclusively in CA within USA)

  1. Mediterranean Fog Belt; Coastal Ranges
  2. Mediterranean Mild Summers: Southern and Central Coast California
  3. Mediterranean Hot Summers: Sacramento Valley
  1. Midlatitude Climates

1. desert: Basin and Ranges, lower Owens Valley

2. semi-arid: Upper Owens Valley

3. Dry Summer/Upland: Foothills of Sierra Nevada, Cascades, Modoc

4. Alpine: Mountain peaks of Sierra Nevada (Mt. Whitney), White-Inyo

Mountains (White Mtn.)

IV. Climate Factors:

  1. Altitude:
  2. Ascending air cools, condenses to form clouds and precipitation
  3. Orographic Uplift: lifting over mountains

a. windward side (western): abundant precipitation and vegetation

  1. lee side (eastern): ‘rainshadow desert’: little precipitation and vegetation sparse

3. Frontal Uplift: Cold and Warm fronts lifting air

4. Convectional uplift: heated ground warms air, which is lifted

  1. Latitude:
  2. Latitudinal changes (320-420) from south to north
  3. Average temperature  with  distance from 320-420
  4. Greater ranges in daily, monthly, and annual temperatures

a. More seasonality to rainfall patterns

  1. Position on Continent
  2. Maritime vs. inland position affects climates
  3. Maritime climates:

a. Less temperature variation daily/annually

b. Oceans absorb and release heat gradually

(1)oceans mix heat to depth

(2)high specific heat

(3)evaporation processes

  1. Coastal areas cooler year-round, with more constant temperatures
  2. Inland climates:

a. Greater variation temperature daily/annually

  1. Land (soils) absorb and release heat quickly

(1) no mixing of heat – heat does not penetrate soils to depth

(2) low specific heat

(3) no evaporation processes at work on land

  1. Summers along NW California coast: cooler and subject to fog
  2. Summers along SW California coast: warmer and drier (less fog)
  3. Summers, in general, in California are dry
  1. Ocean Current Influences
  2. California current: cold ocean current flowing southwards parallel to west coast of North America (aver. Water T: 50-700F)
  3. Linear coastal mountains direct winds that develop the current
  4. Cold water tends to inhibit evaporation, and other rising air processes: no rising air = no cloud formation = little precipitation

E.Air Pressure Systems

  1. Pacific High (Hawaiian High) located in Pacific Ocean off coast of California
  2. Air is descending in the center of a high, and is rotating outwards in a clockwise manner from the center.
  3. Latitudes near ~300N are dominated by high pressure systems
  4. Pacific High blocks the storms during the summer, by moving in a northerly direction.

a. Storms directed to the north or south of the High

  1. Pacific High moves ‘south’ during the winter, allowing the Aleutian Low to move south, bringing wet, cold winter storms from Gulf of Alaska.
  2. Air tends to move from areas of high pressure to areas of low pressure.
  3. Clockwise rotation of air over ocean, encourages development of California Current

F.Upper Level Wind Patterns

  1. Global winds that move around the world influence California’s climate
  2. USA upper level winds: “Westerlies” – moving from west to east across USA.
  3. Storms for CA come from Pacific Ocean

a. Gulf of Alaska

  1. Pacific Ocean “Pineapple Express”

4. Westerlies (and Jet Stream) bring in storm tracks to CA

V. Special Wind Conditions for California

A. Land Breeze/Sea Breeze

1. Differential heating/cooling of land and ocean set up localized high and low pressure systems.

  1. Day time: Highs over cooler ocean, Lows over warmer land = SEA BREEZES as air moves from ocean to land (late afternoon)
  2. Night time: Lows over ‘warmer’ ocean and highs over cooler land = LAND BREEZES, as air moves from land to ocean (late night)
  1. Santa Ana Winds: hot, dry, high speed winds during late Fall to early Winter

1. High pressure north east of southern California (usually Utah)

  1. Air descends from higher elevation in Utah and heats up
  2. Air flow clockwise out of high into southern California deserts
  3. Air is ‘dried’ out as it passes through southern California deserts
  4. Air is lifted up, over, and down Transverse Mountains and channeled or ‘funneled’ through passes and canyons = speeding up
  5. Santa Ana Winds correspond to southern California’s fire season

VI. Special Fog Conditions for California

A. Radiation Fog:

1. Warm ground (daytime); cool air aloft (nighttime)

2. Warm air near ground chills to “Dew Point” (condensation)

3. Thick fog develops along ground – common in valleys, central California, inland Riverside and San Bernardino counties

  1. Occurs mainly in Spring and Fall (warm days, cool nights)

B. Advection Fog:

1. Cool ocean surface

  1. warm, moist air flowing across water
  2. air cools to ‘dew point’ – thick fog forms on water – moves onshore
  3. San Francisco Bay fogs

C Upslope Fog:

1. Warm valley/desert floor

  1. Warm air from valley rises along mountain slope
  2. Air cools, condenses and forms thick ‘fog bank’ on slope – clear above and below
  3. San Bernardino Mountains – Palm Springs

VII SPECIAL CONDITIONS OF SMOG IN CALIFORNIA (SOUTHERN)

A. Low-lying coastal basin, ringed by tall mountains

B. Marine layer of cool moist air at ground

C. Warm dry layer of air above ground (inversion layer)

  1. Cool dry air above inversion layer
  2. Acts as a trap to keep particulates, smog chemicals close to surface
  3. CO (carbon monoxide), CO2, NOx, SOx etc result from internal combustion engines, diesel engines, plants and factories – trapped in lower atmosphere
  4. Ponderosa Pines and some agriculture crops susceptible to pollutants

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© V. Drake

SMC