3.2: Elements of Weather

Understanding the weather requires considering a whole picture. Think of it like describing your day to someone – you wouldn't just say ‘hot’ or ‘rainy.’ You'd mention the temperature, humidity, wind, and maybe even if it's cloudy or raining. The key factors that make up weather are air temperature, humidity, wind speed, cloud types, and precipitation.

The big difference between weather and climate is time. Weather is what's happening outside right now – it can change quickly from sunny to stormy. Climate, on the other hand, is the average weather conditions in a place over a long period, minimally 30 to 100 years. Think of it as a region's usual weather patterns. Similar to weather, climate is influenced by factors like the sun's angle, cloud cover, and air pressure, but these factors affect the average energy an area receives over time. That's why climates tend to be steady and change very slowly.

Temperature

Within the boundaries of the state are to be found areas of moderate temperatures and other places where temperatures reach extreme values of either heat or cold. On the coast the small range in temperature from day to night and from winter to summer produces an unusually equitable regime. Since water heats and cools 5 times faster/slower than land, respectively, coastal locations’ climates are moderate with a smaller temperature range. With increasing distance from the coast, depending to some extent upon the amount of marine influence experienced, temperature ranges become wider. Higher elevations in the mountains also experience large temperature variations.

The lowest temperature recorded in the state was in the city of Boca, in Nevada County at the mouth of the Little Truckee River, when a reading of minus -45°F was observed on January 20, 1937. Here at Boca where sub-freezing temperatures have been recorded in every month of the year, the long-term average minimum for January is only 8°F. Furnace Creek Ranch in Death Valley, on the other hand, at an elevation of 168 feet below sea level, has reported a maximum temperature of 134°F This is the highest temperature observed anywhere in the United States and occurred on July 10, 1913. This is an area where temperatures are persistently high throughout the summer, though they are comfortably cool in winter. In the summer of 1917, there were 43 consecutive days with maximum readings of 120°F or higher at Furnace Creek Ranch (Figure 3.2).

Figure 3.2: California’s Mean Annual Maximum Temperatures for 1971 - 2000. Image by Jeremy Patrich is used under a CC-BY 4.0 license.

Precipitation

Precipitation is an extremely important part of the weather. The most common precipitation comes from clouds. Rain or snow droplets grow as they ride air currents in a cloud and collect other droplets. They fall when they become heavy enough to escape from the rising air currents that hold them up in the cloud. Millions of cloud droplets will combine to make only one raindrop. If temperatures are cold, the droplet will crystallize into a solid, and then will become heavy enough to fall to the ground as a snowflake.

In meteorology, the various types of precipitation often include the character or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is generally more intense, and of shorter duration, than stratiform precipitation (arranged in layers). Orographic precipitation occurs when moist air is forced upwards over rising terrain, such as a mountain.

Precipitation can fall in either liquid or solid phases, or transition between them at the freezing level. Liquid forms of precipitation include rain and drizzle and dew. Rain or drizzle which freezes on contact within a subfreezing air mass gains the preceding adjective "freezing", becoming known as freezing rain or freezing drizzle. Frozen forms of precipitation include snow, ice crystals, ice pellets (sleet), hail, and graupel. Their respective intensities are classified either by rate of fall or by visibility restriction.

Annual precipitation totals more than 50 inches per year are characteristic of the west slope of the Sierra Nevada north of Stockton, the west slope of the Coast Range from Monterey County northward, and parts of the Cascades, (Mt Shasta and Mt. Lassen). The exception to this are totals that decrease to about 20 inches in the Monterey Bay area and parts of the San Francisco Bay Area. In the lee of the Coast Range, annual precipitation drops off to 15 inches in parts of the Sacramento Valley and to less than eight inches over most of the San Joaquin Valley. The northeast interior portion of the state receives from 15 to 18 inches of moisture in a year (Figure 3.3)

Figure 3.3: California’s Annual Precipitation for 1900-1960. Image by Jeremy Patrich is used under a CC-BY 4.0 license.

Snow has been reported at one time or another in nearly every part of California, but it is very infrequent west of the Sierra Nevada, except at high elevations of the Coast Range and the Cascades, (Mt. Shasta and Mt. Lassen). In the Sierra Nevada, snow in moderate amounts is reported nearly every winter at elevations as low as 2,000 feet. Amounts and intensities increase with elevation to around 7,000 or 8,000 feet. Above 4,000 feet in elevation, snow remains on the ground for appreciable lengths of time each winter. Highways are closed for periods of a few hours to two or three days at a time because of blowing and drifting snow. East of the Sierra Nevada at elevations of 4,000 feet, or higher, most winter precipitation is in the form of snow, but amounts are usually quite light.