Northern Alameda Western Contra Costa Counties Region

This area stretches 20 miles from the Richmond area through Oakland to San Leandro. Its western boundary is defined by the San Francisco Bay and its eastern boundary by the Oakland- Berkeley Hills. The Oakland-Berkeley Hills are a significant barrier to air flow having an approximate ridge line height of 1500 feet. The most densely populated area of the region is that strip of land between the bay and the 500 foot elevation, where most people live, drive and work. It is a narrow strip of land averaging about 4 miles in width, with a 2 mile minimum in the Berkeley and southern Richmond areas and an 8 mile maximum at points in the San Leandro and Oakland areas. This area is home to an international airport, major chemical, petroleum, shipping and other industrial operations, a large university, a major military facility (in the process of being decommissioned) and over 3/4 of a million people.

In this area, marine air intrusion through the Golden Gate, across San Francisco, and through the San Bruno Gap is a dominant weather factor throughout the year. The Oakland-Berkeley Hills causes a bifurcation of westerly flow in the vicinity of Oakland, with southerly winds observed over the San Francisco Bay north of the Golden Gate and northwesterlies over the bay to the south of the Golden Gate. The divergent wind field results in diminished speed on the east side of the bay, with a higher frequency of near calm conditions than areas west of this split flow. Temperatures have a narrow range due to the proximity of the moderating marine air. Maximum temperatures in summer average in the upper 60's to low 70's, with minimums in the mid-50's. Winter highs are in the mid to high 50's and winter lows are in the low to mid-40's. Precipitation totals, generally, increase from south to north and from the lowlands to the Oakland-Berkeley Hills' ridge line.

Alameda Naval Air Station is located on the northern end of Alameda Island, some two miles southeast of the Bay Bridge. By virtue of its closeness to the Golden Gate, it is representative of the most marine zone of the northern Alameda - western Contra Costa region. The prevailing wind direction is westerly with a 57% frequency for wind within the northwest-southwest sector. The average speed for this sector is 9 mph and ranges from 7 to 10 mph. Winds less than 5 mph occur 30% of the time. Maximum temperatures in summer average only in the upper 60's, with minimum in the mid-50's. Winter highs are in the mid-50's and winter lows in the mid-40's. Sunshine is somewhat more scarce than at more inland stations. Precipitation averages about 20 inches per year.

The Oakland Airport is 10 miles southeast of the Bay Bridge. The wind regime is very similar to that at Alameda as might be expected from their close proximity. A bay-breeze effect along the immediate shoreline, probably augmented by a low profile in the hills to the east, gives rise to a prevailing wind from the west. Almost 50% of the wind is from the northwest-southwest sector. The average wind speed for this northwest through southwest sector is 9 mph and ranges from 6 to 11 mph. Observations of less than 7 mph occurs 50% of the time. A secondary frequency maximum from a southeasterly direction may reflect drainage of air through the nearby Hayward Gap, particularly in winter, but with lower speeds than for the westerly direction. When compared to Alameda, summer maximum and winter minimum temperatures are slightly higher and lower, respectively, as would be expected of a station slightly further away from the moderating effect of marine air. Maximum summer temperatures average near 70 degrees F and minima average in the low 50's. In winter maximums are in the middle 50's and minimums are in the upper 30's. Precipitation totals near 18 inches annually, on the average. Sunshine is slightly more plentiful than at the more coastward locations, but invasions of stratus in summer keep the amount somewhat lower than at the more inland locations.

Berkeley is built along the eastern edge of the San Francisco Bay and up the Berkeley Hills, ten miles east of the Golden Gate Bridge and two miles north of the Bay Bridge. Maximum temperatures in summer average about 70 degrees with minimums in the mid-50's. Winter highs are in the high-50's to low 60's and winter lows are in the mid-40's. Annual precipitation averages 23 inches.

Richmond, the northern most city of this zone, is ten miles northeast of the Golden Gate. At the AIR DISTRICT 's Point San Pablo meteorological station, 4 1/2 miles west northwest of downtown Richmond, the prevailing direction is south southwesterly with over 50% of the winds coming from the south through southwest sector. The average wind speed at this station is 11 mph. Richmond's maximum summer temperatures average in the low 70's and minimums average in the mid-50's. In winter maximums are in the high 50's to low 60's and minimum are in the low to mid-40's. Precipitation totals near 22 inches annually, on the average.

The air pollution potential of the areas closest to the marine air is minor , due to frequent good ventilation and less influx of high pollutant concentrations from upwind sources. Occurrence of light winds, however, mainly during the night and early morning, may set the scene for occasional elevated pollutant levels. The air pollution potential south and north of this region is higher and might be termed marginal. Its location, downwind and surrounded by air pollution sources, coupled with a relatively high frequency of light winds, mainly in the nighttime and early morning hours, could augment higher pollutant levels.