The mesoscale structure of the lowest 1500 m of the atmosphere for the central Oregon coast region was investigated during August 1973, using meteorological and sea surface temperature data obtained primarily by an instrumented aircraft. Two types of aircraft flight patterns were utilized. The horizontal variability of wind velocity, air temperature, moisture and sea surface temperature are discussed from data collected during level flights at 150 m over the ocean. The vertical structure of temperature, mixing ratio and wind, extending from 50 km inland to 40 km seaward, is examined from a series of horizontal traverses and aircraft soundings made throughout the lowest 1500 m. The mesoscale wind field over the upwelling region has a structure which depends, to a large extent, on the basic stratification and depth of the marine layer. On days with moderate to strong northerly winds, three separate patterns in the seaward variation of wind speed at 150 m above the surface were observed: a maximum along the coast which was the most frequently observed pattern; a maximum 10–30 km offshore oriented parallel to the coast; and otherwise a mostly uniform pattern. Those cases with a maximum offshore were characterized by a shallow marine layer with no significant inversion in the lowest 1500 m and a protrusion of relatively dry air (presumed subsidence from aloft)associated with the wind maximum all other cases were characterized by either a deep marine layer or strong marine inversion. Horizontal gradients in the ambient air temperature appear to reflect the sign of the sea surface temperature gradient to a height of only 150 m or less, as horizontal gradients in the air temperature at 150 m were typically quite small, 1°C (30 km)−1, even days when sea surface temperature gradients were as large as 5°C (30 km)−1.