A mobile observation of pressure was performed to confirm the formation of meso-low under the Kiyokawa-dashi winds which are strong local easterlies in the Shonai coastal plain. The pressure observation was made by means of the American Paulin System Altimeter. Temperature and altimetric height were measured at bench marks where their elevations are shown on the 1/25, 000 topographic map. The barometric pressure and therefore sea-level pressure were obtained by the hypsometric formula. By the procedure geographical precise pressure distribution can be obtained. The observation was made between 11000 and 15:00 on July 11, 1987. Temperature and winds were also measured through the mobile observation by using the Assmann ventilated psychrometer and a Nakaasa-type portable wind vane and anemometer, respectively. At the base station, pressure and winds were recorded by a barograph and by a portable wind vane and anemograph, respectively, during the mobile observation. In addition to the observation, the vertical distribution of upper wind and static stability were analyzed by using the serological observation data obtained at Akita and Sendai Meteorological Observatories. During the observation, an extratropical low was passing over the Sea of Japan(Fig. 3)and pressure distribuution was typical “east high/west low” situation(Fig. 4). The results of the present investigation are summarized as follows: 1. The mobile observation of meso-low by using the altimeter was found to be very useful to examine mesoscale distribution of the barometric pressure. 2. Surface easterlies prevail over the plain under the condition of southerlies at about summit level of surrounding mountains. Wind speed is the highest at the valley mouth where the Mogami River comes out on the plain, and the speed is low in the valley and southern part of the plain (Fig. 6). 3. A meso-low develops over the plain and pressure difference between the center of the meso-low and inner part of the valley reaches above 4mb (Fig. 7). In particular, pressure gradient becomes largest in the vicinity of the valley mouth.