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19 . A look at the wind arrows indicates a problem in the Minturn data. Although the first and last minutes of wind data are not determined in the computational method used, the vertical extent of the direction arrows indicates how high the balloon was tracked. Loss of the rawin- sonde signal is a result of the topography interfering with the line of sight downstream of Minturn. Most ascents were tracked at least to 500 mb., a height sufficient for the orographic cloud analysis. Above that level increased subjectivity is imposed on the time series analysis. The time-pressure fields (Figures 4, 5 and corresponding analyses for other stations and Figure 6) are used to determine parameters of a chosen parcel of air when that air is over each of the stations. If the parcel of air is over the middle station (or the air sampled by a balloon released at the middle station) at a chosen time to' then inter- polation backward in time on the upwind station's time series gives the value of a parameter of the air parcel when it was over the upwind sta- tion. That is, if the parcel took one hour to travel from the upwind station to the central station, the parameter's value may be found to - 1 hour (and at a pressure determined from trajectories which are discussed later) on the upwind station's time series. A similar inter- polation is done forward in time to the downwind station. Time of travel of an air parcel from one station location to the next is required to reduce the time-height cross section data to the trajectories of the air as it flowed over the mountain barrier. A verti- cal profile of travel times for air over the central station at to is found by first determining the wind speed (Vo) profile of that column of air. (The wind field found at the upwind station is considered