A Synoptic Climatology of Winter Precipitation from 700-Mb. Lows for Intermountain Areas of the West

摘要

A synoptic climatology of precipitation resulting from upper closed Lows is developed for the intermountain areas of the West for the winter months of December, January, and February. Precipitation amoounts at about 280 stations for 12-hr. periods, centered at upper-air observation times and expressed as percentages of 7-day station amounts, are related to the positions of the Low centers at the 700-mb. level through the use of a moving grid system. The upper Lows are classified into three intensity categories according to the departure from normal of the central height. For each category the average precipitation amount, extent, and frequency of occurrence over the area of the grid system are presented. The area of maximum precipitation is found just southeast of the centers of intense 700-mb. Lows. As the intensity of the Low center decreases, not only does the frequency of precipitation diminish, but also the area of maximum frequency progressively shifts to positions south and west of the center. (Author)