UIIC 551.~.1:651.613~3)"1972.05" WEATHER AND CIRCULATION OF MAY 1972 Continued Drought in the Southwest

• Main Author: Robert R. Dickson-national
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Hudson Bay; Canada; Pacific; Hudson; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.2633; http://docs.lib.noaa.gov/rescue/mwr/100/mwr-100-08-0648.pdf

Large circulation changes took place from April to May as the relatively flat, high-latitude flow pattern of April (Wagner 1972) broke down into a highly amplified pattern during May (figs. 1-3). Mean 700-mb Lows moved southward over both northern Asia and the North Pacific Ocean, accompanied by a return of the westerlies to more normal latitudes (fig. 4). Height anomaly changes over the mid-Pacific were especially striking (fig. 3). Here, a mean trough replaced a mean ridge. This reversal markedly shortened the wavelength across the Pacific, quite in keeping with the observed decline of the mid-tropospheric westerlies to near-normal values after the relatively high speeds of April. To the east of the deepening mid-Pacific trough, a strong ridge developed over western Canada and Alaska, surmounting a fairly active low-latitude trough near California. The pre-existing blocking ridge near Hudson Bay strengthened to the south during May and continued to be a dominant factor in the weather over the United States. South of the blocking ridge, heights were subnormal over much of the southern half of the Nation, and the 700-mb westerlies were observed well south of their normal position. The normal buildup of the upper level continental ridge in late spring was thus delayed. The 700-