UDC 551.506.1:551.513(73)"1973.04" WEATHER AND CIRCULATION OF APRIL 1973 A Stormy Month With Widespread Flooding
A broad, deeper-than-normal trough extending from the Great Lakes to northern Mexico was the 700-mb circulation feature that controlled much of the weather over the United States during April (figs. 1,2). The western lobe of the double trough that had prevailed over the United States during March (T...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.2368 http://docs.lib.noaa.gov/rescue/mwr/101/mwr-101-07-0597.pdf |
| Summary: | A broad, deeper-than-normal trough extending from the Great Lakes to northern Mexico was the 700-mb circulation feature that controlled much of the weather over the United States during April (figs. 1,2). The western lobe of the double trough that had prevailed over the United States during March (Taubensee 1973) weakened as 700-mb heights rose strongly just off the west coast, due to deepening of the midlatitude portion of a trough south of the Aleutians and strengthening of the ridge over the eastern Pacific (figs. 1-3). The greatest change in circulation from March to April was over the Atlantic and Europe, where the blocking which had been over the British Isles retrograded to a position south of Greenland and 700-mb heights fell rapidly to the east (fig. 3). The lower latitude portions of the trough, which had been over the western Atlantic, moved eastward as heights fell and the westerlies increased south of the block. Blocking was also strong on the Siberian side of the Pole, where heights averaged nearly 140 m above normal (fig. 2). Weaker areas of blocking were located over central Canada and the western Bering Sea. The axis of maximum 700-mb wind was located near its normal April position over the Pacific, but speeds FIGURE 1.-Mean 700-mb height contours in dekameters (dam) for April 1973. FIGURE 2.-Departure from normal of mean 700-mb height in meters (m) for April 1973. FIQURE 4.-Mean 700-mb geostrophic wind speed (m/s) for April 1973. Solid arrows show the observed axes of maximum wind speed, and dashed lines show the normal. F1~*5.--Departure from normal of average surface temperature |
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