30 



story of the change is best told by reviewmg briefly the weather history 

 of the preceding few days and foflowing the movement of the air 

 masses over the Grand Banks area. The evening map of March 9 

 showed a trough about 500 miles east of Newfoundland, a high pressure 

 area just south of Bermuda, and a disturbance over the lower Missis- 

 sippi Valley. Grand Banks weather was fuie and clear with moderate 

 northwest winds. The disturbance moved northeastward and left 

 the coast off the Virginia Capes on the evening of March 10, where it 

 deepened rapidly and traveled northeastward with increasing in- 

 tensity and centered over the Tail of the Banks on the evening of 

 March 11 with a lowest pressure of 28.50 inches. This storm had an 

 extremely steep gradient, the pressure difference being 1.09 inches in 

 150 miles, or 0.007+ inch per mile, and correspondingly high wind 

 velocities were recorded. Whole gales and storms were reported 

 everywhere in the northeast sector. This storm moved slowly off 

 to east-northeastward, but was closely followed by another which 

 crossed the southern part of the area bringing gales but passed quicldy 

 to the eastward and filled up rapidly. By the morning of the 14th a 

 strong high pressure area had built up over Ontario and the upper 

 Lake regions. This mass of cold polar air moved slowly east-south- 

 eastward over the Maritime Provinces and Newfoundland. At the 

 same time an apparently deep current of warm tropical maritime air 

 began to flow northward up the Mississippi Valley and along the 

 eastern seaboard, bringing fog along the coast and widespread rain to 

 the north. This warm air began to influence the Grand Banks region 

 on the evening of March 18 and by the 19th fog, rain, and generally 

 low visibility were general over the area. This was the flrst tropical 

 air to reach the ice area this season and for the first time the semi- 

 permanent North Atlantic high maintained itself over the central part 

 of the ocean, bringing mild and generally summer conditions to the Ice 

 Patrol. Fog set in at midnight the 19th over the cold water and con- 

 tinued until the evening of the 21st, materially interfering with the! 

 scouting of the Patrol vessel for the first time. March 23 and 24 i 

 were stormy and the month closed with a long period of high wind on | 

 March 31, when northerly gales blew for 25 hours. This boisterous* 

 weather was not the result of cyclonic circulation, but was caused by ' 

 the movement of a deep mass of polar air directly south over New-- 

 foundland and the Grand Banks and was followed by a period of! 

 unusually fine weather for this season with clear, blue sky, light winds, 

 and full visibility. The percentage of fog, visibility less than 2 miles, i 

 for the month, was 23.9 percent and the average temperature for the 

 period was 35.2° F. (See figs. 15 to 18.) 



APRIL 



The weather during the first days of April was in general slightly 

 colder than March and somewhat more fog. The outstanding fea- 



