observations. This past season, one berg was traced from a medium 

 dome berg temporarily aground at 47° N., 48°50' W. on 4 May to a 

 growler near 43°05' N., 49°15' W. on 7 June, when it was last sighted. 

 It was estimated to be 135 feet high and 400 feet long on 4 May and 

 survived 34 days in an estimated average temperature of 34.2° F. dur- 

 ing the interval. Sea conditions were estimated normal during the 

 period. 



Wliile an abnormally cold environment is one of the requisites of a 

 heavy ice season and an abnormally warm environment is one of the 

 requisites of a light ice season, other factors must be considered in- 

 cluding the available berg supply upstream, the weather patterns, sea 

 ice conditions, bottom topography and the water circulation. For ex- 

 ample, water temperatures during March, April, and early May were 

 colder than normal in 1963, yet 1963 was a very light ice year on the 

 Grand Banks. This can be explained by the fact that the berg supply 

 available to the Grand Banks at the start of the ice season was ex- 

 tremely low, as climatological conditions were generally unfavorable 

 for berg drift south during the winter and early spring months. Nev- 

 ertheless, all other factors being normal, the normal sea surface tem- 

 perature charts can be used both qualitatively and quantitatively in 

 berg forecasting. If a normal supply of bergs is available upstream 

 at the start of the ice season, normal or abnormally cold surface tem- 

 peratures on the Grand Banks and vicinity will indicate that a normal 

 to heavy ice season is in prospect. During the 2 heaviest ice years in 

 the past 13 years the respective isotherm charts of these years (1957 

 and 1959) indicated abnormally cold water temperatures. During 

 the two lightest ice years (1951 and 1958) the respective isotherm 

 charts indicated abnormally warm water temperatures. The 16-31 

 May and 1-15 June isotherm charts should be consulted prior to any 

 decision to terminate the International Ice Patrol for a given year. 

 Colder than normal temperatures, especially in the berg areas on the 

 northern Grand Banks, the eastern slope and the Tail of the Banks, 

 during the above periods indicates a strong possibility of bergs sur- 

 viving to the major shipping lanes (Track C) as late as mid- July or 

 even later, unless the upstream supply of bergs is very low and berg 

 sizes are small. 



WEATHER 



GENERAL DISCUSSION 



International Ice Patrol personnel over the years have pondered 

 on the reasons for the great variety in the character of each ice season 

 on the Grand Banks. The influence of weather on the annual iceberg 

 problem has long been suspected. Smith's formula forecasting the 

 number of bergs south of 48° N. each year (see Bulletin No. 30 in this 



39 



