normal. This was particular; true during Feb- 

 ruary when the Icelandic low averaged some 17 

 nibs below normal. 



From the extremes of February, the pressure 

 patterns returned to near normal in March with 

 the Icelandic low somewhat deeper and just 

 slightly west of its normal position. This pattern 

 produced winds more on-shore than experienced 

 earlier in the season. April saw an intensification 

 of this on-shore flow off Labrador as the Icelandic 

 low spread to a broad trough extending from 

 just southwest of Iceland to the United States' 

 Northeast. A high dominated the Hudson Bay 

 area at this time. These on-shore winds drove 

 many of the icebergs aground off Labrador. 



This was the primary reason that so few ice- 

 bergs drifted south of 48°N during the latter part 

 of the 1975 season. 



During May. the Icelandic low appeared as a 

 more intense feature and shifted to a position 

 more south and west than normal. This pro- 

 duced northerly winds close to the Newfoundland 

 coast and brought some icebergs south through 

 the Avalon Channel. 



As was normal, winds averaged on-shore for 

 the remainder of the season, inhibiting any fur- 

 ther iceberg intrusion onto the Grand Banks. 



Surface pressure gradients (differences in at- 

 mospheric pressure along a geographically 

 oriented line) provide an indication of wind ve- 

 locities that exist in the area. The steeper the 

 gradients or more rapid the pressure change, the 

 higher the wind speed will be. In an attempt to 

 understand the magnitude and primary direction 

 of winds along the main drift routes of the ice- 

 bergs heading toward the Grand Banks, six such 

 gradients have been defined by the Ice Patrol for 

 Davis Strait and off the Newfoundland and Lab- 

 rador coasts. (See Figure 21). From an anal- 

 ysis of these gradients, inferences can be made 

 as tn the northwesterly winds producing south- 

 erly iceberg drift, accentuating the Labrador 

 Current, reducing the air and sea temperatures, 

 and spreading and developing sea ice along the 

 coasts of Labrador and Newfoundland. 



Gradients assigned numbers 1 and 2 in figure 26 

 measure the winds off the coast of Labrador 

 which are important in setting up the drift for 

 transporting icebergs to the general area north- 

 east of Newfoundland. Gradient 3 measures the 



wind component which assists or impedes icebergs 

 as they drift south along the eastern slope of the 

 Grand Banks. Gradient 4 is a measurement of 

 the influence of westerly (or easterly) winds 

 along the northern slope of the Grand Banks. 

 This is important in determining iceberg drift 

 away from (or toward) the Newfoundland coast 

 and into (or out of) the core of the Labrador 

 Current. If the westerly winds are too strong or 

 persistent when the bergs reach the northeast 

 corner of the Grand Banks, they may be carried 

 out over Flemish Cap and deteriorate rapidly as 

 they are pushed into the warmer waters of the 

 North Atlantic Current. Gradients 5 and 6 pro- 

 vide a preseason indication of probable icebreo- 

 drifts south and west in Davis Strait. 



The 1975 pressure gradient data are shown 

 graphically in figures 27 and 28 with a compari- 

 son provided to their 1946-1974 normals. The 

 most obvious and significant features in these 

 gradients are the high peaks that occurred in 

 gradients 1. 2 and 3 during January and Feb- 

 ruary. These peaks indicate a much stronger 

 than normal southeasterly wind drift accounting 

 for the relatively large numbers of icebergs reach- 

 ing the Grand Banks early in the season. Like- 

 wise, northerly flow and below normal southerly 

 flow indicated in gradients 3 and 2 respectively 

 dining March and April help to explain the de- 

 creased influx of icebergs during the early spring. 

 South winds across gradient 3 during this period 

 also brought warm air into the area accounting 

 for the retreat of the sea ice in late March and 

 April as discussed earlier in the Ice Conditions 

 section. Slightly above normal easterly flows 

 early in the season, as indicated through gradient 

 4. kept the icebergs offshore (hiring this period. 



Air temperatures over Labrador and east 

 Newfoundland waters were predominately 1° to 

 6°F below normal throughout the ice season. The 

 exception was February, when temperatures av- 

 eraged 6° to 13°F below normal. This month 

 was recorded as the coldest on record east of 

 Newfoundland. Graphic presentations of cumu- 

 lative frost degree days and melting degree days 

 are provided in figures 29 and 30 for selected 

 shore stations along Canada's east coast. The 

 locations of these stations are shown in figure 26. 

 A frost degree day is defined as one day mean 

 temperature of one Fahrenheit degree below 32° 



33 



