light. This was to be expected as there was little vertical devel- 

 opment in clouds of the sort that produce precipitation of the 

 showery type, nearly all clouds being stratiform in character. 



3. In forecasting the beginning and ending of precipitation in 

 connection with the passage of occluded fronts, it must be remem- 

 bered that occlusions moving into the eastern part of the Canadian 

 Arctic are well developed and mature by the time they reach this 

 area; hence, rain shields extend well forward of the front and 

 also far to the rear of the front, near the tip of the occlusion. The 

 extension of the rain shield to the rear of the front is a result of 

 well developed cyclonic circulation around the tip of the occlusion, 

 to the north. Rain shields usually diminish in size after the occlu- 

 sion has matured and has slowed in its forward movement. In 

 the Canadian archipelago this does not occur until approaching 

 Baffin Bay. 



4. In forecasting the duration of precipitation after the passage 

 of a cold front, it is important to note that the slope of the cold 

 front is usually very gradual, since the outbreaks of arctic air 

 from the northwest are very shallow. As a result of the gradual 

 slope, the rain shields extend farther to the rear than in a middle 

 latitude cold front with a steeper slope. The rain in these cases is 

 more of a steady type, rather than showery. A rain shield ex- 

 tending 75 miles behind the cold front is not unusual ; and beyond 

 that, stratocumulus clouds often extend as much as 200 miles be- 

 hind the front. 



5. With a strong southerly flow, warm, moist air is carried 

 north across considerable latitude and is subjected to cooling from 

 below when it passes over the maritime Canadian archipelago. 

 This results in the formation of fog, when the temperature of the 

 air is lowered to the dew point or below. With strong winds, 

 mixing occurs in the lower layer of air, and the effect of this is to 

 intensify the fog. It has been observed that with southerly 

 winds of from 20 to 30 knots, the fog is decidedly more dense than 

 with winds of from 10 to 20 knots. 



6. There are times, although relatively few, when precipitation 

 is of the shower type rather than of the drizzle type. An analysis 

 of the stability characteristics of the air mass involved will give 

 an indication of the type of precipitation to be expected in the 

 Arctic as elsewhere. Continental arctic air masses move into the 



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