Unusually warm, sunny weather, such as occurred in midv;inter 1968, causes the 

 snowpack on the north aspect to melt faster in the forest than in the small openings. 

 This is attributed to a difference in the net energy balance between the forest and 

 small openings. The fact that the winter sun traverses a low arc on the southern horizon 

 apparently is not a disadvantage to a dense forest stand on a north slope. The tall, 

 projecting crowns, which expose a dark green mass with some surfaces actually perpen- 

 dicular to the sun's rays, readily absorb solar radiation and in turn reradiate consid- 

 erable amounts of thermal energy to the snowpack. In contrast, the snowpack in the 

 small openings presents a highly reflective surface which slopes to the north and away 

 from the sun's rays, thus reducing the amount of absorbed radiation. This explanation, 

 although conjectural, seems plausible in light of radiation measurements taken by 

 Hombeck (6) in an eastern forest. He reports that on clear days in February a forest 

 (hardwood) site absorbed 2.6 times more downward solar radiation than a clearcut site. 

 He goes on to state: 



. . .That on clearer days sensible heating of the snow cover and 

 subsequent melting may be more rapid for the forest site, provided 

 little or no slash protrudes above the snow at the clearcut site. 

 The above conditions could delay the advance in snowmelt runoff 

 often associated with clearcutting. . . . 



The lysimeter results at Priest River support Hombeck 's speculation as it applies 

 to small openings on the north slope of a western coniferous forest. 



Conclusions 



The release of water from the snowpack in winter is a very important geophysical 

 process, the ramifications of which could apply to any forest conditions and climates 

 similar to those in Priest River. The significant happening in this process is that 

 the volume of outflow beneath the canopy exceeds that in small openings, resulting in 

 less snow water equivalent in the forest by April 1. During a typical winter the 

 evidence suggests that most of the difference in outflow originates in the canopy where 

 intercepted snow is converted to drip which in turn percolates through the snowpack 

 and hence becomes a net loss to snow storage. 



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