The climate of Silverymoon is subarctic.
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The climate of Silverymoon is subarctic, with some notable changes from IRL subarctic climates.
Toril is closer to it's sun during the Silverymoon summer, and also Toril moves closer to it's sun at this time than Earth ever does IRL (and the sun is 7% more luminescent in our sky at Earth's closest approach to the sun, during our southern hemispheric summer.)
North of Silverymoon is the Spine of the World, over which cold air must chinook the year around, warming and compressing as it drops in altitude.
A relentless procession of storms come in off the Trackless Sea, and during the summer the northern part of these storms affect the Silverymoon area.
Permafrost does not underlie Silverymoon.
Thus, summer in Silverymoon is hotter than is normal for any subarctic climate.
There are three full months where the average high is over 75 degrees (24 degrees Celsius) and the average low is above 50 degrees (10 degrees Celsius.)
In July average highs approach 80 (27 Celsius) and average lows approach 60 (16 Celsius.)
There is actually a short frost-free season in Silverymoon, of about 80 days. It does not snow during the three summer months.
Thus, grain crops can be grown in the Silverymoon area, whereas IRL grain crops cannot survive in the Subarctic.
The snow-melt and ice-breakup comes in very late April or very early May, and is sudden and violent, with severe flooding the norm. Average temperatures rise 40 degrees (21 to 22 degrees Celsius) overnight - literally overnight - with this melt, going from glacial to springtime.