In the Crown Tundra, things are slightly different because the weather is based on the fifteenth day of each month.
Jan 15 - Fog
Feb 15 - Overcast
March 15 - Clear
April 15 - Rain
May 15 - Sun
June 15 - Rain
July 15 - Thunder
Aug 15 - Thunder
Sept 15 - Clear
Oct 15 - Fog
Nov 15 - Clear
Dec 15 - Sun
So if you want to find certain Pokemon quickly, change your Switch clock's date to one of these, and the weather will be as listed.
As for Drakloak, according to this source it can be found in all listed weather as a visible encounter in the Old Cemetery. However, it is a rare spawn.
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