We Northerners try and catch Wiley in weather extremes all the time. A coyote is always thinking about its next meal, next date, and its social life. They will still go out looking for food even in nasty weather conditions as their prey is often bedded down. Any call that seems to work that time of year for your location will be just as effective regardless of the weather.
X's 2. When it is nasty, they need nutrition even more. I have had great hunting in cold, nasty weather when I was doing allot of varmint calling. I have also noticed, they are out longer in the morning on day hunts as well, add earlier out in the evening too.