The weather conditions were extreme. Like as in 'not...

The weather conditions were extreme. Like as in 'not normal'...as in 'unexpected'...as in 'unforeseen'...as in 'if it was normal conditions we could have done what we planned'

It has now settled down, and the snow is within normal quantities, so they can clear the site daily to do the drilling as they had originaly planned to do, and would have done if the weather was a normal winter.

-20C is extreme, it's now just below freezing, which is more normal for this time of year, drilling and working in extreme weather conditions is not safe.