Despite my long standing dislike of meteorology I actually faired
reasonably well on that section in the written exam, with a respectable 80 odd
%. Most of the questions I got wrong had very little to do with my
understanding of weather phenomena and more to do with Transport Canada’s dicey
wording.
Still the one I will admit to getting wrong through a lack of
knowledge was to do with a weather phenomenon that simply doesn’t occur in the
UK, it is called virga.
For those of you who can’t be bothered with the wiki article, it is
basically rain that falls from the clouds but evaporates before it hits the
ground. It indicates highly unstable air. That much I knew already.
The question, though, wanted to know about the type of instability
associated with it. I narrowed it down to two answers, basically up or down
drafts. In a futile attempt to apply some logic to the situation I picked “up”;
evaporation = heat and heat rises right?
Apparently not, virga causes downdrafts. So now I know. I’m not
unduly concerned about my lack of knowledge, in the couple of years that I’ve
been flying I’ve never really encountered it, as far as I can tell it is very
much a phenomena of the prairies.
Again, apparently not. Shortly afterwards the word was mentioned in
two consecutive weather briefings I received, with rain bearing clouds being
picked up on the radar but no precipitation being reported on the ground
stations. I don’t know what information they have but the weather specialist
assured me that the clouds were at 6000ft and the virga wouldn’t be an issue
below 3000ft.
As I was planning to do low level airwork (forced approaches and
the like) I was good to go. Sure enough though while I was up there I could see
the cloud bases and the streams of precipitation falling but stopping a ways
below the cloud.
I’ve seen similar conditions, in the air, on at least two other
occasions now. I don’t know if it is due to the weird summer we are having, or
that now I’m aware of it, I’m seeing it everywhere.
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