Question submitted by Jason Williams
1) How do they forecast the UV index for all the different areas of BC
when there is only 1 or 2 UV monitoring stations for the entire
2) I was looking back through the Environment Canada database and
noticed that there are currently no weather stations in the BC mainland
that record hours of sun. If I look 10 years ago or even 40 years ago
there were 20 to 30 weather stations that measure hours of bright
sunshine in the BC interior. Why is this the case?
For the answer, I went to Environment Canada. Here is their answer:
"UV radiation is very strongly seasonally and latitudinally-dependant.
The day-to-day variation due to the presence and strength of high
pressure systems in the upper atmosphere is important during the summer
but still very small compared to the seasonal and latitudinal influence
and of course whether the sky is cloudy or clear. Consequently the rough
value of the index for any location and time can be predicted far in
advance. Measurements of UV radiation (taken on Saturna Island) are
important for research and monitoring but not so critical to producing
the day-to-day forecast.
Regarding sunshine hours, the weather service is no longer officially
recording hours of sunshine.
There are several reasons but most important is that the instruments
used to record sunshine are outdated and crude. A close second reason is
the fact that NAV Canada has taken over the contracting for weather
observations at the airports where sunshine hours were previously
measured by Environment Canada staff or Contractors. Bright sunshine
hours are understandably of little value to flight operations and hence
Nav Can has not made their measurement a requirement at these airports
since they took over.
More sophisticated measurements of solar radiation are now possible and
we expect these measurements to eventually form the basis for
determining sunshine hours. There are apparently very strong
correlations between certain wavelengths of solar radiation and the
previously measured bright sunshine hours. This has implications for
calibrating the past bright sunshine hours to newly measured solar