Getting current and average on a single row

What is best practice when extracting both current and average from a 
table? Demonstration table here contains data from a cheap weather station.

I can obviously get the current reading like this:

select temp_out, dewpoint
from weather
where datetime between (now() - '10 minutes'::interval) and now()
order by datetime desc
limit 1;

and I can get averages like this:

select avg(temp_out) as avg_temp_out, avg(dewpoint) as avg_dewpoint
from weather
where datetime between (now() - '45 minutes'::interval) and now();

In both cases there are a dozen or so columns in total. How are these 
best merged to yield a single row? Some form of join, or window functions?

-- 
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]