This might prove useful to people....
I just came across http://phpweather.sourceforge.net/ which is an open source set of php scripts that will download current weather observations from what seems like an endless set of observation points and decode them into human readable form (the home page defaults to a station that isn't reporting right now, but the sites in the US I used worked fine).
This bit of php code will echo the temperature at National Airport outside of Washington, DC (once installed and setup to use DC as the default, took about 10 minutes):
<?php
require('phpweather.php');
require('pw_utilities.php');
$weather = new phpweather();
$data = $weather->decode_metar();
echo $data['temperature']['temp_f'];
?>
You could call this from applescript via something like:
set dca_temp to do shell script '/usr/local/bin/php /path/to/dca.php'
Obviously this requires a working install of php with the --enable-cli flag turned on, but for those that are willing to set this up it's free and easy.
Other variables like cloud cover, wind chill, wind speed and direction, humidity, etc... are reported as well.
Hope it helps someone,
Ware Adams