UPDATE – 2012-01-06 22:39 GMT – Problem is solved, and everything should now be back to normal. Sorry for any inconvenience!
ORIGINAL NOTE: Our system is currently struggling to fetch temperature data from Weather Underground’s system. This is causing our API to respond slowly, requests for some lower-quality weather stations to fail (the PWS for which we are using average/maximum/minimum data straight out of WU’s system to calculate degree days), and the last day or two of data to be missing for the higher-quality stations (airports and the best PWS for which we are using our own optimized cache of temperature data but for which we still rely on WU’s system to fetch fresh data as it comes in).
All should recover once Weather Underground’s system is functioning fully again.