image source: funkyspacemonkey.com/
Weather Code (Singapore Weather Code is SNXX0006)
Here's how I find my weather location code in Enigma:
1) Go to http://weather.yahoo.com/ and type in your zip code (or your city).
2) If there is more than one choice, pick the one you want.
3) Locate the link "extended forecast" under "6-10 day" column. Click it.
4) Look at the URL address bar. You should see something like
www.weather.com/...../extended/xxxxxx
The 8-letter code xxxxxx should be your weather location code. In your case, it is USVA0262.
Or
Go directly to http://www.weather.com, type in the city or zip code, and then look at the URL in the similar manner.
Source: answers.yahoo.com
Change LockScreen Weather Location
1. Open iFile
2. Hit the "/" button on the top left until you go back to the very first page
3. Tap on Library
4. Scroll down to Themes
5. Tap on the theme name (Should be Upsideright lock screen or whatever it's called)
6. You should see a "LockBackground.html". Tap on that and then you should see the option to open it with "TextViewer".
7. Scroll down until you see ' var locale = "XXXXXXXX" ' Replace your city code with whatever code was in the quotations. To enter text tap on "Edit" on the top left.
8. Then just press save and done. Go back to your homescreen and respring and you should be good to go.
Source: forums.macrumors.com