addressed their free Weather app by making it Windows Phone 7 Mango compatible, with Live Tile and all.
To me a good weather app should satisfy three criteria: provide an accurate weather forecast, a Live Tile (or widget if it is on Android) that is well designed and offers some form of customisation. Most of the free and paid weather apps on Windows Phone do at least satisfy two of those.
After a couple of months of installing and uninstalling tons of various weather clients, I've finally settled on what I would call the weather app to have if you are on Windows Phone. WeatherMaster by Snocc is a commerical app that costs £1.49/US$1.99. It may sound expensive for a weather app but it satisfy all the criteria that I want from a nice weather app.
StormGlass (an excellent freeware weather app), they aren't overpowering with information, which makes them easy to glance over - a key philosophy of the Metro user interface.
The one feature that made WeatherMaster stood out over many of their competitors is the ability to pin a Live Tile specific for the location you are in. Most apps allows you to pin fixed locations to the Start screen, but WeatherMaster at least allows me to keep track of the weather from my current location. Locations and forecasts are updated automatically in the background. It supports seven days of forecast, presented in detail in a chart form with all sort of information (including 'feels like' temperature) that would make any weather geek happy. An animated weather map, including radar layer, is also available.
Windows Phone Marketplace.
In the event that you find the data of WeatherMaster not reliable enough for your location,Windows Phone has plenty of alternative weather apps worth checking out, both freeware and commercial. Weather Flow for example is a beautiful new app by the makers of AppFlow. And if you are someone who swears by Gismeteo weather data, you will be glad to know they have also released their own app.