I have a bunch of modern concepts (XL-IS ish) - a complete package of TWC concepts and now some for WxScan.
The types:
Wave 1 concepts use a blue cloud background, ISv3 style titles, and have a PMX touch with the location name. Examples in Wave 1 use Middletown, Virginia and have file names beginning with TWC Concept.
Wave 2 features a different background, XLv1 style titles, and Charleston as the example city. Wave 2 also contains some WeatherScan designs using Frutiger. Wave 2 designs have just numbers or a number preceded by a W (for Weatherscan) for file names. "Current Conditions.png" is a concept for a 2-site STAR.
There are also other concepts featuring an updated 4000.
Resources used are original, from Martin's IS goodies (Record Temp items and Frutiger), from Robert, Michael, Tyler, and Al Lopez (modified XL icons), the Samurize forums and Stephen (XL icons), or the National Weather Service (weather advisories you see here were actually issued!). Very little of the weather data is real - if it is, it was obtained from weather.com or Weather Underground (almanac). The backgrounds were taken from large-format photos of clouds and then modified to look blurred.
One thing I noticed is that the Samurize forums called the XL icons the "Reference" package. There's no current TWC set, which is ironic enough considering some things TWC hasn't updated in years (the TWC Mac Dashboard widget and some web gadgets) still use the XL icons.