Pilots flying under the FAA jurisdiction have many official sources of weather information available to them. Specifically as it relates to icing conditions, what official sources of weather information can pilots refer to in order to avoid or mitigate the risk of flying in icing conditions?
Here's a list of official FAA weather information sources that pilots can analyze to avoid or mitigate icing risks:
An AIRMET Zulu will be issued for areas where icing conditions are forecast to be light or moderate.
A SIGMET will be issued for icing conditions forecast to be severe.
PIREPs are the best source of icing information. Unlike weather information sources which are forecasts, PIREPs are reports from pilots flying in the actual conditions and should be considered the most accurate source of icing information.
Here's an example of a PIREP where a pilot of a TBM-700 was descending into Atlanta. He reported a cloud layer topping at 7900 feet down to 500 feet AGL and picking up light rime ice between 7900 and 5000 feet.
UA /OV ATL /TM 1200 /FLUNKN /TP TBM7 /SK OVC015-TOP079 /IC LGT RIME 050-079 /RM DURD
Significant Weather Prognostic Charts
The top two panes of a prog chart help pilots visualize the freezing level. A zig zag line shows when freezing level is at the surface and height contours for the highest freezing level are drawn at 4000 foot intervals with dashed lines. This information gives pilots a forecast of temperatures which when combined with known precipitation can predict ice and help to avoid it.
Area Forecast (FA)
An FA is an additional source of information about where cloud tops and bottoms are. If you know that along with the freezing level you can get a better idea of where icing conditions are most likely.
You can get it from Airmen's Meteorological Information or Significant Meteorological Information, a compiled graphical version of which can be found at Aviation Weather Center. FAA Advisory Circular 91-74A, Pilot Guide: Flight In Icing Conditions, notes
Aviation meteorologists at the NWS Aviation Weather Center (AWC), local NWS Field Offices, major airlines, and private companies prepare icing forecasts. In addition, guidance products are available on the Web. Icing AIRMETs, prepared at AWC, cover a 6-hour forecast window and are updated four times daily.
Also it notes the importance of Pilot Reports (PIREP),
PIREPs remain the major source of information for icing location and severity
Note that FAA requires the weather sources to be approved by US National Weather Service. As far as icing conditions go, to the best of my knowledge FAA doesn't mandate any particular source.