Approach plates with a snowflake symbol ( ) require altitude corrections for various segments when the outside temperature is below the listed temperatures. You can find the Cold Temperature Altitude Corrections document with a list of Cold Temperature Restricted Airports in ForeFlight under DOCUMENTS > FAA > WINTER OPERATIONS > COLD TEMPERATURE ALTITUDE CORRECTIONS. Once downloaded, the document is automatically updated each data cycle. At the end of the document is a temperature and altitude table.
Image 1. Aspen (KASE) is a Cold Temperature Restricted Airport, which can be determined by the snowflake symbol.