Approach plates with a snowflake symbol ( ) require altitude corrections for various approach segments when the outside air temperature is below the listed temperatures.
Snowflake symbol for a Cold Temperature Restricted Airport
The Cold Temperature Restricted Airports document is found in ForeFlight under Documents > FAA > Winter Operations > Cold Temperature Restricted Airports. Once downloaded, the document is automatically updated each data cycle. The document includes a list of applicable airports. At the end of the document is a temperature and altitude table.
Expanded Cold Temperature Restricted Altitude Correction Table