First, create a feed to store your data on Adafruit IO called "hightemp"-- this will catch the value from IFTTT and your Feather will check this feed for new values.
Next, create a recipe on IFTTT using the weather channel, and set it to trigger at the time of your choice. Select the Adafruit channel as the output and configure it to send today's forecasted high temperature value to the "hightemp" feed you already created.
Now each day the recipe will update the feed with today's projected high temperature! Substitute this recipe with any value, weather related or not, to customize the project.
You can manually add a value to the feed to test the project, since the IFTTT recipe will only update the feed once per day.