On mobile, simply tap on the overflow menu button + More button from within the post and select Weather.
The current weather is pulled in by your project zip code, but if necessary you can change the overview (ie, “Cloudy” to “Partly Cloudy”) as well as the temperature.
On the web, click into the existing post and tap on the Add weather button at the bottom of the comment box. Here you’ll have the option of updating the condition, temperature, humidity and windspeed. Press Done and then Send to post the update.