We get asked this all the time by users running Facebook campaigns, so we thought we'd clear this up. Short answer is, it's completely normal.
The reason for this is because WeatherAds works by adding and removing locations (based on their localized weather) from your geo targets within the ad set. This way your ads only get shown to viewers experiencing your desired weather condition.
When a location is added back in to your location targeting list, your ad(s) automatically gets re-approved by Facebook - a process that is effectively instantaneous.
These notifications can be disabled from within Facebook's notification settings:
Facebook Ads Manager > Account Settings > Notifications > Ads Approved (uncheck)