Niantic has announced that on March 30th, 2019, there will be a Weather Based Limited Research Day in Pokémon GO with a specific focus on the Pokémon Lotad.

Weather-focused Limited Research, featuring Lotad!

Trainers, Professor Willow is looking to conduct Limited Research on the impact of weather on Pokémon, with a focus on the Water- and Grass-type Pokémon Lotad. Spin Photo Discs at nearby PokéStops to obtain Field Research tasks that lead to encounters with this Water Weed Pokémon. While you’re completing research, keep an eye out for other Pokémon that could be impacted by weather conditions, such as Castform! See more details below:

Date + Time

• Mar. 30, 2019, from 11:00 a.m. to 8:00 p.m. in your local time zone.

Features

• Pokémon that appear due to weather conditions will appear more frequently during the event.
• Limited Research tasks will be available when you spin Photo Discs at PokéStops.
• Completing the Limited Research tasks will award you encounters with Lotad.
• If you’re lucky, you may encounter Shiny Lotad and Shiny Castform in its Normal form!

Move

• The move Weather Ball for Castform will be permanently added to the game.

Remember, Trainers! As long as you’ve collected the Limited Research during the event window, you can complete it at any time. Don’t forget—you’ll need to venture onward to many PokéStops in order to get new Field Research tasks and encounter as many Lotad as possible!

We’re looking forward to seeing you out in the field! Stay safe and happy exploring!

Source: https://pokemongolive.com/en/post/fieldresearch-mar2019/