On page refresh the side menu with the city names are gone. I would suggest storing them in localStorage on first render. On subsequent visits or page reloads, you can then retrieve those cities from storage and just render them accordingly.

If a user enters the same city multiple times they end up populating the menu-list. To curtail this, perhaps check if city is already in the menu-list. If it is, then just make that as the active city, which would then display that city's weather data.

Give users the option to remove cities that they don't need anymore.

Give users the option to star a city. A starred city is always the one displayed on subsequent visits. It would probably be wise to store this is in localStorage as well.

Ref: #2

Sparkly chart is not informative. I would suggest using either d3 or chartjs to draw the chart with axis and maybe a legend.

Currently only render one gif for all conditions regardless of the fact that gif is most likely for clear skies.

On initial page load, data should be rendered for user's current location. Currently it's empty, requiring user to input data first. Maybe get the user's current location, probably via geolocation (and in lon and long), retrieve the data, and render it on page load.

Ref: api.openweathermap.org/data/2.5/weather?lat={lat}&lon={lon}