3D Touch is a very convenient way to interact on the iPhone, many stock apps in iOS support this, but Weather app does not come with support for 3D Touch. This is obviously not a problem in the jailbreak community, a upcoming tweak will solve this.
Banana is an upcoming cydia tweak that will adds a Weather Glance in the 3D Touch menu, gives you a more convenient weather forecast on iPhone 6s, iPhone 6s Plus and even other older devices.
Banana tweak developed by team iOSCreatix, they have mentioned that it will be available for free in Cydia Store. The tweak will also work on iPhone and iPad that without 3D Touch support.
Once you install Banana tweak on your jailbroken device, the only thing you need to do is performing 3D Touch gesture on the stock Weather app to display a weather forecast of the day on the Menu. Such information include the current, maximum and minimum temperatures of the day and a forecast of the weather at different hours of the day along with an icon that represents the weather condition such as sunny, cloudy etc.