how do I get the weather to be fahrenheit from celsius?

Go to -> Settings -> General -> Language & Region -> Temperature Unit

for just the weather app, click on the three bars in the bottom right corner. then click the three dots in the top right corner. there you can change temperature measurement.

The Apple Weather app automatically sync with the Temperature Unit settings.

Unless one uses a 3rd patry app such as Wind Compass app, then one has to set appart in the settings of that app.