hrm current_observation wasn't in the fields and therefore won't be part of data. You could add a mapping of current_observation.temp_f.
However it sounds like this isn't even part of a recordset and you don't need a store.
Have you checked out Ext.data.JsonP.request?
It's funny that the example there is also to retrieve the weather :)
This is great! I actually had two questions answered in one. The first being that of initial question asked here and that of do I need to have store/model configuration for every request on data? It was answered. Thanks for being so thorough and patient.