try and say your city or current location
try and ask Siri the weather in your location. like in example;
"what's the weather for San Francisco today"
"does it look like its gonna rain in San Francisco today"
I find sometimes she "chokes" on some location based questions. the other day I was deep inside a residential warehouse district and she was having troubles finding food or gas locations. but then I tried asking with the current location in my question and she got it each time.
might wanna keep you wifi toggled on. it is noted for geobased reminders work better with that toggled on. maybe it's the same with Siri and geobased questions.
hope that helps.