They RUN on 30 or 40 weight oil.
However when it is near freezing point 30 w oil is about 90w and you will not be able to pull the starter rope,
If you could get it to start it will be near 10 minutes before the oil gets thin enough to properly lubricate the engine.
OTOH if you keep your blower in a heated room and always start it in that room then let it warm up for 10 minutes before going outside, then strait 30 will be fine.
You can use 10w 30 as well just so long as the oil is warm enough to flow when you start it.
The first number is the viscosity of the oil at 20 Deg C ( whatever that is in F ) and the second is the viscosity at 100 C.
When the temperature is in the minus deg C range the oil thickens up to somewhere between honey & treacle .