MB stands for millibars, which is a measure of pressure. Correct me if I'm wrong, but 300 MB storm relative winds would essentially be the steering currents for any thunderstorms in that environment and forecasted time frame. It gives you an idea of which way the storms will most likely travel for the time selected. 300 mb is in the upper levels of the atmosphere for reference purposes. That's the quick and dirty version, and others who are sharper than I can chime in with more detail.
Allisonhouse isn't required for using GRL3 and it will function just fine without it. It's a nice to have option, for me at least, for data reliability and the other perks that come along with it (custom place files, etc.). It's a small price to pay for what you receive in return.
Allisonhouse isn't required for using GRL3 and it will function just fine without it. It's a nice to have option, for me at least, for data reliability and the other perks that come along with it (custom place files, etc.). It's a small price to pay for what you receive in return.