We've been waiting a couple of days for the rain in central and north Texas to push in. Finally, today was the day. What we've been waiting for is a small scale feature called a 'meso high' or 'cold pool' to form. It started with heavy rain in central Texas. Flooding rains near New Braunfels cooled the atmosphere enough to get the process started. That began the chain reaction, an expanding 'cold pool' of air at the surface finally became strong enough to 'shove' the line of storms south and east where they are now pushing off the coast. Leaving Houston with a beautiful, cool, drizzly, rainy afternoon.