A well pointed dish with a clear line of sight (i.e. not through the leaves of a tree, or other obstruction) to the satellite should have a strong signal with over 80+% signal strength. Obstructions such as tall buildings, and trees are the most common sources of permanent blockage that can prevent a clear signal.
To check for a clear line of sight (which I do suggest before you order) go to a web site like
DishPointer or one of the umpteen apps to check what direction and angle (azimuth and elevation) is requires for a dish at your location.
Normal rain fall is not sufficient to interfere with a strong signal, but a heavy downpour, freezing rain, medium to heavy snow fall, or moderate to heavy lightning activity can all disrupt the signal, ranging from a fraction of a second of blockiness (thanks MPEG) to complete signal lost for 20-60 minutes.
I don't know about locations such as Alaska or Hawaii, check with DirectTV for more information.