Concentration

Characters with the Concentration skill are able to keep their full attention on what they are doing despite distractions going on around them (taking damage, harsh weather, etc.). Such actions include casting a spell, concentrating on an active spell, directing a spell, or using a spell-like ability. If you have enough grades in Concentration to overcome the distraction, you continue what you were doing as normal. If you do not have enough grades, whatever you were doing is disrupted. If you were in the process of casting a spell, the spell is lost. If you were concentrating on an active spell, the spell ends as if you had ceased concentrating on it. If you were directing a spell, the direction fails but the spell remains active. If you were using a spell-like ability, that use of the ability is lost.

Difficulty Grades

 * Grade 1: Weather is a high with the wind carrying blinding rain or sleet.
 * Grade 2: Weather is wind-driven hail, dust, or debris; or distracted by nondamaging spell
 * Grade 3: Vigorous motion (on a moving mount, taking a bouncy wagon ride, in a small boat in rough water, belowdecks in a stormtossed ship), damaged during the action.
 * Grade 4: Violent motion (on a galloping horse, taking a very rough wagon ride, in a small boat in rapids, on the deck of a storm-tossed ship), Entangled.
 * Grade 5: Extraordinarily violent motion (earthquake), grappling or pinned. (You can cast only spells without somatic components for which you have any required material component in hand.)

Retrying
Yes, though a success doesn’t cancel the effect of a previous failure, such as the loss of a spell you were casting or the disruption of a spell you were concentrating on.

Special Considerations
A character with the Combat Casting feat gets a +2 bonus to Concentration grade made to cast a spell or use a spell-like ability while on the defensive or while grappling or pinned.