Tropical Storm Irene and a rare pre-Halloween snowstorm taxed utility crews’ capabilities and prompted calls for improved disaster planning. In August, Hurricane Irene swept up the East Coast and left millions of residents without electricity in its wake. Although Irene was downgraded to a tropical storm before it reached Massachusetts, more than 500,000 National Grid customers statewide lost power, with many losing power for up to a week. Then in October, a nor’easter downed trees and power lines, leaving more than a half-million Massachusetts residents without power in the immediate aftermath. More than 80,000 residents lost power for a week. Gov. Deval Patrick asked the state Department of Public Utilities to investigate how major utilities prepared for and responded to the outages.