Before N341PL started takeoff on runway 31L, a Boeing 747 was cleared to taxi southeast down the outer/parallel taxiway. The taxiway was 375 ft right of the runway centerline. The 747 stopped momentarily, then turned 90 deg left onto taxiway KK. Meanwhile, N341PL was cleared for and began taking off. The pilot stated he saw light snow behind the 747, but was not concerned since the 747 had stopped. The tower controller and another witness reported an increasing amount of snow behind the 747 as it turned off the outer taxiway. After lift-off, the pilot remained in ground effect while accelerating to climb speed. He stated he was trained to use this procedure on all takeoffs. The pilot stated that after he called for gear retraction, he entered a whiteout condition, leveled his wings from a roll, and encountered a down-draft. The plane emerged from the snow cloud and struck the runway about 1100 ft before passing behind the 747. Flight Safety Intl stated that during ground/simulator training they recommend a positive rate of climb in IMC and at night.