loom large (on the horizon)
to be coming as a possible problem or danger or threat
A large increase in transportation costs is looming large on the horizon.
Amazing Science Images You Must See
Its getting breezy on the East Coast as Hurricane Sandy approaches the mid Atlantic states. The ghostly lines on this map represent wind speeds, withwhiter, thicker lines representing faster winds. As of about 11 a.m. EDT on Oct. 29, 2012, winds were blowing at speeds between 15 and 30 miles per hour (24 and 48 kilometers per hour). Forecasts call for Sandy to blow in to New York City with winds ranging from 40 to 55 mph (64 to 80 kph) with gusts up to 70 or 80 mph (112 to 129 kph).