July 24, 2008, was predictably warm in Belknap County, New Hampshire, as Jim Doucette drove home from his job with the New Hampshire Highway Department just before noon. The sun was poking through the clouds, but rain was in the forecast—lots of it. He clicked on the radio to catch a weather update.
One state away, in Maine, forecasters at the National Weather Service (NWS) in Gray huddled around Doppler radar. They were keeping a close eye on New Hampshire. A Flood Watch was in effect for the state, and local rivers and streams were already swollen. But despite the prediction for soaking rains, the forecasters were mainly concerned about the mounting evidence that severe weather might be in the making.
A strong, low-level jet shooting up from the south and an unusually strong upper-level low digging in over New York and Pennsylvania had primed the atmosphere to produce damaging winds. A dewpoint gradient, similar to a “dry line” in Tornado Alley, was evident with humid air in the east and slightly drier air over the western half of the state—a classic severe weather set up. At the same time, a cold frontal boundary was working into New England, able to provide the broad atmospheric lift needed to get things going. Would it be the trigger for thunderstorms?