HAILSTORM! Numerous communities around New England saw it during Thursday afternoon's storms. The hail came with a fury at times, pelting cars, rooftops and at times even coating lawns and decks! When the size of hail grows to 3/4" in diameter it is considered a Severe Storm. Towns from Franklin, Milford, Princeton to Portsmouth and Haverhill to the Cape all reported pea- to quarter-size hail, at times reaching 1" in diameter.
An upper level trough over New England with its associated cool pool of air shifted into New England Thursday afternoon. Unseasonal cool, dry air in the mid levels of the atmosphere helped to destabilize the atmosphere during the peak heating of the day. This created what we call steep lapse rates which allows warm air to continue to rise into the cooler air aloft, allowing steady updrafts into the building thunderstorms. The cool dry air in the mid-levels promotes evaporational cooling at first, which lowers the freezing level into the storm. As super cooled rain drops fall to the surface, updrafts push the raindrops back up to the freezing level where the drops begin to freeze. Eventually, the hailstones will become large enough to overcome the updraft and fall to the ground.
We saw mostlly small but intense downpours of hail today. In big thunderstorms, like what occurs in supercell thunderstorms with persistent strong updrafts, hailstones can be suspended within the storm and hover around the freezing level and can grow into the size of golfballs, baseballs or even grapefruit!
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