Thunderstorms will rumble through parts of the northeastern United States into Tuesday evening bringing an abrupt end to a period of dry and delightful late-September conditions, and AccuWeather meteorologists warn some of these storms could potentially become damaging.
The strongest storms are likely to erupt from eastern Virginia and central and southeastern Maryland to Delaware, southeastern Pennsylvania and New Jersey, but heavy and gusty storms are anticipated as far north as southern New England.
More than 16 million people will be at risk for potentially damaging storms as major metro areas of Philadelphia, Washington, D.C., and Baltimore are all included in the threat zone.
A surge in humidity will help to fuel the thunderstorms, and there's just enough warmth around to help them ignite, according to AccuWeather Senior Meteorologist Dave Dombek. On top of that other ingredients will come together to trigger the severe storms. An approaching cool front, a low pressure area along the front and a strengthening dip in the jet stream are all moving into place to set the stage for some big thunderstorms.
"Thunderstorms will be capable of producing strong wind gusts, localized flash flooding, small hail and frequent lightning strikes in the mid-Atlantic region," Dombek said.
A complex of heavy, gusty thunderstorms pushed through parts of the central Appalachians early Tuesday morning. The complex delivered torrential downpours, frequent lightning strikes and loud thunder that may have woken many residents up for their daily activities a bit earlier than usual.
"Even as this cluster of storms moves eastward and slowly diminishes, more storms are forecast to fire up farther to the north and west along the front," AccuWeather Senior Meteorologist Brett Anderson said. It is these storms that can become locally severe into Tuesday evening, he added.
Despite the last several days of dry weather in most locations, the soil remains moist. Much of the rain that falls may run off, which can lead to quick rises on some small streams in the region. The downpours may be intense enough to lead to flooding in poor drainage and low-lying areas in the major cities as well.
As the storms move through, slowdowns are likely on the highways. Airline passengers should anticipate flight delays until the heaviest of the storms have moved through the major hubs of Philadelphia, Washington, D.C., Baltimore and New York City. The storms may force ground stops and limit the volume of aircraft landing and taking off.
Some of the hardest hit communities may face power outages and downed trees. The excess rainfall late this summer has many trees top-heavy and the wet state of the soil may allow trees to fall over even in less extreme wind gusts.
Rainfall has been well above average over much of the region forecast to be affected by Tuesday's showers and thunderstorms. In some cases, rainfall has been more than double that of average since Aug. 1. New York City has picked up more than 20 inches of rain, compared to an average of 8.41 inches from Aug. 1 to Sept. 27.
In the wake of Tuesday's storms, several days of dry weather are forecast for the central Appalachians, the mid-Atlantic and southern New England. However, for those heading to the beaches for a fall getaway later this week and weekend, rough surf may be a problem due to Hurricane Sam which will continue churning out to sea.
Conditions may become favorable for a light, scattered frost over the southern tier of New York state, the Adirondacks, northwestern New England and the northern tier of Pennsylvania late Thursday night to Friday morning.
Frost in these normally colder locations of the Northeast is typical for the end of September and the start of October.
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