The severe storm risk zone includes Washington, D.C., Baltimore, Philadelphia, New York and Boston.
The National Weather Service issued a severe storm watch for the zone from northeastern Pennsylvania to southeastern Maine until 8 p.m., including Scranton, New York, Hartford, Boston and Portland.
“This is an extreme weather environment that is unusually experienced in Southern New England, and the potential for brief tornadoes and straight-line wind damage is a credible risk in environments like this,” the Weather Service office in Boston wrote.
Additionally, a flash flood watch is in place for most of Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire and southern Maine. Storms can train or repeatedly pass through the same areas, dumping heavy rain on an area that has received more than its fair share of water in recent weeks. This could revive concerns about flooding, particularly in urban areas.
Further south in the mid-Atlantic, the Weather Service warned that strong thunderstorms could also develop, but they may not be as widespread as in New England. ONE severe thunderstorm watch also issued until 11 p.m. for the zone from Northern Virginia through east-central Pennsylvania and much of New Jersey, including Washington, Baltimore, Philadelphia and Allentown, Pa.
Despite the blustery forecast, the storms do nothing to dampen the heat. Much of the eastern half of the stretch between Washington and Boston is under heat warnings, with highs forecast to top out in the 90s to near 90 from south to north. Some areas within this zone, including New York, are subject to extreme heat warnings. Here, temperatures in the mid-90s or higher will overlap with oppressive humidity to make it feel at least 105 degrees.
The same storm system that will spark storms in the Northeast brought strong gusts to the Great Lakes and Ohio Valley on Wednesday. Detroit Metropolitan Airport recorded gusts of 67 mph, and a 70 mph gust occurred in Stockton, Ill. Three people were injured by falling trees at Presque Isle State Park in Erie, Pa.
Risk of severe weather on Thursday
- Areas affected: A level 2 out of 5 severe weather risk has been set by the National Weather Service's Storm Prediction Center. It includes parts of the Mid-Atlantic and Tri-State area of New York City, as well as New England away from the immediate southern coast of Massachusetts, the Cape, and the islands. Inside the danger zone is DC. Baltimore? Philadelphia; New York; Scranton, Pa.; Hartford, Conn.; Providence, RI; Boston? Manchester, NH; and Portland, Maine.
- Synchronization: Showers and thunderstorms in the western parts of the Northeast will increase in coverage and intensity as they approach the Appalachian calm until 3 or 4 p.m. after noon? They will then gradually swell as they move towards the coast.
- Belongings: With a fast jet stream moving overhead, storms are likely to mix momentum at the surface in the form of strong to locally damaging straight-line winds. A few gusts over 70 mph are possible. Hail, perhaps the size of a nickel to a quarter, may accompany the strongest storms. A few isolated tornadoes are also possible elsewhere in the region, particularly in the Connecticut River or Blackstone Valleys, as well as north-central Massachusetts, southeastern Vermont, and southern New Hampshire.
A decaying MCS, or mesoscale convective system, exits the Great Lakes. It was sailing in a pulse of strong mid-level west-southwest winds.
This jet stream energy is associated with a thin pocket of cold, high-altitude, low-pressure, spinning air aloft. Because it is a relatively weak trigger, there will not be a significant temperature drop behind the system.
That said, storms won't need a strong trigger to get serious given the abundant heat and humidity present.
The greatest tornado risk will be near the Massachusetts-Vermont and Massachusetts-New Hampshire borders. There will be a warm front there. Warm fronts tend to have a little extra twist, which storms can eat up and use to spin more strongly. In addition, a few rogue supercells, or more distinct, individual rotating storms, are also expected to form there.
Heavy rains and floods
Thunderstorms can also bring heavy rainfall, especially considering how moisture-laden the atmosphere is, especially in northern New England. Precipitable water, a measure of the amount of moisture present in a column of atmosphere, is about two inches, which is well above normal. As the rain falls, the moist air will gradually be replaced by south-southwesterly surface winds. That means storms could squeeze all that moisture out of the air, like squeezing a sponge, and then swallow more moisture and do it again.
At least 1.5 to 2 inches of rain is expected in northern Vermont and New Hampshire and western and central Maine.
In southern New England, weather models are projecting somewhat less rain, or about half an inch to an inch. It's important to note that, given the scattered nature of the storms, some places could receive double or triple that, and some will miss out heavily. This is why some pockets of flooding are possible.
New England has been flooded recently, and with saturated soils, the soil won't be able to handle much extra water. This will increase the risk of flooding.
Hartford's Bradley International Airport experienced its wettest July on record, with 12.43 inches. The records date back to 1949.
Most of New England is running 4 to 8 inches above average over the past 30 days. That's why any extra rain could be problematic.
