Severe storm, flash flood risk to peak in mid-Atlantic states this weekend
The pattern responsible for sparse severe thunderstorm activity and heavy rainfall the past few days will increase the risk to lives and property across the northeastern United States this weekend.
Those sweltering in recent days from blazing sunshine, heat and high humidity will get relief but at a price.
Motorists and those spending time outdoors should be on the lookout for rapidly changing weather conditions. Airline passengers are likely to face delays as storms approach their departure, arrival or connection hubs.
A couple of storm systems will roll eastward from the Midwest this weekend. These storms will tap the high level of moisture in the region as well as a north-south temperature contrast.
Some communities will be hit with severe thunderstorms containing high winds, hail, torrential downpours and frequent lightning strikes.
One severe thunderstorm produced a wind gust of 59 mph at Gaithersburg, Maryland, on Saturday afternoon with wires downed in nearby Rockville.
One person sustained injuries when a tree fell onto a car near Harpers Ferry, Maryland, according to the 911 call center.
<center><blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">Washington DC right now as storms roll in. <a href="https://twitter.com/hashtag/DCwx?src=hash">#DCwx</a> <a href="https://twitter.com/hashtag/dcweather?src=hash">#dcweather</a> <a href="https://t.co/gzCxht7BEd">pic.twitter.com/gzCxht7BEd</a></p>— Paul Blake (@PaulNBlake) <a href="https://twitter.com/PaulNBlake/status/888829392574701568">July 22, 2017</a></blockquote>
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Into Saturday evening, the area from the Ohio Valley to areas within 100 miles or so of the Mason-Dixon line will be at greatest risk for one or more lines of severe thunderstorms.
"Philadelphia; Atlantic City, New Jersey; and close to New York City will be at greatest risk for these dangerous and disruptive storms into Saturday evening," according to AccuWeather Senior Meteorologist Kristina Pydynowski. "After one violent thunderstorms produced a wind gust to nearly 50 mph in Washington, D.C., another violent thunderstorm may follow on Saturday evening."
Severe thunderstorms will also erupt over the Ohio Valley into Saturday evening, targeting Cincinnati, Ohio; Huntington, West Virginia; and Louisville, Kentucky.
Storms along this swath could knock down trees and lead to power outages. A small number of tornadoes could be spawned by the strongest thunderstorms.
Some neighborhoods and rural areas can be hit with flash and urban flooding, where streets suddenly become rivers and small streams become raging torrents of water. Those camping along streams should remain vigilant and keep up to date on flash flood advisories as they are issued.
In some cases, a single thunderstorm can lead to flooding. In others, the cumulative effect of multiple rounds of storms can lead to high water.
"Meanwhile, a soaking rain will spread over areas from northern Pennsylvania, northern New Jersey and the New York City area," Pydynowski said.
"Disruptions to weekend plans and slower travel can be expected in this zone, and localized damaging winds and flash flooding cannot be ruled out," Pydynowski added.
During much of the weekend, a wedge of slightly cooler and less humid air will prevent severe weather across much of New York state and New England.
Dry and cool air may continue to hold off showers and thunderstorms across much of eastern New York state and New England on Sunday.
Farther southwest on Sunday, another round of severe thunderstorms may threaten areas from the upper Ohio Valley and mid-Atlantic.
Some areas, including Washington, D.C., and Baltimore, could be hit with severe weather two days in a row.
"Storms threaten to bring damaging wind gusts and blinding downpours to the major cities along the mid-Atlantic's I-95 corridor, snarling traffic and potentially causing extensive power outages and airline delays," AccuWeather Meteorologist Kyle Elliott said.
An isolated gusty thunderstorm may also erupt over Detroit on Sunday afternoon.
Meanwhile, much of the weekend may be free of rain in Boston on north and east.
Sunday is likely to be the more active of the two weekend days for the Tennessee Valley, southern Appalachians and southern mid-Atlantic.
Behind the second storm, the atmosphere should become cool and dry enough to prevent shower and thunderstorm activity across the western and central Great Lakes and north of the Ohio River on Monday.
However, depending on the speed of the second storm, areas from New England to the mid-Atlantic coast and southern Appalachians could face another day of showers and thunderstorms, some of which could be heavy, gusty and perhaps even severe.
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