Rounds of flooding downpours, severe storms to target Eastern US
Portions of the eastern United States will remain at risk for more episodes of flooding downpours and thunderstorms capable of producing strong wind gusts into this weekend.
AccuWeather’s Jon Porter and Brett Anderson explain the key contributors that led to the horrific flooding that took place in Camp Mystic in Kerr County, Texas, over the Fourth of July weekend.
Conditions will remain conducive for thunderstorms to produce excessive rainfall and damaging wind gusts through the end of this week from the Appalachians to the Atlantic coast, AccuWeather meteorologists warn.
The combination of lingering moisture and weak fronts moving in slowly from the central United States will be enough to set off rounds of slow-moving, but potent thunderstorms. The highest risk to lives and property is from torrential rainfall.
One issue with storms in the summertime is when they erupt, they can grow skyward and move very slowly at the same time--just like they do in tropical rainforests or jungles. This has the potential to unload a tremendous amount of rain. In localized areas, 2-4 inches can fall in an hour's time and quickly overwhelm storm drains, streets, highways and small streams.
Adjacent locations a mile or even just several blocks away may receive little or no rainfall. On Tuesday, this same setup triggered deadly flash flooding in Ruidoso, New Mexico, and inundated streets and cars in downtown Chicago.
Areas from New England to the mid-Atlantic, southern Atlantic and Appalachians will be locked into this pattern into the weekend. The areas of torrential downpours and severe thunderstorms will shift from day to day as the weak fronts from the Midwest approach and depart.
A storm that forms along one of the fronts on Thursday will be embedded within the pattern. That storm could focus a narrow zone of torrential downpours along portions of the mid-Atlantic and southern New England coasts.
"We are concerned about the flash flood threat being enhanced from Durham, North Carolina, into central Virginia, which is in the area that received 2-12 inches of rain this past weekend from Tropical Storm Chantal. The ground across this area is already saturated,” AccuWeather Senior Meteorologist Tyler Roys said.
Drivers are strongly urged not to attempt to drive through flooded roads. Where possible, turn around or move the vehicle to higher ground as water may still be rising or the road may have been washed away, and vehicles can stall or float into dangerous, deep and fast-moving water.
"It is estimated that in this area and other parts of the East, as little as an inch of rain per hour can lead to flash flooding, and the atmosphere is capable of unleashing rainfall of two to three times that amount," Roys explained.
Given the deadly and disastrous flooding events of late, people camping or living along the floodplain of small streams, which are most prone to flash flooding in the Eastern states, are urged to have an audible means of receiving flash flood alerts 24 hours a day. Residents and visitors should be aware of the quickest means to get to higher ground should flash flooding occur.
A flash flood watch means weather conditions are conducive for flash flooding. A flash flood warning means flash flooding is imminent at the location specified--move to higher ground immediately.
Along with the likelihood of flash flooding with the weather pattern will be zones of severe thunderstorms on a daily basis into the weekend.
Just as this setup is conducive to storms with torrential rainfall, some storms are likely to produce powerful wind gusts in certain locations. Tall thunderstorms and downpours can produce a downward rush of air that spreads out as it reaches ground level. These downburst or microburst winds can knock over trees, trigger power outages and cause property damage, similar to some tornadoes.
Into Wednesday evening, the greatest risk of storms packing localized damaging wind gusts will extend from southeastern Pennsylvania and central New Jersey southwestward to eastern Tennessee, northeastern Georgia and the South Carolina midlands.
On Thursday, two main areas where severe thunderstorms will be capable of producing powerful wind gusts are forecast.
One zone is centered on northern New England, northeastern New York and part of the St. Lawrence region of southwestern Quebec. AccuWeather StormMax™ wind gusts in this area are projected at 70 mph.
Farther south, the risk of storms packing damaging winds will extend from southern New Jersey and northern Delaware to eastern Georgia.
Within this zone, a more concentrated area of severe weather is likely from southern Virginia to along the South Carolina/Georgia border. The AccuWeather Local StormMax wind gust for this zone is 80 mph.
On Friday, the risk of severe thunderstorms with high winds will tend to ease, and that lull may last into part of the weekend in the Northeast.
However, on Saturday, the next round of severe thunderstorms will march across the Great Lakes and the Ohio Valley.
As the front associated with the severe weather continues to move along during the weekend, the risk of severe weather is likely to increase in the Appalachians and eastern Great Lakes on Sunday.
As severe thunderstorms and torrential downpours affect the major metro areas of the East into this weekend, substantial and long-lasting travel delays can unfold in a matter of minutes. Severe thunderstorms can prompt ground stops at the airports, while flooding downpours can bring traffic to a standstill on some of the major highways.
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