Northeast Braces For Return Of Downpours And Flash Flooding

Conditions more typical of September swept into the Northeast at the tail end of July, but the clock is ticking on the dry and cool weather pattern, AccuWeather meteorologists say. A familiar regime of downpours and flash flooding may soon return.

Cooler and less humid air swept into the Northeast over the weekend and has shown some staying power following the first official heat wave for cities such as Dover, Delaware, and Atlantic City, New Jersey.

Multiple days with highs in the upper 80s to the middle 90s F have been replaced with temperatures and humidity levels more typical of the middle of September. Temperatures dipped into the mid-30s in New York’s Adirondack Mountains Tuesday morning, and millions in the Interstate 95 cities experienced start-of-the-day temperatures in the middle to upper 60s.

The pattern will remain rain-free Wednesday which will allow the ground to dry out following the onslaught of downpours during much of July.

“Humidity levels will stay low for August through Wednesday night then slowly begin to creep back upward on Thursday and Thursday night,” AccuWeather Senior Meteorologist Dave Dombek said. “It will likely take until Thursday night or Friday for conditions to really feel sticky again.”

The return of higher humidity will not be anything out of the ordinary for the middle of summer, Dombek said. However, the uptick will mark another change in the weather pattern.

“As the air moistens, spotty showers and thunderstorms will begin to pop up on Thursday afternoon with more numerous downpours occurring Thursday night and Friday,” Dombek said.

“The likelihood for drenching downpours will return with the late-week system,” Dombek said, “That may lead to some localized flooding issues, mostly in urban and poor drainage areas.”

One difference with the late-week rain as opposed to bouts of rain in recent weeks is that the ground will have had four to six days of rain-free weather to dry out. While the sun is not as intense as that of late June or early July, its effect can evaporate approximately 0.25 of an inch of moisture from the topsoil on a daily basis.

“The current dry stretch can make a big difference in the scope of the amount of runoff and flash flooding late this week,” Dombek said. “Because of the extended dry period beforehand, there should not be widespread small stream flooding.”

The bulk of the rain will focus on New England and the mid-Atlantic coast from Thursday night to Friday.

Some travel delays are likely Friday throughout the Interstate 95 Northeast corridor from Washington, D.C., to Philadelphia, New York City and Boston.

The late-week storm will be a quick-moving system with rain and clouds departing the Northeast by Saturday, setting the stage for a dry weekend across much of the region.

This weekend, temperatures and humidity levels will dip to early-week levels once again, which is good news for folks attending ballgames, barbecues or many other outdoor events scheduled for Saturday or Sunday.

Beyond this weekend, there are signs that the pattern may revert back to one that favors rain more often, Dombek said.

Since the jet stream might not have as much of a southward dip next week compared to most of July, it may allow storm systems with showers and thunderstorms to continue to move along. However, that can bring brief bouts of heavy rain every other day on average instead of on a daily basis like in recent weeks.

Temperatures are likely to trend somewhat higher next week but are not likely to hover at high levels like the end of July. Highs will be mainly in the 80s with nighttime lows in the 60s to the low 70s. Humidity levels are likely to fluctuate from one day to the next, and are unlikely to stay high for very long.

Produced in association with AccuWeather

Edited by Jason Reed and Kyana Jeanin Rubinfeld