The frequent rain across much of Pennsylvania has led to flooding in many areas.
In particular, the risk of flash floods has grown, as the high moisture in the air and lack of strong winds lead to stationary storms that dump rain into localized areas.
Forecasts from earlier today suggest that mid- to late-afternoon storms may bring around 2 inches of rain. Residents of low-lying areas should be aware that “the potential for sudden flooding remains high.”
The National Weather Service has issued a flood watch for much of central Pennsylvania, including Adams, Cumberland, Dauphin, Lancaster, Lebanon, Northumberland, Perry, Snyder and York counties, among several others, starting at 5 p.m. today.
“If you remember, back in late June, we had that extreme heat wave,” said Kyle Elliot, director of the Weather Information Center at Millersville University. “And then at the end of that, the heat wave was broken by heavy showers and thunderstorms on June 30.”
Those thunderstorms at the end of June were the start of a heavy trend of rain, Elliot said, and “the first of the big flooding events.”
The weather pattern has remained largely in place since then, he said, as other than a brief respite around the July 4 weekend, no cold front has pushed it out of our area.
“We’re left with … this really warm and oppressively humid air mass, with these incredibly high amounts of moisture in the atmosphere,” Elliot said. “And so any time a disturbance comes through and triggers those showers and storms, they tap into those high amounts of moisture and instability.”
He added that the lack of wind, “both at the surface and throughout the depth of the atmosphere,” means that “there’s really no flow to steer the storms from county to county.”
“So when [storms] develop, they essentially move very slowly, or become stationary over the same areas,” he said. “They can sit there and dump out copious amounts of rain for one to three hours at a time.”
The result, as we’ve seen in many places, is several inches of rain — and with already heavily saturated conditions, lots of runoff, which leads to flooding.
Elliot’s forecast calls for “more rounds of showers and heavy storms” over the next seven to ten days.
But after that, we may finally catch a break. And with luck, even the coming rainstorms won’t be quite as stationary as they have been.
“We are going to start to see some more flow throughout the atmosphere,” Elliot said. “So these storms aren’t going to be as slow moving as what we’ve seen over the last two to three weeks.”
Unfortunately, until we see that break, the areas that have been hardest hit with flooding should brace for more.
Elliot said that areas in eastern Adams County, western York County and western Lancaster County were hit hard over the previous weekend.
“It would only take about one inch of rain in a six-hour period to trigger flash flooding,” he cautioned. “If those areas do get hit by the worst storms again, we’re going to have a serious issue on our hands.”
Here is the forecast from the National Weather Service:
This Afternoon
Showers and thunderstorms likely, mainly after 5 p.m. Mostly cloudy, with a high near 88. South wind around 6 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Tonight
Showers and thunderstorms likely, mainly before 2 a.m. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 72. Light south wind. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.
Thursday
A chance of showers and thunderstorms, mainly after 3 p.m. Mostly sunny and hot, with a high near 93. West wind 6 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Thursday Night
A chance of showers and thunderstorms before 8 p.m. Mostly cloudy, with a low around 73. Northwest wind around 7 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.
Friday
Mostly sunny, with a high near 84. North wind around 7 mph.
Friday Night
Partly cloudy, with a low around 66.
Saturday
A chance of showers and thunderstorms after 2 p.m. Partly sunny, with a high near 84. Chance of precipitation is 40%.
If you purchase a product or register for an account through a link on our site, we may receive compensation. By using this site, you consent to our User Agreement and agree that your clicks, interactions, and personal information may be collected, recorded, and/or stored by us and social media and other third-party partners in accordance with our Privacy Policy.
