It has been a busy month for meteorologists who oversee the Baltimore and Washington regions. The local office of the National Weather Service has issued more than five flood warnings a day, on average, far more than anywhere else in the country.
The weather service office based in Sterling, Va., has issued 163 warnings for flash floods, overflowing rivers and water-covered roadways since July 14, according to data gathered by Iowa State University.
That includes warnings issued Monday night as floodwaters trapped vehicles across Baltimore County and forced water rescues.
It also includes flooding during the record-setting July rainfall, with nearly 17 inches of precipitation at Baltimore-Washington International Thurgood Marshall Airport.
Flood warnings also have been common — but only about half as numerous — across Pennsylvania, New Jersey and northern Arizona, according to the Iowa State data.
Weather service meteorologists issue flood warnings when flooding has been sighted, or when radar or stream gauges indicate it is imminent or already happening.
Flash floods occur when rain falls so intensely, water rises rapidly even in areas that are normally dry. What meteorologists call “areal” flooding occurs after long periods of heavy rain, when water ponds in low-lying and generally flood-prone areas.