|Heavy rain and flooding are likely in the Mid-Atlantic States|
over the next few days as a cut-off low in the Ohio
Valley encourages heavy rains
Cut off lows are named appropriately because they are "cut off" from the jet stream.
Usually, storms ride the jet stream, that river of fast moving air that generally goes west to east, with sharp wave, in the northern hemisphere.
Since the jet stream pushes storms along, it usually doesn't rain all that hard in any one area, so flooding from most storms is unlikely, unless they have an unusual amount of moisture with them and/or the rain falls are already soaked ground.
A cut off low usually just sits and meanders aimlessly, often staying in roughly the same place for days, sometimes a week or more. A particularly energetic one is currently settling into the Ohio Valley, and that spells trouble for the Mid-Atlantic states
The low will cause lots of wet air to be drawn in from the east and southeast and dump it on the Mid-Atlantic region. The wind will also be forced to rise as it reaches the Appalachian mountains. When air rises, it cools and condenses, and extra moisture is wrung out as rain.
This means the rain might be particularly heavy, with the greatest danger of flash flooding over the next couple of days in the hills and mountains of western Virginia, eastern West Virginia, western Maryland and southern Pennsylvania.
Many areas in the Mid-Atlantic are expecting three to five inches of rain, with locally more in some areas.
It's already raining in the Mid-Atlantic, with a few inches of new precipitation reported in a couple spots.
Unfortunately, not a lot of rain will move north into New England, which is still having a drought. Some rain will get in this weekend, especially in the southern half of New England, but it won't be a blockbuster storm, that's for sure.
Our cut-off low will weaken and finally move north this weekend, bringing some of those showers north all the way to the Canadian border, but it won't be much.