The risk for flash flooding will return to much of the Mid-Atlantic by the end of this week. This comes as waves of low pressure move through the region, aiding in the development of showers and thunderstorms. Cities like Ellicott City may deal with more flooding depending on how the thunderstorms set up, as the atmosphere will be somewhat favorable to produce training thunderstorms in the general area. With training thunderstorms, it’s basically when heavy precipitation moves over the same area for an extended period, which can eventually lead to flooding.
This Thursday, the best risk for flooding will exist in the Appalachian Mountains back into the western Ohio River Valley. In the Mid-Atlantic, there won’t be much of an organized area of rain. Instead, there will be rounds of showers and thunderstorms that will move through from the west. Some of these storms will be heavy, which will saturate the already wet soil even further. Meanwhile in the Ohio Valley, there will be a line of strong to severe thunderstorms that will develop. As those storms weaken overnight, a couple of them may back-build, dumping heavy rain on some areas for an extended time period, increasing the concern for substantial flooding.
We will then see an area of low pressure move toward the central Appalachians on Friday, which will likely enhance the flood risk for that area and the Mid-Atlantic due to a more organized area of precipitation. The morning itself should actually be mostly dry. The only area of rain will be near the low pressure over the eastern Ohio River Valley. It’s not until the afternoon when an organized line of heavy thunderstorms will form. These storms will be heavy as they track east, but will ultimately weaken and dissipate for the most part before they reach the coastline overnight. Near the Mason-Dixon Line, there may be an area of training thunderstorms that set up, so that’s where we think the highest chance for flooding will be.
Then on Saturday, a weak coastal storm will develop, bringing rounds of showers and thunderstorms throughout the day. These showers will extend as far west as the leeward side of the Appalachian Mountains. Some of this precipitation will be heavy thanks to the persistent tropical moisture in place. Again, the risk for training storms will exist as they pivot in from the north and east.
Through Saturday, night, an area of rainfall of two to three inches is forecast for the Washington, DC area. The surrounding areas may receive up to an inch of rain.
Next week, rounds of showers and storms will continue. This repetitious onslaught of rain will keep the soil very saturated, keeping the risk low for gradual and flash flooding.