Flash Flooding Risk Will Expand Into Southeast and Mid-Atlantic This Weekend

Over the last several days, a longwave trough has remained in place across the western U.S., while a ridge has dominated the pattern across the eastern third of the U.S. Between these two larger-scale features, smaller shortwave impulses have generated favorable conditions for excessive rainfall amounts across parts of the Southern Plains and mid-south.

Rainfall amounts over the last 3 days

Over the weekend, a northern stream shortwave trough will dig into the Northern Plains and move into the Great Lakes by late weekend. This feature will usher in a pattern change and begin breaking down the ridge that has been placed across the Southeast and Mid-Atlantic. Before the cold front associated with the northern system pushes through the Gulf Coast and East Coast states early next week, a period of widespread moderate to heavy rain will fall across a large region of the southern U.S. and extend into parts of the Mid-Atlantic.

Projected 3-day rainfall amounts

Since the northern stream system will begin flattening and weakening the ridge, there will be an eastward expansion of the rainfall and potential flooding risk. Deep, tropical moisture will advect northward and northeastward throughout the weekend; thus, any rain that falls could be heavy and tropical in nature. The next three graphics outline the flash flooding risk for today (Friday), Saturday, and Sunday. Notice how the flash flooding risk will begin shifting eastward with time.

Flash flooding risk for Friday, May 10, 2019
Flash flooding risk for Saturday, May 11, 2019
Flash flooding risk for Sunday, May 12, 2019

Any additional rainfall that occurs across southeast Texas and southern Louisiana today will become problematic given recent heavy rain over the last 24 hours. This includes the Houston and Baton Rouge areas. States east and north of Alabama have remained relatively dry compared to the region just west. Even though soils are quite a bit drier east of the mid-south, high rainfall rates will still result in localized flash flooding farther east. By Sunday, lower rainfall rates will be necessary to cause flash flooding concerns, due to prior rainfall today and Saturday.

Even though I didn’t explicitly mention all regions under a flash flooding risk, please refer to any maps included in this article and future maps we post on social media. The purpose of this article is mainly to give you a heads up on this wet and stormy pattern, especially with Mother’s Day being this Sunday.