Away we go into the last weekend of June, and the month will draw to a close just as it (and we) began life: wet and angry. In fact, we’re closing the month with a storm system that’s more common in fall than the middle of summer. Heavy rain will soon overspread much of the eastern United States this weekend, accompanied by some severe thunderstorms on the southern end of the system.
A cute li’l trough in the jet stream is in the process of dipping down over the Great Lakes at this hour, and when combined with the lift provided by a nearby jet streak (pocket of stronger winds within the jet stream), a well-developed low pressure system will set up in the Ohio Valley tonight and tomorrow. The system will quickly strengthen tomorrow as it move toward the Northeast, but not before it produces a widespread area of heavy rain and severe thunderstorms.
A shield of heavy, steady rain will likely overspread much of the Ohio Valley and Mid-Atlantic on Saturday and Sunday—earlier west and later east. Flash flood and flood watches are in effect from Quincy, Illinois, east toward Washington D.C. and Buffalo, New York, including just about everybody in between. The difference between a flash flood watch and flood watch is pretty much pedantic—if you’re under a flash flood watch, the risk is there for lots of heavy rain in a short period of time that could lead to rapidly rising waters.
Most of these areas can expect a wide slug of two or more inches of rain, with more than four inches possible by the time the precipitation ends sometime on Saturday night or Sunday.
On the southern side of the system, there should be enough lift, instability, and wind shear to trigger severe thunderstorms. A slight (two out of five) risk for severe weather is in place from eastern Georgia north through the Mason-Dixon line. All modes of severe weather—damaging winds, large hail, and tornadoes—are possible from the storms on Saturday. Keep an eye on the weather and listen out for watches and warnings, especially if you plan to be outdoors or away from safe shelter during the day.
It’s going to be a gross, soggy weekend, but it could be worse given the time of the year: at least it’s not 100°F or hurricaning (that’s a verb, right?). Plus, many of these areas—especially deeper into New England and farther south toward the central Appalachians and parts of the Carolinas—could use the rain, as they’ve slipped into a moderate drought over the past couple of months.