As advertised on Armando’s blog from Friday, the North East of the country saw heavy rainfall leading to multiple flash flood emergencies across the region yesterday.
Radar-estimated rainfall totals over the past 24 hours (ending at 8 a.m. Eastern) show a staggering total rainfall in areas located in the lees of the Appalachian Mountains. Here, convergence and topography have worked together to produce wave after wave of slow-moving storms.
And it’s not over yet.
The heaviest rain has left Pennsylvania, New York and New Jersey and is now concentrated in New England – specifically in Vermont, where much of the state is under flash flood warnings.
The sound observed this morning from nearby Gray, Maine shows an atmosphere nearly saturated with Tropopause. Additionally, a small amount of CAPE exists and allows enough instability to further fuel the event.
Also, the observed PWAT value (listed in the statistics on the side) is 49 mm, which roughly converts to 2 inches. Note the Southeast flow in the lower strata. This quasi-tropical moisture is being pushed into the unusually warm Atlantic Ocean and is fueling these downpours.
Don’t forget the role of terrain.
A lower stream from the SSE hits the New England Blue/White Mountains (local name for that part of the Appalachian Range) at an almost perpendicular angle. The stream is then forced to rise above the mountains. In doing so, the moisture in that air is mechanically lifted to the LCL, which can then condense into clouds and fall as rain. This increases the total rainfall for the area.
Simply put: due to Orographic Lifting (the process described above), more rain will be pushed out of the atmosphere, adding to the already high total precipitation.
No wonder WPC identified High Risk for Flash Flood in this area today. In fact, as I said early on, it has already happened.
It is extremely important to know the conditions if you must drive out today. Things can become life-threatening quickly. Be aware of alternative routes in case you need them.
Most importantly: DO NOT drive through floodwaters. It only takes 12 inches to float a car. Also, the depth can be deceiving and the road can be washed away below. The risk is not worth your life.
Stay safe out there today!
About the author
Meghan Gulledge
Meteorologist – ’22 Mississippi State Writer for Weather.us and Weathermodels.com. Focus on weather communication. BoyMom x1, CatMom ​​x5. Twitter: @MegGulledgeWX
