Northeast, mid-Atlantic face flash flood threat as Omega block brings persistent rain, thunderstorms

NEW YORK – Tens of millions of people in the Northeast and mid-Atlantic are facing a flash flood risk as we close out the weekend and begin a new workweek due to relentless rounds of rain and some thunderstorms fueled by a stubborn Omega blocking pattern over the U.S.

An "Omega block" is named after the Greek letter Ω and disrupts the usual zonal flow of weather systems.

The FOX Forecast Center said the blocking pattern has caused a so-called cutoff low-pressure system to stall over the Ohio Valley. This system is feeding moisture off the Atlantic Ocean, funneling precipitation into the region.

"A cutoff low means that it’s cut off from the main flow, meaning that there’s nothing around to steer it, meaning that it doesn’t move very fast at all," FOX Weather Meteorologist Ari Sarsalari said. "So, this thing is going to linger around the East Coast for a couple of days."

On Sunday, scattered downpours and thunderstorms are likely across much of the region, but especially near the Catskills of New York and Poconos of Pennsylvania.

It won't be a complete washout on Sunday, so there will be breaks in the rain – which, in some cases, could be a few hours.

It will be cool and rainy in places farther north, such as Burlington, Vermont; Portland, Maine; and Buffalo, New York.

Farther south, however, it will be warmer. Temperatures in Boston, Philadelphia and Washington will be in the 70s with rain.

NOAA's Storm Prediction Center (SPC) said severe weather is from Florida to interior portions of the Northeast on Sunday. The SPC placed those regions in a Level 1 threat on its 5-point severe thunderstorm risk scale.

"We're down to a Level 1 risk today," Sarsalari said. "It's a pretty large area. I mean, it goes from the interior Northeast down through eastern Pennsylvania, parts of Virginia, parts of the Carolinas, even down along the Southeast coast."

Several inches of rain is likely across portions of the Northeast through Wednesday, with some of the highest totals expected in New York's Hudson Valley and Capital Region, as well as in Connecticut, western Massachusetts, Vermont and New Hampshire in New England.

"This is a needed rain," Sarsalari continued. "The other thing that’s going to come along with this is a flood threat. It’s not the highest flood threat we’ve ever seen."

NOAA's Weather Prediction Center (WPC) has highlighted a flood threat across portions of the Northeast, New England and mid-Atlantic through at least Tuesday.

So far, the risk is relatively low – only a Level 1 out of 4 threat of flooding. However, flooding can be dangerous and potentially deadly if safety precautions aren't taken. Never drive over a flooded roadway if traveling, and listen to the advice of local officials if Flash Flood Warnings are issued.

Omega blocking pattern fuels flood threat this week

A rather unusual weather pattern for early May is setting up across the U.S., one that meteorologists warn will lead to a stagnant pattern with prolonged periods of warmth in some areas and steady rain in others.

This so-called Omega block will cause two distinct regions of precipitation to dominate the workweek: one stretching from the southern Plains to the Gulf Coast and another affecting the Northeast.

"Plenty of moisture will be underneath those lows," FOX Weather Meteorologist Jane Minar said. "It's a slow-moving pattern that will kind of keep us locked in place with rain."