It’s going to be a messy week across much of the United States and parts of Canada.

A snowstorm that already pummeled the Seattle area is moving through the Midwest and heading toward the Northeast, according to the National Weather Service. Farther south, moisture moving in from the Gulf of Mexico will result in heavy rains, thunderstorms and, possibly, flash floods from Louisiana to Ohio. Those two systems are going to merge by Tuesday morning.

Elsewhere, the Bay Area in California is expecting an “atmospheric river.” (More on that below.) Hawaii was recovering on Monday from a “historic” winter storm over the weekend that saw a 191-mile-per-hour wind gust, 60-foot waves and snow on Maui. And the Northwest, which was also cleaning up after unusually heavy snowfall last week, was getting a fresh coat of snow on Monday from another storm.

Significant flight and transit delays and cancellations are expected, officials said, and downed trees and power disruptions are also possible. At Seattle-Tacoma International Airport, more than 275 flights were canceled by midday on Monday.

David Roth, a forecaster at the National Weather Service, reiterated the official advice to stockpile three to seven days of nonperishable food if you are in an area that could get heavy snow.