CNN
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A potent storm that already plunged parts of California underwater has started to deal a serious blow to the eastern half of the US with flooding rain, severe thunderstorms, tornadoes, snow and ice all expected.
Snow is already blanketing parts of the Great Lakes while rain is falling to the south, in parts of the Ohio Valley and thunderstorms are starting to rumble in the Mississippi Valley.
The storm strengthens Saturday as it pushes east and reaches its peak strength overnight into Sunday as it barrels through much of the East. The storm largely comes to an end Monday, but lake-effect snow could bury parts of the Great Lakes in its wake.
Here’s how each hazard will unfold this weekend:
Millions at risk of flooding rain
Heavy, flooding rainfall is the storm’s most widespread threat and much of it will fall Saturday.
A swath of more than 1,200 miles from the Gulf Coast to the Northeast could experience flooding with more than 2 inches of rain expected in many locations.
Some locales will get much more.
A rare level 4 of 4 high risk of flooding rainfall is in place for more than 1.5 million people in parts of northwestern Tennessee and western Kentucky where “life-threatening and significant flooding is anticipated,” according to the Weather Prediction Center. More than 500 miles of the country, from eastern Arkansas to West Virginia are under a level 3 of 4 risk of flooding rainfall Saturday, according to the center.
“A major, potentially historic, flash flood event is possible this afternoon and tonight,” the National Weather Service in Paducah, Kentucky, warned Saturday morning.
The long-duration rainfall event began before dawn and triggered flash flood warnings in Tennessee and Kentucky, but the worst flooding is still to come in the early afternoon and evening.
It’s hard to overstate just how significant these events are. They are issued on fewer than 4% of days per year on average, but are responsible for more than 80% of all flood-related damage and 40% of all flood-related deaths, research from the WPC shows.
The threat level is raised because the atmospheric setup for the storm is “quite unusual for mid-February” and could support rainfall rates up to 2 inches per hour in the heaviest storms, according to the WPC. A half a foot of rain could fall in the high risk area where heavier bouts of rain essentially get stuck for an extended period.
Almost no area could absorb that much rain without flooding, but recent storms have already soaked soils in this region and made the threat that much more dire.
Kentucky Gov. Andy Beshear declared a state of emergency Friday ahead of the storm.
“We want everyone to be careful,” Beshear said. “The amount of rain coming down will make it hard to drive, and flash flooding, especially across our roads, can create dangerous conditions.”
Strong tornadoes possible
Severe thunderstorms will roar to life south of where the heaviest rain falls Saturday. These storms could pack a serious punch and a level 3 of 5 risk of severe thunderstorms is in place for portions of Louisiana, Arkansas, Mississippi, Tennessee and Alabama, according to the Storm Prediction Center.
Damaging wind gusts and tornadoes are likely in these storms, especially from late Saturday afternoon through the overnight hours.
While almost any severe thunderstorm could produce a tornado on Saturday, locations in the level 3 of 5 risk area – particularly Mississippi – are at the greatest risk for strong ones rated EF2 or higher.
EF2 tornadoes have winds of 111-135 mph, capable of tearing roofs from homes and shifting them off their foundations.
Some of the most violent storms are also expected after dark, making them even more dangerous. It’s difficult to spot a tornado at night, even for those who are awake or are awoken by warnings.
Nighttime tornadoes are twice as likely to be deadly as those that occur during the day, a 2022 study found. A deadly tornado roared through a Tennessee community after dark just last week, killing at least two people.
Some severe thunderstorms will persist into Sunday morning and could bring damaging winds from Florida through the mid-Atlantic.
More snow and ice incoming
The storm will dump snow and ice on its northern, colder side while flooding rain and severe thunderstorms pound areas caught under its warmer side.
Snow is falling over the Great Lakes and reaching into the Northeast while icy conditions unfold in parts of the Ohio Valley Saturday morning. Snow will reach more of the Northeast Saturday afternoon before changing over to an icy mix of snow, sleet and freezing rain in many locales as warmer air surges north late Saturday.
This messy mix will slam much of New York state and New England overnight and Sunday while the storm is at its peak strength.
Strong winds will also roar across the Northeast and could knock out power especially in any areas also dealing with snow and ice. Travel in impacted areas will be tricky.
Snow totals through the weekend could hit double digits in parts of the Great Lakes, northern New York and in northern New England. Any mixing with ice and sleet will limit totals in areas just south of the heaviest snow, especially in the Ohio Valley and southern portions of the Northeast.
Lake-effect snow will kick up across the Great Lakes in the wake of the storm on Monday.
Another round of frigid air will also spill into much of the US after the storm departs. Temperatures could plunge more than 30 degrees below normal for much of the central US early next week.