Atmospheric river of moisture will trigger storms and tornadoes this week

By Jennifer Gray, CNN meteorologist

You may have heard of atmospheric rivers impacting the West Coast. We had several notable ones this year that brought flooding, staggering snowfall amounts to the mountains in the west, and even landslides.

An atmospheric river is a long, narrow region in the atmosphere that can transport moisture thousands of miles, like a fire hose in the sky.

We talk a lot about them in the West because large-scale storm systems bring the region up to 40% of their yearly rainfall.

But we started wondering: Is there anywhere else where these happen?

Apparently, atmospheric rivers also occur in the eastern US, unleashing a river of moisture like what we will see this week.

The reason East Coast atmospheric rivers aren’t talked about much isn’t because they are rare. In fact, they are quite common.

“Atmospheric rivers are more frequent on the East Coast than they are on the West Coast,” said Jason Cordeira, Associate Professor of Meteorology at Plymouth State University. “They’re just not as impactful and don’t usually produce as much rainfall.”

While Cordeira noted it is tough to give an exact number of how many atmospheric rivers impact the East every year, he says a rough estimate would be anywhere from 80-100 per year!

WOW.

The West gets about half that number of atmospheric rivers each year, yet they account for double the annual rainfall percentage.

“The West Coast is a much more arid climate. And they usually get precipitation during just half of the year,” Cordeira pointed out.

The East Coast accumulates its annual rainfall from several sources: afternoon storms, cold fronts and hurricanes, which can bring MUCH higher rain amounts than an atmospheric river.

“Some of the strongest atmospheric river events that are perfectly oriented, can produce 6-8 inches of rain,” Cordeira reported. “Those totals are dwarfed by the amount of rainfall that we can get from a hurricane.”

Some recent hurricanes such as Harvey, which hit Houston in 2017, have resulted in rainfall totals measured in FEET, not inches.

This week’s atmospheric river won’t leave the footprint Harvey did by any stretch, but it could affect the same areas as Harvey.

The Deep South will once again be hit by a series of storms this week, along with the Plains, the Rockies and the Pacific Northwest.

So, needless to say, this week’s weather will be much more far-reaching.

It has no doubt been a super active stretch of severe weather in the South and Southeast, as this is the fourth week in a row where active weather is affecting the same areas.

However, as we get deeper into April and May, we should start to see the storm tracks shift a little farther north into what is traditionally, “Tornado Alley,” which is what we will begin to see this week.

The storm’s timeline

A series of storm systems will impact the US this week from coast to coast. It will bring everything from blizzard conditions to tornadoes to flash flooding, an exhausting week to say the least.

The Storm Prediction Center (SPC) has placed a Level 3 out of 5 “enhanced risk” of severe weather today for central Arkansas, however, anywhere from San Antonio to the Ohio Valley could see storms today.

The extreme northeast of Texas, southeast Oklahoma and western and central Arkansas, including Little Rock, are under a tornado watch until 11 p.m. CT Monday.

Large hail — possibly greater than baseball size — and wind gusts to 70 mph are also a concern for the area.

While this is happening in the central part of the country, a robust system will be entering the Pacific Northwest, and will crisscross the country in dramatic fashion today, bringing heavy rain to the coastal areas of Washington, Oregon and California, and several feet of snow for the Cascades.

“This system will deepen as it moves farther inland, setting the stage for an intense late season winter storm to impact the Rockies and Northern Plains,” noted the Weather Prediction Center (WPC). “Over a foot of snow is likely to accumulate between eastern Montana and central North Dakota on Tuesday.”

Blizzard warnings are in effect for portions of the Dakotas and Montana from Tuesday through Thursday.

“Total snow accumulations between 12 and 24 inches [are forecast],” said the National Weather Service (NWS) office in Bismarck. “Winds gusting as high as 50 mph [are also possible].”

The heavy snow and high winds will make travel nearly impossible for those areas due to whiteout conditions and will also create avalanche dangers. Many of the western mountain ranges have some sort of avalanche danger today, so be sure to check here before heading out, especially in the backcountry.

We wrote a story earlier in the season about what causes extreme avalanche dangers and why you only have about 15-30 minutes to be found alive after burial. Click here to read more.

After the system blankets the West with its late-season dump of snow, the storm will amplify as it heads east. It will combine with the available moisture provided by the atmospheric river we talked about and will result in the perfect setup for severe weather.

The tornado threat will be even stronger for Tuesday and Wednesday in the midsection of the country. But the storms will be impacting areas much farther north than the previous rounds of severe weather we have seen during the last three weeks.

Tuesday there is again a Level 3 out of 5 “enhanced” risk of severe storms from Dallas to Omaha, which includes more than 16 million people. While it is the area with the highest likelihood of storms, nearly 40 million people will have some possibility of seeing storms.

“Any thunderstorms that can develop in this very favorable thermodynamic environment will likely become severe quickly,” the SPC advised. They mentioned any supercell (strong thunderstorm) will be capable of producing tornadoes, saying “some of the tornadoes could be strong.”

By Wednesday, we enter Day Three of this multiday severe event. The main threat area will shift east with the third day of a Level 3 out of 5 “enhanced risk” of severe weather. The bullseye will be from northern Louisiana to the south side of Chicago and include places like Shreveport, Little Rock, Memphis, St. Louis, and Indianapolis.

“Large to very large hail, damaging winds and tornadoes will all be possible,” said the SPC. “Strong tornadoes may occur.” Dallas, Houston, New Orleans, and Chicago could all see storms as well.

The good news is the severe threat will be over in time for Easter weekend. We could still see some lingering showers in the eastern half of the country, and some mountain snow in the Rockies, which could affect egg hunts and sunrise services. While things could change between now and then, right now the SPC doesn’t have any areas highlighted for severe weather during Easter weekend as of now.

As if severe storms and blizzard conditions weren’t enough of a headline this week, extremely cold air will follow the front, plunging overnight temperatures into the single digits is forecast for portions of the northern Plains.

“Low temperatures in the single digits are possible and this could cause issues,” said the NWS office in Billings. “Do not be deceived by the sun, it is going to be fighting a very cold airmass.”

And as the climate crisis continues to change the dynamics of our weather, expect atmospheric rivers to become more intense as well.

“It’s expected that as the air temperatures increase, the air can hold more water vapor and therefore any storms that are comprised of water vapor will have more of it,” Cordeira explained. “So, an atmospheric river, which is defined as a region of water vapor, will likely become more intense. Their frequency may not be more common, but their intensity could become larger.”

Weather in focus

The drought-stricken West is getting even drier, according to the latest drought monitor.

“Central Washington, Idaho, and northwest Montana also saw increases in drought extent or severity as short-term dryness continues to build upon long-term moisture deficits extending back to last year,” according to the drought monitor. “Many parts of southern Idaho, and the rest of the West, have set records for the driest three-month period (January to March) going back 100 years or more.”

Texas is also facing extreme drought with 95% of the state in some level of drought. At 26,000 square miles, Texas has more “exceptional drought” area than any other state, per the latest US Drought Monitor. The 26,000 square miles of exceptional drought is larger than the state of West Virginia (or more than three times the size of Massachusetts).

The drought is only making fire conditions worse. From Texas to Kansas, there will be an extreme fire danger especially on Tuesday, as dry conditions and winds topping 50 mph will cover the area. Read more here.

Our friend Bill Weir went and walked on the bottom of Lake Powell. Here’s what he saw.

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CNN’s Taylor Ward contributed to this report.