Updated Apr 2, 2024 - Science

Intense April storm threatens much of U.S. with severe weather

Satellite image of storm clouds and lightning over the U.S. over Monday night.

Satellite image: CIRA/X

A "highly impactful, major Spring storm" that lashed parts of California with heavy snow and flooding rains over the weekend is bringing multiple severe weather impacts across the U.S. as it marches eastward in a multi-day outbreak.

The big picture: Tornado and severe thunderstorm watches on Monday evening stretched from Texas to Illinois, with flood watches from Illinois to West Virginia due to the storm that disrupted travel in parts of California and caused a major road slip on a section of the state's Highway 1.

  • The National Weather Service warned of potentially heavy rains and flash flooding into Tuesday from the lower Missouri Valley, across the mid-Mississippi Valley, Ohio Valley and into the Central Appalachians.
  • "A substantial severe weather risk will exist Tuesday afternoon and evening across portions of the Ohio and Tennessee valleys and into the Mid-Atlantic states," the NWS noted in a Tuesday morning forecast discussion.

Threat level: "Tornadoes, damaging winds, and large hail are expected with supercells that evolve across the warm sector of affected regions," the NWS' Storm Prediction Center said in a Tuesday morning forecast discussion. "Some tornadoes may be long-lived and strong."

  • There was a "moderate risk" of severe thunderstorms in this "potentially substantial severe weather outbreak" that was expected to be centered over the Ohio Valley, according to a post early Tuesday from the NWS' Storm Prediction Center.
  • A moderate risk is a Level 4 out of 5 on the center's threat scale. An enhanced risk, which is a level 3 out of 5 on the threat scale, covers a larger area, and 24 million people are covered by either enhanced or moderate risk.
  • The storm had the potential to unleash "a few significant" tornadoes. "Severe risk exists as far south as the Gulf Coast, and as far east as western portions of Virginia and the Carolinas," the SPC said.
  • There were reports of tornadoes in Oklahoma, where the National Weather Service's Tulsa office extended a severe thunderstorm watch in the state's southeast and western Arkansas through 3am local time and warned: "Golf ball size hail and wind gusts to around 60 mph are possible."
  • Meanwhile, flood watches stretched from central Illinois, across large portions of Indiana, Ohio, northeast Kentucky, much of West Virginia, far southwest Pennsylvania and far western Maryland.

Between the lines: Multiple studies show that climate change is increasing the frequency and magnitude of precipitation extremes. San Diego saw a new record daily rainfall on Saturday, where the NWS said 1.26 inches fell.

  • The NWS has highlighted areas with a "slight risk" of excessive rainfall through Tuesday.
  • This region will stretch from Tennessee to West Virginia. Flood watches are in effect for some of this region, as showers and thunderstorms move along a slow-moving front.

What's next: The storm may take a retro turn, harkening back to winter. Computer models show a likelihood for an unusually intense and heavy elevation-dependent snowstorm in New England Wednesday and Thursday, with high winds, a mix of rain and snow at the coast, and heavy, wet snow inland — possibly measured in feet.

  • "The most concerning aspect of this storm is the potential for 6+ inches of heavy wet snow that combined with strong winds could support downed powerlines and power outages," the NWS forecast office in Boston said.
  • Meanwhile, the California Department of Transportation said late Monday that engineers were continuing to assess a slip out of the roadway on Highway 1 caused by the storm on Saturday.

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Editor's note: This story was updated with the latest forecast information and more details on the road slip in California.

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