Major storm to sweep United States with severe weather, snow, flooding

A strong storm system is poised to roll across the United States and deliver widespread hazardous weather. It arrived Saturday in California, where it produced thunderstorms, flooding and heavy mountain snow. As it charges eastward, few areas will be spared from its effects.

On Monday and Tuesday, it will sweep through the Central and Eastern states, bringing the threat of severe thunderstorms and tornadoes. Some areas - especially from the Midwest to the Mid-Atlantic - could also see flooding rain.

The storm’s last stop will be in New England midweek, where some areas could see an usually intense late-season snowstorm.

Spring is known as one of the most chaotic times for seriously disruptive weather in North America. Clashing air masses - stemming from crescendoing seasonal warmth and lingering winter cold - can brew powerful weather systems such as this incipient storm.

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California hit by downpours, hail and mountain snow

The storm began Saturday as it swung an atmospheric river into the West Coast. The rains were continuing Sunday, with flood watches covering Southern California, including San Diego and Los Angeles.

In San Diego, 1.30 inches fell Saturday, setting a record for March 30. High water flooded several streets.

Around Los Angeles, 2-3 inches had fallen through Sunday morning, and the National Weather Service warned that continued downpours could dump up to 0.75 inches of rain in an hour.

Santa Barbara had received 3.93 inches of rain through Sunday morning, and the mountains just to its north have posted up to 6.5 inches. Flooding submerged five vehicles and forced the closure of U.S. Highway 101 southbound at San Ysidro Road in Santa Barbara County on Saturday night.

The Bay Area was hit by thunderstorms late Saturday, which prompted a warning in Santa Clara County and produced hail in Santa Cruz County.

Heavy snowfall blanketed the mountains of central and Southern California. Winter storm warnings covered the Sierra Nevada, where up to several feet of snow had fallen, and extended to the mountains east of Los Angeles, where up to 8 inches were possible through Sunday night. Fourteen inches of snow were reported at Big Bear Mountain Resort in San Bernardino County on Saturday evening.

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Multiday threat of severe thunderstorms

The same storm system affecting California is forecast to give rise to a serious multiday threat of severe thunderstorms as it spawns a new zone of low pressure east of the Rocky Mountains late Sunday.

Ahead of this new low, high pressure parked over the eastern United States is causing a ribbon of warm, moist air from the Gulf of Mexico to swirl into the central states that will serve as fuel for severe storms.

Meanwhile, a jet stream dip will nudge into that warm, humid air mass. It will kick up storms over the course of several days. The added high-altitude winds associated with the jet stream will induce shear - a change of wind speed and/or direction with height. That could induce rotation and a tornado risk within some of the storms.

- Sunday

While storms may not be particularly numerous on Sunday, a few could turn severe along the northern periphery of the high-pressure zone - and associated warm air mass - from Missouri to southwest Virginia. Storms will probably be most numerous through northeast Missouri, central Illinois and western Indiana, where the Weather Service’s Storm Prediction Center has drawn a Level 2 out of 5 risk zone.

The main concerns are for gusty to locally damaging winds and hail to about quarter-size in any storms that form; the risk of an isolated tornado is minimal.

-Monday

A more pronounced threat of severe weather will develop Monday as the storm system becomes better organized over the central states. A Level 3 out of 5 enhanced risk of severe storms stretches from the Oklahoma City metro area to southwest Indiana and includes Tulsa and the Missouri cities of Springfield, Joplin and St. Louis.

Three zones, in particular, will need to be monitored:

- A warm front from central Missouri to Indiana. The warm front could increase spin and the tornado potential starting early in the afternoon.

- Along the storm’s “triple point” in Oklahoma. The triple point is where dry air, moist air and cold air all meet near the center of low pressure. That could bolster low-level easterly winds and increase the tornado risk, as well as the chance of large, destructive hail as large as baseballs.

- A squall line in the southern Plains. Much of Oklahoma, Texas and Arkansas will be affected by merging storms that could form a windy squall line. Embedded quick-hitting tornadoes could form within kinks of spin nestled in the overall squall line. That will last into the night.

- Tuesday

As the storm system heads east Tuesday, the zone from Kentucky into western West Virginia is under a Level 3 out of 5 risk of severe weather. Cincinnati, Louisville and Charleston, W.Va., are included in this zone. A Level 2 risk extends from northern Mississippi and Alabama into the Mid-Atlantic.

“The greatest tornado threat is forecast to be from eastern Kentucky into West Virginia,” the Storm Prediction Center wrote.

Thunderstorms may plow into the Mid-Atlantic by Tuesday evening, with a lesser tornado risk but continued chances of damaging winds. While the Washington-Baltimore region is in the Level 2 risk zone, a wedge of cool air may limit severe storm chances there.

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Snowstorm is possible in interior New England midweek

The storm system’s final act could come in the form of a late-season snowstorm.

On Tuesday, the same jet stream dip tied to the severe thunderstorms in the central states will become absorbed into an even stronger upper-air disturbance over the Great Lakes. That disturbance will tug cold air south and could flip rain to snow Tuesday night as far south as Chicago and southern Michigan.

As the disturbance over the Great Lakes dives into the Northeast into Wednesday, a coastal storm may develop east of Long Island. While rain is most probable in coastal areas, heavy snow could develop in interior New England on Wednesday and Thursday. It is too soon to predict amounts, but some areas could easily see at least 6 to 12 inches, especially in the high elevations.