Severe weather outbreak in central U.S. is possible this week

SWEETWATER, Tex. — The past 10 days have featured a relentless stretch of severe weather across the central United States, and more nasty storms are in the cards across a broad region this week. Destructive tornadoes, damaging straight-line winds and crushing hail are probable over parts of Oklahoma, Kansas and Nebraska on Monday before the severe weather threat shifts east as the week wears on.

The National Weather Service Storm Prediction Center is forecasting a Level 4 out of 5 risk area for severe weather in northern and central Oklahoma and south-central Kansas. “Multiple strong/potentially long-track tornadoes, very large to giant hail, and severe/damaging winds all appear likely,” the agency warned, and confidence is increasing that a corridor from Oklahoma City to Wichita in particular will be affected.

The Weather Service office in Wichita even noted that conditions are “similar to some past higher-end and even historic severe weather and tornado events,” in an online forecast discussion Saturday.

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A Level 3 risk of severe weather has been expanded to include areas from Wichita Falls, Tex., to Lincoln, Neb., while a Level 2 risk reaches east to Springfield, Mo; Kansas City; Omaha; and Des Moines.

By Tuesday, at least some risk for severe storms will expand east from Little Rock to Detroit, and could affect Nashville, Louisville, Cincinnati and Indianapolis.

The area of elevated risk on Wednesday includes Waco, Tex.; Dallas; Little Rock; Nashville; Columbus, Ohio; Indianapolis; Cincinnati; Louisville; and St. Louis — encompassing 44 million people.

Over the past week and a half, nearly 230 preliminary reports of tornadoes have been received. A whopping 300 twisters were logged across the continental United States in April, the second-most on record. Even Alaska had a brief tornado on April 19.

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The weather pattern shows no signs of slowing anytime soon. May is the historical peak of tornado season, and this one promises to be extra-busy.

Basic ingredients Monday

Unfortunately, at least a regional outbreak of tornadoes is possible Monday in Oklahoma and south-central Kansas. A few of the tornadoes may be intense.

Even outside of the zone at greatest risk for strong tornadoes, severe weather will be widespread.

A number of ingredients should come together to incite many dangerous storms:

• A strong high-altitude disturbance. Basically a pocket of cold air, low pressure and spin aloft, this upper-air disturbance will be the impetus for storms. It will slip over the Rocky Mountains on Monday morning and approach the central and northern Plains on Monday evening. Storms will break out as its influence arrives. This same disturbance is energizing a significant storm in California this weekend.
• A well-defined dry line and very warm, humid air ahead of it. Storms tend to form on boundaries where air masses clash. Beneath our high-altitude disturbance will be a pronounced dry line, or the border between warm, moisture-rich Gulf of Mexico air to the east and bone-dry air from the Desert Southwest. That sultry air mass — which could set heat records in the South — will be replete with instability, or storm fuel. As the disturbance moves overhead, storms will erupt on the dry line, which will be positioned somewhere near or just west of Interstate 35 in central Oklahoma and Kansas, and reach up into eastern Nebraska.

• Wind shear. Wind shear is when winds at different heights are moving in different directions or speeds. In this case, southerly or south-southeasterly winds at the surface will contrast with strong southwesterly jet stream winds aloft. Storms that grow tall enough to blossom through multiple layers of atmosphere will feel those changing winds and will rotate. That will increase the risk of strong tornadoes.

This is one of the more pronounced signals in recent years of a classic large-scale Great Plains severe weather outbreak. (Many of the tornado events in recent days have been more localized. This episode will probably be more geographically expansive.)

More storms Tuesday and Wednesday

As the cold front (and dry line) associated with this system pushes east, more storms are likely. On Tuesday, parts of the Corn Belt, Midwest and even Ozarks are at play. By Wednesday, an enormous zone from northeast Texas, including Dallas, all the way to the northern Ohio Valley could be affected.

It’s far too early to offer any specific forecasts, but the same overarching upper-air disturbance will be moving east into a very warm and humid air mass. That’s a recipe ripe for storms.

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