RaveVlog

Three rounds of severe weather, including damaging tornadoes, have already hit the central states this week. Now a fourth is on the way, and it could be the most violent. A severe thunderstorm outbreak is predicted for much of Kansas, Oklahoma and parts of northern Texas on Saturday, and it includes the risk of strong tornadoes.

The National Weather Service Storm Prediction Center has drawn a Level 4 out of 5 risk of severe weather covering central Oklahoma, including Oklahoma City, Tulsa, Norman and Lawton; and much of eastern Kansas, including Wichita.

Surrounding that Level 4 zone is a Level 3 risk, which covers Kansas City and Springfield in Missouri and Wichita Falls, Tex.

At 3:25 p.m. Central time, the Storm Prediction Center issued a “particularly dangerous situation” tornado watch in effect until 11 p.m. for extreme north central Texas, western and central Oklahoma and south central Kansas. It includes Oklahoma City and Wichita.

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“Intense supercell thunderstorm development is expected to continue through this evening, with storms moving generally east across the watch area,” the Storm Prediction Center wrote. “The risk for strong, long-track tornadoes will exist, in addition to giant hail, possibly up to 5 inches in diameter. Damaging thunderstorm wind gusts in excess of 75 mph can also be expected.”

The Storm Prediction Center said “an uncommon environment” supports the potentially dangerous storms, even for the time of year — which is the peak of tornado season.

There remain uncertainties, however — namely with regard to the amount of available moisture, and where the most intense storms will form and how widespread they’ll be.

In addition to the thunderstorm threat, forecasters have declared an “extreme” fire risk in parts of New Mexico, because of exceptionally dry and windy conditions on the back side of the storm system.

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The year to date has already been the sixth most-active on record for tornadoes. On Thursday, a strong tornado carved a path through southwest Oklahoma, amazing storm chasers while scientists probed it to capture potentially groundbreaking data.

After Saturday, the threat of severe storms will shift toward parts of the Ozarks, Midwest and Ohio and Tennessee valleys on Sunday and the Mid-Atlantic on Memorial Day.

A recipe for storms

On Saturday morning, an intense high-altitude disturbance containing cold air, low pressure and spin had swung east over the Great Basin of Nevada. That upper-air disturbance was helping to generate a zone of low pressure in eastern Colorado in the lee of the Rocky Mountains.

As the low-pressure area intensifies and shifts into Kansas, it will begin to draw north a tongue of warm, humid air — which will contain instability, or storm fuel — and drape it across Texas, Oklahoma and Kansas.

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At the same time, the low will drag a dryline east. That’s the leading edge of bone-dry air from the Desert Southwest as it impinges on Gulf of Mexico moisture to the east. The resulting clash will brew strong to severe storms in the Red River Valley of Texas, western Oklahoma and adjacent central/south central Kansas by the late afternoon or early evening.

Timing

Severe thunderstorms began to develop between 3 and 3:30 p.m between Abilene and Wichita Falls in Texas. By 5 p.m., storms will probably be rotating and prompting tornado warnings as they expand north into western and central Oklahoma. They’ll shift east, with the threat reaching Oklahoma City and the Interstate 35 corridor around 7 or 8 p.m.

After sunset, the storms will probably progress into eastern Oklahoma, southeast Kansas and extreme northern Texas. Because there are fewer visual cues and some people are asleep, nighttime tornadoes are 2.5 times more likely to be deadly.

Hazards

Storms will be capable of all severe weather hazards. That will include:

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• Large to giant hail. Considerable storm fuel will become present at the mid-levels of the atmosphere at levels where temperatures are below freezing. That means there will be enough upward motion to help hailstones grow — perhaps larger than softballs in a few instances.
• Hurricane-force winds. Initial storms that form will probably be rotating thunderstorms or supercells, which, in addition to producing tornadoes, may unleash localized gusts of 60 to 80 mph, known as microbursts. By late evening into the overnight, storms might merge into large, organized complexes as they barrel eastward. If this is the case, the threat of hurricane-force winds over 80 mph could increase after about 10 p.m.
• Tornadoes, perhaps strong. An exceptional amount of wind shear will be present. That means winds will change speed and direction with height. Any storms that grow tall enough to feel the changing winds will rotate. Tornadoes are probable with storms, and some strong and/or long-track tornadoes are possible.

How to prepare

If you live in the zones of elevated risk, here are some tips:

• Charge devices and ensure you have switched on wireless emergency alerts on your mobile phones. Have multiple, redundant ways to be notified of tornado and severe thunderstorm warnings.
• Structure your day such that, after 4 p.m., you’re only ever 5 minutes away from a shelter. That means a below-ground place of refuge. Mobile homes and flimsy aboveground spaces will not withstand high-end tornadic winds. A database of tornado shelters can be found at FindYourTornadoShelter.com.
• Prepare your storm cellars. Consider grabbing bike helmets and placing those in the shelter. (Most tornado casualties stem from head injuries.) If you happen to own a whistle, bring one along in case you need to call for help.
• If you have the option to park your vehicle under a carport or in a garage, that will help minimize hail damage.

Storm risks on Sunday and Monday

Additional storms are likely across parts of the Ozarks, Midwest and Ohio and Tennessee valleys on Sunday as the storm system works its way east.

A broad Level 2 risk of severe weather spans from Chicago to northeast of Dallas, and includes Little Rock, Memphis and Springfield, Mo. A more concentrated area of storminess, within which a squall line with tornadoes and severe winds is possible, is evident from eastern Missouri and Illinois to Middle Tennessee. That’s where a Level 3 risk has been drawn; it includes St. Louis, Cincinnati, Louisville and Nashville.

Some additional severe weather is possible on Memorial Day in the Mid-Atlantic — mainly between Philadelphia and Charlotte, where there’s a Level 2 risk of severe storms. Baltimore, Washington, Richmond and Raleigh are included in this zone.

Jason Samenow contributed to this report.

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