A hyperactive stretch of severe weather will hit the Plains this weekend
A dramatic uptick in severe weather is set to hit the central U.S. beginning this weekend, with at least four consecutive days of storms. Damaging gusts, hail and a few tornadoes are likely, with storms set to reach a peak on Tuesday.
The severe conditions began Thursday across northern Kansas, where a couple of rotating supercells produced large, damaging hail bigger than golf balls. Hen-egg-size hail was reported in Greenleaf in Washington County, Kansas. Despite rotating, the storms were rooted atop a shallow dry layer near the surface, which prevented tornadoes from materializing.
Only marginally severe storms were expected across the southern Plains on Friday before a greater chance of rotating storms crops up Saturday.
April tends to be when severe weather kicks into overdrive. From April to June, an average of 700 tornadoes occur in the Lower 48. May is the busiest month, but the largest-scale outbreaks tend to happen in April.
A seasonal clash of air masses – the building warmth of summer contrasted against the slow retreat of winter’s chill – brews tall, severe thunderstorms. Meanwhile, fierce jet stream winds aloft help storms to rotate.
Outlook for Friday
Only a marginal (Level 1 out of 5) severe weather risk exists, mainly along the Kansas-Oklahoma border. It also extends back into the Texas Panhandle and extreme northeast New Mexico.
There’s a stalled boundary lurking nearby that will serve as a source for a few afternoon storms. Moisture is still somewhat scant; it will be another day or two before deeper tropical humidity from the Gulf of Mexico will fully waft northward across the central and southern Plains.
That’s why some gusty winds or hail are possible, but there’s no real tornado risk.
Isolated hail is also possible in California’s Sacramento Valley as a high-altitude disturbance with frigid air moves overhead. The same setup produced a severe thunderstorm that prompted a tornado warning southwest of Redding on Thursday evening.
A few additional strong storms are possible in the northern Great Basin of Nevada and southwest Idaho.
Outlook for Saturday
Saturday will feature a dry-line setup, which marks the divide between dry desert air west and moisture-rich Gulf air to the east. That clash will help spawn scattered strong to severe thunderstorms from the Big Bend and Pecos Valley of Texas to the Panhandle. A warm front may also touch off an isolated severe thunderstorm as far north as Omaha, but forecast confidence remains low.
Moisture will be increasing across the Permian Basin, but mid-level winds will still be somewhat weak. That’s why thunderstorms may form clusters and lines and produce wind and hail, but may not be organized enough to produce tornadoes.
Thunderstorms will probably congeal into windy squalls as they push east overnight.
Outlook for Sunday and beyond
Sunday will also feature a dry-line setup, with a greater severe weather risk. A slight (Level 2
of 5) risk stretches from Texas Hill Country to Wichita and encompasses western and central Oklahoma, including Oklahoma City, as well as the Red River Valley, including Wichita Falls, Texas.
Confidence is lower in terms of whether thunderstorms will erupt. While instability (thunderstorm fuel) is plentiful and the winds aloft will be stronger, there will also be a strong cap. That’s a lid of hot, dry air about a mile above the ground that suppresses storm growth by preventing surface air from rising.
Will thunderstorms form? Unclear. But if they do, they may be significant and produce destructive hail and tornadoes. It’s a conditional risk.
Conditional risks are notoriously difficult to communicate and forecast. Sometimes there isn’t an option between all or nothing. In this case, there’s an 80 & chance that most of the region sees run-of-the-mill storms, but a 20 percent chance of tornadic supercells.
“Mostly sunny with a chance of tornadoes” isn’t necessarily an actionable, or satisfying, forecast, but it’s the best that can be offered – especially in Kansas. It’s the most appropriate forecast given the conditionality of the risk. It will be key to monitor the forecast as it evolves.
Monday will feature a somewhat similar situation, but the corridor of risk will span from the Texas Hill Country to near Minneapolis. Oklahoma City, Kansas City, Wichita and Des Moines are in the Storm Prediction Center’s zone to watch.
On Tuesday, the zone expands to include portions of Lake Michigan, as well as Chicago and Green Bay.
On both days, capping may limit the areal coverage of storms across the central and southern Plains. But in northern regions, including the Corn Belt and Upper Midwest, a greater trigger for storms will exist as a high-altitude disturbance swings overhead. That will make it easier for thunderstorms to form there. Damaging gusts, hail and a few tornadoes are likely.
On Wednesday, thunderstorms are likely between Dallas and Chicago. Confidence in specific impacts remains low.
Role of global disturbances
These rising severe storm risks can be traced back in part to a rare triplet cyclone pattern unfolding in the western Pacific Ocean, which is also fueling the development of a formidable El Niño event.
That pattern is energizing the subtropical jet stream, which will blow across the Southwest into the Plains from this weekend into next week – contributing to twisting atmospheric winds that can form tornadoes.
Tornadoes so far this year
There have been 313 tornadoes reported across 16 states so far this year.
That compares to a long-term average of around 275 tornadoes through early April. This time last year, there had been more than 500 tornadoes.
Here’s a list of states with the most tornadoes through April 9.
- 59 in Illinois
- 43 in Mississippi
- 31 in Louisiana
- 24 in Oklahoma
- 23 in Alabama
These tornado counts are expected to soon grow as a volatile stretch of severe weather takes hold.