Severe Won’t Let Up: Major Outbreak and Flood Threat Looming for Monday

May 18, 2019, 5:46 PM EDT

Above: Wesley Mantooth lifts a wooden chair out a window of the home of his father, Robert, in Abilene, Texas, on Saturday, May 18, 2019, after high winds from a possible tornado struck just before dawn. Image credit: Ronald W. Erdrich/The Abilene Reporter-News via AP.

Tornadoes ignored the clock this weekend, striking the Texas city of San Angelo just before dawn Saturday and the Oklahoma town of Geronimo around 7:30 am CDT. Damage of at least EF2 level was found by storm surveyors in San Angelo, where numerous homes were reportedly struck. Forecasters at the San Angelo office of the National Weather Service were forced to take shelter as the distinct radar signature of a tornado passed overhead.

Another tornado from the same storm struck near Ballinger, Texas, later Saturday morning. At least half a dozen homes were damaged, some heavily, according to weather.com.

Further north, damage was reportedly widespread in Abilene, Texas, where a tornado-warned storm struck just before sunrise Saturday. The west side of the city was apparently hardest hit. No major injuries were reported, according to city officials.

A survey team found EF2 damage with the short-lived Geronimo tornado, which struck about 100 miles southwest of Oklahoma City. Two homes were destroyed and several minor injuries were reported, according to county emergency management officials.

Saturday’s storms arrived after a Friday-evening outbreak that produced more than 40 tornado reports in Oklahoma, Kansas, and Nebraska. All of the tornadoes came from just two long-lived supercell storms, one that tracked from far northwest Kansas into southwest Nebraska and the other forming in far northwest Oklahoma and tracking across southwest Kansas. A couple was injured when an apparent tornado from the northern storm struck their home near McCook, Nebraska. At least two EF1 tornadoes have been confirmed in southwest Nebraska.

See weather.com for a comprehensive look at impacts from the storms ongoing since Friday. Also, our post from Thursday covers the TORUS project, a major study of supercells and tornadoes that gathered data from the Nebraska storm on Friday—the project’s very first day of field operations.

A powerful squall line continued to wreak havoc as it moved into Missouri and Arkansas on Saturday afternoon and evening. High winds and heavy rains will be the main threat, but hail and tornadoes are possible. Severe weather should be more muted on Sunday, but bands of storms capable of severe wind and hail will rumble from the Mississippi Valley up to Michigan and across to western Pennsylvania and New York by evening.

All eyes on Monday for a potential high-end severe outbreak and flood risk

The weekend onslaught of severe weather serves as a prelude to what is shaping up to be a high-end tornado and flood threat from Monday into early Tuesday.

The NWS/NOAA Storm Prediction Center placed most of western and central Oklahoma under a moderate risk of severe weather in its Day 3 outlook, issued Saturday for Monday, with the odds of significant severe weather within 25 miles of any point as high as 45%. Note that in this time range, SPC does not issue high risk areas or probabilities above 45%, so we should consider this a top-end outlook for what’s likely to be an unusually volatile situation. I wouldn’t be surprised if parts of Oklahoma end up in a high-risk outlook by Monday.

Note that Day 2 high risks have only been issued twice, one in 2006 and one in 2012. Even the infamous Super Outbreak of April 2011 wasn’t designated a high-risk event until the night before it occurred.

What’s so concerning about Monday is that it involves an unusually intense, widespread, and prolonged mix of all the classic ingredients of severe weather. First and foremost is the exceptionally potent upper-level trough in the western U.S. This storm system wouldn’t be out of place if it occurred in February, given the frigid air in its core and the shrieking jet stream rotating around its base, packing winds of 120 to 160+ mph at flight level.

A strong lobe of this upper low will punch across the southern Plains on Monday, where the unusually cold upper-level air will overtop a warm, moist air mass more typical of late spring. Very strong southwest winds aloft and southeast winds at lower levels will lead to very favorable wind shear for rotating supercell thunderstorms.

What’s more, the structure of the upper low will push the cold air and strong jet-stream winds over the plains well in advance of the surface front. The upshot will be a large area with high instability and extremely strong wind shear, especially within the lowest mile of the atmosphere—a region where wind shear is especially conductive to tornadoes if a supercell happens to form.

The slow advance of the surface front means that multiple rounds of potentially tornadic supercells may move from northwest Texas into Oklahoma and southern Kansas during the day on Monday and perhaps well into the night. As we saw on Saturday, damaging tornadoes can strike at any hour when the conditions are right.  The storms may eventually congeal into a powerful squall line moving from eastern Oklahoma and Kansas into Missouri and Arkansas on Tuesday.

Projected precipitation totals for the 7-day period ending at 7 pm CDT Saturday, May 25, 2019
Figure 1. Projected precipitation totals for the 7-day period ending at 7 pm CDT Saturday, May 25, 2019. Image credit: NOAA/NWS/WPC.

The biggest flooding threat will be across and just north of the peak severe weather risk area, most likely from western Oklahoma across southern and eastern Kansas into western Missouri. Intense thunderstorms are expected to “train” along the same area, leading to a few hours of very heavy rain across saturated ground. The NOAA/NWS Weather Prediction Center issued a Day 3 outlook on Saturday for a moderate risk of excessive rainfall from Monday into early Tuesday, with unusually strong wording: “The environment will be primed for a significant, widespread flooding event across portions of the Southern and Central Plains on Monday….These storms will be very efficient rainmakers.”

Rainfall totals of 3” to 6” may be common along this corridor on Monday and Tuesday, and local totals could be considerably higher.

Odds are rising for tropical development in the Atlantic and Northeast Pacific

As of Saturday, odds were close to 50-50 for development next week of each of a pair of tropical cyclones, one in the Atlantic and the other in the Eastern Pacific.

Hurricane season in the Atlantic doesn’t officially begin until June 1, but NHC issued a special tropical weather outlook on Friday to highlight an area well east of the Bahamas with some potential for development. As of midday Saturday, NHC gave 40% odds that a tropical depression will form in this area during the early to middle part of next week. Any tropical cyclone that does develop would be pulled away from the U.S. East Coast.

In the Eastern Pacific, a festering area of showers and thunderstorms (convection) south of Mexico and west of Central America is slowly gaining organization. In its Saturday morning tropical weather discussion, NHC gave this area 30% odds of spawning at least a tropical depression by next Wednesday.

We'll be keeping an eye on both these areas over the coming days.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Bob Henson

WU meteorologist Bob Henson, co-editor of Category 6, is the author of "Meteorology Today" and "The Thinking Person's Guide to Climate Change." Before joining WU, he was a longtime writer and editor at the University Corporation for Atmospheric Research in Boulder, CO.

bob.henson@weather.com

@bhensonweather

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