March Going Out with a Weeklong Roar of Severe Weather
Severe weather watches may be a daily occurrence into at least the first weekend of April, as upper-level energy continues to stream across the U.S. atop an increasingly rich supply of low-level moisture. Already, 2017 has been a noteworthy year for severe weather. Even after tornado reports for earlier decades are inflation-adjusted (in order to balance the more complete reporting of tornadoes in recent years), the total of 325 preliminary tornado reports through Sunday is the highest for the period Jan. 1 - Mar. 26 in records dating back to 1954.
A hail-strewn Sunday in TX/OK
Moisture from the Gulf of Mexico returned just in time on Sunday to produce a bumper crop of intense thunderstorms ahead of a sharp dry line in Oklahoma and Texas, especially between the Oklahoma City and Dallas-Fort Worth metro areas. Fortunately, the conditions didn’t coalesce to produce many tornadoes—only one was reported, near Ada, OK (see photo at bottom)—but more than 100 reports of severe hail had been compiled by the NOAA/NWS Storm Prediction Center (SPC) as of Monday morning. Just southeast of Denton, TX, the town of Corinth was bombarded by hailstones as large as 4.25” (for comparison, a softball is about 4” wide). Supercells in south-central Oklahoma dropped widespread 2” - 3” hail, with one report of a 3.25” hailstone southeast of Francis, OK. There was considerably less high wind than large hail in Sunday’s storms, although a gust to 65 mph was reported near Anthony, KS.
Figure 1. Rick Smith, warning coordination meteorologist for the National Weather Service office in Norman, OK, took this photo of a supercell in eastern Oklahoma from the National Weather Center offices in Norman around 6:00 pm CDT Sunday, March 26, 2017. Image credit: Rick Smith, used with permission.
Stop in the middle of a highway? Hail, no!
Sunday’s prolific hail producers reignited a problem familiar to those in the Southern Plains: the specter of people parking beneath bridges, right in the middle of highways (even interstates!), in order to protect their vehicles. It goes without saying that this practice not only puts everyone behind the stopped car(s) at risk of hail damage, but it impedes any emergency vehicles from using the roadway. If a tornado were to strike one of these traffic clots, a major disaster could easily result. Dennis Mersereau (@wxdam) included plenty of photographic evidence and food for thought in his 2015 post on this issue: “This is one of those instances where people have to remember that we all live in a society, and that they have to think of the safety of those around them, as well.”
Figure 2. Damage expert Tim Marshall (Haig Engineering) captured this 3” diameter hailstone from the storm that struck Double Oak, Corinth, The Colony, and Frisco, TX, just north of Marshall’s house. “Looks like I’ll be booked evaluating the damage through at least mid-summer,” said Marshall. “Spring has roared in like a lion.” Image credit: (c) Tim Marshall, used with permission.
Figure 3. As of Monday morning, March 27, 2017, the NOAA/NWS Storm Prediction Center had designated “enhanced” risk areas for parts of the Tennessee Valley from KY to MS on Monday and for parts of TX and OK on Tuesday, March 28. Significant risk may also emerge on Wednesday and subsequent days this week.
Day by day through the week ahead
Very large hail was a continuing threat on Monday afternoon, as the pocket of very cold air aloft migrated into the mid-Mississippi Valley. In its outlook issued at 11:30 am CDT Monday (see Figure 2), SPC was highlighting far western TN and northern MS with a risk for significant large hail (2” or more diameter). A preexisting cluster of thunderstorms moving through northeast AR at midday Monday was expected to segue into new supercells toward the southeast. A solid swath of low-level moisture evident in the 12Z Monday sounding from Jackson, TN, will be moving into the area by afternoon, enhancing the severe threat. Late Monday, high winds may become more of a concern as the supercells morph into one or more squall lines further east toward Nashville, TN, and Huntsville, AL. As with Sunday, the tornado threat appears fairly low on Monday afternoon.
The U.S. pattern will recharge on Tuesday as another compact but strong upper-level low swings into the Southern Rockies. Deep low-level moisture will surge into Texas ahead of the upper low, with dew points of 60°F to 70°F likely to be widespread by Tuesday afternoon. Severe thunderstorms may form along a warm front expected to lie near the Red River of west TX/OK, as well as along a dry line in the South Plains of TX. The greatest likelihood of tornadoes will likely be near the intersection of the dry line and warm front (the “triple point”), but upper-level wind shear and instability could be more than adequate for tornadic supercells along either boundary.
Another round of intense storms appears likely on Wednesday from eastern OK and TX into parts of AR and LA, especially if the remnant activity from Tuesday night doesn’t interfere. It’s unclear if low-level wind shear will be as strong on Wednesday as on Tuesday, but conditions still appear ripe for widespread storms dumping heavy rain, hail, and high wind, as well as the possibility of embedded tornadoes.
More severe weather could erupt on Thursday, especially in and near Mississippi, and on Friday as far east as the Carolinas, as the upper low translates across the eastern U.S. Meanwhile, yet another upper low will be diving into the southwest U.S., poised to trigger the next multi-day round of severe storms. This one may begin on Saturday across western TX if moisture returns in time. A better bet for severe weather in TX/OK/LA may be on Sunday, with the upper low expected to stall out as unstable air continues streaming north from the Gulf of Mexico. Patterns like this sometimes evolve into more of a heavy-rain threat than a tornado-favorable setup, but there is still ample time to see how this one evolves.
Both the GFS and ECMWF suggest that the pattern will remain progressive into next week, with at least one more significant upper low traversing the U.S.
We’ll be back with our next post on Tuesday. For more on Tropical Cyclone Debbie, which was approaching the Queensland, Australia, coast early Monday afternoon EST, see Jeff Masters’ post from Monday morning. Please free to discuss Debbie in the comment section of this post!
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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.
Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather
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