Earth Day Updrafts: Supercell in Texas, Volcano in Chile

A spectacular supercell thunderstorm over the Texas Panhandle on Wednesday afternoon morphed into a sprawling complex that moved across North Texas overnight with strong winds, heavy rain, and hail. The original supercell dropped several brief tornadoes south and east of Amarillo and displayed some impressive structure (see Figure 1) before it merged with other storms to form a mesoscale convective system (MCS). These large clusters of showers and thunderstorms can persist for more than 12 hours, often forming in the evening and persisting until morning.


Figure 1. This supercell northwest of Floydada, Texas, has the classic corkscrew appearance produced by the rotation of the entire thunderstorm. The supercell produced several brief tornadoes. Image credit: Brock Burghardt.


Wednesday night’s MCS drew from a pool of deep moisture over Texas, and it was hustled along a northwest-to-southeast frontal zone by powerful jet stream winds, exceeding 140 mph above the DFW area at 0000 GMT Thursday. Further south, another complex of storms developed near Corpus Christi earlier in the day, toppling power poles and downing power lines with wind gusts estimated at 70 mph, before moving into the Gulf of Mexico, where it maintained impressive vigor into the night. A buoy about 100 miles south of Houston reported a wind gust to 87 mph. Remnants of this MCS moved across Florida on Thursday morning. The strong upper winds prevalent across the East also worked their way to the surface in and near New Jersey on Wednesday afternoon. A batch of modest rainshowers produced downburst winds that gusted to 71 mph at Philadelphia International Airport around 3:00 p.m.


Figure 2. The Day 2 convective outlook valid on Friday, April 24, shows an enhanced risk of severe weather across parts of the southern Great Plains. Image credit: NOAA/SPC.


More severe weather on the way into next week
Conditions are ripe for more tornadic storms and MCSs over the next several days across the south-central states, as upper-level energy ripples along the strong jet stream and rich moisture remains in place. A slight risk of severe weather is in place for Thursday across parts of central Texas, southern Louisiana, and eastern Colorado/western Kansas. More significant severe weather is expected on Friday, with NOAA’s Storm Prediction Center already highlighting the possibility of strong tornadoes ahead of a dry line that should extend from central Kansas to central Texas. SPC’s Day 2 outlook for Friday shows an enhanced risk of severe weather in two pockets ahead of the dry line (see Figure 2). The ultimate locations of elevated risk will hinge in large part on where storms develop on Thursday night; any widespread activity could leave clouds and rain-cooled air that reduce the amount of instability available on Friday afternoon. The zone of greatest severe risk will shift east across the lower Mississippi Valley and into the Southeast on Saturday.

Another strong upper low could bring renewed severe weather in Texas and Oklahoma by late in the weekend. SPC’s Day 5 outlook is already pointing to a ramped-up probability of severe weather on Monday in central Texas, a rare upgrade for so far into the future. The last several runs of the longer-range GFS model suggest this upper low would continue eastward as a distinct system across the Gulf states early next week, with very strong thunderstorms and heavy rain eventually possible as far southeast as Florida, while the latest run of the ECMWF model (issued at 0000 GMT Thursday) moves the upper-level energy more slowly and in a weaker form. Before the month is done, Kentucky should get one or more bouts of heavy rain, possibly giving several cities their wettest April on record, including Frankfurt (10.68” to date; record 13.95” in 2011); Lexington (10.61” to date; record 12.70” in 2011); and Louisville (10.61” to date; record 13.97” in 2011).



Figure 3. Children in Puerto Varas, Chile, watch the Calbuco volcano erupt on Wednesday, April 22, 2015. The volcano’s huge ash cloud spread over a sparsely populated, mountainous area in southern Chile. Authorities ordered the evacuation of the inhabitants of the nearby town of Ensenada, along with residents of two smaller communities. Image credit: AP Photo/Carlos F. Gutierrez.

Chile’s Calbuco volcano springs to life
For sheer visual power, Wednesday’s U.S. thunderstorms were eclipsed by the surprise eruption of Calbuco in southern Chile, just north of Patagonia. The volcano, located near Puerto Montt in the Los Lagos region, has a peak elevation of about 6,500 feet. Wednesday’s event was Calbuco’s first eruption since 1972 and the first major one since 1961. The initial burst of ash formed a narrow column that quickly reached the stratosphere (at least 10 km high) and spread out into an anvil cloud resembling that of a severe thunderstorm (Figure 3). Overnight, a second eruption was reported, with lava flows and lightning painting a eerie, brilliant scene. This Mashable photo album shows the many faces of the Calbuco eruption as the day and night unfolded. About 4,000 nearby residents had evacuated by late Wednesday, but there were no immediate reports of injury.

Vulcanologist/blogger Erik Klemetti at Wired pointed out that the eruption’s initial phase was “a classic Plinian column”—a term derived from the infamous A.D. 79 eruption of Mount Vesuvius, which was documented by Pliny the Younger. The apparent height and nature of the plume from Calbuco would put the volcano’s first eruption on Wednesday at a ranking of at least 4 (“cataclysmic”) on the Volcanic Explosivity Index, which runs from 0 to 8. It would take a much more potent eruption to generate the massive impacts on climate described by Jeff Masters in his recent post on Indonesia’s Mount Tambora, which produced a colossal eruption 200 years ago.


Video 1. This amazing time-lapse sequence, from Chile’s Centro Información Monitoreo Alerta Temprana, shows the eruption of Calbuco through nightfall Wednesday.



This week’s WunderPoster: Dust devils
If you can appreciate the power of rising air on a more modest scale than a volcanic eruption or a supercell thunderstorm, check out this artistic take on dust devils, the latest installment in our WunderPoster series (Figure 4, right). When the summer sun bakes a field or a desert, a pocket of surface air may heat up enough to create a narrow, rotating updraft. Most dust devils spin harmlessly across the landscape--too small, weak, and short-lived to cause much trouble--but the most powerful can be dangerous, lasting for 10 minutes or more and packing winds exceeding 60 mph. All WunderPosters can be downloaded in formats suitable for posters or postcards.

Bob Henson