Springtime in November: Tornadoes Rake High Plains from Nebraska to Texas

The latest tornado outbreak on record west of the 100th meridian left damage strewn late Monday across parts of western Kansas and the Oklahoma and Texas Panhandles. The tornadoes emerged from a batch of long-lived supercell thunderstorms spawned by a very strong upper-level low that encountered near-record levels of atmospheric moisture for mid-November. The same upper-level storm has plastered the southern Rockies with heavy snow and produced blizzard conditions over parts of the High Plains, but the tornado outbreak was far more exceptional for the location and time of year. As of Tuesday morning, the NOAA Storm Prediction Center had logged an amazing 41 tornado reports. Many of these are likely to be multiple reports of the same tornado, so the final count may well drop, but it is clear that a remarkable event unfolded. Based on photos via social media, several of the tornadoes were large “wedges.” A Halliburton oil-field servicing plant was largely destroyed by a tornado east of Pampa, Texas, according to the county sheriff’s office. Nobody was in the building at the time, and chemicals and gas leaks produced by the tornado strike have reportedly been contained. Damage reports from this and other tornadoes on Monday are summarized in a weather.com roundup. For a dramatic time lapse of the Pampa storm, see the Twitter clip from JR Hehnly embedded with permission at the bottom of this post.


Figure 1. This tornado was photographed at 6:43 p.m. on Monday, November 16, 2015, just north of Groom, TX, by Quincy Vagell (weather.com). The tornado was first visible at 6:39 p.m. and on the ground for quite some time after. “Downed telephone poles/wires cut my chase short,” he said. A prior tornado from the same storm produced considerable damage south of Pampa. Image credit: Quincy Vagell, @stormchaserQ.


Much like last week’s central U.S. system, which produced tornadoes over Iowa, Monday’s upper-level storm arrived on a powerful midlatitude jet stream that’s kept weather features moving quickly across the nation over the last few days. This week’s upper storm is quite energetic, as evidenced by the tornado that struck on Sunday near Denair, California. Another key to Monday’s events is the unusually moist air mass brought up from the Gulf of Mexico ahead of both systems. Sea-surface temperatures are above average throughout the tropical and subtropical North Atlantic, with near-record values 1-2°C above average covering most of the Gulf of Mexico and Northwest Atlantic. Moisture evaporating from these warm waters flowed into the southern Great Plains on Monday in an extremely juicy airmass. Dewpoint temperatures rose into the 55-60°F range beneath a zone of very strong upper-level forcing and vertical wind shear. This setup favored the development of discrete supercell thunderstorms--the kind most likely to produce strong tornadoes--for several intense hours, until a Pacific cold front barrelled across the region after dark. The tornado threat then declined, as a north-south squall line swept across Oklahoma and north central Texas during the overnight hours. Wind gusts above 60 mph were common along the squall line, and a station near Red Rock, OK, reported a 99-mph gust at 1:55 am CST.


Figure 2. All tornadoes (F/EF0 - F/EF5) reported in the era of reliable records, from 1950 to 2014, during the months of November through February. Initial tornado reports from November 16, 2015, across Texas, Oklahoma, Kansas, and Nebraska are shown in white triangles. Image credit: Ian Livingston and ustornadoes.com, used with permission.

An unprecedented High Plains outbreak for November
Dynamic upper-level storms like the one on Monday often pull moisture up into the Central Plains and Mississippi Valley, which is why places like Iowa can occasionally see tornadoes even in November. Mid-autumn tornado outbreaks are much more likely across the Deep South, where rich low-level moisture is more readily available. Some of the deadliest and most destructive tornadoes in Southern history have struck in November.

In contrast, big upper-level storms seldom allow warm, moist low-level air to be swept northwest into the Texas and Oklahoma Panhandles and western Kansas this late in the autumn. For one thing, the elevation of Monday’s tornado-struck areas is around 2500 to 3000 feet, which reduces the potential depth of available moisture for severe thunderstorms. Monday’s upper low had a pronounced north-south orientation early in the day, which allowed the deep moisture to be pulled further northwest than usual. Often in such cases, the upper low is “cutting off,” or becoming detached from the jet stream, which would tend to reduce the amount of wind shear. In this case, however, there was plenty of jet-stream energy behind the low, which forced it eastward late Monday and quickly boosted the amount of vertical wind shear. The dynamics strengthened so dramatically that nearly all of the tornadoes occurred near dusk or after dark, without any help from daytime heating to add instability to the atmosphere.


Figure 2. When ENSO is in a warm, or El Niño, phase (top), the frequency of springtime tornadoes goes down. When it is in a cool, or La Niña phase (bottom), tornadoes increase (indicated by red areas). The effect is strongest in the boxed area. Image credit: IRI from Allen et al., Nature Geoscience, 2015.


Did El Niño or climate change have anything to do with this?
Strong El Niño events are associated with cold-season tornadoes along the Gulf Coast, and especially in Florida. There is no established link between El Niño and fall/winter tornadoes in the Great Plains. In fact, El Niño tends to reduce the likelihood of springtime tornadoes across the Southern Plains, as we discussed in an April blog post (see Figure 2). It’s possible that the ongoing strong El Niño event is playing a role in the jet-stream configuration, or the availability of deep moisture, but if so, this is more a function of the particulars of this autumn rather than a well-established fingerprint of El Niño.

Likewise, any direct role of climate change in this event would take time and research to establish, ideally through attribution research. “I don't know how to put this event in the context of lengthening tornado seasons or climate. It's such an outlier,” said Harold Brooks (National Severe Storms Laboratory), who is one of the world’s foremost experts on tornado climatology and the influence of climate change on tornadoes. Brooks added: “Even in the absence of climate change, you can have extreme outliers,” such as the 32 tornadoes that struck on January 24, 1967, from Oklahoma to Wisconsin.

More severe weather, heavy rain possible Tuesday in Mississippi Valley
The exceptionally moist air mass fueling Monday’s storms has been shunted east into Arkansas and Louisiana, raising the potential there for severe weather and flash flooding on Monday afternoon and evening. The 00Z Tuesday radiosonde profile from Oklahoma City showed near-record amounts of moisture for November (3.71 cm or 1.46”), and at 12Z Tuesday, the sounding from Lake Charles, Louisiana, contained 4.91 cm (1.93”) of available moisture, also near the top end of moisture content observed in November. SPC’s convective outlook issued at 10:30 am CDT Tuesday has an enhanced risk of severe weather across eastern AR and LA, which is at risk for high winds and heavy rain from the advancing front and squall line as well as tornadoes from any supercell storms that form ahead of or within the line. Heavy rains and potential flash floods are another threat for Tuesday, with bursts of 3-5” of rain possible. NOAA’s Weather Prediction Center has a moderate risk of rainfall exceeding flash-flood guidance criteria, centered on northeast Arkansas and southeast Missouri, as a low-level jet stream blowing at up to 90 mph will be importing ample quantities of Gulf moisture.


Figure 4. Enhanced infrared image of Invest 90E in the Eastern Pacific as of 1730Z (12:30 pm EDT) Tuesday, November 17, 2015. Image credit: NOAA/NESDIS.

Invest 90E in the Eastern Pacific likely to become a very late-season tropical storm
Satellite images show that an area of disturbed weather (Invest 90E) in the Eastern Pacific several hundred miles southwest of Mexico’s Baja Peninsula has acquired some spin and a respectable amount of heavy thunderstorm activity. The 7 am EST Tuesday run of the SHIPS model showed ocean temperatures were a  near record-warm 30°C (86°F) and wind shear was a low 5 - 10 knots, conditions that favor continued development. The 00Z Tuesday runs of both the GFS and European models showed 90E becoming a tropical depression by Thursday. In their 1 pm EST Tuesday Tropical Weather Outlook, NHC gave 2-day and 5-day odds of development of 40% and 70%, respectively. If 90E does become Tropical Storm Rick, it would be one of the latest-forming tropical storms in the history of the Eastern Pacific. Since accurate records began in 1949 (with higher-quality satellite records beginning in 1971), the Eastern Pacific has seen only four tropical storms form after November 18: December 5, 1983 (Winnie), November 27, 1971 (Sharon), November 27, 1951 (Unnamed), and November 20, 2011 (Kenneth.) None of these storms hit land. 90E will wander slowly to the west-northwest or northwest at speeds less than 5 mph through Thursday. A turn to the northeast towards Mexico’s Baja Peninsula is possible early next week, but the models are showing a variety of long-range solutions for the path of 90E, and it remains uncertain if this storm will pose a threat to Mexico or not.

Tropical Storm In-fa a threat to Guam
In the Western Pacific, Tropical Storm In-fa formed on Tuesday morning in the waters about 1200 miles east-southeast of Guam. In-fa is expected to track west-northwest and intensify into a typhoon later this week, and could put pass very close to Guam on Saturday. There is the potential that In-fa could rapidly intensify into a major Category 3 storm before reaching Guam.

The Atlantic is quiet with no tropical cyclone formation expected for the next five days.

Bob Henson (severe weather), Jeff Masters (tropical)

Last night's #tornado with power flash as it moves through Pampa in the #Texas Panhandle #TXWX pic.twitter.com/WBcOSqon79

— JR Hehnly (@stormchasing) November 17, 2015