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

[phantom power]

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.”

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.

http://www.wunderground.com/blog/JeffMasters/springtime-in-november-tornadoes-rake-high-plains-from-nebraska-to-te

[Warpy]

1. Snow here in the valley in NM on Monday night.

after 2 days of heavy rain showers. I did warn people downstream that this storm would pack a punch.