As rescue efforts to save passengers and crew trapped aboard a capsized Yangtze River vessel, it's increasingly clear that the cause was at least in part related to the inclement weather at the time.
The passenger boat that capsized Monday night with at least 456 people on board encountered fierce thunderstorm-related winds, and possibly a tornado.
The storms it ran into were not unusual for the area at this time of year. They're comparable to what occurs in the Midwest U.S. each spring -- towering clouds up to 55,000 feet in height dumping large amounts of rainfall and unleashing damaging wind gusts underneath them.
The China Meteorological Administration (CMA) has said that winds were a 12 on the Beaufort Scale, which corresponds to winds close to hurricane force of 74 miles per hour.
Many media outlets, including CNN, have been reporting that a small tornado struck the ship, a report evidently sourced to the CMA.
However, a tornado would have been extremely difficult to confirm over water -- since it would be difficult to see and may not have left damage patterns that would reveal a circulation.
In the U.S., tornadoes are confirmed using ground surveys, aerial photographs and Doppler radar imagery after the fact, usually the next day. To have a confirmed tornado on a river, at night, and to know exactly how wide it was and whether it hit a particular vessel, would be unusual so soon afterward -- even with the U.S. National Weather Service's rigorous verification system.
China has a professional weather service, and is even close to jumping ahead of the U.S. in some aspects of its weather satellite program. However, the country gets far fewer tornadoes per year than the U.S. does. Therefore, its meteorologists may be less experienced at recognizing their signs on radar and in damage patterns, particularly boat damage.
The website China Daily reports that a "destructive tornado" occurred when the boat capsized, and that the tornado lasted between 15 to 20 minutes in the region of the Yangtze River where the accident occurred. The tornado is said to have been less than .62 miles wide.
This would have made it a relatively average-sized tornado, if on the slightly larger than average side. If it did in fact occur this way, the boat was extraordinarily unlucky to have been hit directly by it.
A weather station 35 kilometers, or 22 miles, away from the accident site recorded winds of 35 miles per hour, China Daily reported, and that station also picked up 64.9 millimeters, or 2.55 inches, of rain in the one hour between 9 and 10 p.m.
It's not clear what the Chinese authorities are using to verify that a tornado occurred -- or if there was a mistranslation of the word "cyclone," which can be used to refer to storms in general.
It is clear from satellite imagery, radar data and computer model simulations that severe thunderstorms were occurring along the Yangtze River where the accident took place. This time of year is the rainy season in that area, when sultry, humid air from the southeast clashes with cooler and drier air moving in from the northwest.
That clash of air masses was present in abundance Monday night.
According to Harold Brooks, a meteorologist with the National Severe Storms Laboratory in Norman, Oklahoma, the environment in that area at the time of the accident was supportive of tornadoes. But that does not mean that one definitely occurred.
Crude look at soundings indicate environment in area when Yangtze ship sank supportive of supercells/tornadoes. #Yangtzeshipsinks #tornado— Harold Brooks (@hebrooks87) June 2, 2015