The tragedy of this loss is compounded by the fact that it was totally avoidable: National Weather Service forecasts and warnings were excellent, and the weather radar showed the developing threat well before the boat even entered the water.
Unfortunately, this kind of avoidable tragedy is not an isolated incident, highlighting the need to connect the ever increasing abilities of meteorologists with the needs of society to be warned and to avoid severe weather.
The cause of the tragedy was a severe line of thunderstorms, with outflow winds in front of them. The incident occurred over southwestern Missouri around 7:00 PM central time (5 PM PDT, 0000 UTC) on Thursday.
Radar imagery clearly showed the approach of the severe convective line and strong evidence of associated powerful winds. Let me show you using Springfield, Missouri NWS radar imagery. Remember the accident occurred around 0000 UTC 20 July (meteorologists use a 24-h clock with the time at the Greenwich meridian).
At 2246 UTC (5:46 PM Central Time), a very strong convective line was approaching the area. Red colors indicate heavy precipitation, perhaps with hail. (this field is called reflectivity, the amount of radar return from the precipitation, which is related to intensity)
At 6:17 PM, before the boat went into the water, the line was heading straight towards the lake, with many intense cells. Look closely and you will see a faint line ahead of the main action--that is the gust front, the leading edge of strong outflow winds in front of the convection.
Fifteen minutes later, the system was still approaching
And was stronger and imminent at 6:45 PM.
At 7 PM, the gust front had crossed the lake and the heavy precipitation was on them.
Modern radars are Doppler radars that provide the velocity of the precipitation (and the air it falls through) towards or away from the radar. The Doppler velocities at the lowest elevation angle from the horizontal (.5 degree) at 6:31 PM shows very strong winds behind the gust front.
Blow up radar reflectivity and Doppler velocities at 659 PM show the threat clearly.
11:20 a.m. — Severe thunderstorm watch issued for all of southwest Missouri, including Stone and Taney Counties (and the Table Rock Lake area) until 9 p.m. Potential for severe thunderstorms and isolated wind gusts of 70-75 mph.
5:45 p.m. — Severe thunderstorm warning for Newton, Cedar, Polk, Barry, Greene, Jasper and Dade counties. 60 mph wind and 3/4-inch hail possible.
6:32 p.m. — Severe thunderstorm warning for Taney, Stone, Barry counties until 7:30 p.m. Branson and Table Rock Lake are specifically mentioned in this warning. 60 mph winds and hail less than 3/4 inch possible.
6:45 p.m. — Severe thunderstorm warning for Webster, Douglas, Wright, Christian, Stone, Barry, Lawrence, Greene counties until 7:45 p.m. 70 mph winds and 3/4-inch hail possible.
So we had a failure mode with excellent observational data and official warnings of the event, but lack of protective action by the tour operator. This type of failure mode is not limited to this event.Another potent example: the wine country fires of last October. 44 people died and billions lost from a severe weather event (strong Diablo winds) that were well forecast. Many of the deaths of wildfire fighters of recent years were also from completely predictable weather events. I could easily give you a dozen more examples of this kind of thing.
Our ability to diagnose and predict the weather has improved immensely during the past decades, but we are not making full use of this information to save lives and property. Some of the problem is education. Some of it is poor communications. But in a world of internet almost everywhere and smartphones in every hand, we should be able to do better.
Diagnosing and forecasting the weather is only half the battle...the easier part. Communication and effective use is the hard part.
from Cliff Mass Weather and Climate Blog https://ift.tt/2LcWH8Z
No comments:
Post a Comment