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Posted on Thu. Feb. 14, 2013 - 12:01 am EDT

Derecho’s force underestimated

Report faults advance forecasts of storm

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Derecho damage

The intense windstorm that hit Indiana June 29, 2012, caused damage from central Indiana and then moved on to the East Coast, killing at least 13 and leaving millions without power during a heat wave:

State

Peak number without power

Virginia…1,076,051

Ohio…915,366

Maryland…899,171

West Virginia…643,284

New Jersey…135,322

Indiana135,177

Washington, D.C.…68,567

Kentucky…52,616

Source: FEMA via National Weather Service

FORT WAYNE — The National Weather Service’s local offices did a good job of issuing warnings about the derecho that slammed Fort Wayne on June 29, but those warnings failed to communicate the danger the rare storm presented, a new report says.

The National Weather Service issued an internal review of its performance during the event, which in Fort Wayne brought down hundreds of trees and left more than 118,000 people without power in the region – some for more than a week – during a record heat wave. The storm traveled all the way to the East Coast, killing at least 13 people and leaving 3 million without power.

Short-term forecasts the day of the storm were accurate, the report said, but forecasts the day before failed to predict the devastating storm.

“Unlike many major tornado outbreaks in the recent past, this event was not forecast well in advance,” the report said. “The National Centers for Environmental Prediction operational forecast models … provided little assistance in forecasting this event more than 24 hours ahead of time.”

Because the storm was not predicted until just hours before it formed, forecasters on the East Coast predicted it would follow the usual weather pattern of breaking up over the Appalachian Mountains. It didn’t, leading to yet more last-minute warnings, the report said. The storm also moved so quickly that forecasters had trouble issuing warnings ahead of it.

The storm formed over northern Illinois, and by the time it moved into Indiana at 60 mph, it was organizing into a fast-moving storm almost 200 miles across and building in strength. As it roared into Whitley County, wind speeds were estimated at 75 mph, and by the time it ripped into Allen County, radar showed winds at 2,500 feet were 104 mph. On the ground, a wind gust was measured at 91 mph at Fort Wayne International Airport, but more intense winds were hitting central Fort Wayne.

A derecho (pronounced “deh-REY-cho”) is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms. That, too, led to problems because people saw or heard severe thunderstorm warnings and thought they did not need to worry because it was not a tornado warning.

“There was this interpretation that it’s just a severe thunderstorm warning,” said Michael Lewis, the warning coordination meteorologist for the National Weather Service’s Northern Indiana office in Syracuse. “There was more to it.”

Lewis said the forecasts included information about the dangerous winds, but the technology used to spread the information cannot yet read it.

“So while we were calling for 90 to 100 mph winds, that wasn’t being communicated,” he said.

The report found that same scenario occurring all over the 600-mile path of the storm.

“Despite the use of enhanced wording in many of the warnings, nearly everyone interviewed was surprised by the intensity of the winds with this derecho,” the report said. “As a result, most people surveyed did not take any special precautions as the storms moved through their area.”

The National Weather Service has become more precise in its warnings and now issues them in polygons based on the shape of where the danger is. But most warning systems can issue them only by county, leading to more warnings that are unnecessary, dulling their impact, Lewis said.

“How many times will you do that before you say it doesn’t mean anything?” Lewis asked. “We’ve been trying to reduce the rate of false alarms, but we’re limited by technology using existing models of county-based warnings instead of polygons.”

Lewis said that is particularly important because people already underestimate the danger of thunderstorms.

“When you look at northern Indiana, wind damage is our primary threat. In fact, when you look at fatalities associated with wind damage over a 30-year period, it’s comparable to tornadoes,” he said. “We’ve got to find a way to heighten their awareness without freaking them out.”

Lewis said one thing that went well for the weather service’s northern Indiana office was compiling and issuing storm damage reports after the storm moved through.

“With all the information we were getting, the staff was very efficient in processing the information and pushing it out, and that is monitored by both the media and emergency responders,” he said. “It’s a quick way to see what’s going on.”

The northern Indiana office was singled out for praise in the report for lowering the criteria for issuing heat warnings in recognition of the fact that thousands of people had no electricity, and thus no air conditioning or even fans, and the report said all forecast offices should be encouraged to do the same.

Lewis said the report is aimed at one thing: improvement.

“Our mission is to save lives and minimize loss,” he said. “So in the grand scheme of things, you have to ask, did we fulfill the mission? And can we do it better?”

dstockman@jg.net


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