Monday, February 18, 2013

Report Available on June 2012 Derecho

On June 29, 2012 thunderstorms in northern Illinois and Indiana evolved into a destructive derecho. The derecho traveled 700 miles through 10 states. Winds gusting to 80 mph snapped trees and power lines, and 4 million people were without power for a week or more. Thirteen people lost their lives, mostly due too falling trees. Oppressive heat and humidity settled in over the affected area in the wake of the storms, and another 34 heat-related deaths occurred in the days after the storm. Without power residents were left without air conditioning.

This event happened to be the subject of my first post for the CoCoRaHS blog and you can read more about the derecho in that post. You also read more about this derecho in a report recently released by the National Weather Service. This report, called a Service Assessment, is a type of report that the NWS often produces after weather events with major impacts. These are events that result in multiple fatalities, numerous injuries requiring hospitalization, significant impact on the economy of a large area or population, extensive national public interest or media coverage, or an unusual level of attention to NWS operations (performance of systems or adequacy of warnings, watches, and forecasts). Their purpose is, in general, to evaluate the response and performance of the NWS in operations related to the event.  The report also identifies best practices and makes recommendations on improving products and operations.  As part of the assessment, surveys of the general public were conducted to help assess the timeliness and effectiveness of the warnings.

As you might expect, there were a number of findings, recommendations, and best practices identified in the report.  Many of the findings dealt with the forecast process (models) and NWS procedures during the event. In general, the event was poorly forecast in advance by the forecast models, but warnings were accurate and wording emphasized the heightened threat from these storms. Three findings, in particular, caught my attention:

  • Many Weather forecast Offices (WFOs) had some difficulty keeping up with the rapid forward progress of the derecho, which was approximately 60 mph. This resulted in minimal lead time near the western fringes of several warning polygons issued for this event.
  • 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. As a result, most people surveyed did not take any special precautions as the storms moved through their area.
  • Nearly all conversations with members of the media highlighted the usefulness of Facebook and Twitter in reaching the public and in receiving observations and damage reports throughout the viewing area.

You can download the report at this link:  The Historic Derecho of June 29, 2012.

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