event in twenty-four hours at Montpelier is about four inches. There would only be a 4% chance (1/25) in seeing such an event occurring within any given year. A 500- year event would only have a 0.2% chance (1/500) of occurring within any given year. A more useful perspective is offered from taking a longer view, since the probability compounds over time. For example, over a period of fifty years, the probability of seeing a 200-year event is 22.1 % and the probability of seeing a 500-year event is 9.5%. These statistics support the idea of it only being a matter of time before experi- encing such rainfall/flooding extremes. When comparing the observed rainfall
(Fig. 5) to the rainfall amounts for a 500- year event in twenty-four hours (Fig. 6), most locations did not reach this threshold, with the exception of the maximum strad- dling Washington and Addison counties. This drainage included the Mad River near Moretown, which crested at 19.06’ on Au- gust 29, 2011, just shy of the historical crest of the Flood of 1927 of 19.40’ on Novem- ber 3, 1927. However, when comparing ob- served rainfall (Fig. 5) to the 500-year event in twelve hours (Fig. 7), one sees a number of locations exceeding this threshold. Thus, this analysis shows that one of the biggest contributors to extreme flooding was the relatively short time window over which the rain occurred. Flood control measures along waterways installed since the flood of 1927 helped to mitigate flood damages. One of the most notable examples was at Montpelier, where the Winooski River crested at 19.05’ on Au- gust 29, 2011, well short of the 27.10’ high crest on November 3, 1927. Historical fre- quency of river and stream levels is likely being conducted, but from a forensic me- teorology perspective the rainfall inputs in the most severely flooded locations place this event as 200-year or greater event.
Summary Meteorology is a rapidly advancing sci-
ence, with improvements in weather fore- cast skill and abilities to diagnose and re- construct weather conditions. The forensic meteorologist has copious data and tech- nology to employ a variety of analysis tech- niques to reconstruct local weather con- ditions. Whether it’s determining the tim- ing and location of a lightning strike, what storm warning information was present, or the rarity of a rain storm, the forensic mete- orologist will add value to an investigation. In order to ensure professional standards, the American Meteorological Society has a long-standing, “Certified Consulting Me- teorologist” program to certify consulting meteorologists.3
In order to become a Cer-
tified Consulting Meteorologist (CCM), one must have at least five years of work expe-
www.vtbar.org
Figure 6. 500-year, 24-hour extreme precipitation estimates, courtesy Northeast Regional Climate Center, Cornell University,
http://precip.eas.cornell.edu/.
Figure 7. 500-year, 12-hour extreme precipitation estimates, courtesy Northeast Regional Climate Center, Cornell University,
http://precip.eas.cornell.edu/.
rience, provide an example his/her written work, and undergo an extensive written and oral examination. The CCM program ensures high standards of competency and character.4
____________________ Jason Shafer, PhD., is Associate Profes- sor of Atmospheric Sciences at Lyndon State College and Certified Consulting Me- teorologist #662. He can be reached at Ja-
THE VERMONT BAR JOURNAL • WINTER 2012
son.shafer@
lyndonstate.edu.
____________________ 1
hmfrm.html. 2
home.html. 4
http://www.ametsoc.org/memb/CCM/ccm http://www.ncdc.noaa.gov/oa/ncdc.html.
3
http://www.ametsoc.org/memb/ccm/ccm
A directory of CCMs is available at http://www.
ametsoc.org/memb/CCM/ccmhmfrm.html.
21
The Forensic Meteorologist—“Reconstructing Weather”
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