Natural or Man-Made Icing?

One winter morning in a Mid-Western city, a multi-car pile-up occurred on an interstate bridge. The direct cause was a formation of ice on the bridge. Claimants alleged that the ice had been created from nearby natural draft cooling towers belonging to an industrial facility.

Research and onsite investigation, plus analysis of low- and upper-level weather conditions by Meteorological Evaluation Services meteorologists, determined that the winds during that morning could not have taken the effluent from the cooling tower in the direction of the bridge. Further investigation of the weather data revealed that fog and sub-freezing conditions early that morning were responsible for the ice formation, and that the meteorological principle, "bridge freezes first," was applicable in this instance. MES documented the weather conditions and conclusions in a report.

Negligence or an Ongoing Snowstorm?

A slip and fall incident occurred at 6 AM.  Using certified weather records, MES determined that all snow ended 72 hours prior to the incident.  There was no additional precipitation.  Hourly weather records showed that there were 4 inches of snow on the ground at 8 AM on the morning preceding the incident.  Temperatures that day reached 39 degrees, before falling below freezing during the night.  Therefore, MES determined that there may have been ice on the pavement due to the melting and refreezing of the snow cover. 

Lightning or Arson?

A factory burned to the ground on a July evening.  The cause of the fire was unknown.  However, the nearest airport recorded a thunderstorm in the vicinity near the time of the incident.  MES used weather radar records and lightning data to determine that no cloud-to-ground lightning strikes occurred at the location or in the vicinity and estimated time of the fire.  Therefore, lightning did not cause the fire.

Natural or Spill-Induced Fog?

On a damp day with intermittent precipitation and fog, a multi-vehicle chain reaction accident occurred on a rural section of interstate highway. Industrial facilities bordered the service roads. Just prior to the incident, a tanker truck was overfilled with liquid nitrogen and a spill resulted.

Onsite meteorological data from an adjacent industrial facility, specifically, ambient dry bulb and dew point temperatures, wind direction, speed and stability pointed to the spill as the source of the dense fog that engulfed the interstate highway without warning. The National Weather Service airport and Cooperative station data confirmed the dispersion characteristics and calculations performed with the onsite data.

Act of God or Faulty Construction?

A retaining wall collapsed, destroying a frequently used commuter railroad track.  The incident took place 10 days after a blizzard left over a foot of snow in the area.  Conditions before the blizzard were dry.  Significant rain in the 6 hours preceding the incident resulted in melting of the remaining snow pack.  Using past weather records, MES determined the maximum water content in the melted snow pack.  Coupled with the precipitation, the amount of runoff for the 6-hour event was equivalent to a 6-hour rain event with a maximum return period of 8.6 years at that location.  Therefore, the retaining wall should have supported this runoff without a problem.