Some Considerations When Evaluating Wind Damage – A Case Study (Study #1)
Case Study #1 – July 10, 2013 – Bellevue, Ohio
A severe storm passed through Ohio on July 10, 2013 causing various wind related damages. The National Weather Service at Cleveland Hopkins Airport measured maximum winds of 38 MPH out of the WSW. This wind speed is indicative of a storm or front passing through the area. However, the most severe portions of the storm were reported by local media to be south of the suburban Cleveland area, thus the wind speed readings at Cleveland airport were lower than the wind speeds experienced south of the Cleveland area. One particular area was Bellevue, Ohio.
The review of private weather station records surrounding Bellevue disclosed winds generally out of the west, that is, WNW and WSW. This was also the general direction being reported for the storm during weather warnings. The recorded wind speeds at these private weather stations varied from 15 MPH to 62 MPH. One private weather station in Bellevue did not record any wind speeds for a three hour period that began about the time the winds passed through Bellevue, indicating that it may have been damaged or was without power when the high winds passed through there.
Local news media reported and/or showed downed trees, downed power lines, a string of broken utility poles, structural roof damage, flattened corn crops, trees with their tops sheared off, etc. around the Bellevue area. The pattern of these damages seemed to be concentrated to a few areas rather than widespread throughout and around the city. The severity of these damages were indicative of winds significantly over 55 MPH.
Our personal observations in the Bellevue area generally disclosed wind related building damages such as, siding damage, severe damage to roof coverings, damaged masonry walls, damaged wood framed walls, lifted and/or dislodged roof framing, etc. Some wind related damages appeared to be more severe than may be expected due to framing that had been weakened by decay or other previous damage producing mechanisms. The damages we observed generally extended in a line that stretched west to east or southwest to northeast. The trees in the paths of the damage exhibited sheared off tops.
Over the past thirty years of forensic investigations we have observed that a pattern of damage that stretches along a line and includes sheared off tree tops is usually indicative of damages caused by a tornado. Another evidence of tornado damage is the multi-directional scattering of dislodged building debris. Local news media later reported that weather experts concluded that there had been a tornado touchdown in Bellevue.
We have also observed that a pattern of wind damage that appears to have been caused by a high pressure bulldozer is indicative of high straight-line winds such as caused by a micro-burst. This pattern was also reported and observed in and around Bellevue.
In summary, the records from the National Weather Service and the private weather stations were helpful in determining that there had been a storm with very high winds around Bellevue with maximum wind speeds measuring up to 62 MPH at one location. And, although damage to poorly sealed three-tab shingles is possible with 62 MPH winds, winds of this speed are generally not expected to cause structural damages to reasonably well-maintained structures. However, the structural damage reports from local news media and the severity of the building damage that we personally observed indicate that some areas in and around Bellevue experienced wind speeds well over 55 MPH. The body of evidence in this case indicates that the most severe damages were probably due to a tornado or high straight-line winds such as a micro-burst. Thus, in the engineering evaluation of wind damages the effects of the wind pressures generated by a tornado or micro-bursts are considered in addition to the effects of high winds, especially when the physical evidence indicates that one of these passed through the area.