Thomas W. Schmidlin

Response to Warnings during the 3 May 1999 Oklahoma City Tornado: Reasons and Relative Injury Rates

Residents of homes that sustained F4 or F5 damage in the deadliest of the 3 May 1999 tornadoes were surveyed to determine their responses to the tornado warning, reasons for their responses, and relative injury rates. There were 190 people in 65 surveyed houses at the time that warnings were issued. Television was the most commonly cited source of the warning (89%), followed by a telephone call (37%), sirens (37%), and AM/FM radio (25%), and 55% received the warning from more than one source. Nearly one-half (47%) of the residents fled their homes before the tornado struck. Of those who fled, 65% went to a tornado shelter, of whom 70% ran to the shelter (median distance 30 m) and 30% drove to the shelter (median distance 4.8 km). About one-half (53%) of those who fled their homes left in a vehicle. None of those who fled their homes, by foot or by vehicle, were injured. Of those who stayed in the home, 39% sought shelter in a bathroom, 38% in a closet, 9% in a hallway, and 15% in other rooms. Reasons for not leaving included believing the storm would not strike their house, believing it was too late or too dangerous to leave, having no transportation available, or having no alternative shelter available. Thirty percent of those who remained in their homes were injured and 1% killed. The rate of serious injury was not significantly different for those in a closet (14%), hallway (20%), or bathroom (23%). Tornado preparedness and warning programs should recognize that long tornado warning lead times and street-level television coverage allow residents to make reasoned decisions to minimize risk and that those decisions may include driving out of the path of the tornado.

Impacts of Severe Winter Weather during December 1989 in the Lake Erie Snowbelt

Abstract December 1989 was the coldest December in over 100 years in the Lake Erie snowbelt of Ohio, Pennsylvania, and New York. Mean temperatures of −9°C were 7°C lower than average and extreme minima reached −30°C. Snow fell on 20 to 25 days of the month and snowfall totals of 100 to 200 cm were twice the December average. Some locations reported record snowfalls and the greatest snow depths of this century. Several segments of society were studied to assess the impacts of this severe winter weather. The severe weather had minimal impacts on school districts. Over half (54%) of the districts had no closures due to snow but costs for snow removal increased for schools. Ski centers reported a 50% to 100% increase in revenues over December 1988 and the best December skiing in many years. Lake ports had higher operating costs and loss of shipments. Costs for snow and ice control on Interstate 90 (I-90) in the snowbelt increased at least

Vehicle-occupant deaths caused by tornadoes in the United States, 1900–1998

1326 km−1 over December 1988, but traffic flow was maintained. Person-...

Antecedent Upstream Air Trajectories Associated with Northwest Flow Snowfall in the Southern Appalachians

Abstract Occupants of vehicles encounter an uncertain degree of risk during tornadic storms. The current National Weather Service guidelines suggest we abandon vehicles to lie in a ditch if no sturdy shelter is available. However, these guidelines were developed without the benefit of supporting research. As we are an increasingly vehicle-dependent society, it is important to explore the historical record of vehicle-occupant deaths to see if the National Weather Service guidance is appropriate. The objective of this paper is to investigate the number, distribution, and broad spatial and temporal trends associated with vehicle-occupant deaths that have occurred as a result of tornadoes, and to define the proportion of tornado-induced deaths that have occurred in vehicles. There were 15,047 deaths caused by tornadoes from 1900 through 1998. Of those, 5685 occurred at a defined site, and 270 were known to have occurred in vehicles. The number of vehicle-occupant deaths, as a proportion of all site-known, tornado-induced deaths, was constant from 1959–1979, but decreased significantly between 1980–1998. The number of deaths was related to several influencing factors. Linear regressions and correlations were employed to determine the degree of relationship between the number of deaths and several explanatory factors. While population, number of vehicle registrations, and number of tornadoes all seemed to influence the number of deaths to some degree, the most significant factor to influence the number of deaths appeared to be vehicle safety features. Most vehicle-occupant deaths occurred during rare F4 tornadoes, when vehicles where thrown from roadways. Regionally, the Great Plains had the highest number of vehicle-occupant deaths from tornadoes.

Climatology of Blizzards in the Conterminous United States, 1959–2000

Abstract Northwest flow snow (NWFS) events are common occurrences at higher elevations and on windward slopes in the southern Appalachians. Low temperatures and considerable blowing and drifting of snow, coupled with significant spatial variability of snowfall, substantially increase societal impacts. This paper develops a synoptic classification of NWFS events in the southern Appalachians using 72-h antecedent upstream (backward) air-trajectory analyses. Hourly observations from first-order stations and daily snowfall data from cooperative observer stations are used to define snowfall events. NCEP–NCAR reanalysis data are utilized to identify NWFS events on the basis of 850-hPa northwest flow (270°–360°) at the event maturation hour. The NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory tool is used to calculate 72-h backward air trajectories at the event maturation hour and composite trajectories are mapped in a geographic information systems format. Analyses of vertical soundings are coupled...

Automated quality control procedure for the 'water equivalent of snow on the ground' measurement

Abstract A blizzard is defined by the U.S. National Weather Service as winds over 16 m s−1 and falling or blowing snow causing visibility less than 400 m lasting for at least 3 h. Blizzard occurrence by county was tallied from Storm Data for the 41 winters from 1959/60 to 1999/2000. This revealed 438 blizzards for an annual average of 10.7, ranging from 1 blizzard in 1980/81 to 27 blizzards in 1996/97. The average area affected per blizzard was 150 492 km2 and the average number of people in affected counties was 2 462 949 per blizzard. There was a significant linear increase in the number of blizzards but no linear trend in the total area affected by blizzards or the population in affected counties during the period. Blizzards were most common in a “blizzard zone” of North Dakota, South Dakota, and western Minnesota where each county had 41 or more blizzards in these 41 winters and the annual probability of a blizzard in each county exceeded 50%. Monthly occurrence of blizzards peaked during January in m...

Behavior of Vehicles during Tornado Winds

Snow water equivalent (SWE) has been measured daily by the United States National Weather Service since 1952, whenever snow depth is 2 in. (5 cm) or greater. These data are used to develop design snow loads for building, for hydrological forecasting, and as an indicator of climate change. To data they have not been subjected comprehensively to quality control. An automated quality control procedure for these data is developed here, which checks daily SWE values for common data entry errors, values beyond reasonable limits, and consistency with daily precipitation and estimated melt. Potential effects of drifting in high winds and of the intrinsic microscale variability of SWE are also considered. An SWE measurement is declared suspicious if a sufficient discrepancy is found with respect to the expected SWE data from the northeastern United States are also summarized. 26 refs., 2 figs., 3 tabs.

Unsafe at Any (Wind) Speed

Abstract The degree to which motor vehicles offer protection to occupants from tornado winds and associated debris was examined. The goal is to improve tornado safety recommendations for those in isolated mobile homes and in vehicles when a tornado approaches. Field surveys were made after tornadoes in northern Georgia (March 1994), Middlefield, OH (May 1995), Louisville, KY (May 1996), Arkansas (March 1997), and Texas (May 1997). A sample of 180 vehicles parked outdoors adjacent to a home and exposed to tornado winds were examined from these five events to determine the behavior of the vehicles in relation to estimated wind speed. Wind speeds on the vehicles were estimated by the adjacent building damage and the Fujita scale. About 35% of the vehicles were moved by the wind but there was no difference in percent of vehicles moved among F1 (73–112 mph), F2 (113–157 mph), and F3 (158–206 mph) wind speeds. There was a significant difference in the percentage of vehicles tipped by the winds between vehicles at sites with F1 or F2 damage (4% tipped) and sites with F3 damage (15% tipped). There was also a significant difference in the probability of potential vehicle occupants being seriously injured between vehicles at sites with F1 or F2 damage (16%) and sites with F3 damage (39%). Most vehicles parked outside houses with damage as high as F3 were not moved by the wind and were not tipped by the wind.

Automated quality control procedure for the {open_quotes}water equivalent of snow on the ground{close_quotes} measurement

The goal of this research was to examine the relative safety and stability of stationary motor vehicles exposed to severe winds. The focus was on private passenger vehicles. 1) The behavior of two instrumented storm-chase vehicles that were exposed to severe winds, 2) the behavior of 291 vehicles exposed to a tornado, and 3) the wind speed required to upset a sedan and a minivan exposed to winds in a wind tunnel were studied. A wind as strong as 47 m s−1 (105 mph) has been measured by a storm-chase pickup truck and 44 m s−1 (98 mph) by a storm chase sedan. The vehicles were not adversely affected by the wind. Also studied were 291 vehicles parked outdoors at homes struck by tornadoes, and the behavior of the vehicles was compared to the F-scale damage to the house. At sites with F1 or F2 damage, 72% of the vehicles were not moved by the wind and 96% were not tipped over. At sites with F3 or F4 damage, 50% were not moved by the wind and 82% were not tipped over. Wind tunnel tests on a sedan and minivan sho...

Design Ground Snow Loads for Ohio

Snow water equivalent (SWE) has been measured daily by the United States National Weather Service since 1952, whenever snow depth is 2 in. (5 cm) or greater. These data are used to develop design snow loads for building, for hydrological forecasting, and as an indicator of climate change. To data they have not been subjected comprehensively to quality control. An automated quality control procedure for these data is developed here, which checks daily SWE values for common data entry errors, values beyond reasonable limits, and consistency with daily precipitation and estimated melt. Potential effects of drifting in high winds and of the intrinsic microscale variability of SWE are also considered. An SWE measurement is declared suspicious if a sufficient discrepancy is found with respect to the expected SWE data from the northeastern United States are also summarized. 26 refs., 2 figs., 3 tabs.