NWS Increases Severe Hail Threshold

If you step outside in a thunderstorm and get bonked on the head with penny size hail, don’t blame your misfortune on a severe storm. On January 5, the National Weather Service changed the criteria for severe thunderstorms by upping the minimum size hail from ¾ to 1 inch—quarter size. The wind threshold—50 knots, or 58 mph—remains the same.

Hail size penny vs. quarter
Comparison of the diameter of a penny to a quarter, and an actual quarter atop hailstones to show relative sizes.

The reason for the change, according to a statement issued by the Fire and Public Weather Services Branch of the NWS, is that research reveals “significant damage” doesn’t occur from hail smaller than an inch. Hailstones the size of quarters or larger are the ones most destructive to cars, homes, buildings, and crops.
Over the years, and particularly in the Plains states, the statement reads, “the frequency of severe thunderstorm warnings issued for penny-size and nickel-size hail might have desensitized the public to take protective action during a severe thunderstorm warning.” Too many warnings for events that were not damaging garnered complaints and made the warnings somewhat meaningless.
Experimental warnings for 1-inch hail in Kansas the last few years expanded in the central and western United States in 2009. Emergency managers and media outlets in the areas that previously made the changes noted that people seem to take warnings for severe hail more seriously now as they carry more weight.
Of course observing hailstones 1 inch or larger and forecasting hail size are two different things. But, just as research has supported increasing the severe hail threshold, scientists are making strides toward more accurately predicting hail size from radar observations of severe thunderstorms. A poster that will be presented by Matthew Kramar of the NWS office in the Washington, D.C. area, et al., on Wednesday afternoon at the Annual Meeting (January 20, 2:30-4:00 PM, Exhibit Hall B2) reveals results of correlating radar hail cores to hail size for the Mid-Atlantic region—a study that piggybacks on successes in establishing operational hail prediction in the Plains states.

On Mars, the Dust Devil's in the Details

Discoveries about the atmospheres of other planets have been closely linked to insights about our own. When a young Carl Sagan confirmed the effect of high CO2 concentrations—a runaway greenhouse effect—on Venus in 1960, for instance, he helped intensify interest in potential anthropogenic warming on Earth.
Conversely, climate models, and now mesoscale weather models such as the WRF, developed for Earthly forecasting, are applied to modeling conditions elsewhere.  At the AMS’s first Symposium on Planetary Atmospheres in Atlanta, Scot Rafkin of the Southwest Research Institute will present, “Application of Mesoscale Atmospheric Models to Mars Missions” (Thursday, 11 a.m., B211). He’ll discuss how terrestrial weather models helped engineers anticipate landing conditions on the Red Planet as well as

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When Wars Are Hot, Crops Are Not

As if it weren’t enough to keep track of arms trafficking, political mischief, and ethnic tensions around the world, now international aid agencies and national security watchdogs are told they have to watch temperatures, too. An article last week in the Proceedings of the National Academy of Sciences links warm years in West Africa with major civil conflicts (defined to include battle deaths of at least 1,000).
The authors, led by Marshall Burke, an economist at the University of California, Berkeley,  show that temperature has a stronger relationship to internal strife than typical indicators like per capita income or type of political regime. They predict more conflict in the region as the world warms.
Other studies, noting the centrality of rain-fed agriculture in West Africa, have identified precipitation as a regional security indicator. However, the new study shows that temperature may be an even better

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Walking through Problems of Urban Air Quality

Doctors tell us to get more exercise—walking is as good for the body as for the environment. But is it healthy to take a walk in neighborhoods where walking is actually practical? If Vancouver, British Columbia, is representative of most urban areas, then the answer is “no.”
A recent study in Environmental Health Perspectives found that areas that rate highly for both walkability and air quality house only about 2% of the city’s population (they tend to be high-income regions a few miles from downtown).
The nitric oxide and the resulting ozone from auto emissions tend to concentrate in different parts of the city: nitric acid is more pervasive downtown, because ozone takes longer to form and has often drifted from its city sources before reaching its greatest concentrations in the suburbs.
The authors suggest that living in high-rises have an unintended health benefit: they are usually in a walkable environment and also allow most residents to spend much of their time farther away from street-level emissions.
These roadway air quality problems can be quite serious. A new study of the Los Angeles area connects asthma in children with proximity to heavy-traffic areas, with 9% of all childhood asthma cases in Long Beach and 6% in Riverside attributable to living within 75 meters of a major road.
“The impact of roadway proximity on the overall burden of asthma-related illness is remarkable,” said principal investigator Rob McConnell of the University of Southern California. “Air pollution is a more important contributor to the burden of childhood asthma than is generally recognized, especially to more severe episodes requiring visits to a clinic or emergency room.”
The study in the American Journal of Public Health also highlighted the impact of shipping in the region—the Los Angeles-Long Beach port is the largest in the United States—by estimating that 21% of asthma-related bronchitis episodes in Long Beach (about 1,400 cases total) and 8% in Riverside (3,400 cases) were caused by nitrogen dioxide emitted by ships.
If the air is the problem, then meteorology may offer some of the solutions. In a poster to be presented Monday (2:30 pm; Environment and Health Symposium) at the AMS Annual Meeting, David Quesada will report on correlations between weather—including humidity, rain, and winds—and asthma in Miami, Florida, where residents suffer above-average asthma incidence.
With pollen and particulate data in hand, the project may identify ways to help residents live well in an urban environment—without necessarily building more high-rises.

Are Smarter, Safer Roads Good for Us?

It’s not often you hear that congested traffic arteries are good for you. But this is what you find in a thought-provoking recent Op-Ed in the Wall Street Journal on managing traffic problems in an environmentally sustainable way:

Congestion isn’t an environmental problem; it’s a driving problem. If reducing it merely makes life easier for those who drive, then the improved traffic flow can actually increase the environmental damage done by cars, by raising overall traffic volume, encouraging sprawl and long car commutes. A popular effort to curb rush-hour congestion, freeway entrance ramp meters, is commonly seen as good for the environment. But they significantly decrease peak-period travel times—by 10% in Atlanta and 22% in Houston, according to studies in those cities—and lead to increases in overall vehicle volume. In Minnesota, ramp metering increased overall traffic volume by 9% and peak volume by 14%. The increase in traffic volume was accompanied by a corresponding increase in fuel consumption of 5.5 million gallons.

The author, David Owen, goes on to recommend solutions—part pricing and part planned scarcity—to maintain congestion while raising funds and demand for more sustainable urban transportation systems.
This counter-intuitive argument sets a good context for the Interactive Information and Processing Systems conference at the AMS Annual Meeting in Atlanta. Much of Monday’s agenda for IIPS (and other conferences) focuses on the coming age of intelligent transportation—intelligent cars, roadways, and drivers based in part on ingenious means of collecting and using high resolution weather data. You’ll want to get a glimpse of this safer and more efficient future in Paul Pisano’s report on the “Clarus Regional Demonstration” project and other talks Monday starting at 11 a.m.
Because the presentations in Atlanta focus on engineering systems for more roadway efficiency, it would be disconcerting to think of them as contributing to the environmental morass rather than helping to solve it. But that would be an oversimplification of Owen’s essay as well as market-based solution in general. Don’t economists generally tell us that uninhibited flow of information helps balance markets? Better weather information may be the essence of economical solutions to the environmental dilemmas of roadway planning and use.
The talk that addresses congestion from a weather perspective most directly will be Monday afternoon. Ralph Patterson of Utah’s Department of Transportation will discuss results from a study of vehicle speed, spacing, and other factors in winter traffic last year. He also adds in psychological dimensions, looking at the way drivers respond to various forms of weather information. The fast growing state is looking for ways to decrease the $250 million annual costs of traffic congestion. This session should give us a glimpse at the myriad ways meteorologists can help improve an international urban quandary.