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Answer: Specific lightning strikes to particular locations cannot be predicted, but it is possible to make reasonable predictions as to when lightning strikes are a possibility by using observations and computer model forecasts of vertical distributions of temperature and humidity, and recently developed techniques have begun to have some success in determining when thunderstorms are likely to be especially prolific lightning producers. In addition, there are some special applications in which sensors called field mills can measure changes in the electric field around sensitive locations to give clues about the potential for lightning near that location.
Aug. 15, 2009 | Tags: instruments, lightning

Answer: It's more likely you're noticing the coincidental influence of some other weather features, namely a marine airmass boundary and/or a weak line of low pressure called the "Piedmont Trough" that are not influenced by the highway, but happen to align themselves in its vicinity with some frequency at certain times of the year. Both of these features are products of North Carolina's topography, its soil types, and the orientation of its coastline relative to the Atlantic Ocean.
Aug. 14, 2009 | Tags: fronts & airmasses, thunderstorms

Answer: A few do indeed, due either to the influence of solar radiation and its daily cycle, or directly to the rotation of the earth itself. There are, for example, diurnal (daily) and semi-diurnal (twice daily) variations of surface pressure that trace back to the sun's influence on temperature and density, there is a regular variation of relative humidity that is inverse to that of temperature, and there is a daily oscillation in surface wind speed (highest in the afternoon and lowest in the early morning) just to cite a few. Any of these, of course, may be masked or offset at times by the effects of transient weather systems.
Aug. 13, 2009 | Tags: general meteorology

Answer: Ideally, if you can clearly determine the direction of movement of the tornado and there is a route that will take you at a right angle to its motion, that will be most effective in moving you out of the storm's path. Most tornado safety references do not advise trying to outrun the tornado by driving away from it in the same direction that it is headed. You can read more about tornado/automobile safety at www.spc.noaa.gov/faq/tornado/#Safety.
Aug. 12, 2009 | Tags: preparedness, tornadoes

Answer: The principal summertime meteor shower seen from our state is the Perseid shower, which begins around July 13th and ends around August 26th, with peak activity around August 12th. The shower can result in around 60 meteors per hour on that date under favorable conditions, although the presence of a gibbous moon this year may produce enough interfering light to obscure many of the fainter streaks and reduce the visible rate by around half. There is also a much less active summer shower called the Delta Aquarids that peaks around July 30th.
Aug. 11, 2009 | Tags: astronomy

Answer: It has been observed that some hail and/or tornado-producing clouds have a greenish tint to them, but it has not been established that most do, and one can't assume a greenish cloud means a tornado or large hail is imminent, nor can one assume that those things will be absent from a cloud that is not green. The precise reasons for the green apperance remain in some doubt, but one theory is that sufficiently tall and wide cumulonimbus clouds scatter light in such a way as to take on a bluish cast, and then in some cases reddened or deep-yellow light from a low-angle sun (many green cloud observations occur near sunset) combines with the blue to yield the green appearance.
Aug. 10, 2009 | Tags: atmospheric optics, clouds, thunderstorms

Answer: The answer depends on exactly what you're asking with the question and what assumptions we make in answering. If, for example, we keep the temperature constant, and you are asking how much the actual water vapor in the air decreases when relative humidity drops from 69% to 61%, the answer is about 11.6 percent. It's worth noting, however, that you could also keep the amount of water vapor exactly the same, and decrease the relative humidity by simply increasing the temperature a few degrees. For example, if you start with air at 70 degrees and 69% RH, you can reduce the RH to 61% by warming the air to about 73.9, without changing the amount of water vapor.
Aug. 9, 2009 | Tags: humidity/dew point

Answer: El Nino episodes historically produce some tendencies in precipitation and temperature across North Carolina, with the main effects during the colder months from late fall into early spring. El Nino years produce winter season temperatures around one half to a little over one degree below normal for central NC, with that range of temperatures occurring in roughly 60% of El Nino years. Precipitation averages a little below normal for the mountains, a little above normal for the southeastern half or so of the state, and near normal across west-central parts of the state in El Nino patterns, while snowfall averages about 1-3 inches above normal for the mountains, foothills and western Piedmont, and near normal for central and eastern Carolina. These tendencies are sufficiently variable that it is difficult to use them as a confident predictor for any single year, and current Climate Prediction Center outlooks for the winter ahead indicate equal chances for precipitation and temperature over most of North Carolina to be above normal, normal or below normal. The outlooks do lean toward below normal precipitation for the mountains, and weakly toward below normal temperatures across the southern coastal plain.
Aug. 8, 2009 | Tags: el nino/la nina, winter weather

Answer: A check of local storm reports compiled by NOAA's Storm Prediction Center for that date, along with local news stories, shows that straight-line winds associated with a severe thunderstorm was the most likely reason for a number of trees that were toppled in the vicinity of Red Mountain Road around 2 pm. There were two tornado reports in the state that day, near Pinetown and Washington, both in Beaufort County. You can see storm reports for that day at www.spc.noaa.gov/climo/reports/090717_rpts.html, and can also scroll to the bottom of the page to select another date.
Aug. 7, 2009 | Tags: cool sites, past weather, severe weather, tornadoes

Answer: All safety rules of thumb are subject to variations arising from unique circumstances, but even with a natural gas furnace in a basement, it is likely among the safest locations available should a home be struck directly by a strong or violent tornado. If active gas lines are damaged by the tornado, there is at least some risk of fire or explosion, but it is worth noting that unlike propane, for example, natural gas vapor is lighter than air and will tend to disperse rather than collecting in low spots. Of course, if you smell gas in the wake of tornado damage, avoid lighting matches or creating sparks, evacuate the property and contact 911 or your gas provider. You can find a good collection of tornado safety advice at www.spc.noaa.gov/faq/tornado/safety.html.
Aug. 6, 2009 | Tags: preparedness, tornadoes