Ask Greg

Recent Questions

Question: Just an interesting note. My Dad is a 1959 or 1960 Gradute of Elon College. One of his professors told the class that if we don't stop paving the earth, flooding will become an increasing problem. I think he hit the nail on the head. — Dina Grinstead

Answer: Replacing permeable, natural areas with more urbanized development featuring significant impervious surfaces and drainage systems has long been recognized as contributing to increased flooding problems. Water that may have soaked into the ground and either recharged groundwater or slowly traveled to creeks and streams instead rapidly runs off or is carried to streams it wouldn't otherwise run into, and in a much shorter time. This has been observed to cause rapid increases in water levels for streams in and near urban areas, while similar rainfall amounts produce slower rises and lower peak levels in rural streams subject to similar rainfall rates. There is a good U.S. Geological Survey fact sheet on the effects of urbanization on flooding, including some ways for developers and municipal planners to mitigate these effects somewhat, at
May. 25, 2017 | Tags: climate change, cool sites, flooding

Question: Dear Greg....I am a fellow Pennsylvanian, been here since 1981. Do you remember the tornado event from 1985? — Jane Newberry

Answer: Yes, indeed - you're referring to an outbreak that formed south of a powerful low pressure area, and along or ahead of an especially strong and active cold front, on May 31, 1985. The storm led to tornadoes that formed over Ohio, New York and Ontario as well, with most of them following a west to east track. Overall, there were 43 tornadoes in the outbreak, with 23 of those affecting parts of Pennsylvania. The storms resulted in 89 fatalities, including 22 in Pennsylvania, and since that day there have only been two more tornado days in the entire U.S. with a higher number of deaths. Only once have we in North Carolina had a greater number of tornadoes in our state than Pennsylvania did on that day (there were 30 in NC on April 16, 2011). It's also notable that one tornado in that 1985 outbreak was rated F5, the only twister of that intensity in Pennsylvania history. So far, there has never been an F5 or EF-5 tornado recorded in the Tar Heel state. For more on the 1985 outbreak, including some maps and satellite images illustrating the weather pattern that spawned the tornadoes, see
May. 24, 2017 | Tags: cool sites, past weather, severe weather, tornadoes

Question: Please, can you explain me the meaning of averaging time used in measurement of wind speed? — Lara Betty

Answer: In measuring and reporting winds, some standards and definitions have to be applied in order to obtain consistent data from one site to another. To account for the highly variable and often turbulent nature of winds, the concept of averaging is applied. For basic surface wind measurements, it goes like this: Winds at official reporting stations are measured 10 meters above the ground (about 33 feet), and the most common types of automated weather stations take a reading of the wind speed every second. These readings are then averaged over a period of 5-seconds, which is considered to be the "instantaneous" value. These readings are stored and compared to 2-minute averages of those 5-second readings, and if there are fluctuations of the 5-second readings of 10 knots or more during the 10 minutes prior to an official observation, the highest of the 5-second readings in that 10-minute period is reported as the gust speed, while the 2-minute average value is reported as the "wind speed." The system also keeps track of the highest 5-second speed during the entire time since the previous official observation (usually 1 hour earlier), and if that highest value is 25 knots or greater, it will be reported as the "peak wind" during the interval between observations. At the end of each day, the highest 5-second wind from the entire day is reported as the daily peak wind, while the highest 2-minute average value is reported as the maximum daily sustained wind. Generally speaking, turbulent surges and lulls in the wind speed mean that averaging the winds over time lowers the value compared to the highest "instantaneous" values, but also produces a value that is higher than the lowest "lulls" in the wind. The averaging is done to try and obtain a more reasonable report of what is experienced most of the time. So to summarize, when you hear the current wind speed is, say, 13 mph gusting to 26 mph, the 13 mph is a two-minute average, while the 26 mph is the highest 5-second average taken in the previous 10 minutes.
May. 23, 2017 | Tags: instruments, maps & codes, winds

Question: Yesterday I sent you an e-mail requesting the dates of lightning strikes in the Clayton-Archer Lodge area between April 20th and May 6th. The information is needed so I can file a claim for financial help in replacing parts on my heating unit. — Doug Packard

Answer: We are able to display real-time and lapsed lightning strikes as storm systems move through, but do not have access to archives. While historical lightning strike data is available, it is owned and controlled by private companies that require you pay a fee to retrieve strike data or view strike maps for any particular time and location. For those interested in purchasing lightning strike data for research or insurance purposes, see (especially the links to Lightning Incident Archive Search (LIAS) reports) and, where you'll see a box that serves as a link to purchase lightning reports from CoreLogic. We're not sure how detailed your need for specific data is, and whether it rises to the level of paying for these kinds of reports. We can tell you more generally that thunder was reported at the RDU airport on April 20 and 21, and May 1 and 5, while at the Johnston County airport, thunder was reported on April 24, 25 and 28, in addition to May 1, 2 and 5.
May. 22, 2017 | Tags: cool sites, lightning, past weather, thunderstorms

Question: How can you measure the speed of rainfall by looking at radar from one town to another? Does any of WRAL's apps provide means to measure the speed rain is traveling? — Bobby

Answer: The radar sections of our apps do not have a readout or built-in means of showing what the speed of rain areas is, but you can get a sense of that by using the lapse functions either on the Dual Doppler 5000 displays, where you would choose the view you’re interested in and then select the “1-hour” lapse, or by viewing the iControl radar display and clicking the “play” arrow, which will show about a 50-minute long lapse. You can figure a rough speed by following a rain area or storm cell across an area of known distance and dividing that distance by the elapsed time. For example, on the 1-hour lapse, if a band of rain moves halfway from Raleigh to Rocky Mt, that’s about 25 miles, so the band is moving around 25 mph.

Also, in situations where there are severe thunderstorm or tornado warnings in place, you can read the text of the warning and it will usually include a statement that gives the direction and speed of movement of the storm responsible for the warning.

May. 21, 2017 | Tags: rain, thunderstorms, weather radar

Question: Why doesn't the map used when WRAL airs the weather on TV show NC Hwy 540 (toll road)? — Ron

Answer: You may not have seen the map on air yet when we have it zoomed in sufficiently far to have that part of the road show up. At somewhat wider views, we restrict the roads that show up on the map to interstates like 40, 85 and 540, and then at somewhat closer views U.S. highways, like 1, 64 and 401 appear, but still leave the clutter level of the map on the low side. Zooming in even closer shows NC routes like 147, 55 and the toll portion of 540 that you're asking about. Zooming in even further, when appropriate, brings county roads and surface streets into view on the map.
May. 20, 2017 | Tags: maps & codes, weather radar

Question: No one that I know (especially me) has a clue what dew point means. Whether you report a dew point of 25 or 75, it means nothing. However, everybody I know understands humidity. I could never understand why weather experts insist on reporting dew point vs humidity. If you forecast a high of 85 with humidity of 80%, I know exactly what to expect. Forecasting dew point? Who knows? — Marc Sullivan, Clayton

Answer: The reason many meteorologists use dew point and have been attempting to help the public become more familiar with it is that it is a much more direct measure of humidity level than the relative humidity you prefer (in percent). While relative humidity depends on both the temperature and the amount of water vapor in the air, dew point depends only on the water vapor content. For most people in very warm weather, a dew point in the mid 50s or below feels fairly dry, while upper 50s to low 60s begins to feel a little humid, mid 60s to near 70 feels noticeably humid, and dew points above 70 quickly rise to the oppressive or "steamy" level. In the example you gave, of 85 degrees and 80% relative humidity, the dew point would be a very high 78 degrees (and the associated heat index value would be 97 degrees). That is an unusually high dew point for our area, where having the dew point reach 80 degrees or higher is a very rare and usually short-lived occurrence. You mentioned dew point of 25 or 75 not having a meaning - what it would mean is that the air is quite dry with a dew point of 25 (skin lotion might be a good idea for some people) while it is quite humid at 75 degrees (there is about six times as much water vapor in the air). Depending on the temperature, either of those dew points could be associated with an 85% relative humidity, even though there is such a great difference in the actual moisture content in the air.
May. 19, 2017 | Tags: heat, humidity/dew point

Question: I'm currently having problems with my T.V. and computer. Is there any way to receive a forecast on my phonograph? — Hugh M

Answer: We probably shouldn't take the bait here, but nonetheless will suggest that it may be possible, on days with a record high.

We now return you to our regular programming...
May. 18, 2017 | Tags: folklore

Question: Why did you remove the current rainfall amounts from the "Current Conditions" page? — Stefan M

Answer: When the web site was being changed a bit to accommodate changes in the graphics system that we use on-air, we decided it made sense to have the rainfall data consolidated with other kinds of maps in the "Map Center" section of the site. You can find the most recent daily precipitation values (the amount since midnight) for many stations around the viewing area by going to the Map Center page and clicking "other maps" where you'll see "rainfall" as one of the selections. There is a Map Center link in the "Maps & More" box just below the 7-day section of our main weather page.
May. 17, 2017 | Tags: maps & codes, rain,

Question: Why were the county outlines removed from the state radar map? It is much more difficult to track the exact location of a line of storms without the outlines. — Mack Hilliard

Answer: In the process of changing the online maps to reflect the new graphics system we began using on-air recently, the zoom level that triggered county lines to appear on that map was set a little differently and resulted in only state borders appearing on the "North Carolina" view of the regional composite radar display. We agree with you that the county borders at that scale make it easier to gauge the location and movement of radar echoes, and we've already implemented a change that addresses the issue (this refers to the map that appears when you go to the "DualDoppler 5000" page, and change the selection to "Radar" using the blue buttons above the image). Thanks for contacting us about that!
May. 16, 2017 | Tags: maps & codes, weather radar,

Questions 31 - 40 of 5335.

Ask Greg Your Question Now!

Please understand that the volume of Ask Greg questions makes it impossible to answer every one or to list them all here. You may find it helpful to search for your own question using the form at the top of this page to see if it has been posted in our database.

When you submit a question you understand that your question and e-mail address will be sent to our editorial staff. Accordingly your question will not be subject to the privacy policy of this site.