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Question: California has placed black balls on top of their water to prevent evaporation. You always speak about available moisture in the air. Would this not affect them in a way that would prevent them from getting rain? — Elizabeth Passo

Answer: That's certainly a good question to ponder. The balls you're referring to have been placed atop several reservoirs there, primarily to maintain water quality and prevent the development of algae, but with a secondary effect of substantially reducing evaporation from the reservoir surfaces, which can certainly be a good thing during a drought. As to precipitation being related to moisture in the air, that is quite true, but the development of widespread, significant rainfall is typically much more influenced by larger scale sources of moisture (oceans, large lakes and large rivers) and the passage of atmospheric features like low pressure centers and frontal systems, so that except on a very localized basis, the reduced evaporation from a few reservoirs shouldn't lead to a substantial change in overall rainfall for the state.
Aug. 28, 2015 | Tags: drought, general meteorology, rain

Question: How many 90+ degree days have we had so far in 2015? Is this above average? — Jasper Caudle

Answer: We checked the numbers through August 24th for this answer, and at that time the RDU airport had reached 90 or higher 47 times in 2015. This is indeed a little above the "normal" (which is the 30-year average for 1981 to 2010) of 40.8 days, but it doesn't represent a very extreme value either way. The lowest number of 90+ days we've had by August 24th was 7 back in 1973, while the most was in 2010, with 69 such days.
Aug. 27, 2015 | Tags: heat, past weather, records/extremes

Question: I read an article on Facebook this morning that stated that NASA has confirmed that the Earth will experience 15 days of total darkness , between November 15 and November 29, 2015. The article stated that the world will be in complete darkness during these days. The article stated that the event is caused by another astronomical event between Venus and Jupiter. It stated that this event hasn't occurred in over 1 million years! I haven't seen this talked about anywhere on any network in TV. Is this just a hoax. I know you can't believe half of what you read on Facebook and the Internet! — Randy Walton

Answer: This story seems to be a slightly altered re-hash of a similar tale that flew around the internet (and Facebook) about a year ago. In that case, the darkness was supposed to be for 6 days in December (there was also a very similar story before that back in 2012). Of course, that was a hoax based on a "fake news" web site, and the current story has similar origins according to This falls squarely into that "half of" stuff you mentioned that you can't believe from the Net!
Aug. 26, 2015 | Tags: astronomy, cool sites, folklore

Question: What dates are the hottest time period for Raleigh, and what are the coldest? — Caravaggio

Answer: The stretch of dates with the highest combination of normal high and low temperatures (the average values for the 30-year period 1981-2010) runs from July 13-18, while the coldest time period according to the normals covers the stretch from January 7-10. Of course, in any given year the timing of the hottest and coldest temperatures can vary a good bit outside these time frames.
Aug. 25, 2015 | Tags: cold, heat, normals

Question: I've asked Greg questions many times but I never get an answer but here goes again. I love to weather watch and have wanted to know where the best place to go here in the Raleigh to do that so I can see all the sky. Do you know where that might be? — Candy Chitty

Answer: There are probably many other options, but just for a sample we'd suggest the observation deck area at the RDU airport, an open area that's part of the North Wake Landfill District Park, and, a bit farther out, there is the Ebenezer Church Recreation area at Jordan Lake, which is also used at night for occasional Morehead Planetarium and Science Center Skywatching sessions.

Also, regarding your previous questions, keep in mind that when you go to the "AskGreg" page on our web site, there is a search box at the top of the page. We entered "Candy" there, and found that there are two questions with your name that have been answered in the past, along with two others that are from a "Candy" with no last name listed. Since these questions are not necessarily answered in the order we receive them, and in some cases we may return to a given question days or weeks later, it can be helpful, if you don't check the site all that often, to search now and again for the name you submitted the question under to see if we've responded.
Aug. 24, 2015 | Tags: atmospheric optics,

Question: We were on the beach recently when a thunderstorm came up suddenly. Rather than be walking for the 10 or so minutes it would have taken us to get off the beach, we decided to lie flat on the beach to make ourselves lower than our surroundings. I know the goal is not to be (or be under) the tallest object around - but for what radius? Will a taller object such as a tree that's 50 yards away provide any protection from lightning? 100 yards? 1/2 mile? — Bob

Answer: A tall, pointed object standing alone above flat ground can be shown to be statistically more likely to be struck than an area within a circle that is about the same radius as the height of the tall object. However, this does not translate into a useful safety measure, for two reasons. First, the statistical probability that the object will be struck instead of another location within that radius is low enough that there is still a significant chance of direct strikes within the "cone" surrounding the object, and also because except in very idealized circumstances, there is a significant risk of dangerous side flashes or ground currents that radiate a significant distance from the object even if it is the only location struck.

The bottom line is that trying to utilize a tall structure in a protective manner is not a good lightning safety option since the farther you are from it, the more likely a direct strike becomes, but the closer you get, the more exposed you are to potentially deadly secondary strikes, and there isn't a reliable sweet spot somewhere in between. There is a semi-humorous take on this in a series of cartoons at

If at all possible, it is best to retreat to a safe location indoors or in a vehicle. If caught out in the open with absolutely no way to get to safer shelter, it is not recommended to lie down flat on the ground either, as this can expose you to significant step voltages in the case of a nearby strike that produces strong ground currents. The recommended "lightning position" involves crouching with the feet as close together as possible. This keeps you fairly low to the ground, but also minimizes the voltage difference for potential ground current entry and exit points.
Aug. 23, 2015 | Tags: cool sites, lightning, preparedness, weather & health

Question: How many days so far in 2015 has Raleigh reached a high temperature of 90 or above? — Larry W. Fish

Answer: The latest confirmed data we had when writing this answer was August 17th, and through that date the RDU airport had recorded 45 days with temperatures reaching that level. This already slightly exceeds the total for all of 2014, which was 43 days. There were only 28 the year before that!
Aug. 22, 2015 | Tags: heat, past weather

Question: Do you have a map to show the variability of rainfall over Wake County over a given period, say July of this year? It seems there is a huge discrepancy from one part of the county to another when we have scattered storms. Some parts of the county got 6" or more, and some less than 2". — Marilyn Gist

Answer: At present, we don't have something on the web site that covers the situation you're asking about. Our rainfall maps generally cover 24 hours and a larger area than focusing on details around a given county. However, as you noted, rainfall can vary greatly from one part of the county to another, and more generally across various parts of our viewing area. There is a product you may find very helpful that is available from the National Weather Service Precipitation Analysis page at, where you'll initially see a map of the U.S. with the most recent 24-hour precipitation totals (ending around 8AM). Below the map, though, you'll see several controls that allow you to select a variety of time periods and map views, along with the type of data (total precipitation, normal precipitation, departure from normal and percentage of normal). You can also pan and zoom the map, and add county borders. This kind of map clearly shows, for example, that while the area near the RDU airport received notably above normal precipitation over the past few months, many other parts of Wake County were substantially below normal at the same time. The data on these maps is made from a combination of estimates from radar, and measurements made using surface rain gauges.
Aug. 21, 2015 | Tags: cool sites, rain, water resources

Question: I work near downtown Raleigh. Walking outside today at around 10:30am, I noticed the sky was hazy, and I smelled a faint odor of wood burning. I've experienced this several times before - most frequently when I lived in CT. Occasionally, wildfires burning as far away as Canada would have smoke that drifted hundreds of miles away, leading to a haze and the faint odor of wood burning. I understand today's haze may be unrelated, however. Are there any wildfires burning in or near NC that may have had smoke carried here because of the prevailing wind and weather patterns? — Julie Halatek

Answer: Your question came in a while back and referred to the morning of July 29th. We checked back for any significant wild fires in the state at that time and could only find one, the Bald Knob fire north of Marion. That one seems unlikely to have impacted the area that morning, and it's tough this much later to confirm whether there might have been an out-of-state fire that you noticed, or whether a much more local and transient source of smoke may have been involved. We would note a couple of resources you might like to keep handy and bookmarked that may help in real time or just after you notice smoke of this sort. First, there is an incident information site with reports on significant fires underway around the nation, available at Also, the National Weather Service has an interactive air quality forecast map that includes surface and vertically integrated smoke concentrations that can help you visualize the transport and intensity of smoke from any fires that might be affecting our state and nearby areas. It's located at
Aug. 20, 2015 | Tags: air quality, cool sites, weather & health

Question: My family and I have a question about the 7-day forecast display -- I say that the blue column represents relative humidity but the rest of my family says that the height of the blue column doesn't convey any meaning. I've noticed that even when temperatures are the same, the height of the blue columns can still vary. We have a lawn-mowing chore riding on the outcome of this, so it's important! — Brandon Buchanan

Answer: The blue column inside the 7-day "tubes" we show on TV broadcasts are scaled to indicate the high temperature, so that a bar on a day with a high of 90 should be taller than a day in the same forecast with a high of, say, 81. There is no scaling on the low temperatures, so they all appear at the same level. There are times, of course, when one or two days in the forecast are much warmer or colder than than most of the others, which can force a lot of the values to have bars that are quite close in height even though those numbers vary a bit. As to your having noticed times when the high temperatures were the same, but the bars were different heights, we can only assume that you may have caught one that involved a technical glitch or a mistake on our part in producing the graphic, since that shouldn't be the case. Since it is possible that's happened a time or two, maybe you can be absolved of the lawn-mowing chore. Just blame it on us!
Aug. 19, 2015 | Tags: maps & codes

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