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Recent Questions

Question: What is the 1st freeze date for the Wake County area? — Pat Aprea

Answer: Statistics from the Raleigh-Durham airport indicate a "normal" (30-year average for 1981-2010) first freeze date of October 31st. The standard deviation associated with that is around +/- 9 days, and generally the average date is a little later as you head southeast from the airport and vice versa. The earliest first freeze there was reported on October 2, 1947, and the latest on November 28, 2009. There is a contour map of normal first frost dates available in a blog post by the State Climate Office at climate.ncsu.edu/images/blog/2014FirstFrostFreeze/first_freeze_map_NC.png, which indicates the normal first frost dates across Wake County range from about October 30th in the northwest corner of the county to perhaps November 3rd or 4th in the southeast.
Sep. 2, 2015 | Tags: cold, cool sites, maps & codes, normals, past weather

Question: How many days of 90-degree heat did we have in Charlotte in 2014? — Rich

Answer: For 2014, Charlotte recorded 37 days at 90 or higher, compared to a long-term average of 45 days. There have been as few as 8 in 1967 and as many as 88 in 1954.

By comparison, Raleigh in 2014 had 43 days at 90 or higher, compared to a long-term average of 42 days. There have been as few as 11 in 1889 and as many as 91 in 2010.
Sep. 1, 2015 | Tags: heat, past weather, records/extremes

Question: When is the next flyover of the spacestation and is there a website for this? — John Williams

Answer: There is a very nice pass scheduled for Tuesday morning the first of September beginning at 6:03 AM. To see it, look low in the southwestern sky at about that time and watch for the bright, steadily moving light to ascend. It will reach a maximum altitude around 66 degrees above the southeast horizon a couple of minutes later, and then disappear in the east-northeastern sky at about 6:07 AM. All these numbers apply to Raleigh. For other locations or other dates, a good web site to check is spotthestation.nasa.gov/sightings/
Aug. 31, 2015 | Tags: astronomy, atmospheric optics

Question: I have been seeing on Facebook that on August 27th at 12:30 a.m you will be able to see Mars. Is this correct? — Tammy Scott

Answer: This answer comes a few days past the 27th, but we suspect you are referring to an old e-mail hoax about the appearance of Mars and the moon that has started floating around Facebook from time to time just about every August. The post gives the idea that Mars and the Moon will appear about the same size in the sky, which is simply an impossible situation. Just in case it makes the reounds again next year you can find more background on the hoax, and the corresponding reality, in these two blog posts -- www.wral.com/mars-will-not-be-as-big-as-the-moon/13921252/ and earthsky.org/astronomy-essentials/double-moon-on-august-27.
Aug. 30, 2015 | Tags: astronomy, folklore

Question: Last summer one day saw a cloud formation like you would hold your hand up and spread your fingers out. Like thick fluffy rays coming up from a central point on the horizon. The were not plane contrails. And they lasted for hours. We were driving in Michigan and Wisconsin for hours. Clouds don't hold together like that, do they? They kept a very clear definition. — Chris Wild

Answer: You don't mention how high or low the clouds appeared to be, but we take it from your description that the visual effect is one that would be produces by a series of long, parallel linear clouds that you were viewing in the direction of the lines, such that those lines appeared to converge to a vanishing point in the distance. If that's reasonably on target, two kinds of cloud formations come to mind that could give the impression you described. One is "cloud streets," which occur when the proper combination of vertical moisture distribution, instability and vertical wind shear lead to the formation of "horizontal roll vortices" that lead to long parallel lines of upward and downward motion. The downward portion of these parallel tubes of rotating air tends to be clear, while the upward moving portions can generate clouds. Such streets can extend over many miles and persist for hours under the right conditions. In this kind of pattern, the lines of clouds are oriented parallel to the low level wind shear vector, which is often pretty close to the mean low level wind direction.

A second possibility that comes to mind is the presence of "stratocumulus undulatus" clouds, in which case wind shear across an elevated stable layer sets up a series of waves, like swells on a water surface, so that air flows up and down through the troughs and crests of the waves. With the right amount of water vapor present, this can lead to a very uniform series of banded clouds separated by clear intervals. In this case, the cloud bands are oriented perpendicular to the direction of the winds and wind shear vector.

A web search for each of those cloud types should turn up a lot of photos, and perhaps you can get a sense from those as to whether they might be what you saw.
Aug. 29, 2015 | Tags: clouds, general meteorology

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 snopes.com. 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, wral.com

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