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Question: I loved the fall-like weather prior to Hurricane Irma when it was getting into the 50's at night. All I see is upper 80's during the day for a while. Is there a way to forecast for the Fall this year? Do you think it's going to be a warm one? — William
Answer: It does look as if much of the work week will continue to run above normal temperature-wise, but by the time you see this answer there should be cooler readings ahead in the 7-day forecast, as we appear to be setting up for the passage of a cold front that will deliver notably cooler and much less humid air to the region by the end of the week. As for the fall in general, of course longer range seasonal outlooks are fairly general and lower in confidence, but so far it appears the overall temperature trend is to lean toward a better chance of averaging above normal for temperatures, with somewhat lower chances for averaging near or below normal through the season. In part, this may relate to an increasing probability that a La Nina pattern develops ion the Pacific as we head into and through the fall. That pattern tilts the odds a bit for NC weather during the cooler half of the year to be warmer and drier than normal, although it doesn't guarantee that outcome in any given year.
Sep. 25, 2017 | Tags: el nino/la nina
Question: Can you tell me a site that will allow me to follow the barometric pressure throughout the day. — Dana
Answer: Sure, you can go to our main weather page at wral.com/weather, and click on the blue "current conditions" link near the top. On that page, you'll see the most recent pressure readings from the RDU airport and from our sensor at WRAL in Raleigh. There is also a box near the top of the page where you can enter a city or town name or zip code to check the latest reading near that location. In addition, you can click the blue "Almanac" link and then click the "Send" button under "Get Historical Data." The resulting page will include a graph showing how pressure has changed during the day, and you can change the date to see the same information from previous days, months or years.
Sep. 24, 2017 | Tags: cool sites, past weather, wral.com
Question: I was curious as to some recent cloud "formations" would be called, and how they are formed, and if they are related to the remnants of Hurricane Irma. — Marty Massey
Answer: We received a pair of photos with the clouds you were asking about, that you had taken near Kenly late on September 11th. At that time, the center of Irma was moving northwest across the southwestern corner of Georgia, and the large circulation around the system was producing a stiff, somewhat cool, northeast flow near the surface, while much stronger winds a few thousand feet up were sweeping warmer air in from the east, helping to create a strong temperature inversion about 5,000 feet above the ground. This inversion created a fairly sharp density gradient that allowed waves (like waves on water when the wind blows across its surface) to form at the level of the inversion. It turned out that the amount of moisture available at that level was just right to form clouds where air moved upwards along the leading edge of those waves, and then to dissipate the clouds where air descended at the back of each wave. The result was a series of smooth, linear clouds that would give the appearance in a time lapse of "rolling" along, with cloud-free gaps between the lines. These kinds of clouds are referred to as "undulatus." They can take on a variety of appearances, depending on altitude and the specific characteristics of the atmosphere at the time they form. A web search for the term undulatus will turn up a good number of photos, with some rather similar to the ones you sent in.
Sep. 23, 2017 | Tags: clouds, general meteorology
Question: What is the difference between air pressure and barometric pressure - or are they the same thing? — David
Answer: The term air pressure is probably a little more general, in the sense that you might be talking about the amount of air pressure in a bicycle tire or basketball, for example, while a reference to barometric pressure usually pertains to the atmosphere, as measured by a barometer. Barometric pressure is the amount of force exerted by the air per unit area on any given surface. It is a function of how deep and how dense the entire column of air directly above you is, and in some sense is proportional to the weight of that column of air due to gravity. A standard value of pressure near ground level is about 14.7 pounds of pressure per square inch, but of course it can vary noticeably as high and low pressure systems cross the area, and it also varies rapidly with height, so that most of us notice pressure changes when ascending or descending in aircraft, or when traveling in the mountains.
Sep. 21, 2017 | Tags: fronts & airmasses, general meteorology
Question: There are talks about big storms in the 1930s as we are talking about hurricane Irma. What tools did weather forecasters have to know storms are approaching? — Rebecca Stahlbusch
Answer: In the later 1800s, weather stations had been established at a number of Caribbean island locations to monitor weather conditions for signs of tropical cyclones, and during the early 1900s the advancement of radio technology added substantially to this ability to detect storms and provide useful measurements, both by allowing for observations to be transmitted by ships at sea in the vicinity of storms, and also by allowing for the development of the radiosonde by the 1930s, which allowed for measuring weather variables not just at the surface, but over a deep profile of the atmosphere at several of those locations. The idea of also watching for storms and tracking their movement by way of aircraft reconnaissance flights came up and gained support in the 1930s, although it was a bit into the 1940s before this method became truly established.
Sep. 20, 2017 | Tags: general meteorology, hurricanes, instruments
Question: What was that low rumbling thunder type sound that lasted a long time - maybe 5 mins - near the beginning of the storm on Friday, September 1st? — Carol Witt
Answer: The storms that day were fairly numerous, some were arranged in long bands, and several produced a large amount of frequent lightning. In that kind of a situation, one cause for the long-duration rumbling you noticed is the combination of thunder arriving from multiple lightning discharges at differing distances from your location. When there is very frequent lightning, some cloud to ground and a good bit of in-cloud and cloud-to-cloud as well, the sound of thunder can become almost continuous. The can be enhanced even more if some of the strikes are along a lengthy lightning channel that happens to line up so that one end is a good deal closer to you than another end, which can lead to a long period of thunder from one strike, since the sound from the more distance end takes longer to reach your location. Finally, some of the storms that day produced outflows that created a temperature inversion that can sometimes bend sound waves downward in a way that allows them to travel farther than they usually would. This could have added to the ability for multiple rumbles of thunder, some from closer storms and some more distant, to blend together over a period of time in the way you observed.
Sep. 19, 2017 | Tags: lightning, thunderstorms
Question: I took pictures of an upside down rainbow on the afternoon of the eclipse last week while fishing at Cedar Island. I had never seen one. Is there an association with the eclipse? — Dick Fritz
Answer: We suspect that you saw either a partial 22-degree halo (if you saw mainly the lower portion of the halo it would look like an "upside down rainbow"), or perhaps, if the sun was fairly low in the sky at the time, something called the "circumzenithal arc," which has commonly been referred to as an upside down rainbow. These are both associated with high, fairly thin cirrus clouds composed of the right type and of ice crystals, which existed in many ares along the southeast coast on the day of the eclipse. That was just a coincidence, however, that was not related to the astronomical event itself. You can read more about the halo and arc, including diagrams, explanations and galleries of example photos, at www.atoptics.co.uk/halo/common.htm.
Sep. 18, 2017 | Tags: astronomy, atmospheric optics, clouds
Question: How is it possible that upper clouds can go in a different direction than lower clouds? — Pamela O'Connor
Answer: One of the complexities of the atmosphere is the fact that horizontal variations in temperature (for example, across a front, across land/water boundaries, from cloudy areas to sunny locations, and more) lead to variations with height in the gradient and direction of differences in pressure. Since the wind blows in a direction more or less parallel to lines of equal pressure and at speeds that depend on how large the change in pressure is over a given horizontal distance, the changes with height in the direction of and intensity of pressure variations leads to corresponding changes with height in wind direction and speed in many cases. When these common variations occur at the same time that multiple layers of clouds are visible, the clouds at each layer will move along with the wind at that altitude, making the differences in wind evident by the differing motions of the clouds. This kind of vertical shear is quite common, although there can also be situations where over a limited area the wind direction and speed doesn't vary a lot with height, and during those periods there can be clouds at multiple levels that move at roughly the same speed and direction.
Sep. 17, 2017 | Tags: clouds, general meteorology, winds
Question: What was the actual path of Hurricane Harvey compared to its daily forecast track along the way? Do you have a graph for this? — John Streit
Answer: We don't have that on our web site, but there is something you can approximate it with on the National Hurricane Center web site. If you open www.nhc.noaa.gov/archive/2017/HARVEY_graphics.php?product=current_wind in a window and stop it toward the end of the lapse, the track of the storm will be left behind on the map as a dashed black line. You can put this window on one side of your screen. Then open a new window beside the first one and go to www.nhc.noaa.gov/archive/2017/HARVEY_graphics.php?product=5day_cone_with_line_and_wind. On that page, you will see an animation of all the 5-day forecast paths that you can visually compare to the actual center track. Note that with Harvey, there was a period where the storm dissipated as a closed low, so the NHC did not issue advisories and forecast tracks for a time, until the storm regenerated over the Gulf of Mexico. The dashed line track in the first window therefore connects the two separate storm center tracks with a long straight line.
Sep. 16, 2017 | Tags: cool sites, hurricanes, past weather
Question: A recent seven day forecast showed a predicted high of 84. The hourly breakdown for the same day never exceeded 73. Where does this discrepancy come from? Which should we give the most attention to? — Rich
Answer: In order to allow for our forecast page to be set to cover any input zip code or city, the hourly forecast pulls data from a gridded National Weather Service database that covers the entire country. The same database also populates 7-day forecasts outside of the local region surrounding the Triangle. However, the 7-day forecast you see on our main weather page for the Triangle, along with the text description of that forecast, is input directly by those of us in the WRAL WeatherCenter. In most cases, the two forecasts are reasonably close to one another, but in rare cases, usually involving complex weather patterns with nearby fronts or fast-moving disturbances, there will be a larger discrepancy in the forecast.In the particular instance you asked about, we forecast a high of 84 degrees, while noting that temperatures might run a good deal cooler just to the north and west. The gridded database reflected a forecast that the sharp gradient in temperature would have the Triangle area remain on the cool side of the boundary through the end of the day. The eventual observed high for that day at RDU was 83, while the high at Greensboro was only 68. Note that it is fair to say that the temperature in the Triangle area that day could easily have swung either way based on a relatively small shift in the location of the southeast edge of a shallow cool and cloudy wedge of air trapped between the mountains and the middle of the state.
Sep. 15, 2017 | Tags: maps & codes, wral.com
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Published: 2007-10-09 14:40:00
Updated: 2014-06-24 16:06:51
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