Ask Greg

Recent Questions

Question: I really love looking at weather radars and observing forecasts in my area. I really want to be a meteorologist when I am older. I was wondering is it possible for it to snow when the temperature is above 32 degrees? — Eric Magoon

Answer: For snow to form, the temperature at the altitude where the snow crystals grow does have to be below 32 degrees, and in fact to get a decent snow usually requires there be a moist layer that is in the range of about -4 to 14 degrees F. However, those crystals, and the snowflakes that are often composed of multiple crystals stuck together, can sometimes survive falling through a shallow layer of air that is above freezing near the surface. In that way, at ground level it can indeed snow at temperatures above 32 degrees, and on rare occasion it can do so with surface readings well into the 40s. Good luck to you if you decide to pursue meteorology in the future!
Oct. 1, 2014 | Tags: cold, snow

Question: When wind direction is given for my town, Rocky Mount, NC, why is the direction on my yard's weather vane often showing a different direction even though the wind is substantial and not being blown about by gusts? Is this a normal for wind directions in most places? — Carlisle

Answer: Winds do tend to be fairly variable in direction, although at higher speeds they do tend to be a little more uniform over space and time. Even then, local topography, the orientation of wind relative to obstacles like buildings and wooded areas, and the complexities of flow near the surface in the presenace of such obstacles. You don't mention how high your vane is off the ground, but the standard wind measurements reported by airport weather stations are taken at 10 meters, about 33 feet, off the ground in an open, usually rather flat area. Finally, you're probably aware of this, but just to make sure, the direction of winds reported in weather observations give the direction the wind blows from, rather than the direction the wind blows towards. One thing you can do is look at winds reported not only for Rocky Mount, but for several surrounding airport stations. If many of those are in good general agreement and your vane differs significantly, you may have either some significant localized effects, or a vane that isn't calibrated quite correctly.

Sep. 30, 2014 | Tags: general meteorology, winds

Question: Are global models truly global, or northern- and southern-hemispherical? For regional models (European, Canadian) how do they handle a weather system just outside and upstream of their region? — Chris

Answer: Global models, as implied in the name, do indeed represent the atmosphere around the entire world, and when you see a regional map from the American GFS (Global Forecast System), Canadian GEM (Global Environmental Multiscale) and European (usually referred to as the ECMWF, or European Center for Medium Range Weather Forecasting, also called the Integrated Forecast System) and a couple of others run by the United Kingdom Met Office and the U.S. Navy, you are in fact seeing just a section of that model presented for a limited portion of its global domain.

On the other hand, there are regional models that do run, usually at higher time and space resolutions that provide greater detail, over more limited portions of the globe. These models have to have horizontal "boundary conditions" provided along their edges, and these values are often provided by the initialization and/or forecast fields from the larger global models. There can, as you alluded to, be problems simulating systems that move into the domain of these models from more distant locations, so the domain and time frame over which these models are run are usually chosen to be large enough (domain) and short enough (duration of the forecast) so that these "edge effects" mainly impact portions of the domain outside the area of primary interest.

Sep. 29, 2014 | Tags: general meteorology, maps & codes

Question: Where can I find daily air quality information, such as green, yellow etc? Since I have asthma, this is important information for me to have. — Nadine

Answer: On our main weather page, look for the "Resources" link in blue letters near the top. Then scroll down a bit on the resulting page and you'll see a link to "NC Air Quality Forecast." That will take you to a forecast page prepared by the NC Division of Air Quality that provides expected levels of ozone and particulate pollution, and where those forecasts fall on the color-coded scale from green (good) to purple (very unhealthy).
Sep. 28, 2014 | Tags: air quality, wral.com

Question: When was the first "official" day of fall? My calendar says September 22nd, but when I Google the question I get September 23rd. So... now I am coming to "the expert." :-) — Faye B

Answer: The traditional definition of the first day of Fall is based on Astronomy, and is the day on which the Autumnal Equinox occurs. This year, that was at 10:29 PM EDT on Monday, September 22nd. However, when you look up the time of the equinox, it is sometimes given in "Universal Time," which corresponds to the time at the Zero-degree meridian, which runs through Greenwich, England. At that location, 10:29 PM EDT for us is their 2:29 AM on September 23rd, so the fact that parts of the world are already into the next day on the calendar when the equinox happens may account for some of the variation in dates you noticed. Just to make things even more complicated, those of us in the weather and climate business usually think of the seasons in terms of typical mid-latitude weather conditions, and consider September 1st the beginning of "meteorological Fall!"

Sep. 27, 2014 | Tags: astronomy, general meteorology

Question: In your answer about the safety of submerged scuba divers you neglect one possible issue. Many divers maintain a diving flag above their diving location to warn away small boats. These flags are sometimes pulled by divers using a line, or are anchored nearby diving operations. During a lightning strike, this line could form a path of least resistance, and allow the lightening to conduct current down the path. — Mark Erickison

Answer: That's a good addition to the recent question and answer. We would think that a flag buoy connected via a non-conductive line wouldn't lead to much of an increase in current conducted into the water, although perhaps an argument could be made that there might be a slight enhancement due to the interface between the line and water. One certainly wouldn't want to be near a "diver down" buoy line that was composed of metallic cable or a chain, though.

Sep. 26, 2014 | Tags: lightning, weather & health

Question: Do you promise to continue at WRAL and NOT retire for at least 10 more years? The viewers are not ready for an un-O'Fishel weather team. That's just my 2¢ worth. — Denise Hughes

Answer: Denise, thanks very much for your kind words and support. I don't have any plans to leave or retire anytime soon. I also know that every day is a gift, and should not be taken for granted. So I try to take life one day at a time. Ten years is a long time :-)
Sep. 25, 2014 | Tags: wral.com

Question: What is the record for the fewest 90 degree days in August? — Neil G.

Answer: We just finished off an August (2014) with relatively few days reaching 90 or higher, in this case six. However, you might be surprised to find that the record for fewest is actually zero, which occurred in 1969. In records for the Raleigh area that stretch back to 1887, there are three other years (1887, 1889, and 1971) in which only one day in August reached or exceeded that threshold.
Sep. 24, 2014 | Tags: heat, records/extremes

Question: Pacific storms turning back to hit the North American west coast: How rare is this and has there been a statistical change in its frequency of late? — Paul Schrum

Answer: The majority of eastern Pacific tropical cyclones take a mainly west-northwesterly track that keeps them primarily out at sea. However, it is not especially rare for these storms to either track far enough north-northwest, or curve back to the northeast, such that they make landfall or brush along the coast of Mexico or Central America. We took a look at tracks from the past 25 years (including 2014 so far) and found an average of three storms per year that impact the coast in one of those ways. There have been as many as six in a single season (2008) while five occurred in four different years and four in four others. As for a detectable trend, there is a hint of an increase over the 25-year period (all four years with only one land impact occurred in the first 12 years of that time span), but with a lot of year-to-year variability.

Sep. 23, 2014 | Tags: hurricanes, normals, records/extremes

Question: Did anyone else see a pattern of blue lights in the Northwest sky tonight around 8:30? They were like little led's in a contiguous pattern, but not totally circular. They appeared for about a second, then just went out. They appeared again about a minute or so after the first, in a slightly different pattern. I hear that the solar flares are active, but I have never seen anything like this before in my entire life. I called my son out to look at them, but they did not reappear. They were not like fireworks, since they remained stationary for the short time they were visible. — Rick Voltz

Answer: We haven't received other reports corresponding to this so far. At the time you're referring to, there was a line of showers and thunderstorms extending southwest from about the southwestern corner of Wake County and tracking toward the south-southeast. We wondered if you might have seen a small hole in the cloud cover a couple of times that allowed for seeing a cluster of otherwise obscured stars, but we'd guess that would be probably be apparent to you. There are also rare times when people are in a very dark place with eyes well-adjusted when they might see electrical phenomena called sprites and jets above the top of distant thunderstorms, but these are very brief and, in the case of jets especially, very faint, probably more so than it sounds like for the lights you saw. We also doubt this is related to recent solar activity, as you saw these lights the evening of September 16th, which was in between arrivals of significant material from coronal mass ejections (which peaked September 12th and less so on September 17th). For now, this has to go down as a question we can't offer a definitive answer to. Thought we'd go ahead and post it, and invite anyone else who saw something similar that evening to let us know.

Sep. 22, 2014 | Tags: atmospheric optics, thunderstorms

Questions 21 - 30 of 4375.


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.