Ask Greg

Recent Questions

Question: When was the last hail event that occurred in the Piedmont Area? — Deborah L Trogdon

Answer: The last event we could find with several hail reports around the Piedmont was on Sep 30, 2016. Most of the hail was in the dime to nickel size category, not quite reaching the severe weather criteria of 1 inch diameter (quarter size) or greater. There was a more sizable outbreak that included some severe-level hail reports, though, two days earlier on Sep 28th. You can see a map and listing of the reports for that day at, and there are links above the map that let you step forward or backward by one day.
Feb. 2, 2017 | Tags: cool sites, hail

Question: I'm going into high school this year and I was wondering what classes I need to take to be a meteorologist. Are there any specific classes I need to take? — Luke

Answer: If you're planning to pursue a meteorology degree in college, you would do well at the high school level to take courses in mathematics (the most advanced available at your school), physics, chemistry, statistics if they offer it, and computer science. To supplement these nicely, courses in geography and geology, if offered, along with writing and public speaking classes, would be very beneficial. Good luck!
Feb. 1, 2017 | Tags: careers & education

Question: Do you have any suggestion for an app for my laptop to watch the sky? — Tony White

Answer: We certainly haven't tried all the products and programs that might be available, but for visualizing the night sky as seen from a selected location on any given date or time, we've had good luck with one called AstroViewer, and we'd also note that the visuals you see in the Carolina Skies segments we do on Saturday mornings in collaboration with the Morehead Planetarium and Science Center are made with software called Stellarium. It's in a different vein, but you might also enjoy a program from the Jet Propulsion Laboratory called "NASA's Eyes." All of these and more should turn up in a web search by name, or more generally searching for "planetarium software."
Jan. 31, 2017 | Tags: astronomy

Question: Can you please explain what dew point is so an ordinary person can understand it? — Lynda

Answer: Sure thing! Dew point is a measure of how much invisible water vapor is in the air, so that the higher the dew point, the more water vapor and vice versa. Dew point is expressed as a temperature, and if the actual temperature of the air becomes equal to the dew point, the air is considered saturated with water vapor so that any additional cooling of the air or increase in water vapor will result in condensation, or a change of the water vapor molecules into liquid water. This can lead to the formation of cloud or fog droplets in the air and, when conditions are appropriate, the development of precipitation. Another common illustration of this is when you see "sweat" form on the outside of an iced beverage. If or when the outside of the glass cools down to the dew point of the air surrounding it or below, water vapor in contact with the glass will condense onto its surface.
Jan. 30, 2017 | Tags: general meteorology, humidity/dew point

Question: I know its very early but we want to have a Patriots Superbowl party and turn on the projector in the garage, but if it is going to be freezing it will change the plans. Any idea if the current warmth will continue 13 days from now? — Tim Urdi

Answer: Long range projections that far in advance have been giving mixed signals by then. After a return to typical winter temperatures late last week, it appears we'll vary a little above and below normal in the week ahead. Early indications from ensemble systems extending to that Sunday center around lows below freezing and highs potentially in the 40s, but they also indicate a large spread in solutions and therefore pretty low confidence about that period. We have to suggest keeping your plans flexible for now, and then following more specific forecasts for that day that we will be making as we move through the second half or so of the week.
Jan. 29, 2017 | Tags: general meteorology,

Question: Can it snow at temperatures above freezing? I've heard that some of the most powerful snowstorms dropped snow at temperatures around 36 degrees. Is this true? — Luke

Answer: It can certainly snow at surface temperatures well above freezing, although there has to be air above in the region where the snowflakes form that is well below freezing. While it is fairly unusual for snow to fall with surface temperatures warmer than the 30s, on rare occasion snow has been observed at the surface with temperatures, at least briefly, in the mid 40s. This can happen when a pocket of very cold air a few thousand feet up moves across an area in the presence of moderate amounts of low level humidity and warm ground (creating significant instability that can touch off showers or snow showers), and usually involves variable cloud cover that allows some sun to reach the surface. This results in a rapid decrease in temperature with height, so that snow from above only has to fall through a shallow layer of warm air that fails to melt it before it reaches the surface. We're not sure where the 36 degree reference comes from, but it is possible for heavy snow to fall at such a temperature, although if the snow continues at a heavy rate it would tend, through absorption of heat by melting, conduction and evaporation, to lower the temperature of the surrounding air. Conversely, if the above freezing temperature is reinforced by warmer air being advected into the region over a deeper layer, it would tend to eventually change the snow over to rain.
Jan. 28, 2017 | Tags: snow

Question: What is the longest period of continuous below 32 degree temperature to occur in the Raleigh or central NC region? I am curious if this past weekend is close to a record. — Ingrid Harm-Ernandes

Answer: You're asking about the weekend (Jan 7th and 8th) that snow and sleet fell across the area. We did have cold air persist in the wake of that system, enough that out at the RDU airport the temperature was at or below 32 degrees for 83 consecutive hours, finally climbing above freezing after 10 AM on Tuesday Jan 10th. That's only a little over half as long as the record for consecutive hourly reports of 32 or colder, though. With some assistance from the helpful staffs of the State Climate Office of NC and the Southeast Regional Climate Center, we found the longest such period for Raleigh went on for 157 hours (about 6 and a half days) ending on Jan 16th in 1982.
Jan. 27, 2017 | Tags: cold, records/extremes

Question: When it is -47 degrees...does that mean it is 47 degrees below 0 or 47 degrees below freezing? — Patricia

Answer: You didn't mention whether the -47 is in Fahrenheit or Celsius, and the answer depends on which scale is being used. On the Fahrenheit scale, freezing is 32 degrees, so -47F is 47 degrees below zero, and therefore 79 degrees below freezing. On the Celsius scale, freezing is zero, so -47C would be 47 degrees below both zero AND freezing.
Jan. 26, 2017 | Tags: cold, maps & codes

Question: It's not end of the month so why are we having a full moon? It's scary. — Trish

Answer: Full moons can occur at any time of a month, and are not restricted to the end of months. Keep in mind that the lunar cycle is such that the moon's orbit puts it into position for a full moon about every 29.5 days, while the length of months varies, mostly between 30 and 31 days, but also with February at 28 (and sometimes 29) days. So, typically the timing of a full moon will move back (earlier) by about a day or so each month.
Feb. 15, 2017 | Tags: astronomy

Question: On today's morning commute, we saw intense white fog that made it difficult to see. Can fog be generated from melting snow and ice, or was this simply regular fog? — Amelia

Answer: There are a number of different formation mechanisms for fog, most of which involve cooling a humid airmass near the surface until the temperature reaches the dew point or below, causing the cooled layer of air to become saturated so that fog droplets develop. In the case of fog over a snowy or icy surface, this often involves the movement of a warmer, humid airmass into the region where the snow or ice is already on the ground. The warm air is cooled from below by contact with the cold surface, and this can lead to fog formation. There can also be some contribution of melting and/or evaporating snow increasing humidity of the air, but often the warmer airmass moving in already has enough humidity for fog to form anyway upon cooling from below. When warmer, moist air moves over a cooler surface in that way, the resulting fog is called "advection fog."
Jan. 24, 2017 | Tags: general meteorology, snow, visibility/fog/dust

Questions 51 - 60 of 5245.

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.