Ask Greg

Recent Questions

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

Question: What are those streaky clouds out there tonight? They are unusual. The moon was awesome as I came home from work, just huge!!! — Daine

Answer: You wrote in on the evening 9of Thursday, Jan 13, 2017. Later that afternoon into the evening we had scattered to broken stratocumulus clouds at about 4 thousand feet above the ground. Those largely dissipated before sunset, and we saw some big streaks and bands of cirrus cloud at about 25,000 feet above the ground that may have been generated in part by lifting of stable air flowing across the mountains to our west. You can see a timelapse of the clouds shot from a wide angle camera at NCSU. The lapse runs from midnight to midnight on that Thursday, soo the clouds you mentioned (and the setting moon) are toward the end of the video. You can view it at
Jan. 23, 2017 | Tags: clouds, cool sites, past weather

Question: Why is Elizabeth doing the evening weather? Where are you and Mike? — Judy

Answer: We got a number of questions about that, making reference to "musical meteorologists" and such! The schedule at the time had to accommodate myself and Nate attending an out of state workshop for the first three days of the week, while Mike Maze was away on vacation. So, we had a few days there with Mike Moss and Aimee covering mornings, while Elizabeth shifted to evenings.
Jan. 22, 2017 | Tags:

Question: In watching the coverage of the upcoming potential ice storm in middle of the country, I am reminded of maybe the worst case I have heard of: the massive ice storm that affected the Northeast U.S. and Quebec area a couple of decades ago. Do you know of a site that discusses this storm. As bad as an outage is around here, I can't imagine being without power for weeks with the much colder temps of the more Northern areas. — Dave Crotts

Answer: You're thinking of one of the worst cases of freezing rain and glaze icing on record, when freezing rain occurred for as many as six consecutive days over parts of the affected area and clear ice accumulations reached as high as one to nearly four inches. This brought down thousands of power line towers and poles and did tremendous damage otherwise, in addition to leading to at least 45 deaths in Canada and the northeastern U.S. The event has come to be known as the Great Ice Storm of 1998, and you can find quite a few articles and video reports about it with a web search. On site you may find interesting is a summary paper covering the event that is located on a server at McGill University, titled simply "Ice Storm '98." You can find it at There was also a Discovery Channel episode of "Perfect Disaster" that addressed this storm, with a combination of dramatized re-enactments and news footage from the event.
Jan. 21, 2017 | Tags: past weather, winter weather

Question: 68 today, 47 tomorrow. Tonight I've heard thunder but the radar is totally clear. A dry thunder I suppose. Is that common? — Brian Lowery

Answer: While dry thunderstorms are a real phenomena, involving elevated storms that occur with a deep layer of low humidity below the cloud base, such that precipitation generated in the storm cloud evaporates before it reaches the surface, we suspect something not weather-related was behind the sound you heard. Your message was written on Friday night, Jan 13, 2017, and as you noted through the day and much of the evening there were no echoes nearby on radar (late in the evening a few spotty sprinkles and light showers developed west of the Triangle and drifted east, but these were around or after the time of your e-mail). We couldn't find any other evidence of storms in the region that day or night, so it seems likely you may have heard noise from a jet aircraft, a dump truck, transformer failing or some other source of noise that could sound like thunder under the right conditions. True "dry thunderstorms" are very rare in our part of the country, but somewhat more common in western parts of the United States. Of course, around here it isn't unusual to hear thunder and receive no rainfall at a given location, but that is generally associated with storm cells passing within ten miles or so (a typical distance beyond which thunder is usually not audible), with those storms producing rainfall that reaches the ground elsewhere. Incidentally, the high temperature on the day you wrote made it all the way to 76 degrees, while the afternoon high the following day ended up being 48.
Jan. 20, 2017 | Tags: general meteorology, thunderstorms

Question: Has this winter been more cloudy than usual? It seems like we've barely had any sunny/mostly sunny days since before Christmas. The current 7-day forecast seems to indicate it will continue. I want the sun! — Samantha

Answer: Records from RDU seem to bear that out. We took a look at sunrise to sunset cloud cover for December and the first 15 days of January, and found that there were 8 days through that period that were classed as clear to mostly sunny (0-3 tenths cloud cover), compared to a "normal" value of 14.5, so bright days have been a little limited compared to usual over that time frame. Longer range models are projecting more frequent sunshine over the last week or so of January, but that is far enough in the future that we can't place a lot of confidence in that just yet.
Jan. 19, 2017 | Tags: clouds, normals, past weather

Question: Where can I find today's actual recorded low temperature on the WRAL Weather site? Or do I need to go to another site? Best wishes. — Thomas Moorefield

Answer: The simplest way though our site to find the observed low for the day so far is to go to the "Almanac" page and click the "Send" button under "Get Historical Data." That will default to a summary of the current day's observations from the Raleigh-Durham airport, and will include a minimum temperature that would typically be the lowest observed around daybreak. You can also see the temperature trend in a graph by scrolling down a bit. If you're interested in a different location, there is a "search for another location" box along the right side of the summary window.
Jan. 18, 2017 | Tags: past weather,

Question: Why is sleet mistaken for snow on the Dual Doppler? What causes this? — Tommy

Answer: On both local and regional radar displays showing winter precipitation types, it is not the radar itself that determines precipitation type. Instead, the radar measures the intensity of the radar return. Software is then used to color code the returns according to whether the precipitation is snow (usually a blue shade), rain (shades of green, yellow and red) or a mix (usually shades of purple or pink, often indicating sleet and/or freezing rain). The software depends on a combination of inputs to assign the most likely precipitation type to each radar echo location, with surface observations of temperature and precipitation type playing a role, in addition to very short-range computer model analyses and forecasts that provide information on the vertical structure of temperature, pressure and humidity through the atmosphere. These algorithms do a generally good job at displaying the correct precipitation type, but are not perfect. In a recent winter storm, many models indicated that air a few hundred to a few thousand feet above the ground warm enough to change snow to sleet and freezing rain would remain a little farther southeast than it really was. This led to a band of radar echoes coded as snow, when sleet was actually the predominant precipitation type reaching the ground along that band. Note that these ways of color-coding the radar returns do not use the dual-polarization capabilities of our radar or that of the local NWS system. These "polarimetric" systems can do a good job of determining the most likely precipitation type based on direct measurements by the radar itself - however, they indicate the type of precipitation within the radar beam, which increases in height above the ground as you move out in distance from the radar location. Since the type of precipitation in the radar beam can change between falling below the beam height and reaching the ground in many wintry precipitation scenarios, using the model and surface observation-based software to color code the display often better reflects what is occurring at the surface.
Jan. 17, 2017 | Tags: snow, weather radar, winter weather

Question: What's the average temperature for NC in January? — Julie Davis

Answer: The overall "normal" January temperature for our state (defined as the 30-year average for the period 1981-2010) is 39.9 degrees F (with the normal high being 50.3 and the normal low of 29.4). Of course, a statewide average masks a lot of variation across different parts of the state - for example, the normal temperature for the northern mountains region is 34.9, while for the southern coastal plain it is 43.3 degrees. These numbers were calculated using tools available online at the National Centers for Environmental Information, using their "Climate at a Glance" feature.
Jan. 16, 2017 | Tags: cool sites, normals

Questions 31 - 40 of 5217.

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.