The most direct way to find your question is to search for the name you used when you submitted it (first name, last name or both). If you did not include a name, then you can search using keywords from your question. Of course, since many weather-related terms are common to a lot of the questions we receive, this may turn up a number of others in addition to your own.
Thanks again for sending your questions to Ask Greg!
Question: I understand how clouds moving in at night can stop the temp drop, but how can they make the temp rise? (where does this energy come from?) — Bill Current
Answer: Some background helps to set up the explanation here. All objects having any temperature beyond absolute zero emit infrared radiation at an intensity that is proportional to the temperature. The air temperature falls on a typical night because once the sun sets incoming shortwave infrared radiation is no longer heating the ground, which continues to lose energy by emitting longwave infrared radiation (it does this during the day as well, but that loss is more than offset by the energy from the sun). The cooling ground and other surfaces in turn cool the air near the ground through a combination of conduction and convection.
On a clear, calm night, the surface cools rapidly and efficiently because the outgoing radiant energy is largely unopposed by incoming energy from above. If the night begins with clear skies and the ground cools substantially, and then a layer of clouds moves in overhead, the situation changes because the clouds will emit longwave radiation as well, some going upward from the top of the cloud, some going downward from the base. The intensity of the downward radiation is dependent on the height, thickness and temperature of the cloud. If those factors combine in such a way that the downward radiation from the cloud is of greater intensity than the upward radiation from the ground, then the surface temperature will begin to climb. This is most likely when the clouds are fairly low or when the clouds exist in the presence of a temperature inversion that leaves the clouds warmer than the ground is. There may also be cases in which the clouds only partially offset the radiant heat loss from the ground so that temperatures fall more slowly than they would otherwise, but do not necessarily rise.
A number of other complexities can affect the outcome on any given night. Even if the clouds do not entirely balance the heat loss from the surface themselves, for example, they might get it close enough that heat stored deeper in the soil is able to well up to the surface and cause the temperature to rise. Heat is transferred very slowly through the soil so that on clear nights it would not be able to keep up with radiant cooling, but with some cloud cover may be enough to help temperatures creep upward. In addition, the can be some nights when frontal systems lead to warmer air blowing into the region from elsewhere and causing temperatures to rise. At times, this process can bring an increase in temperatures regardless of cloud conditions.
Dec. 21, 2013 | Tags: clouds, general meteorology
Question: Has a record high and low temperature ever been recorded on the same day? I am not talking only about the Raleigh area, but anywhere. — Gerald
Answer: Those are very unusual events for most stations that have a long period of record, since in most cases the patterns that would lead to a record high would oppose a record low on the same day. However, there are some special circumstances that can accomplish this, even for stations with records long enough for such an occurrence not to be a trivial matter. One example is Oklahoma City, OK, which has a period of record going back to 1891 and for which the record low and high for November 11 were both set on the same day in 1911 with the passage of a tremendously intense cold front. You can read about that front at www.crh.noaa.gov/lmk/?n=nov_11_1911_cold_front, and some other ways in which such record combinations have been set at www.wunderground.com/blog/weatherhistorian/sameday-record-high-and-low-temperatures.
Dec. 20, 2013 | Tags: cool sites, past weather, records/extremes
Question: My family and I thought we heard thunder a couple times today, mid afternoon. Is it possible? Any snow forecasted in the next 10 days? — Kathy Holt
Answer: We didn't have information about where within our viewing area you were located at the time, but the day you wrote in (Sun, Dec 8, 2013) there were some convective cells in the area that produced a few lightning strikes, so it is quite possible you heard some thunder. Since that time, we haven't had snow in the same area to validate the old rule of thumb about snow within 10 days after a winter season thunderstorm. While there are some reasons why similar patterns, involving highly amplified wavy flow aloft that brings a lot of warm unstable air northward and cold air southward, can lead to both thunder and wintry precipitation, one doesn't always neatly follow the other and the rule of thumb is not an especially reliable one.
Dec. 19, 2013 | Tags: folklore, snow, thunderstorms
Question: Why does your main weather graphic list the evening temps for the current evening on the next day? e.g., Friday evening's low of 33 is shown under "Sat". — Randy Yates
Answer: We presume you're referring to our 7-day forecast graphic, in which the low temperatures are offset slightly to the left at the bottom of each day's "tube." The reason for where the low temperature location is that we do not show "evening" temperatures on that graphic. Instead, we show the high temperature for each day at the top, and the low temperature for each day at the bottom. Except in unusual circumstances, the high occurs during the mid-afternoon hours and the low occurs near or a little after sunrise. SO, in the case of the example you were looking at, 33 is shown under "Sat" because it is the low temperature that would typically be reached around daybreak on Saturday morning.
Dec. 18, 2013 | Tags: maps & codes, wral.com
Question: With all this cold air, I was wondering if we would see snow either this year or in 2014? — Holly
Answer: The big question is always how cold air interacts with passing storm systems that sweep moisture into the area and provide lift to translate that moisture into clouds and precipitation. While there are techniques that show some skill at projecting whether seasonal average temperatures and precipitation have a greater chance of ending up below normal, near normal or above normal, those techniques are not able to reliably project the same assessments for seasonal snowfall amounts or frequency. That leaves us unable to answer your question except to say that we have to be content to wait and make forecasts of snow or the lack thereof on more of a short-term basis up to a few days in advance as each precipitation-generating system develops.
Dec. 17, 2013 | Tags: snow, winter weather
Question: We've noticed that you don't show Chapel Hill on your temperature map anymore. The only thing you show is Roxboro and then Greensboro. As you well know, the weather and temperatures can fluctuate tremendously, and we'd appreciate it very much if you could show our temperature. — JN
Answer: We have a variety of different temperature maps that we show on air, ranging from very close in on the Triangle to fairly close maps that pan from north to south, to a larger projection focusing broadly on central NC, to a map that shows the entire state. Chapel Hill is shown on a couple of those maps but not on others, and as we vary during the course of a show from one set of maps to another (in order to include more communities in our viewing area) Chapel Hill does get covered, but like some other locations it may not be included in every weathercast.
Dec. 16, 2013 | Tags: maps & codes
Question: This is not a question, it is more a correction of the Appalachian pronunciation. It is pronounced apple-a-shin. Please use the correct pronunciation. — Ed
Answer: The name of that mountain range has more than one accepted pronunciation, with most areas south of roughly the Mason-Dixon line, including those of us here in the Weather Center and, for example, most people who attend the State University of the same name, using the pronunciation that features more of a "latch" sound in the middle. The "long a" version that you seem to be suggesting appears to be more commonly used in the northeastern United States.
Dec. 15, 2013 | Tags: controversy
Question: What happened to the Hurricane page? We used to be able to see the historical track of storms - at least in current year - but now all I see is are maps of current activity. — John Phillips
Answer: The newer storm tracking map is currently limited to active systems, but in its full-screen mode there is a link below the map to the older tracker that you can use to review past systems by selecting a year and then the storm name from that year. You can also find it directly at www.wral.com/weather/hurricanes/flash/1441335/.
Dec. 14, 2013 | Tags: hurricanes, past weather, wral.com
Question: What is the UV ray index on a nice sunny day like today and for a person with low vitamin D do you think being outside this time of year has benefits? — Juanita
Answer: The UV index on mostly sunny or sunny days this time of year is on the low side, around 3 or so, due to the low angle of the sun compared to the warmer half of the year, and the index for December only averages 1-2 when you also account for cloud cover. Most resources on Vitamin D indicate that during the higher sun angle portions of the year for our latitudes, one can generate most of the Vitamin D needed if exposed to the sun for about 10-15 minutes per day, but that lower UV values in the winter mean that there is very little D generated, and we have to depend on diet or supplements during that time.
Dec. 13, 2013 | Tags: weather & health
Question: I've been seeing a really bright star or planet in the southeastern sky lately and I'm wondering if you could tell me what it is. — Judy
Answer: That would likely be Venus, which can appear startlingly bright on a clear, crisp evening. It is currently situated in a part of its orbit that allows it to shine as the "evening star" in the southwest and will remain so for much of the rest of this month, then shift through late December into early January to become visible instead as the "morning star" in the southeastern sky.
Dec. 12, 2013 | Tags: astronomy
Questions 81 - 90 of 4152.
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.
Published: 2007-10-09 14:40:00
Updated: 2013-08-13 13:37:27
Triangle Area Special Offers
— Wed 1:50 p.m.
— Wed 1:38 p.m.
— Wed 1:07 p.m.
— Wed 12:42 p.m.
— Wed 12:42 p.m.
— Wed 12:41 p.m.
— Wed 12:41 p.m.