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!
Weather Questions tagged “maps & codes”(remove tag filter)
Question: When you state "Raleigh/Durham Airport visibility.. 1/4 mi." What does that mean? — Barbara
Answer: It means that in the vicinity of the airport weather sensor, a person would be able to distinguish and identify objects reliably to a distance of no more than one-quarter mile, due to some obstruction that limits visibility, such as fog, smoke, snow, dust or heavy rain. Visibility at airport weather stations is usually measured using an automated sensor, most often a forward scatter meter and less typically a transmissometer, both of which involve measuring the light that reaches a detector after passing through some air, and converting that to the approximate distance a human would be able to see. Some larger airports also have human observers that can "augment" the visibility observations when needed. Visibility plays a significant role in safe flight operations, and can also be important to drivers and traffic, especially when it falls to 1/4 mile or less.
Mar. 6, 2014 | Tags: instruments, maps & codes, visibility/fog/dust
Question: I used to like to look at weather maps for the rest of the country. How can I get them back on the new site? — Kay Lindquist
Answer: There are a couple of links on the main weather page that take you to the "Map Center." On that page, you'll find selections for radar and satellite maps. Clicking wither of those brings up that kind of map centered on our state, but you can then click the state label to select from a variety of other views covering different sections of the United States.
Feb. 28, 2014 | Tags: maps & codes, wral.com
Question: I've seen names mentioned in the media for our recent winter storms. Are they named and, if so, how does this happen? — Mary Wiley
Answer: One media company (the Weather Channel) decided last winter season to start naming winter storms for purposes of their broadcasts. This is different from tropical cyclones, which are named by committees of the World Meteorological Organization, with those names recognized and utilized in an official capacity by government organizations such as the National Weather Service and National Hurricane Center. Government organizations and most other media sources (including WRAL) do not currently use names for winter storms.
Feb. 25, 2014 | Tags: maps & codes, winter weather
Question: Was that a skew-T graphic you put up last evening (Feb 11, before the ice storm) showing altitude vs temperature and the freezing point where snow versus rain would occur? I've rarely seen a graphic like that one and it seemed to me it was similar to the old skew-T figures I used to portray wet and dry adiabatic temperature lines as a function of altitude/pressure. — Anonymous
Answer: It was indeed a chart you would have known more completely as a "Skew-T, Log-P" diagram, with skew-T referring to a slanted set of temperature lines and log-P to a logarithmic set of pressure levels on the chart. These are commonly used by meteorologists to examine how temperature, moisture and wind vary from the surface upward through the atmosphere, with the information either measured by radiosonde balloons or calculated/projected by computer models. These charts help identify features like freezing and melting layers, cloudy and dry layers, stable or unstable layers, and the kinds of temperature variations with height that can determine whether precipitation will be liquid, frozen or freezing in the winter, or whether instability and winds might indicate a chance of severe storms under warmer conditions.
Feb. 15, 2014 | Tags: general meteorology, maps & codes, winter weather
Question: What is the difference between a winter storm warning, watch or statement? — Deborah Kelbaugh
Answer: The difference has to do with lead time and the likelihood that the winter weather in question will actually happen. For central North Carolina, the National Weather Service uses the following criteria: a winter storm watch is issued when there is potential for a blizzard, heavy snowfall or ice storm within 18 to 48 hours and there is a 50% confidence or greater of at least 3 inches of snow, one-half inch of sleet and/or one-quarter inch of ice. When the likelihood of these conditions occurring exceeds 60% in the judgement of the forecaster, the watch may be upgraded to a warning, which implies the winter event is considered imminent.
A winter weather statement is usually information about the progress of the storm and any short-term updates on what is expected to happen in the next several hours, and various statements may be issued throughout the duration of the storm.
Feb. 14, 2014 | Tags: maps & codes, winter weather
Question: How can we access the national radar map now with the new website? I like to check the weather in Texas where my daughter lives. — Joni Amerson
Answer: Those images and animations are collected under the "Map Center" section. Just click there and you'll see a blue bar with selections that include "radar" and "satellite." Under either of those, select the "Southern Plains" view for a scene nicely centered on the Lone Star state.
Another option on the Map Center page is to open the "iControl Doppler" application, where you can pan and zoom the map view to your daughter's area and see animated satellite or radar data, and switch to the "future" option to see computer model forecast contours of rain and clouds, temperatures, wind speed and so on.
Feb. 7, 2014 | Tags: maps & codes, wral.com
Question: On the new WRAL weather page, I have trouble telling the overnight low. which night is it for? I know the first number is the high for the day. After the slash bar /, is the 2nd number for that night? For example Friday says 48/33. Does that mean 48 is Friday's high and 33 is the low Friday night and into Saturday morning? — Julie
Answer: Your interpretation is exactly correct. On the on-air "tubes" we use for a 7-day forecast, the low temperature is shown shifted a little to the left on the day it would occur (usually around sunrise). However, this didn't seem to work well for the vertical arrangement used on the main page of the new site design. Here the number on the left is the high for the day in question, then the low temperature that follows would typically be reached the next morning around daybreak, and should match up with the text description when you click the "overnight" button above the text description. As an aside, the on-air format version of the 7-day forecast remains available on our site, located in the "Map Center"/"Other Maps" area.
Jan. 29, 2014 | Tags: maps & codes, wral.com
Question: First off, thanks for years of professional and educational weather reporting and forecasting. Now for my question: Years ago, and I mean YEARS ago, you first introduced us to "isobars" and you fitly described them as "lines of unequal pressure", which makes sense, since unequal pressure produces wind speeds of varying degrees. But lately (maybe last six months) I've notice that when you are explaining weather map details and icons, you define the isobars as "lines of equal pressure". Hmmm, it seems that if the pressure were equal across a certain geographical region, there would be no variance in wind speed, hence no lines to separate one amount of wind from a differing amount. Do you see why I'm confused? — Steve Hester
Answer: It seems likely there may have been a simple slip of the tongue on-air sometime long ago that you happened to hear in regards to isobars being lines of unequal pressure, because it has always been the case that they are lines of equal pressure, that is the lines run along locations where the pressure is the same in order to outline areas of relatively high or low pressure, making pressure centers, troughs, and ridges evident on a weather map in the same way that contours of elevation on a topographic map (which could technically be called isohypses) help us visualize hills, depressions, valleys and ridges in terrain.
On a terrain map, a series of near-parallel isohypses close to one another represent a steep slope perpendicular to the contour lines. Likewise on a weather map, a number of isobars spaced closely together indicate a strong gradient of pressure crosswise to the isobars, and is usually an area where the strong horizontal pressure difference translates into rather strong winds, while the opposite applies for isobars that are widely spaced from one another.
Jan. 27, 2014 | Tags: general meteorology, maps & codes
Question: Where can I find that map which showed rainfall amounts during the previous 24 hours? I have referred to it often. — Henry Nuttle
Answer: The new site design collected a lot of the maps into one selection page, and that's where you can find the 24-hour rainfall map. Just click "Map Center" and then click the "other maps" tab. One of those is "rainfall," and it is the map you are looking for.
Jan. 24, 2014 | Tags: maps & codes, rain, wral.com
Question: Can you explain what the NAO and AO are and how they impact our winter weather? — Bryan Peed
Answer: Those are two climate indices called the "North Atlantic Oscillation" and "Arctic Oscillation," respectively. In each case the state of the oscillation is measured based on the intensity of semi-permanent high or low pressure areas compared to their average climatalogical values. In the case of the Arctic Oscillation, whether it is positive or negative depends on whether the high pressure area aloft typically in place over the north polar region is weaker or or stronger than average. When it is weaker, we have a positive AO and vice versa. The NAO, on the other hand, depends on the intensity of both a semi-permanent low pressure area near Iceland and a semi-permanent high pressure area to its south that is typically located in the vicinity of the Azores. When both systems are stronger than average, the NAO is considered positive and when they are weaker than average, the NAO is negative.
These two indices are not entirely independent from one another and in both cases, positive phases correlate with strong jet stream winds across the northern U.S. and Canada that tend to keep the coldest arctic air moving eastward rather than spreading deeply into the United States, while their negative phases tend to have the opposite effect, allowing deeper and more sustained cold outbreaks here. The positive phases both tend to relate to warmer winter temperatures and somewhat greater amounts of precipitation (mainly rain) for our area, while the negative phases make less precipitation likely overall, but due to the colder air often involved, increase the potential for wintry weather.
You can get a better sense of all this by looking over some graphics and additional details on a nice page at the State Climate Office of NC web site. Just go to www.nc-climate.ncsu.edu/climate/patterns/NAO.html for those illustrations.
Jan. 15, 2014 | Tags: maps & codes, winter weather
Questions 1 - 10 of 99.
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
— Thu 10:38 p.m.
— Thu 9:45 p.m.
— Thu 9:35 p.m.
— Thu 9:31 p.m.