Ask Greg

Recent Questions

Question: Can y'all give the wind speed and directions the same as you give rain chances in the morning. It would be helpful for fishermen to have in the early morning forecast. — David Almers

Answer: If you mean the bar graphs we sometimes use for precipitation chances as they vary through the day, we can look into adding something along those lines. In the mean time, keep an eye on our "Skycast" graphics that we use periodically through the morning newscasts. These are the ones with the city skyline and the projected view of the sky in the background. We typically show these for morning, noon, afternoon and evening time frames, and they usually include projected temperature and wind speed/direction for those times in boxes near the right-hand side of the image.
Jul. 7, 2017 | Tags: maps & codes, winds

Question: What barometric pressure determines a high or low; for example, 30" Hg or above is a high and below 30" is a low. — Don E

Answer: Actually, low pressure centers or systems and high pressure centers or systems are defined more by the relative pressure at their locations compared to surroundings (and the related circulations of air that result), rather than by particular values of pressure. In a very rough sense, you could take the idea that standard sea level pressure is 29.92 inches of mercury (equal to 1013.25 millibars), so you could take a pressure value notably higher than that to be high and vice versa. However, again, it is possible for a pressure lower than that to be higher than surroundings, and thus a "high" on a weather map, and likewise the other way around.
Jul. 6, 2017 | Tags: fronts & airmasses, general meteorology, maps & codes

Question: Just something interesting I think you should know. My husband's name is Greg, his birthday is February 19th, our anniversary is June 14th, he loves snow and is crazy about the weather. Sound like anyone you know? How does it feel to have a twin? — Linda

Answer: A little eerie, but tell him happy birthday for me when it rolls around again! Just to clarify, as well, in my case June 14th is the anniversary of my employment with WRAL.
Jul. 5, 2017 | Tags: records/extremes

Question: I don't know how much statistics actually goes into precipitation chances and if those calculations are universally applied across networks. For instance, if I look at a site right now that projects weather well beyond 7 days, it is telling me that there is a 60% chance of precipitation on July 5th. It seems to me that longer range forecast precipitation chances should start out low (some cap that can be proven statistically) and only increase if models converge as that particular day approaches. I guess ultimately, if you look out far enough in the longer range forecast, you would probably arrive at and only be able to publish a historical average chance for every day if you were to go that route. I guess where I'm going is that it seems pointless to predict a 60% chance of rain 11 days out. — Brad

Answer: We agree, and most forecasters seem to, that precipitation chances, in effect a statement of confidence that measurable precipitation will occur during the valid time of the forecast, should tend to trend down to climatological values with increasing lead time. Around here, those values are on the order of 20-35% depending on time of year. We restrict our forecasts to a 7-day period, and while there are occasions when we might see enough agreement among multiple deterministic and ensemble computer model projections, along with model output statistics post-processing, that indicate significant potential for precipitation that far in the future, to include a probability of around 60-70%, we would rarely if ever go higher than that, and in many cases due to lower confidence would show lower values. Likewise, there are times of the year when we rarely show a percentage lower than 5-10% even when models indicate a dry pattern that far in advance, due to some lack of certainty that the projected pattern will not change over time. As you noted, there may be times that the probability would grow considerably if projections of a wet pattern remained consistent as we moved within 3-4 days of the event. Of course, there are times when the opposite happens, and changes in speed, intensity, and/or location of potential precipitation-producing systems results in a lowering of the probability for a given day as we approach.
Jul. 4, 2017 | Tags: general meteorology

Question: Is there a place I can look up whether we were under the influence of High or Low systems by the day for each month? — Done

Answer: The most straightforward way we can think of to do that is to examine weather maps that show the pressure patterns across the United States on a daily basis, to examine them an see if a center or ridge of high pressure, or a center or trough of low pressure, were in place over NC or nearby on the days in question (sometimes you might find that we fall somewhere in between, during a transition day of sorts). If you are interested in seeing daily weather maps for your dates of interest, they are available from NOAA at www.lib.noaa.gov/collections/imgdocmaps/daily_weather_maps.html. Note that this link includes access to weather maps going back to 1871. If you are interested in maps for dates since September 1, 2002, a more direct address is www.wpc.ncep.noaa.gov/dailywxmap/index.html.
Jul. 3, 2017 | Tags: cool sites, maps & codes, past weather

Question: What is the Radar near Hwy 50 & 98? — Michael

Answer: You are no doubt referring to the radar tower and radome visible just off Old Creedmoor Rd northwest of the 50/98 intersection you mentioned. That is the Terminal Doppler Weather Radar (TDWR) that serves the Raleigh-Durham airport. It is a more localized radar than the National Weather Service NEXRAD radar located near Clayton. The TDWR system is part of an FAA-operated network of radars that are designed to provide short-range, high-resolution detection of wind shear, gust fronts, microbursts, heavy precipitation and other weather phenomena that are potentially dangerous to aircraft in the immediate vicinity of airports.
Jul. 2, 2017 | Tags: weather radar

Question: Is there a place where I can find running 24 hour rainfall totals? — Glenn

Answer: There are a couple of locations where you can get running 24-hour precipitation estimates based mainly on radar returns. One map of that sort is hosted at the Southeast River Forecast Center, at www.weather.gov/images/serfc/24_hour_precip.png, and a similar, but zoom-able, and more interactive, map at www.iweathernet.com/total-rainfall-map-24-hours-to-72-hours (you can click on any point there, and after a short delay, a box will appear that shows the estimated precipitation amount for that location).
Jul. 1, 2017 | Tags: cool sites, rain, weather radar

Question: Durham is missing on your weather map. Can you explain why? — Suzanne

Answer: Upon checking back with you, we found you were asking about the radar display, where we can move around and zoom in or out to highlight areas of precipitation or thunderstorms that are crossing the area. When we do that, the display software automatically picks town and city labels depending on the zoom level and what part of the area is shown, and it works to avoid having labels from nearby towns overlap with one another. It may have been that by chance at the time you were watching we set a couple of views where the software left Durham off. When moving around the range of available views, there are times when almost every town (including larger ones like Durham, Raleigh and Fayetteville), are labeled and others where those labels disappear in favor of some other nearby places. We use a number of other maps that have standard views (like our current temperature maps, some of our model-projected temperature, wind or dew point maps, our viewing area forecast map, and some others) and the great majority of those include Durham specifically.

On the radar view, it might be possible to force certain cities to always be labeled. However, we try to avoid that since if we set a couple of key places to always be there, it would preclude some other nearby locations from ever showing up, and we like to allow some of the smaller communities to appear as well. We could also set it so a lot more town names are visible at the same time, but then we’d end up covering a lot of the radar data we’re trying to show with labels, so we try our best to find a happy medium somewhere in between.
Jun. 30, 2017 | Tags: maps & codes, weather radar

Question: This time of year, through August, overnight low temperatures do not seem to vary much. Forecasts can go for days with lows being close to 70 degrees. We have some cool nights in the long range with lows about 10 degrees below what we normally see. How unusual is that? I would guess the odds of an overnight low being close to 60 for mid June through mid to late August to be about 1%. — Joe Freeman

Answer: At the time you wrote, we were forecasting a low around 57 degrees on June 28th, which is indeed fairly unusual. The normal low for that date is 69 degrees, with a standard deviation of about +/5 degrees (as you noted, temperatures are less variable in the summer - in January, the standard deviation for the low is about +/- 11 degrees). The record low for June 28th is 53, from back in 1988, so it can get notably cooler than 60 degrees. As for the odds, it turns out that temperatures have dipped to 60 or below in Raleigh on June 28th about 15% of the time in observations going back to 1887. More generally, for "meteorological summer" overall, the average chance of falling to 60 or below on any given day is about 11 percent.
Jun. 29, 2017 | Tags: normals, records/extremes

Question: How good will the viewing of the total eclipse be in Raleigh? Should we consider going elsewhere to see it? — Susana Merritt

Answer: The Raleigh area is outside the path of totality, and so a partial solar eclipse will be seen from here. At maximum coverage, the moon will stretch about 94% of the way across the sun's diameter, leaving a crescent of the sun visible. While this can make for an impressive image, even a relatively small crescent is very bright, and there is a big difference in experiencing a total eclipse and even a substantial partial eclipse. Several phenomena associated with totality, such as shadow bands, Baily's beads, the "diamond ring" effect at the onset and end of totality, and visibility of the sun's corona and chromosphere, do not occur in areas seeing a partial eclipse. To experience those effect would require traveling to a location within the path of totality.
Jun. 28, 2017 | Tags: astronomy

Questions 41 - 50 of 5385.


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.