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Question: I grew up in Salisbury. When I was about 10 years old we had a MARCH in which it snowed 3 or 4 Wednesdays straight. This would be around 1957. Is it possible to find some details on this? — Jim Shoaf

Answer: We dug up records from Salisbury and the nearby Rowan Research Station, and as near as we can determine, you are probably thinking of March 1960 (maybe you were really 13 when it happened!). This month was already known to us for being the coldest March on record for Raleigh, and for having several consecutive Wednesdays with snow. It appears the same systems extended their reach into the western Piedmont as well, because we found that Salisbury recorded 10.5 inches of snow on Wednesday March 2nd, 8.5 inches on Wednesday the 9th and 2.5 inches on Wednesday the 16th, all part of a total of 22 inches of snow for the month. So, your memory of having 3 straight "hump days" with snow was correct (but not 4 in a row).
Mar. 9, 2015 | Tags: past weather, records/extremes, snow

Question: Do you know where we can obtain a listing of the daily highs and lows in the weather from August 2014 to the present date? We need it for research and would greatly appreciate your assistance. — Anonymous

Answer: Sure! You can click the "almanac" link on our main weather page, and there you'll find a "Get Historical Data" section where you can enter a date of interest and click the "send" button. That will default to a page with observations from the RDU airport for that date, but once you are there you can either search for another location using the search box near the top of the page, or change the weather history location using a box along the right hand side of the page. In addition, you can change the display from "daily" to "weekly" or "monthly" and scroll down to see a listing of daily high and low temperature, along with other data such as precipitation, winds, observed weather phenomena and more.
Mar. 8, 2015 | Tags: cool sites, past weather,

Question: Does DualDoppler make the distinction between rain, snow and ice? iControl and radar showed snow and DualDoppler only showed some green which I will assume is rain — Joseph Grissom

Answer: The DualDoppler 5000 does have the capability to transmit both horizontally and vertically polarized radar pulses, and by doing so we can use a "hydrometeor classification" algorithm to determine the kinds of precipitation particles encountered by the beam. However, these require some additional interpretation and independent data in order to translate what's in the beam to what may be occurring at ground (snow in the beam could melt before reaching the surface, rain in the beam could freeze into sleet below, etc). For that reason, the images we put on the web from DualDoppler 5000 show only the intensity of precipitation, and are not color coded according to the most likely type reaching the ground. On the other hand, we do apply a "mask" to the regional radar and iControl data so that areas that are expected to be receiving sleet or freezing rain or a mix of types show up with a magenta shading, while areas with snow likely to reach the surface are tinted in shades of blue. The colors in this case do not come from the radar information itself, but from software that uses surface observations and computer model estimates of vertical temperature and moisture profiles to determine the most probable precipitation type at ground level.

It can be a good idea to check both DualDoppler and the other displays, since the others give some info on the type of precipitation, while the DualDoppler often has greater detail and is generally a little more up to date (especially the live streaming version). In that sense, the different kinds of radar information complement each other.

Mar. 7, 2015 | Tags: weather radar, winter weather,

Question: A recent 7-day forecast showed "tomorrow" (Feb 20th) with a high of 22 and the day after with a low of 38. Unless there is an instantaneous jump of 16 degrees at midnight, this seems impossible. How am I supposed to interpret that data? — William Faulk

Answer: Looking back at the actual progress of temperatures in that stretch of time shows the first day ended up with an actual high of 26, the following day had a low of 18 and then the second day high was 40. We suspect there was a data entry typo on our part in which the forecast high for the second day was entered into the space where the second day low should have gone and this caused the odd sequence on the displayed 7-day.

While that was likely a simple error, the weather does make it tough to choose which numbers to show in those spaces on occasion. In providing a forecast for rough planning purposes, we usually shoot for showing the high and low that most people are likely to experience in typical day to day activities rather than strictly meeting the 24-hour (midnight to midnight) definition used to maintain climate records. There are occasions when this creates an odd-looking 7-day in which the afternoon high may be the same value as the preceding or following low temperature. This usually means that we expect temperatures to be climbing or falling at a substantial rate in a non-typical manner (usually, lows occur near or a little after sunrise and highs around mid-afternoon). For example, if you see a low of 40 with a high of 40 the same day, you may find that our on-air or web forecast explanation for that day might show that the temperature will be around 40 at daybreak, then fall as the day continues. There are rare occasions when this general protocol leaves us with few really good options on how to set those numbers, but we still feel it's a better idea in general than showing numbers that might only be applicable at, say, 1 or 2 AM.
Mar. 6, 2015 | Tags: maps & codes,

Question: My wife Pam and I have been debating what makes ice slippery. Do you know? — Bill Mandulak

Answer: That has actually been the subject of some serious study and thought by chemists, physicists and others, and has not been as easy as you might imagine to pin down with certainty. However, the most recent prevailing theory has to do with the existence of a very thin liquid-like layer at the interface between ice and other objects, a layer that exists even when the temperature is below-freezing. This has been referred to as a "pre-melting" layer and attributed largely to the fact that the water molecules at the surface are exposed on one side and not bound together chemically the way molecules in the interior are, allowing them more freedom of movement, and this movable layer leads to some loss of friction between any object in contact with the ice and the bulk of the ice below. This effect is enhanced by the application of pressure to the ice (for example, by a person's shoes, tires of a car or skate blades), which lowers the melting temperature a bit to help form an actual thin layer of liquid water, making the interface even more slippery. In addition, to pressure, frictional heating caused by the movement of another object across an ice face can heat the ice a bit, again producing a thin, slick layer of meltwater.
Mar. 5, 2015 | Tags: cold, general meteorology

Question: As a follow-up to the recent question about cold weather in Rocky Mount area in winter of 69-70, what is the longest period of below 32 degrees in Raleigh? — Dave Crotts

Answer: The answer isn't quite as easy to track down with certainty as you might think, but here is what's available. We checked back through data from the Raleigh-Durham airport, and also asked for a check of past hourly records by the State Climate Office and received a search result from the Southeast Regional Climate Center as well. They found a stretch of 157 straight hours at or below freezing (that is, 32 or lower) ending on January 16, 1982, and a streak of 100 consecutive hours below freezing (31 or lower, which is what your question asks) ending on Feb 5, 1996. Their databases, however, rejected observations from 1966-1971 from the search based on quality control checks, due to observations being archived only every three hours in that time frame. While we could not narrow it down to an exact number of hours, a search of some different archives turned up what appears to be a similarly long stretch of sub-freezing temperatures in January 1970, with the temperature falling below freezing on the 19th and rising back to 32 and above on the 24th. The data in that set is only available every three hours, so there is some uncertainty about exact numbers, but it appears there were at least 124 consecutive hours below freezing in that event.
Mar. 4, 2015 | Tags: cold, past weather, records/extremes

Question: What effect, if any, does wind chill have on freezing water pipes? — J.P. Gibson

Answer: The wind chill value per se does not apply to non-biological objects like water pipes. So, for example, if the air temperature is 35 degrees but the wind is blowing such that the wind chill value is 28, that doesn't mean the pipes will freeze, because the temperature of the pipes and the water in them will remain at 35 degrees.

On the other hand, if the temperature falls to, say, 20 degrees and wind is blowing strongly across an exposed pipe, it may cause the temperature of the pipe (and eventually the water inside) to fall to 20 degrees more rapidly than it would if the wind were calm.
Mar. 3, 2015 | Tags: apparent temperature, cold, winds

Question: Could the term back door cold front be explained? I keep hearing that but it is not clear exactly what that means. — Kent Riedling

Answer: The majority of cold fronts that cross our area, and the eastern U.S. in general, are oriented in a line that runs from north to south or northeast to southeast, and they tend to move through here from the west or northwest. This being the most common mode of arrival, the cold air behind the fronts can be figuratively said to enter through the "front door." Less commonly, a cold front will have more of a west to east orientation, and will push across our area from the north or the northeast, often because of a strengthening cold high pressure center over eastern Canada or New England. When the cold air arrives in this manner, the front that marks its leading edge is called a "back door" front.
Mar. 2, 2015 | Tags: folklore, fronts & airmasses, general meteorology

Question: Explain thunder snow heard in Sanford on Wednesday 2-18-2015 at 1715 as the snow came down. — Anonymous

Answer: Even though temperatures became quite cold on that day, we had a strong cold front moving in and some very cold air aloft, so that the lapse rate, or decrease in temperature from the surface to about 10,000 feet above the ground, was very sharp due to extremely cold air aloft. That difference made the lower atmosphere unstable, in quite a similar way that we form summertime thunderstorms. In addition, there was strong lift associated with the approaching front, and the line of snow showers swept through in a similar structure as a convective season squall line. That structure was enough for strong vertical motions to separate charges within the clouds enough to generate a few lightning strikes here and there, producing the thunder that you and some others heard.
Mar. 1, 2015 | Tags: snow, thunderstorms

Question: Is there a scientific or official definition for what some call an "Indian Summer"? What causes them? — Jennifer Burns

Answer: The Glossary of Meteorology defines Indian Summer as a period of abnormally warm weather, with mainly clear skies and cool nights, that occurs after a substantial stretch of seasonably cool weather, usually after the first killing frost of the fall season. Indian Summer can occur multiple times, or not at all, in a given year. In Europe, comparable terms include Old Wives' Summer and Halcyon Days. The cause is usually development of a slow-moving ridge of high pressure aloft over or just east of the area experiencing the warm-up, one that allows for a southerly or southwesterly flow that results in fair skies and temperatures well above normal. There isn't anything unique about this pattern, other than the time of year that it occurs. A similar warming in mid-winter is often referred to as a "January Thaw."
Feb. 28, 2015 | Tags: folklore, general meteorology, heat

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