Ask Greg

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!

Answer: For the Raleigh-Durham airport, the earliest first occurrence of a freezing air temperature was October 3rd in 1974, while the latest first freeze was November 17, 1989. The average date for a first freeze is October 28th, with a standard deviation of +/- 9 days. Under the right conditions, frost can form on surface objects despite air temperatures that remain above freezing, and most reporting stations do not have reliable records of days with frost but not freezing temperatures, so all we can add regarding first frost dates is that they can potentially happen anywhere from a few days to a couple of weeks before the first freeze.
Oct. 26, 2009 | Tags: cold, past weather, winter weather

Answer: This is pretty speculative, since it isn't obvious whether you are asking about the appearance of the sky during the storm or after it cleared up later, or whether you observed a constant glow or something that was intermittent. Sometimes during heavy storms failing transformers and arcing power lines can produce intermittent flashes or periods of blue, green or purple light in the sky. Perhaps more likely you are referring to night skies after the storm, in which case you may have observed an aurora that colored the morning sky.
Sep. 27, 2009 | Tags: astronomy, atmospheric optics, winter weather

Answer: El Nino episodes historically produce some tendencies in precipitation and temperature across North Carolina, with the main effects during the colder months from late fall into early spring. El Nino years produce winter season temperatures around one half to a little over one degree below normal for central NC, with that range of temperatures occurring in roughly 60% of El Nino years. Precipitation averages a little below normal for the mountains, a little above normal for the southeastern half or so of the state, and near normal across west-central parts of the state in El Nino patterns, while snowfall averages about 1-3 inches above normal for the mountains, foothills and western Piedmont, and near normal for central and eastern Carolina. These tendencies are sufficiently variable that it is difficult to use them as a confident predictor for any single year, and current Climate Prediction Center outlooks for the winter ahead indicate equal chances for precipitation and temperature over most of North Carolina to be above normal, normal or below normal. The outlooks do lean toward below normal precipitation for the mountains, and weakly toward below normal temperatures across the southern coastal plain.
Aug. 8, 2009 | Tags: el nino/la nina, winter weather

Answer: In the 1940s, J.E. Miller classified Type A cyclone systems as those involving formation of low pressure along a front in the vicinity of the Gulf of Mexico, which then tracks northeast along the Atlantic coast. Type B systems involve a primary low moving northward west of the Appalachians and then a secondary low forming and intensifying near the mid-Atlantic coast as the initial low weakens. The two types can have different distributions of precipitation intensity when temperatures are too warm for wintry precipitation. When temperatures are colder, there are differences in how precipitation types are arrayed. Type A lows usually feature a sharp transition between snow northwest and rain southeast, while more complex Type B patterns involve more areas of sleet and freezing rain as well.
Jul. 28, 2009 | Tags: general meteorology, winter weather

Answer: The mean temperature at the Raleigh-Durham airport for December 2008 - February 2009 was 44.4 degrees, about 2.6 degrees above normal. By comparison, the same period in winter 1995-1996 averaged out to 40.0 degrees, notably colder. The coldest on record for the same location was December 1976 - February 1977, when the average temperature for the winter was only 34.3 degrees.
Jun. 26, 2009 | Tags: cold, past weather, winter weather

Answer: More than likely the heavy rain during the storm washed up some soil that contained an artificial moisture retention agent in the form of water-holding polymer crystals that can take on the appearance of clear gel when they are saturated. These and similar silica gel pellets can look like ice and be visually confused with small hail, except of course they feel soft and do not melt!
May. 25, 2009 | Tags: hail, winter weather

Answer: On the day you wrote about, the upper atmosphere was dry enough to be free of natural clouds but did develop a combination of cold temperatures, low wind shear and low turbulence levels above about 35,000 feet that was favorable for formation of lengthy contrails. Some of the ice crystals then persisted long enough to spread out into streaks and sheets of cirrus cloud.
Apr. 28, 2009 | Tags: clouds, winds, winter weather

Answer: The symbols highlight areas of heavier rain, strong wind potential, snow, possible tornadoes, lightning and so on. Most symbols will provide an arrow indicating the speed and direction of movement when you hover the mouse pointer over them, and more information if you left-click on the symbol. You can see an icon legend for iControl at content.myweather.net/iradar/more_help_future.html.
Apr. 27, 2009 | Tags: snow, tornadoes, winds, winter weather

Answer: It didn't snow toward the middle of that month, but there was a tremendous snowstorm that affected much of North Carolina March 1-3 as an intense nor'easter moved out of the Gulf of Mexico and along the southeastern U.S. coast. During that storm, Fayetteville reported 24 inches of snow, Enfield 25 inches, and there is a report of 31 inches from the Nashville area.
Apr. 17, 2009 | Tags: snow, winter weather

Answer: Liquid cloud droplets are formed when water vapor condenses onto hygroscopic particles, called "cloud condensation nuclei," that can include dust, soot, some organic compounds, sea salt particles and others. A smaller subset of these aerosols, including some minerals and possibly even bacteria, can act as ice nuclei that support the formation of clouds composed of ice crystals.
Apr. 12, 2009 | Tags: clouds, winter weather