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Question: Is there any hope for us wintry weather lovers out here??? I search the 7 and 10 day forecasts, and all I see are warmer and warmer temps! I know February and even March is not out of the question for snow.... what do you think? — Loren
Answer: There is hope, of course, as we're answering this in mid-February. It's important to note, though, that such hope isn't based on any particular indicators of a winter storm that are evident in specific forecasts out through the next week or two, but only in the historical record. It tells us that, though increasingly unlikely in a statistical sense, significant snow storms are at least possible here out through April (1.8 inches fell in Raleigh on the 18th in 1983, and 10 inches occurred on the 3rd in 1915). The lingering effects of the recently ended La Nina tilt our temperature and precipitation odds toward warmer and drier than normal conditions over the next several weeks, but that doesn't guarantee that a short-term colder, active pattern or two can't slip in as well. Past the next week or so, we simply have no way of knowing for certain.
Feb. 14, 2017 | Tags: el nino/la nina, winter weather
Question: Why is it so warm this winter? — Paul Stancil
Answer: The winter so far has featured warmer than normal temperatures, with the mean temperature in Raleigh turning out one degree F above normal for December and 5.5 degrees above normal for January, and we've seen a number of warm days in February so far. The proximate reason for the mild weather has been a frequent pattern aloft that features either zonal, mainly west to east flow or the presence of an upper ridge over the eastern U.S., which often corresponds to southwesterly or southerly flow in the lower atmosphere and a lack of thick cloud cover and precipitation. While we have had a few occasions with development of upper troughing in the eastern U.S. that allows for a notable intrusion of colder air, they have tended to be infrequent and short-lived. In a more ultimate sense, some of this is likely part of typical year-to-year variability, but some is also connected to the La Nina pattern that we started the winter with, in which upper flow patterns across North America are modulated by cooler than normal equatorial Pacific sea surface temperatures in a way that tilts the odds across the deep south and southeastern U.S. toward having above normal winter temperatures and below normal precipitation.
Feb. 13, 2017 | Tags: el nino/la nina, winter weather
Question: Did anyone else report seeing light pillars this morning? At least, that's what I think I was seeing -- tall vertical reflections from headlights and traffic lights . . . . Can you explain more about this phenomenon? — Sam
Answer: Your description sounds like light pillars, but based on the date and time you reported seeing them we can't confirm that's what it was, and we suspect there is some other explanation. At the time you noted, temperatures were in the mid 50s, much warmer than those that support the existence of the kinds of ice crystals (both plate-like and column-shaped) that can lead to ice pillars. The phenomenon occurs when the air is filled with tiny ice crystals that are preferentially oriented with the long portion of the plates parallel to the ground. Then, the bottom faces of the crystals can act as very small mirrors to reflect the light from a variety of ground based sources, creating columns of light that take on the color of the source. A similar effect can occur with sunlight, and under the right conditions the "sun pillar" can extend well above and below the sun itself, with the light below being reflected off the tops of the ice crystals. You can read more about the pillars, and see some good diagrams explaining their formation, at www.atoptics.co.uk/halo/lpil.htm. In addition, a search for "light pillars" on the web will turn up many very nice recent photos of the phenomenon.
Feb. 12, 2017 | Tags: atmospheric optics, cool sites
Question: In your pro opinion, is there anymore cold weather in this HOT winter or is it over? I looked at the CPC and the NAO and AO and they both look solidly positive, so? — Ricky Adkins
Answer: So far, as you note, the winter here has been a relatively warm one with just a few substantial cold outbreaks, at least reasonably in line with the earlier projections associated with heading into the season with a La Nina pattern in place in the Pacific. Sea surface and subsurface temperature trends of late have shown a likely return to neutral conditions, but the atmospheric effects often linger a bit and it may well be that we finish out the winter season on a warmer than normal note overall. However, this doesn't preclude the chance of another significant cold outbreak or two. At the time we were writing this, ensemble model projections of the indices you mentioned looking at at the CPC (Climate Prediction Center) web site hint at cold air intruding into the central and eastern U.S. in the period near and following after Valentine's Day, but it is hard to have great confidence beyond that. In this particular case, the NAO (North Atlantic Oscillation) and AO (Arctic Oscillation) values are projected to dip below normal for that time span, while another notable index, the PNA (Pacific North America) pattern rises well above normal. While these large scale patterns don't offer absolute guarantees about local temperatures, the tendency is for below-normal AO and NAO values to correspond to cold air in the central and eastern U.S. and vice versa, while such cold air is favored when the PNA values run above normal, with mild air in the east often corresponding to a below-normal PNA.
Feb. 11, 2017 | Tags: cold, general meteorology, winter weather
Question: Is it possible for a high pressure system to bring rain? I know that most storms are brought by a low pressure system, but is it possible? — Luke
Answer: This is a good example of how, in order to make weather understandable and more easily communicated, we often greatly simplify what are in fact very complex patterns and processes in the atmosphere. While we commonly associate low pressure with precipitation and high pressure with fair skies (and rightly so in many cases), there are exceptions and there are situations in which interactions of relatively low pressure at one altitude correspond to relatively high pressure at another, sometimes resulting in precipitation. That's a long way of saying that it IS possible for precipitation to occur when there is a high pressure system in place. One common example for us is the "cold air damming" pattern, in which high pressure extends into the state from the north or northeast, creating a north or northeasterly wind flow and bringing a shallow layer of cold, dense air into the region. Sometimes, that air undercuts and lifts warmer, moister air that condenses into clouds and precipitation. In many cases, this only yields sprinkles, drizzle or very light rain, but in some instances the precipitation can be more substantial. Another example would be high pressure building in from the west in the winter, producing strong northwesterly winds for our state. For a lot of us, that is generally a dry pattern. However, it isn't uncommon in the mountains for air flowing up the western slopes within the eastern or northeastern portions of the surface high to be moist enough to produce flurries or snow showers there. One other note is that tropical cyclones often are best organized and set up to intensify if the low pressure center near the surface is lined up nicely with a high pressure center in the upper atmosphere more or less directly above it.
Feb. 10, 2017 | Tags: fronts & airmasses, general meteorology, rain
Question: What is the "perfect" indoor humidity? We have a new weather station, and I just want to know if we have too much or too little humidity indoors. — Susan Smithson
Answer: There isn't a single absolute best number to shoot for, as the optimum setting for a particular space may take a little trial and error to settle on, and can vary some by season. Most recommendations on indoor humidity levels that maximize comfort and minimize problems with mold, mildew, condensation and other structural/health issues range between 30 and 50 percent, often in the lower half of that span for winter and the upper half for summer.
Feb. 9, 2017 | Tags: humidity/dew point, weather & health
Question: A question for the weather team. I have a 7-year old grandson who is interested in weather. He's quite smart and I was wondering if you could recommend a weather-related book that is a step above his age range. — Mel
Answer: Some good choices for weather books in general, including for younger readers, are the "National Audubon Society First Field Guide: Weather" by Jonathan D. Kahl, "Weather: A Golden Guide" by Paul E. Lehr, and "DK Guide to Weather", by Michael Allaby. You might also consider the slightly more advanced Firefly ”Guide to Weather Forecasting” by Storm Dunlop, and “The AMS Weather Book” by Jack Williams. There are many others out there as well, and a visit to the library or your favorite bookstore should turn up plenty of additional options.
Feb. 8, 2017 | Tags: careers & education
Question: Why is it that the air sometimes smells noticeably fresher? This evening is one of those times. — K. Schaffer
Answer: There can be a number of reasons, and it varies depending on the kind of "un-fresh" smell that existed before. Sometimes it is a simple matter of the air being stagnant or blowing from the direction of a source of pollutants, and then having the wind direction shift or the speeds pick up such that turbulent mixing brings cleaner air down from a few hundred or few thousand feet above the ground. There can also be a fresh smell in the wake of a rainfall in which the rain captures some of the particles in the air and scours them out, depositing them on the ground. In the case of the evening you wrote in, we had a warm afternoon followed by a cold frontal passage that occurred around mid-afternoon. You may have been noticing the effects of cooler, less humid air flowing in from a different direction and perhaps a mixing effect as well. In the case of this front, we went from a high temperature of 76 that day to a high of 55 the next, indicating a notable airmass change.
Feb. 7, 2017 | Tags: air quality, fronts & airmasses
Question: Here in the Triangle, we have had multiple days of weather reaching the mid-to-high 60s. I could understand one or two days of this as an outlier, but not multiple, back to back like we have seen the past week or so. Is this string of high-60 days unusually high for this time of year based on historic averages? — Andy
Answer: While we've had warmer-than-normal temperatures through the first two months of winter overall, and we have had some streaks of 60-degree or higher maximum readings, they haven't occurred at anything all that close to record levels when you take a look at the history from RDU, which we did with assistance from the good folks at the State Climate Office of NC. This winter we've had a streak of consecutive 60-plus days as long as five in a row, ending on December 29th, and another 4-day streak ending January 26th, but there are eight times since the mid 1940s that we've strung together 10 or more straight days reaching highs that warm. The record was 14 consecutive days ending on January 25, 1999, while the most recent such lengthy streak was just over a year ago, with 10 consecutive days ending on December 31, 2015.
Feb. 6, 2017 | Tags: past weather, records/extremes
Question: I'm looking at the sky tonight and I am seeing one of the biggest and most beautiful stars. It is so bright, I can see points all around it. Is this unusual or do I not look up in the sky enough because I have never seen a star this close to earth? — Candice L.
Answer: You noted that the time you saw this was around 8:30 PM on January 26th. We think it is almost certain that you were noticing the planet Venus, which is currently in it's "Evening Star" position well to one side of the sun, so that it is visible at nearly its highest angle of the year above the horizon in the hours after sunset. As long as clouds don't interfere, you can see it night after night for a good while yet in the western sky, and gives exactly that sense of being VERY bright and "close." One that that you might notice on close inspection is that it is a very steady light, whereas even bright stars tend to "twinkle," with their brightness and precise position fluctuating just a bit. That difference is a common way to discern the much closer planets in our sky from the vastly more distant stars.
Feb. 5, 2017 | Tags: astronomy, atmospheric optics
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Published: 2007-10-09 14:40:00
Updated: 2014-06-24 16:06:51
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