WRAL.com: Raleigh, Durham, Fayetteville

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Answer: For Holly Springs and most of central North Carolina, prevailing wind directions are from the southwest (from a compass direction of 230 or 240 degrees) ten months out of the year. The months of September and October are the exceptions, with a prevailing wind for those months from the northeast (030 to 040 degrees). Keep in mind that these are long-term averages, and there can quite a bit of short-term variability of wind direction in any given year, month or week.
Jun. 10, 2013 | Tags: normals, winds

Answer: For Raleigh and most of central North Carolina, prevailing wind directions are from the southwest (from a compass direction of 230 or 240 degrees) ten months out of the year. The months of September and October are the exceptions, with a prevailing wind for those months from the northeast (030 to 040 degrees). Keep in mind that these are long-term averages, and there can quite a bit of short-term variability of wind direction in any given year.
May. 13, 2013 | Tags: normals, winds

Answer: Unfortunately, there isn't a good, specific way to forecast when the last frost will occur in a given season, but we can look at history for some guidance in regards to the last freeze date in the spring. It is also important to note that records are lacking for frost per se, due to the fact that frost can occur on surface objects even with measured air temperatures remaining above freezing. We have reliable records for last freeze dates, meaning those on which air temperatures fell to 32 degrees or below. The average last freeze date for the Raleigh-Durham airport is April 10th, but there is quite a bit of variability from year to year, such that there is still about a 20% chance of a freeze as late as April 17th and a 10% chance as late as April 23, with the latest freeze in 69 years of measurement coming on May 10th. These dates are about 9-10 days later than similar statistics for stations closer to or in Raleigh. Generally locations in central NC that are located in urban areas are closer to the those numbers, while those in more rural locations area closer to the numbers from RDU.
Mar. 21, 2013 | Tags: cold, dew/frost, normals, past weather

Answer: Climatological spring is a reference to the time of year when the sun angle has already increased significantly and average temperatures have climbed notably from their wintertime lows, so that periods of weather we consider "springlike" become more frequent, with the resulting responses from plant and animal life. It more specifically refers to the calendar months of March, April and May, used by meteorologists and climatologists for calculation of "spring" weather statistics, due in part to the changes in weather that have typically already taken place by March 1st, but also to the greater record-keeping convenience of not splitting seasons in the middle of calendar months. Hence for climate record-keeping we usually think of June-July_august and summer, September-October-November as fall and December-January-February as winter.

The more traditional definitions of the start of spring and the other seasons are tied to astronomical events associated with earth's position in its orbit around the sun. Spring is said to begin with the Vernal Equinox, summer with the Summer Solstice, fall with the Autumnal Equinox and winter with the Winter Solstice. The "climatological" seasons used by for weather records start about 3 weeks earlier and typically align a little more closely with the warmest and coldest average periods of the year (for summer and winter) and the intervening transition seasons.
Mar. 17, 2013 | Tags: astronomy, normals

Answer: The start and end of pollen season can vary by a couple of weeks year to year depending on weather patterns through the winter leading up to it, but it usually starts in our area around mid-March and lasts for about 2-4 weeks, before winding down by late April or early May. Last year it kicked off a little early after a mild winter. This winter has been warmer than normal overall so far, and while that can't be taken as a guarantee that we'll see noticeable pollen early again, it wouldn't hurt to plan accordingly just in case and cover your deck near the end of February or early March.
Feb. 18, 2013 | Tags: normals, pollen

Answer: Most of North Carolina has a very low probability of a white Christmas, which can be defined in various ways. Regardless of the defining statistics used, towns in our state that have the highest likelihood of either experiencing measurable snow in the window from 24-26 December (the criteria used by our State Climate Office for an interactive feature on their web site) or of having at least one inch of snow on the ground on Christmas Day (used by the National Climatic Data Center for a map of the United States highlighting where that definition is most likely to be met) are those at the higher elevations of our central and northern mountains, like Boone, Jefferson, Marshall, Banner Elk and so on. You might enjoy perusing the State Climate Office feature on White Christmas probabilities at www.nc-climate.ncsu.edu/white-christmas.php, or having a look at the NCDC map at www.ncdc.noaa.gov/sites/default/files/White_Christmas_3%20v2.jpg.
Jan. 14, 2013 | Tags: cool sites, normals, snow

Answer: Using the rainfall measured at the Raleigh-Durham airport, we find that for the 8-year period 2005-2012 the accumulated rainfall anomaly is roughly -5.8 inches, for an average yearly deficit over that time of -.73 inches. Of course, an average for that short a period masks a lot of variability. We had very dry years in 2007 (-7.3 inches) and 2010 (-6.2), while it was quite rainy compared to normal in 2006 (+10.6) and 2008 (+7.4). The current yearly "normal" for RDU, based on a 30-year period from 1981-2010, is 43.3 inches.
Jan. 12, 2013 | Tags: drought, normals, past weather, rain

Answer: The 30-year averages for temperature are recalculated every ten years using a period that ends with the most recent "zero" year, and by international agreement serve as the "normal" temperatures until the next update ten years later. These normals were last calculated in early 2011, based on data from 1981-2010, and were published/distributed in mid-2011. For the most part, changes in temperature, at least for the United States, were about as expected given that the 1970s were a relatively cool decade that was dropped from the dataset, while temperatures in the early 2000s have been quite warm on average. As a result, the overall yearly "normal" maximum and minimum temperatures for the United States increased, on average by about .4 to .5 degree F for highs, and about .5 to .6 degrees for lows. Some more specific results might be seen as a bit surprising; for example the average July maximum temperatures ran about .5-1 degree cooler in the new normals than the old ones across a sizable section of the country just west from the middle Mississippi Valley. In addition, average minimum temperatures for the northern plains and upper midwest were much warmer than the older values, by about 2.5-3.5 degrees. You can see some maps comparing new normals to the older ones at www.climatewatch.noaa.gov/article/2011/the-new-climate-normals-gardeners-expect-warmer-nights-2.
Jan. 1, 2013 | Tags: maps & codes, normals

Answer: As you note, it is quite possible in our state to have very cold weather and occasional winters with frequent snow and ice, and occasionally large storm with heavy snowfall, but we also have our share of relatively snow-free winters. This all relates to how large-scale patterns in the middle and upper atmosphere vary from year to year, and even within a given winter. These long-wave patterns help determine the track and frequency of the smaller-scale frontal and low pressure storm systems that create precipitation more directly, and the longer wave pattern also helps create a background temperature tendency as to whether it will be cold enough for wintry precipitation when those systems pass through.

It is difficult to predict general outlooks with great accuracy or precision, but some skill can be obtained based on medium-term climate trends, on forecast phase and intensity of the El Nino/Southern Oscillation pattern, and more recently, using climate-scale computer prediction models. Generally, the outlook can be made with more confidence when there is a well-defined El Nino or La Nina pattern expected, since those influences tend to have fairly well-known impacts on the long wave patterns mentioned above. In the absence of those features, or when they are very weak, smaller-scale influences can become more dominant and result in a more variable pattern that can't be predicted very well more than a few days to a week or so ahead. That seems to be the case this year, as it now appears the Pacific will remain in a neutral phase through the winter. As a result, much of the U.S. is simply given an equal chance of being above, below or near-normal in terms of both temperature and precipitation for the Dec-Feb time frame, although the climate models do favor above normal temperatures across the southwestern U.S., and that is reflected in the seasonal outlook.
Dec. 24, 2012 | Tags: normals, winter weather

Answer: For the Raleigh-Durham airport, the "normal" yearly rainfall based on the 1971-2000 period was 43.0 inches, and that normal changed only a little 10 years later with the next update, based on 1981-2010, to 43.3 inches. By comparison, the most recent 10-year average, covering 2002-2011, is actually a bit higher at 44.3 inches, while the most recent 5-year average, for 2007-2011 is a bit drier at 41.5 inches. The driest and wettest of those last 5 years came back-to-back, with 35.8 inches in 2007 followed by 50.5 inches in 2008.
Dec. 10, 2012 | Tags: normals, past weather, rain