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Answer: Standard sea level pressure can be expressed in a number of different ways. For example, 14.7 pounds per square inch, 760 mm Hg, 29.92 inches Hg, 1013.25 millibars, 101.325 kiloPascals, 1 atmosphere and so on. Since they all represent the same pressure, you can use those values to convert between units.
Nov. 14, 2009 | Tags: general meteorology, normals

Answer: As you imply with your question, it is certainly possible to have below normal rainfall while receiving rain in trace or rather small measurable amounts fairly often. This year has fit into that category to some extent. Through the end of October, we had six months with above normal number of days with at least one hundredth of an inch of rain, while four months were below normal. In total during that time, 104 days brought measurable rain, when the normal for the first ten months of the year is 95.
Nov. 12, 2009 | Tags: normals, rain

Answer: Climate statistics for the Raleigh-Durham airport indicate an average of about 73 days each year with a low temperature at or below freezing, while there are about 4 days per year with a high temperature at or below freezing. As a very simplistic first approximation, this would suggest about 69 freeze-thaw cycles. Of course, whether a specific location or material freezes solidly or thaws completely can be impacted by its location, exposure to open sky or lack thereof, its exposure to wind that might reduce the time required for the item to rise or fall to a changed ambient temperature, and the amount of time on a given day that the air temperature spends significantly above or below freezing.
Nov. 2, 2009 | Tags: cold, normals, records/extremes

Answer: While not exactly the same in long-term averages, the two cities' weather with respect to the type of events you asked about are close enough that other considerations would probably be more important to you, thanks to something of a balance between Raleigh's more northerly latitude and Charlotte's more westerly longitude. In terms of winter weather, both cities average about 4-5 "snowfall events" and about 4-6 "sleet and freezing rain events" per year, with some overlap between those two sets of numbers due to the tendency for winter storms here to produce multiple and rather variable precipitation types. Raleigh averages a little more snow overall, at 7.6" annually versus 5.8" for Charlotte. Thunderstorm days for the region run about 40-50 per year, with Charlotte averaging about 2-3 more days than Raleigh. Most of this information is summarized in various portions of the State Climate Office web site at www.nc-climate.ncsu.edu.
Nov. 1, 2009 | Tags: cool sites, normals, snow, thunderstorms

Answer: According to a climatology of severe weather for central NC produced by our local NWS office, the Raleigh county warning area (covering 31 counties) averages about 5 tornadoes per year. Comparing tornado rates for different parts of the country requires balancing the area involved in the estimates, and a few different methods have been applied in various studies and technical reports. For example, a method estimating the number of tornadoes occurring within 25 nautical miles of any given point shows a value of .4-.8 per year for central NC versus about 1.0-1.4 per year over central OK in the heart of "tornado alley." A similar statistic for F2 and stronger tornadoes shows about 5-15 per century for our state versus about 35-40 there. Another estimate of the fraction of land surface disturbed by tornadoes each year in NC is about 2.1 x 10^-4, compared to around 4.4 to 4.8 x 10^-4 in the most active regions of the country. Finally, an analysis of tornadoes from 1950-2003 that counted tornado events within 2-degree latitude by 2-deg longitude boxes across the U.S. showed 303 in a box including our area, while boxes in the central plains states ranged from around 700 to as high as 942. Taken all together, then, we see that the "tornado alley" areas have about 2-3 times as many tornadoes over a given area as we do overall, but if you exclude the weak F0 and F1 tornadoes and look in particular at the more powerful F2 intensity and higher storms, those are about 4-5 times more likely in states like Oklahoma than they are around here.
Oct. 29, 2009 | Tags: normals, severe weather, tornadoes

Answer: According to a severe weather climatology for central North Carolina compiled by the Raleigh National Weather Service office, about 43 percent of our tornadoes form in the spring, 26 percent during summer and 23 percent in the fall, with the greatest percentage occurring between March and June. Over half of the tornadoes in our area form during the later afternoon and early evening, between the hours of 3 and 8 pm.
Jul. 30, 2009 | Tags: normals, tornadoes

Answer: That would be quite an exaggeration, although it is certainly the case that a passing shower or thunderstorm occurs there on a lot of days during those months. On average, Orlando receives measurable rainfall 14 days in the month of June and 17 days in July, compared to only 5 days in the months of November and April. For another point of comparison, Raleigh averages 9 days with measurable rain in June and 11 in July.
Jul. 14, 2009 | Tags: normals

Answer: What you're really referring to are the daily "normals" for max, min or mean temperature, which can differ a bit from the actual 30-year averages for the same period, which encompasses the three decades ending with the most recent "zero" year. The National Climatic Data Center ensures a smooth curve for those normals, one that cycles cleanly up to summer warmth and down to winter cold, by computing monthly averages from the data, fitting a smooth curve called a cubic spline to those 12 data points, and then basing daily normals on the value of that curve at any point in the year.
May. 28, 2009 | Tags: normals

Answer: It may seem that both the high and low would be either near normal, above or below, both in the same direction. However, when the air is quite dry, skies are mainly clear and winds are light, the "diurnal range" from low to high temperature can be notably larger than the difference between the normal low and high. The opposite often holds true for moist, cloudy and windy days.
Jul. 10, 2009 | Tags: clouds, normals, winds

Answer: As of mid-April, the Raleigh-Durham airport was at just over 12 inches, a little under an inch below normal since January 1st. A map of precipitation amounts based on combined rain gauge and radar data, available through water.weather.gov indicated an average across the broader Triangle area that was around 3-4 inches below normal, or about 70-80 percent of normal rainfall.
Apr. 17, 2009 | Tags: normals