WRAL.com: Raleigh, Durham, Fayetteville

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Answer: It isn't clear if you meant days with highs that fall below those thresholds or lows, so we'll take a quick look at both. Checking 69 years of records from the Raleigh-Durham airport, we find that the longest stretch of days with a high temperature reaching 30 degrees or less was 4 days in a row during January of 1970. Of course it isn't as difficult here to have a notable string of days in which the low temperature dips to 30 degrees or below - we had 32 straight days meeting that criteria from early February to early March of 1968.

Twenty degrees makes a tougher threshold to meet, especially for a daily high temperature. In fact, only once have we had two consecutive days with a high of 20 or less at RDU, those being January 8th and 9th, 1970. It is a little more common to string together some days with a low of 20 or colder, the longest stretch being 9 in a row during January of the very cold winter of 1977.
Apr. 23, 2013 | Tags: cold, records/extremes

Answer: It's easy to understand why you would ask the question, but March 2013 did not end up being a record cold month. However, it didn't miss by all that much, either! In 69 years of records from the Raleigh-Durham airport, this was the 5th coldest on record with an average monthly temperature of 44.9 degrees F (Note that 5 other years were colder, but two of those tied for 4th coldest). This year came in 6.2 degrees below the normal temperature for the month, and a full 15.5 degrees colder than last year (however, 2012 did set the record for warmest March at RDU). The coldest March out there was that of 1960, with an amazingly cold average temperature of 37.6, which was a rather large 4.4 degrees colder than the 2nd chilliest year of 1947. We also checked the records from a site on NCSU property that has a period of observations going back to 1892, and March 2013 was also the 5th coldest in that record, out of 118 years listed (and again, with two of the colder years tied for fourth place).
Apr. 11, 2013 | Tags: cold, past weather, records/extremes

Answer: In records going back to 1944 at RDU, the high temperature has been 20 degrees or colder 13 times. This includes two days, Jan 16, 1972 and Jan 21, 1985, with highs of 17 degrees. We also maxed out at 18 degrees there on Feb 17, 1958 and Jan 19, 1994.

In the last year or two, the local National Weather Service has produced a set of climate record data for the Raleigh area called ThreadEx that combines observations from several successive observing sites to run the start of the data set back to 1887. Checking that database, we find that the lowest high observed for the Raleigh area was 10 degrees on Feb 13, 1899. There were also observed highs of 13 degrees on Feb 12 that same year and 16 degrees on Dec 30, 1917.
Mar. 23, 2013 | Tags: cold, past weather, records/extremes

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: Because that temperature is 16 degrees above the freezing point of water, you would not freeze. However, 48-degree water is still quite cold relative to a human's body temperature and, assuming you were not wearing special protective clothing and remained in the water, you would rapidly lose heat to the water and either perish from exhaustion and drowning within about 45 minutes to an hour, or from hypothermia in 1-3 hours. For a brief overview of what happens upon immersion in cold water, see www.ussartf.org/cold_water_survival.htm.
Feb. 15, 2013 | Tags: cold, lakes and rivers, weather & health

Answer: There were some instances of scattered frost in late October and early November, and on the morning of Friday, November 2nd a large portion of central NC recorded low temperatures in the range of 28-32 degrees. The National Weather Service considered this occurrence to mark the end of the 2012 growing season.
Nov. 16, 2012 | Tags: cold, dew/frost

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 28, 2009. The average date for a first freeze is October 29th, with a standard deviation of +/- 9 days. We don't really have any good way weeks or months in advance to project the date this will occur in a given year, although you could argue for an earlier time if seasonal outlooks call for below normal temperatures, and vice versa. This year, however, seasonal projections only offer up an equal chance of above, below or near normal temperatures for the October-November time frame, so it may be reasonable to expect this year's first freeze will come somewhere in the range of that average period covering the latter third or so of October and the first third or so of November.

Regarding frost - under the right conditions, it 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. Of course, the timing can also vary a good bit from location to location within our viewing area owing to localized topography and land use. Hopefully the cooling temperatures that should develop fairly soon will help with your stinging insect troubles!
Oct. 7, 2012 | Tags: cold, weather & health

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 28, 2009. The average date for a first freeze is October 29th, with a standard deviation of +/- 9 days. We don't really have any good way weeks or months in advance to project the date this will occur in a given year, although you could argue for an earlier time if seasonal outlooks call for below normal temperatures, and vice versa. This year, however, seasonal projections only offer up an equal chance of above, below or near normal temperatures for the October-November time frame, so it may be reasonable to expect this year's first freeze will come somewhere in the rnage of that average period covering the latter third or so of October and the first third or so of November.

Regarding frost - under the right conditions, it 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. Of course, the timing can also vary a good bit from location to location within our viewing area owing to localized topography and land use.
Sep. 25, 2012 | Tags: cold, dew/frost, records/extremes

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 28, 2009. The average date for a first freeze is October 29th, with a standard deviation of +/- 9 days. We don't really have any good way weeks or months in advance to project the date this will occur in a given year, although you could argue for an earlier time is seasonal outlooks call for below normal temperatures, and vice versa. This year, however, seasonal projections only offer up an equal chance of above, below or near normal temperatures for the October-November time frame.

Regarding frost - under the right conditions, it 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. Of course, the timing can also vary a good bit from location to location within our viewing area owing to localized topography and land use.

Finally, the first snowfall is kind of like the first freeze, except even more variable (some winters we never have any measurable snow) so that there really isn't any mechanism by which we can predict a time for the first snow with any confidence more than a few days in advance.
Sep. 9, 2012 | Tags: cold, dew/frost, snow

Answer: The answer to your mystery is that the overhanging objects you mentioned can actually lead to a crucial difference in the two cars' skin temperatures.

Frost can form on a surface if the temperature of that surface falls to the dew point or below. In the case of your cars, the one in the driveway that faces upward to open, clear sky will lose energy by way of upward directed infrared radiation with relatively little energy returned from the sky, allowing it to cool to a sufficiently low temperature, usually a colder temperature than the ambient air a few inches away. The vehicle in the carport also loses heat radiatively, but this loss is partially balanced by downward radiation emitted by the ceiling of the carport so that the sheet metal or windshield temperature of the covered car stays a little above the dew point and leaves the car free of frost.

Parking under a tree can have the same effect, as the branches, leaves and to some extent trunk of the tree are giving off infrared radiation that is absorbed by the metal and glass of the car, partially offsetting the heat being transported away by the car's own infrared radiation, and leaving it a little warmer than it would be if fully exposed to open sky.

It is worth noting that if the air is sufficiently dry, so that the dew point (which may also be called the frost point when it is 32 degrees F or lower) is very low, it is possible for both the covered and uncovered cars to remain frost-free even in subfreezing weather. Likewise, a significant amount of persistent wind can sometimes keep the air mixed around the cars and prevent the surface of the exposed car from cooling as much as it would otherwise, and may prevent frost from forming as well.
Mar. 15, 2012 | Tags: cold, dew/frost, humidity/dew point