Published: 2018-01-11 06:00:00
Updated: 2018-07-13 15:19:10
Posted January 11, 2018 6:00 a.m. EST
Updated July 13, 2018 3:19 p.m. EDT
What's the best day of the year to simply stay in bed?
A mattress maker compiled data on which day of the year each state is forecast to experience the coldest temperature and least amount of solar energy. Upon taking a look at the interactive map the company was promoting, I found the concept they used was not really a forecast, but kind of a fun exercise in using statistical information that may or may not be all that meaningful when it comes to specific planning, but is interesting to note.
The Sleepopolis map: Most miserable day by state was constructed by consulting climatological data, based on 30-year averages similar to those used by NOAA's National Centers for Environmental Information (NCEI). They found the day with the lowest mean daily temperature of the year for the capital city of each state, then looked up the day of the year with the lowest average amount of solar radiation for the same city, and declared that the date halfway between those two days is the "most miserable of the year." For North Carolina (the entirety of which is represented by Raleigh in this case), the site lists Jan. 11 as most miserable.
While it makes for an amusing conversation starter, perhaps, there is really too much year-to-year and week-in, week-out variability this time of year to put much stock in a single day as meaningfully most miserable, even leaving aside the degree to which one person's concept of the term might differ from another's. (We just finished a weekend with highs below freezing and lows that ranged between -4 and about 9 degrees across our area on Sunday, which might fit some people's concept of misery better than the average low of 32 and high of 55 for Jan. 11 over the past 20 years. Some others might find a humid August afternoon with a high of 103 to be the worst.)
In addition to the variability, long-term average conditions are quite slow to change over the course of a 4-6 week period surrounding the winter solstice, so picking a single day as the "coldest & darkest" misses that our lowest normal high temperature rounds off to 50.3 degrees from between Jan. 6 and 10 annually, while our lowest normal low rounds off to 30.6 degrees between Jan. 7 and 11. In terms of darkest, the "most miserable day" technique does use a solar radiation average that includes both the length of time from sunrise to sunset and long-term average daily cloud cover amount, but there, too, cloud cover is extremely variable on a given day year to year, and the length of the day, though it does increase following the Winter Solstice on Dec. 21, does so very slowly at first. In fact, rounded to the nearest minute, the length of the sunrise to sunset period remains at 9 hours, 44 minutes all the way from Dec. 17 through the 25, and by Jan. 11 has only increased by 12 minutes. (The rate that day length increases picks up through February and March reaches a maximum day-to-day change around the time of the equinox in late March, and then slows again as we head into summer.)
All that said, there's nothing wrong with having some fun with statistics, but if you take a look at the "Sleepopolis" map for our state or some other, know that the conditions represented by the date for each state are, on average, spread over a number of weeks and not concentrated on a given day, and that even that is really concentrated to the location of the state capital.
What about Jan. 11 itself? Here in Raleigh over the past 20 years (shown in the table above), our high on that date has been as cold as 32 and as warm as 70 (reaching 50 degrees or higher about 70 percent of the time). The most precipitation was just over six-tenths of an inch, and the most snow was just a trace.
As for 2018, it appears we'll see a low around 40 and a high that may edge into the low 60s late in the afternoon or evening on Thursday the 11th, with an increasing chance of rain as the day wears on. Given that we remain in moderate drought from around I-95 west, and that we're coming off a record-setting 201 consecutive hours at or below freezing at the RDU airport, some needed rain with temperatures reaching around 60 doesn't sound very miserable at all!