Armagh Observatory, 3rd February 2023: Armagh Observatory reports that January 2023 was warmer and slightly drier than average, though feeling damp, and sunnier than average.
Total precipitation was 65.1 mm (2.56 inches) including 4 trace values, that is, 64.9 mm if trace values are ignored. This is approximately 89.5% of the 183-year long-term (1838–2020) average January precipitation at Armagh and also of the most recent (1991–2020) 30-year average. The wettest day was the 11th with an unremarkable 11.0 mm of precipitation, followed by the 9th and 3rd with 7.0 mm and 6.0 mm respectively.
Although drier than average, the month was characterised by trace or relatively small quantities of precipitation on almost every meteorological day, that is, the 24-hour period ending at 09:00 GMT on the day observations are taken.
A meteorological day’s rainfall can therefore sometimes refer to precipitation occurring over two adjacent calendar days, while the accumulated rainfall from a passing weather system or storm can occasionally be divided across two distinct meteorological days. By convention, largely on the ground that the 15-hour period 09:00 to midnight is greater than the 9-hour period midnight to 09:00 and the idea that rainfall occurs randomly on average versus time, the precipitation recorded during a given meteorological day is associated with the previous calendar day.
With this understanding there were only 12 meteorological days with measurable precipitation greater than 1.0 mm this month, and only one (the 19th) totally dry. The absence of more than one totally dry day may help to explain why an otherwise drier than
average month felt damp.
A cool spell around the middle of the month (from the 16th to the 19th) produced hail on the 18th and snow on two days, namely the 17th and 18th. Snow lay on the ground, at least partially, for three days from the 18th to the 20th, with an average depth of
approximately 5 cm on the 18th. With a mean air temperature of 5.51 C (49.9 Fahrenheit), the month was approximately 1.3
C warmer than the 225-year long-term (1796–2020) average January temperature at Armagh (4.17 C) and 0.5 C warmer than the most recent (1991–2020) 30-year average (5.0 C).
As with precipitation, each day’s maximum temperature is conventionally taken to refer to the first of the two calendar days covered by each meteorological day. This is usually justified on the ground that a day’s highest temperature is more likely to occur during the afternoon. Conversely the lowest daily temperature is taken to have occurred on the calendar day that the observations are recorded, on the ground that a lowest temperature is most likely to occur in the hours after midnight and before 09:00 GMT. We note, however, that at Armagh, and depending on the time of year and the exact weather conditions, the highest temperature can sometimes occur after midnight and therefore on the same calendar day that the observations are taken, and the lowest temperature can often occur before midnight and therefore on the previous calendar day.
With this understanding the highest maximum air temperature, notionally the warmest day, this month was 13.4 C on the 10th, followed by 12.8 C on the 3rd and 12.1 C on the 5th. The 10th was the warmest January day for three years, that is, since 7th January 2020 (14.1 C).
The lowest maximum air temperature, or coolest day, was 2.4 C on the 17th followed by 3.2 C on the 16th and 4.0 C on both the 18th and 19th. It was during this cool spell that snow fell.
The highest minimum air temperature, notionally the warmest night, was 8.3 C conventionally assigned to the 25th followed by 8.2 C on both the 4th and 23rd. The lowest minimum air temperature, or coolest night, was -4.3 C conventionally assigned to the 20th followed by -4.0 C, on both the 17th and 21st.
However, on this occasion the three highest minimum daily air temperatures in fact occurred on the 24th (not the 25th), the 3rd (not the 4th), and the 22nd (not the 23rd). Similarly, the equal-second lowest minimum air temperature attributed to the 21st in fact occurred on the 20th. Such issues occur surprisingly often especially in winter. At Armagh, the lowest temperature achieved during a given meteorological day in December and January occurs on the previous calendar day on average approximately 50% of the time.
This month there were 8 meteorological days with night frosts, that is, minimum air temperatures less than or equal to zero Celsius, and 18 with ground frosts, days when the minimum grass temperature fell to less than or equal to zero. The coldest ground frosts were -10.8 C on the 17th (that is, during the night 16th/17th January), -10.6 C on the 20th, and -9.7 C on the 16th.
January 2023 was another remarkably quiet winter month, with no gales or named storms and with the strongest winds only approaching near gale a few times on the afternoon of the 12th.
As in 2022, gulls can now be seen or heard in or around Armagh on most days, showing that many of these former coast-dwelling scavengers have set up permanent colonies inland where waste food, rubbish dumps and landfill sites provide a more plentiful, readily accessible supply of food than the sea.
Comet C/2022 E3 (ZTF), the so-called “green” comet, was seen through binoculars from Armagh on the 19th and remained easily visible with binoculars throughout the month and then into early February given occasional favourable, though rare, clear skies.
With 52.4 hours of strong sunshine recorded during the month, almost the same as last January, the month was rather sunnier than both the 140-year long-term (1881–2020) January average at Armagh (46.2 hours of strong sunshine) and the most recent (1991–2020) 30-year average (47.4 hours). The sunniest day was the 20th with 7.0 hours of strong sunshine, followed by the 19th with 5.0 hours and the 31st with 4.7 hours.
These data refer to observations at Armagh Observatory, which has been recording the weather at Armagh since 1795.
FOR FURTHER INFORMATION PLEASE CONTACT: Mark Bailey at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; email@example.com; URL: http://climate.armagh.ac.uk/