Change in month BUT not change in weather

The cold northeasterly on Sunday meant anther cold day with the thermometer not exceeding 1.9C being 5.2C below average. At 1310 the first flakes of light snow were observed getting heavier a little later. It was wet snow that melted on hard surfaces, a little remained on grassed areas. The snow turned very light in the late afternoon and had ceased by 1700. This precipitation added another 1.7mm to the mknthyk total that reached 101.6mm.

The thermometer remained above freezing all night hovering around 1.6C.

Monday dawned with yet more low cloud limiting visibility at first to 900m.

January 2021 Review

The cold end to December continued during the first ten days of January when no daytime maxima or night minima were above the 37-year average. Frost occurred on every night with a severe frost in the early hours of the 1st when the thermometer dropped away to -6.7C making that the coldest night since 3rd February 2019 when the thermometer then dropped to -11.3C.

The four days after the 7th were noted for the persistence, by day and night, of fog that at times limited visibility to 200m. Also noteworthy were the very cold days with a maximum of 0.4C and 0.6C on the 7th and 9th respectively. In fact during this period we had 32 hours of continuous below freezing temperatures.

Although the snowfall was light, what little snow that fell soon melted away being observed on the 1st, 2nd and 6th.

The weather changed again on the 10th due to a westerly air steam that brought warmer air and the warmest day all month. The 11th saw the temperature rise again to a maximum of 9.1C, which made it the warmest day since 26th December bringing to an end a run of 15 consecutive below average days.

The World Meteorological Organisation (W.M.O.), using five leading international data sets and new data from the EU Sentinel satellites show that 2020 rivalled 2016 as the world’s warmest year being 1.25C above the long-term average. Key factors were the level of heat in the Arctic and Siberia. Europe itself set a new record being 0.4C warmer than 2019. All five datasets surveyed by WMO concur that 2011-2020 was the warmest decade on record, in a persistent long-term climate change trend.

It would be appropriate to mention that 2020 was the warmest year I have recorded in Marlborough since the station was setup in 1984 with a mean temperature of 20.54 when the average was 17.45C. Other data for 2020 saw a record mean temperature for Spring being 2.5C above the 36-year average and May another record, which was 3.09C above average. We endured the hottest August night since 1984 with a minimum of 19.2C being 7.6C above the average.

Records for rainfall were also set in 2020 with the wettest April and October days with 33.2mm and 49.9mm respectively. The monthly rainfall for October was also a record with a total of 191.0mm.

It is interesting to note that raindrops are normally represented in the shape of a teardrop but in reality they are not. Initially, high up in the atmosphere, they are spherical in shape then as they fall their shape changes when they collide with one another. Finally, air resistance causes the bottom of the drop to flatten and curve upwards, resembling the shape of a jellybean. A typical droplet of drizzle is 0.1mm in diameter; a typical raindrop is 4mm in diameter with the largest recorded raindrop measured at 8.8mm in diameter.

A south-westerly air stream arrived on the 18th bringing mild air and temperatures by day and night well above the average rising to 10.7C on the 19th being 3.6C above the 37-year average. This was followed by a very mild night when the thermometer did not drop below 9.1C, which was 7.7C above average.

Storm Christoph arrived on the 20th that produced a very wet day with 23.2mm of rainfall in total and the wind gusting for many hours in excess of 25mph and a peak gust of 41mph. There followed four days of mild, moist air when the thermometer rose well above the average. We enjoyed a maximum of 11.7C on the 28th, not seen since 2rd December, which was 4.5C above the 37-year average.
Snow fell overnight of the 23rd/24th that by morning measured 5cm in depth being level snow due to minimal air movement. The equivalent rainfall from this snow, after slowly melting what was contained in the 5” cooper rain gauge, measured 5.2mm.

The month concluded with the wind swinging into the northeast limiting the temperature and producing a wind chill. The maximum on the 31st was only 1.9C being 5.2C below the average maximum with the first flakes of light snow observed at 13.10.

January was notable not only for the many dark, wet and gloomy days but that snow fell on six separate days and five days with snow cover in excess of 50% at 09.00. There were also five mornings that started with fog.

The facts bear out the memory of a dismal month with global sunshine (100w/sq. m.) of just 53 hours, the lowest I have recorded since this instrument was installed in 2009 and 21 hours below the 11-year average. Actual sunshine totalled just 27 hours.

The total precipitation from rain, drizzle and melted snow totalled 101.6mm, which was 11.1mm above the 37-year average. My records show that the two contrasting years were in 1997 with only 9.4mm and the extremely wet January of 2014 when 219.1mm was recorded.

With the above average cloud and rain it is not surprising to find that the mean temperature was 0.8C below the 37-year average. Analysing the data for mean maximum and mean minimum I found little difference being -0.7C and -0.9C respectively. The mean temperature of 3.2C was not exceptional as in 1997 the mean temperature was -0.15C and by contrast the balmy January of 2007 gave a mean of 6.53C. Air frosts occurred on 18 days, the coldest being -6.7C on the 1st.