Warmest December day for six years

On Friday the thermometer rose to 14.0C, (6.0C above the 37-year average) making it the warmest day since 18th & 19th December 2015 when the thermometer reached 14.4C. There was a little brightness and a little rain, just 0.2mm, that took the monthly total to 72.6mm, which was 79% of the 37-year average.

The south to southwest breeze was again strong with a maximum gust of 28mph.

The temperature only fell 2.3C overnight with a low of 11.9C being a significant 9.3C above the average.

Saturday dawned a little brighter but that was soon overcome by increasing cloud from yet another weather front bringing rain late morning.

December 2021 Review
Dull and dry

The 27 hours of sunshine hours for the UK were 38% less than the national average with Marlborough figures similar totalling just 26.4 hours. There were 15 days when the sun never made a visual appearance. The UV figures were worse as there were 20 days when it was so dull and gloomy no UV light was registered.

The rainfall total for December reached 72.7mm being just 79% of the 37-year average or almost 20mm below. Evaporation from ground sources and plant life at this time of year is minimal but 6.8mm of equivalent rainfall was lost to the atmosphere on the drier days. The wettest day brought 10.1mm followed close behind with 9.8mm on the 27th.

The month began with topsy-turvy weather that brought alternating warm and cool days and an air frost with a minimum of -2.2C in the early hours of the 3rd.

The news was full of images and facts about the second named storm Barra that approached on the 5th. It was the shortest period between named storms since 2018 and named by Met Éireann. On the 7th we felt the effect of the storm with wind gusting to 31mph, but very modest compared to the considerable destruction in the north of the country.

A ‘weather bomb’ was declared by the Metrologocal Office on the 7th, or explosive cyclogenesis. That event occurred when the central pressure of the depression to the west of Ireland fell more than 24mb in a 24 hour period, from 1017mb to 961mb from 06.00 on the 6th to 06.00 on the 7th.

It was all change from the 11th as we enjoyed a sequence of 5 days when the wind backed into the southwest bringing warm air. A peak of 12.6C was recorded on the 12th, which was 4.6C above the 37-year average. There were eight consecutive days with above average maxima before the cooler air on a north-easterly breeze, that arrived on the 17th, took effect.

A peak barometric pressure was recorded on the 17th of 1041.7mb as an anticyclone moved north from the continent. It was the highest barometric pressure since 27th February. As it eased to the north then east the wind veered into the northeast.

There followed a brief period of cooler weather as a north-easterly set in with a sharp air frost on the 22nd as the thermometer dropped to -3.2C making it the coldest night since 17th April.

Christmas Day and Boxing Day dawned with fog that in the early morning limited visibility to 400m due to warm moist air brought on a south-westerly and southerly air stream.

Due to the persistent thick cloud the diurnal range of temperatures was minimal with a variation of less than 3C between maximum and minimum on the 25th and 26th. Earlier in the month there were variations of 10C or more on the three days of the 11th to 13th.

Exceptional warmth from mid-Atlantic, from around the Azores area, arrived on the 29th that saw the thermometer soar to a maximum of 13.9C and the 31st higher again to 14.0C. This latter peak was exactly 6.0C above the 37-year average. However, this was not a record as on the 18th and 19th of December 2015 the thermometer rose to 14.4C on both days. During the evening of the 29th/30th the thermometer did not drop below 13.2C, which was a significant 10.9C above the 37-year average.

On the 26th, a study from the charity Christian Aid identified 10 extreme events that each caused more than $1.5bn of damage. Earlier in the month I discovered the following article from the World Meteorological Organization.

As the economic and human impacts of extreme weather and climate change increase, forecasts not just of what the weather will BE, but of what the weather will DO are vital to save lives and livelihoods.

As a result, there is a paradigm shift towards impact-based forecasting, driven by the international meteorological and humanitarian community and facilitated by leaps in science and technology.
“Over the last 50 years there has been a five-fold increase in recorded weather, climate and water-related hazards, with long-lasting socio-economic consequences. The number of deaths has decreased thanks to increased availability of accurate and timely warnings. But it is still unnecessarily high, as a result of lack of understanding of potential impacts,” says Cyrille Honoré, Director, Disaster Risk Reduction and Public Services Branch at the World Meteorological Organization. “This needs to change,” he says.

The World Meteorological Organization has consequently expanded its Guidelines on Multi-hazard Impact-based Forecast and Warning Services, first produced in 2015 as a standard reference text.

The guidance provides practical information and case studies on how to move from weather forecasts and warnings issued by National Meteorological and Hydrological Services to the provision of impact-based forecast and warning services of multiple cascading hazards (for instance a tropical cyclone, which triggers flooding, storm surge, wind damage, impacts on infrastructure, transport and energy and on health systems).

The new edition benefits from significant research into exposure and vulnerability and incorporates extensive input from both service providers and the user community. It underlines the paramount importance of partnerships and dialogue between scientists, forecasters, disaster managers, community leaders and decision-makers.

Anticipatory Humanitarian Action.
The publication also embraces the concepts of anticipatory actions – using weather and climate information to underpin humanitarian interventions such as shelter strengthening before a tropical cyclone makes landfall and using forecast-based financing to limit the impact of a drought or flood.