METAR EGBB 281150Z 11012KT 080V140 9999 SCT018 SCT022 M02/M07 Q1018
TAF EGBB 281100Z 2812/0112 06012KT 9999 SCT030 TEMPO 2812/2818 09015G25KT 1000 SHSN BKN004 BKN020CB
The Met data above prompted a question from a fellow pilot: how can cumulo-nimbus (CB’s) develop in sub-zero temperatures? Surely they are a phenomenon of warm summer days?
The short answer is no, they can occur at any time of year. The fundamental requirement is unstable air which relates to its vertical temperature profile, not its actual temperature. Because sub-zero air holds less water vapour than warm air, we might expect less precipitation (in weight terms) out of a winter CB. In addition, the CB’s may not be as ‘vigorous’ as in summer.
If you want to know more take a look at this analysis:
Winter CB's