According to the Portuguese Institute of Sea and Atmosphere (IPMA), since 1931 there had not been a December this hot, with the average maximum air temperature reaching 15.72 °C (plus 1.84 °C), the second highest value of the last 90 years (in 2015 it reached 16.21 °C).

The average minimum air temperature value was 7.66 °C, also higher than normal (plus 1.62 °C), being the ninth highest value since 1931.

As for the average air temperature, the IPMA points to an average value of 11.69 °C, 1.73 °C more than the normal recorded in the period 1971-2000.

The month of December 2021 had daily values of maximum and minimum air temperature almost always higher than the monthly average value, particularly the maximum temperature, according to IPMA, which highlights the last day of the year, with values that exceeded or equalled the previous December highs in about 10 percent of stations on the mainland.

The IPMA highlights the value recorded in Zambujeira, 26.4 °C, "a new maximum for this season" and which represents "a new extreme for the month of December in mainland Portugal since 1941".

The average value of the amount of rainfall in December (93.4 mm) was below the 1971-2000 normal value, corresponding to 65 percent.

During the month of December, the IPMA highlights the 20th of the month, "with precipitation sometimes strong and accompanied by thunderstorms in the regions of Barlavento Algarve, Baixo Alentejo and the region of Setúbal and Sado Valley", and the period between 23 and 26, "with moderate and persistent precipitation in the northern and central regions".

At the end of December 94 percent of the territory was in a situation of meteorological drought, according to IPMA, which points to a "slight decrease" in the percentage of territory in the class of severe drought and an increase in the class of moderate drought.

The IPMA report indicates that at the end of December the meteorological drought situation remained in almost the entire territory, with a slight decrease in the percentage of the territory in the severe drought class and an increase in the moderate drought class.

According to the meteorological drought index, more than half (57.7 percent) of the territory was in weak drought, 27.3 percent in moderate drought and 8.7 percent in severe drought (12.6 percent in November).