November 2018 is showing very mild temperatures in the N.E. of Italy, with only few days observing temperatures below average (see Italy: First cold spell of the season). It might be possible that the current November will be one of the warmest ever recorded (especially regarding the minimum temperatures), but before claiming that we need to wait few days still.
However, in the past (also quite recently) November has observed coldwaves with snow also in the Po valley (e.g. 2005, 2008). I have considered the temperature data from 1973 to 2017 from Treviso S. Angelo in Veneto. Unfortunately, some daily data are missed in few years, thus the monthly average is not completely exhaustive (especially for the years 2005 -2012 where I have used data from Treviso Istrana, which is only few miles from S. Angelo). The idea is to give a general overview of the historical temperatures in November in the Veneto plains.
In Figure1 is shown the monthly maximum and minimum temperatures average.
It is clear how the monthly average temperatures in the 00s have been only few times below the long term average 1981-2010 (4.6/12.7 °C). The warmest November occurred in 2014 , instead the coldest one in 1988 for both minimum and maximum values. The minimum temperatures, especially, tend to be higher than the long term average in several years during the 00s, with only 3 years observing lower values (2001, 2007 and 2011) (Figure2).
It is interesting to notice how the frequency of mild temperatures in November is increasing from the end of the 90s, instead in the 70s and 80s only few years observed mild temperatures in November.
If we consider the top and bottom 10% of both the minimum and maximum temperature distribution (thus the coldest and warmest November), the analysis has shown that the coldest November (the lower 10% of the distribution) occurred mainly in the 80s, and no one is observed after 1993. Instead the top 10%, thus the mildest November, is observed only in the 00s, which explain what found in Figure2. In conclusion, it seems that there is a (positive) shift in both maximum and minimum temperatures in November, with the last two decades observing the highest values.
I have considered the data from Treviso airport (N.E. Italy) to sum up the monthly analysis (Figure1) in the N.E. of Italy.
The mean minimum and maximum temperatures (11.84/21.17 °C) have been considerably above the 1971-2000 average (8.8/18.9 °C). This is due to the continuous mild conditions especially between the first and second decade, with no cold spells during the whole month (Figure1) and numerous days with maximum temperatures above 20 °C and minimum above 10°C.
In fact, the number of days observing maximum temperatures above 20°C is 22, with 15 consecutive days (in the first two decades) when the maximum values never fall below 20°C. Moreover, during this period, for 3 consecutive days the maximum values reached 24°C, almost 6°C above the climatological average, and, during the whole month, this values has been reached 6 times.
During the long period of very mild maximum temperatures, also the minimum values were well above the average, with 18 consecutive days observing minimum temperatures above 10°C, 5 consecutive days above 13 °C (almost 6°C above the climatological average). To notice that, even if the maximum values decreased during the intense rainfall event occurred in the last week of October, the minimum values stayed high due to the strong southerly winds blowing from the Adriatic Sea which caused still mild conditions and due to the continuous overcast conditions which have limited the radiative cooling at surface during the night.
The observed rainfall (135 mm) ,instead, has been above the average (92 mm). This is due to the intense event occured in Italy during the last week of October,which has caused floods in several areas. Thus, though the total observed rainfall is above the climatological average, it was not evenly distributed during the month, with 20 consecutive days (between the 6th and 26th) with no rain (anticyclonic conditions), and only 9 with observed rainfall, 6 of them consecutively during the last week of the month.
Using the data from Heathrow airport (1950-2018, Met Office), I have tried to sum up the analysis on both minimum, maximum temperatures, number of days with air frost and cumulative rainfall during October 2018 and compared with the average 1971-2000 (Figure1).
Both October 2018 minimum and maximum mean temperatures (8.50/16.50 °C) are slightly above the 30 years average (8.17/15.70 °C), especially the maximum values. This is due to the mild temperatures observed in the first two decades, which were ‘counterbalanced’ by the cold spell occurred during the last decade which has caused a day of air frost (the first one after 7 years, thus after 2010).
Regarding the rainfall, the total cumulative precipitation observed (61 mm) is slightly above the monthly mean (60 mm) and it occurred mainly in the second decade.