Annual Weather report 2021

 Much of the commentary about weather will have been revealed already by the "year to date" charts as we have progressed through the toenail of 2021.  So I will try in what follows to present stuff in a slightly different way.  For those who wish to explore the data for other gems, I have loaded it to a Google Sheet.

The overall summary would be a wet, about average temperature, and calm year.

Rainfall

The 4th wettest year since 1975.  The fall of 211.8 mm was 146% of median annual fall and 137% of mean annual fall.

The data prior to 2019 is all from the BoM site close to the Airport.  I have compared the results for the last 3 years between the two sites and they are very close (within 10mm) for 2020 and 2021 but the airport recorded an extra 50 mm in 2019.  That was a very dry year at both sites and the difference appears to accumulate through a lot of events where the airport scored a few mm more, possibly reflecting storm cells moving along the coast.

Looking across the months, the  211.8 mm in December 2021 was the wettest December in the 45 month series.  With 145 mm August was the 3rd wettest while March and May were both ranked 4.  Only 3 months recorded below median rainfall.

Temperatures

The average temperature for the year (calculated as (avg daily min + avg daily max)/2) was 15.51C compared to 15.42 C for the long term average.  (Note that the long term value has been adjusted to allow for the BoM maximum being (on average) lower than the values recorded on my WS, as the latter has less exposure to the cooling sea breezes.  The next chart shows the difference in average temperature x month.

Looking at the components of the calculations nearly every minimum value was above average and nearly every maximum value was below average.  This is consistent with cloud cover preventing warming during the day, but also preventing back radiation cooling at night.    (It is of course always possible that my sea-breeze adjustment has overcompensated.)

Minimum temperatures

The term 'average' can include both mean and median.  For minimum temperatures according to my combined series there is effectively no difference between these indictors.  They are shown in the following chart together with the average 2021 daily minimum by month.  The 2021 series is very similar in shape to the average series charted above.

An annual time series of daily average minimum shows a upwards trend with a fairly good correlation coefficient (0.53).

Maximum temperature

Much the same story as with the minimum temperatures: long term mean and median almost identical for each month and the shape of the curve for 2021 very similar.  There is enough similarity in the graphs at this level to make me think that the adjustment process - which I have done separately for every month -  is not very far out of whack.  

The time series again shows an upwards trend, with an even higher value for R2 (0.63).  I'm sure someone from Institute of Public Affairs with a PhD in Inuit Studies (or some background of similar irrelevance) would argue the point!

Humidity

There is a fairly consistent pattern of humidity through the day.  Clearly a drop from the quite stable level overnight to mid afternoon then rising again.  Also clear that 2021 was damper than the other 2 years (especially 2019).

The 2 standard times match closely with the morning "drop-off" and the nadir of the pattern.  I charted the monthly averages recorded at my WS for the standard times for each year.

For the 0900 hrs set the three years show a similar pattern until October: I have no idea why they differ so much in November and December.

The chart for 1500 hrs humidity is all over the place, albeit within a fairly small range.  Possibly the most interesting aspect is the downhill side in the second half of 2019: no wonder the bush was dry by the end  of the year!

Wind

I looked at 2 measures of wind.  The average maximum gust per hour and the average daily wind run.

The two series are 99% correlated!  Winds were relatively calm at my WS in 2021.  The Airport is usually somewhat windier than home.

To put the average runs into context:

• in "The Home of the Blizzard" Mawson comments about a day in which the wind averaged 90mph for 24 hrs.  That equates to a run of close to 3,500 kms.  He commented on the same period of the wind reaching 200 mph. 
• Checking BoM climate data on line for Hogan Island - Bass Strait - gives average per month daily runs of 735 km [April] to 861 km [Sept].  
• The same source gives an average daily run for September at Maatsukyer Island (south of Tasmania) of 971 km.

To compare the pattern across months I have calculated average daily run.  As expected 2021 was the calmest year and 2019 the windiest.

For comparative purposes and giving a much wider view, here is an ABC article covering BoM's national view of 2021.