Weather report December 2022

 A somewhat schizophrenic month with a wet cold patch developing into a hot dry finish.

A particularly interesting set of records come from 26 December when around 1330 hours my WS was reading 31.6C and the airport site showing 24.2C.  That situation continued until late afternoon when the wind at the Airport swung from NE to N and dropped a few kph, around 1600hrs, and the temperature quickly rose, reaching 29.7 at 1832.

Rainfall 

We ended the month with 110.6 mm well above the median fall of 65.8 mm  and the (very low) 43.6 mm recorded in December 2021.

The concentration of the rain in the early-mid part of the month is indicated by the blue line (LH axis) while the squally nature of the events in indicated by the pale orange line (RH axis).

Temperatures

The anomaly, mainly using BoM data from the airport, ended up at -0.91C which is a reasonably large divergence from zero.  I have added "mainly" as the BoM site was AWOL for 6 days early in the month due to maintenance issues.  (I shall examine the scope for using my weather station (WS) data for the anomaly going forward and report in a separate post.)

Here are the extremes from my WS.

On the topic of temperature generally I have done some research into time series for the BoM stations at Mallacoota and Gabo Island (the latter comes with a side-serve of Green Cape) The conclusion is that I am not confident to say that they show the expected climate change towards  warmer temperatures (but I would be confident to say they do not support change towards cooler temperatures).  I will comment on Hot spells and cool spells in the next two subsections.

Minimum temperatures

The average minimum temperature for the month was 12.75C, 1.01C below the mean and somewhat below last year.

The time series looks like a profile of the Alps (with Mt Blanc a feature in 2016).  A linear trend does slope upwards, but not a significant trend.

The equivalent to a Heat Wave is probably a Cold Snap and an equivalent definition would be " 3 consecutive days with both minimum and maximum significantly below long term averages".  I haven't researched the history of Cold Snaps in the same was as I have for Heat Waves (see links above) but for December the following analysis applies:

• 7 days with maximum more than 1 SD below average;
• 8 days with minimum more than 1 SD below average;
• 3 days with both extremes more than 1 SD below average; 
• No periods of 3 consecutive days with both extremes more than 1 SD below average.

Maximum temperatures

As I have explained before consideration of long term maximum temperatures is a little complicated as the BoM site is very exposed to cooling sea breezes, while my WS is somewhat sheltered from them.  I have adjusted the BoM data in my long term series of monthly maxima to allow for this.  Looking at this adjusted series,  the mean temperature of 22.3C was 0.8C below the long term average (and about 1 degree below 2021.

Again there is a lot of variability in the time series of average temperatures and the trend, while upward-sloping is not significant.

In terms of Heat Waves:

• 3 days with maximum more than 1 SD above average;
• 5 days with minimum more than 1 SD above average;
• 2 days with both extremes more than 1 SD above average; 
• No periods of 3 consecutive days with both extremes more than 1 SD above average.

Humidity

Here is a chart of daily readings at the standard times.  The number of times the 1500hrs reading is the higher is unusual, as is the number of times the 0900 reading was below 90%.  

For both standard times the average mean rH was above the longer term average but below last year's equivalent value.

Wind

The windiest day was the 8th, with a run of 214km (the 108th longest recorded by my WS).  The daily readings show the continual passage of squally events.

Overall, windier than last year but slightly under average.