December 2019: very hot and dry

Sun in smoke

Red Sun 17 Dec

After the first week, each week in December was very hot, reading up to 5.9° above normal. Both days and nights were hot, but only one record was set: 42.2° on the 21st was the hottest December day. That was well below the record hot day of 44.9° set on 11/2/17.
Twenty mornings were cloudless which was twice the usual number. Smoke from mainly coastal bushfires reduced visibility to 15 km or less from the 8th to the 25th. Early in the month, rain fell on three days, the highest reading being 12.4 mm on the first day.

December 2019 weather

Comparing December months

This month broke 21st century records for December mean monthly temperatures. The mean minimum of 18.7° just beat 18.6° of December 2009, the mean average of 27.6° easily beat 26.1° last year, while the mean maximum of 36.5° was far above last year’s 33.9°.
On balance, indicators of moisture make this the driest December of the century. Rainfall, at 19.6 mm, was lower than any but December 2006 (18.8 mm), and the dew point was equal lowest with 2013. This month had by far the fewest cloudy mornings (10%) and the widest daily temperature range (17.8°).

December 2019 climate

Drought

I will report separately on the on-going drought that continues to break low-rainfall records at durations of 15-months and longer.


Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available. Recording resumed on 20 July 2019.
My estimates of early morning dew point have drifted anomalously low. From August 2019, I use data from the Tamworth Airport published graphs.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to December 2019

December dry and very hot

3-year trends of climate anomalies

December raw anomaly data (orange)

Temperatures

Daily maximum temperature anomaly (all x-axes) extremely high: now five degrees above 21st century normal and three degrees above the record for smoothed values.
Daily minimum temperature anomaly (lower left): very high, just above the record smoothed value.
Subsoil temperature anomaly (lower right): still near normal.

Moistures (moist is at the bottom)

Rainfall anomaly (upper left): extremely low.
Cloudiness anomaly (upper right): extremely low.
Dew point anomaly (middle left): still rather low.
Daily temperature range anomaly (middle right): very high.

 Fully smoothed data values (red) 

Smoothed anomaly values now include June of 2019. From the rather static values of the spring, nearly all smoothed values for June began to move in the direction towards drought that seems to have prevailed since then.
There were two exceptions. Daily minimum temperature anomaly continued to fall very rapidly. Subsoil temperature anomaly approached a peak value.

Detail of rainfall vs. max temp

Rainfall and temperature anomaly trendsThe relation of smoothed rainfall anomaly to smoothed daily maximum temperature anomaly (top left graph) is important, but the graph is hard to read. I have drawn a part at a larger scale here.
The value for September 2017 is the first to show the current drought by falling on the hot-dry side of the normal range (aqua). Values became successively warmer and drier until March 2018 (max temp) and May 2018 (min rain). Values (especially temperature) then cycled away from drought until August-September 2018, and back to record-breaking drought in January 2019.
After January 2019, there was a retreat from drought until May 2019, when anomaly values were like those of 17 months earlier, in January 2018 (red square).
June 2019 began a renewed cycle towards drought, seemingly confirmed by later data.


Notes:

January data points are marked by squares.

Smoothing Continue reading

January 2019 very hot

Sun sets through gum tree

Eucalypt Silhouette

Weekly temperatures were high all month, peaking at 6.4° above normal on the 17th and never less than 3.4° above normal. Seven days had peak temperature over 40° (fewer than the nine in February 2017). Only one day was cooler than normal, while no nights were.
There were four rain days, with 18 mm recorded on the 21st.

Graphical log for January 2019

Comparing January months

January 2019 was very hot: more than two degrees hotter than any recent month. Mean temperatures were far above the normal January temperatures for this station (means for the decade from March 1999):

Mean Maximum: 38.4°, above normal by 4.6°.
Mean average: 30.8°, above normal by 4.8°.
Mean minimum: 23.2°, above normal by 5.2°.

Manilla was not the only hot place. Australia-wide, this was the warmest January on record.

Apart from high air temperatures, Manilla’s climate was near normal. Even the subsoil temperature was normal. So were the cloudiness, dew point and daily temperature range.
The rainfall of 25.0 mm was at the 15th percentile, far below the average (87 mm). I will report the on-going drought in another post.

Climate for January months


Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available.  Since no 9 am readings have been recorded since August, I have substituted my non-standard gauge readings for all days.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

December 2018 dry and hot

Tropidoderus stick insect

Stick Insect

Weekly temperatures, which began normal, then remained high all month, peaking
around four degrees above normal on the 18th and again on the 29th. Only a few days or nights were cooler than normal.
There were six rain days, grouped around the 16th, which had 25 mm. Earlier and later times had sunny skies and low dew points.

Graphical log of weather December 2018

Comparing December months

Remarkably, the three mean temperatures this month are practically the same as those of both December 2017 and December 2016. They are higher, but by no more than 0.2°, near the limit that can be read on my thermometers. The mean daily maximum of 33.9° and the mean daily mean of 26.1° are the hottest for December in this record from 1999. (The mean daily minimum of 18.3° was exceeded by 18.6° in December 2009.)
This was one of the most sunny December months. The percentage of cloudy mornings (19.4%) was the same as in December 2006, but higher than in 2002 or 2005 (both 16.1%).
The rainfall of 34.5 mm is at the 22nd percentile, far below the average (74 mm). Lower rainfall totals occurred in December of 2001 (34 mm) and 2006 (19 mm). I have reported the on-going drought in another post.

Climate in December months


Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available.  Since no 9 am readings have been recorded since August, I have substituted my non-standard gauge readings for all days.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to December 2018

December hot and dry

3-year trends to December 2018

December raw anomaly data (orange)

In December 2018, the top two graphs show that rainfall was low and skies sunny.
The daily maximum temperature (x-axes, all graphs) and daily minimum temperature (lower left graph) were extremely high, but the subsoil was cool. Dew point and daily temperature range were near normal.

 Fully smoothed data (red)

Climate anomaly data when smoothed in this way do not show changes from month to month, but only those cycles that last for a year or more. The smoothed data identify the month when a peak occurs in a cycle .

By June 2018, the last date for which data can be fully smoothed (as described below), some variables had already peaked in their contribution to the current extreme drought.

The anomaly of daily maximum temperature (x-axis, all graphs) had peaked in March 2018. Two months later, in May 2018, the rainfall anomaly peaked (negative) to a 21st-century record low value of minus 28.3 mm. (In the 2002 drought daily maximum temperature had not peaked until after the peak of minimum rainfall.)
By June, cloudiness was decreasing towards a minimum (perhaps in August 2018) without becoming much less cloudy than normal. Dew point anomaly was still decreasing, and seemed likely to reach a record low value about August.
The anomaly of daily temperature range had been at a (high) level characteristic of drought since the previous winter (2017). It had changed little, and peaked in May 2018 without getting near the record high value of July 2002.
The anomaly of daily minimum temperature has a cryptic relation to drought. In this case, the value peaked sharply in February 2018 before falling rapidly. It may have reached a minimum about August 2018.
The anomaly of subsoil temperature was high in June 2018, and seemed likely to peak about July, lagging four months behind the daily maximum temperature anomaly.


Notes:

January data points are marked by squares.

Smoothing

Smoothing uses Gaussian functions.
For fully smoothed data the function has a Standard Deviation of 2.5 months, it spans 13 monthly data points, and has a half-width of 6 months, which suppresses cycles shorter than 12 months. For partly smoothed data, the span of the function is reduced to 11 months, 9 months and so on.

Fully smoothed data points are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange.

Limiting values

Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

 * Normal values for rainfall are based on averages for the 125 years beginning 1883.

3-year trends to December 2017

Hot days and nights

3-year trends to December 2017

December raw anomaly data (orange)

December 2017 had hot days and hot nights, but the subsoil remained cold. Rainfall was low, while other measures of moisture were near normal.

 Fully smoothed data (red)

The latest fully-smoothed data point is for June 2017. By that time, all variables were within the normal range except for dew point. Even dew point was in the centre of the range of low values that has become “normal” since 2010. Three variables were static: daily maximum temperature, subsoil temperature, and rainfall. Cloudiness, dew point, and daily temperature range. were moving towards aridity. Daily minimum temperature was falling.


Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.
Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

 * Normal values for rainfall are based on averages for the 125 years beginning 1883.

December 2016 was hot

A bearded dragon camouflaged on a bush

Hidden Dragon

Hot weather in this month came in the first and last weeks which, on average, were 4.8° and 3.6° warmer than normal. On the 5th, both day and night were nine degrees above normal. There was just one 40° day, on the 30th. In December months from 1999, there have now been five with one 40° day, but none with more than one. The two hottest, at 40.6°, came in 2005 and 2012.
Rain fell frequently (on 12 days), but it was light (max: 17.8 mm). Plants dried out.
Throughout the month, tiny “flies” swarmed in millions. They are native Rutherglen Bugs (Nysius vinitor), a sap-sucking pest of crops such as sunflower.

 Weather log December 2016

Comparing December months

This was the hottest December of the new century. December 2009 had been the hottest, but this month had a higher mean daily maximum (33.8° vs. 33.1°) and a slightly higher average (26.0° vs. 25.9°). December 2009 still had the warmest nights: the daily minimum was 18.6° then versus 18.2° now. As this month’s days and nights were both so warm, the daily temperature range was quite normal (15.6°).
Contradicting the high air temperatures, the subsoil temperature was well below the normal value of 24.3°. At 22.7°, it was the coolest December value since 1999, when it had been 22.5°.
The month was rather cloudy, which does not match well with the rather low dew point and rainfall. The monthly rainfall total of 48.8 mm is in the 34th percentile, well below the average of 74 mm.

Climate fro December 2016

The Year 2016

As in 2015, the average temperatures for the year 2016 were close to normal by day, and half a degree above normal by night. The subsoil temperature, which had been normal in 2015, fell to half a degree low. Air temperatures had been warmer in 2014 and 2009, and cooler in 2008.
Rainfall, at 775 mm, was in the 76th percentile, well above the 125-year average of 652 mm. The mid-year months of June, August, and September were very wet, while November as well as February, March and April were dry. High rainfall is rare in mid-year months, but 1998 had a similar pattern.
Temperatures also were far from normal in some months. They were about 2° higher than normal through the autumn and 2° lower than normal through the spring.


Data. Rainfall figures are usually from the automatic rain gauge at Manilla, published on the internet by the Bureau of Meteorology as Station 55031. However, the gauge ceased recording on the 8th of October, and later readings are from my non-standard gauge. All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.