Keepit Dam at 0.9%
This season had a series of warm spells separated by normal autumn temperatures. The warmest, about 4° above normal, came in early March, late April and late May. Dry air came at cooler times, near the 1st of March and the 12th of April. Most of the rain came in two very wet days: the 30th of March and the 4th of May (61 mm).
Comparing autumn seasons
As in 2018 and 2016, autumn was very warm. Although autumn 2016 had the highest mean temperature of the new century, this autumn had the warmest nights: 12.7°.
Despite the on-going drought, measures of moisture were near normal for the season. Cloudy days reached 37%, the daily temperature range (14.3°) was quite narrow, and the early morning dew point (7.2°) not low. The rainfall total, 117 mm (est.), was at the median value, not far below the mean of 134 mm.
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. Station 55312 recorded no readings this autumn. I used my own readings for the whole season.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
Gumnut and Gum-Blossum
The air became four degrees warmer than normal by day and by night in mid-March and continued warm until late in April. As normal temperatures returned the climate became dry, with no rain for thirty-nine days.
Both autumn 2016 and autumn 2018 had record high average temperatures. This season had the highest mean daily maximum (27.7°), but 2016 had the highest mean daily minimum (12.1°). In the combined average, 2016, with 19.9°, was warmer than 2018, with 19.7°.
All four indicators of moisture (rainfall, dew point, cloud, and daily temperature range) agree in showing this autumn to be drier than last autumn, and even than the three autumns before that.
The total rainfall of 45 mm was the 12th driest on record, but it was not the driest in the 21st century. Similarly dry autumns occurred in 2002 (60 mm), 2005 (35 mm), 2006 (53 mm), and 2008 (37 mm). That is about twice as many as history would suggest.
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. During this autumn season 30 daily readings were missed, and I replaced them with my own readings.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
Autumn this year had normal temperatures, in stark contrast to very high temperatures both in the summer and in the autumn of last year. The decline to winter was not smooth, however, but went by steps. For three weeks in each month there was no cooling then, after some rain, there was a sudden cooling through three, four, or five degrees.
Rain fell frequently except for two gaps of a fortnight each, the first coming in mid-April. The second ended with 32.8 mm of rain registered on May the 20th. There were 26 rain days, which is twice usual number, and more than in any autumn in the new century.
There was plenty of moisture. Only the early morning dew point (8.1°) was low, by half a degree. The daily temperature range was a narrow 14.5°, and the cloudiness a high 41%.
The total rainfall of 192.8 mm was at the 80th percentile, far above the autumn average of 134 mm. There has not been a wetter autumn since 1990 (203 mm). A little earlier there was a cluster of wetter autumns: 1977 (307 mm), 1979 (203 mm), 1982 (238 mm), 1983 (314 mm: 4th wettest), and 1988 (231 mm). Autumn 1894 was the very wettest, with 388 mm.
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. All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
The season was marked by a series of warm spells. The three warmest, coming early in each month, reached 3° to 4° above normal. In the first two, days and nights were equally warm; in the third, nights were much higher above normal than days, making the daily temperature range narrower than normal by 4°. The only cool spells having temperatures below normal were in the third week of March and the last week of May. All three frosts of this season came in the final week .
Rain came in five episodes, spaced a week or two apart. There were 12 rain days, which is the usual number, but the highest reading was only 20.8 mm.
This was the warmest autumn in this short record. Daily maximum, mean, and minimum temperatures were all more than 1.5° above the average for the decade beginning March 1999. The subsoil temperature at 750 mm was also rather high.
The composite Moisture Index was normal, rainfall being a little low and cloudiness rather high (36%, when the autumn “normal” is 25%).
The total rainfall of 88.3 mm was below the autumn average of 134 mm, and in the 35th percentile.
All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla. Rainfall data up to 26/3/15 is from Manilla Post Office, Station 055031.
Eucalyptus albens in bloom
For a time around the 20th of April, days averaged five degrees colder than normal. At that time nights were warm, making the daily temperature range a remarkable eight degrees less than normal. On three occasions the dew point (humidity) was down by six degrees or more: early and late in March, and in mid-May. The sub-soil temperature was low most of the time by up to half a degree, but ended one degree high. Rain fell in each fortnight. The number of rain days (19) was high, but the highest daily reading (26 mm) was normal. This autumn, like the last, was moist. The rainfall, at 137.5 mm, was a little higher (on the 60th percentile) and the mean daily temperature range was a new record narrow value of only 14.0°. The season was very cloudy, with 41% cloudy mornings, but did not beat last year’s record 48%. The early morning dew point, 7.2°, was not even up to normal (8.5°). Warm nights and cool days made the mean temperature normal.
Temperature, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.
There were two severe cold spells in late March and early May. Days were several degrees colder than normal, and the daily temperature range was narrow. To compensate, there were three spells of very warm nights in early April, late April, and late May. The last of these also had warm days and lasted a fortnight.
Rain fell on 23 days (twice the normal number), totalling 132.8 mm. Most of it (84.8 mm) fell in the week beginning on the 24th of March. The autumn total is on the 125-year average, and in the 58th percentile.
In autumn seasons from 1999, this was equal warmest with 2007, but nights (11.8°) were by far the warmest, 1.3° above normal. The mean daily temperature range, at 14.1°, was the narrowest, and the percentage of cloudy days (48%) the highest. All these point to a more moist (maritime) climate than does the rainfall or the dew point.
Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Temperature, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.
Three quarters of the rain this autumn fell in the first two days: 31 mm and 45.4 mm. After that, the heaviest falls were 6.2 and 6.8 mm late in May. Days were cool with the rain, and warm in late March and late April. The warm days in late March came with warm nights, but the warm days in late April brought very wide daily temperature ranges instead.
This autumn was like autumn last year. That is, it was near average in most respects, but with high subsoil temperature and plenty of cloud. Dew points were even lower, reaching a record low value of 6.1°.
Rain fell on 11 days (normal), totalling 103 mm. This is below the 125-year autumn average of 133 mm, and in the 46th percentile.
Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Temperatures, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.