All Tmin seasonal inversions in Melbourne

In my previous post, I made a brief discusison of the phenomenon of “seasonal inversions” over Melbourne and more generally over Victoria. Major “seasonal inversions” are rare but by no means unknown in southeastern Australia. The previous post shows seven clear cases of T_mean inversion outside of the summer months over Victoria since 1910, and available temperature data from earlier years strongly implies four or five more between 1855 and 1909. There are two further cases of Victoria-wide T_max inversion only since 1910, whilst October-November 1866 and September-October 1864 look likely from the Melbourne data but have no means for further investigation, at least those accessible to myself.

T_min inversions, as I noted, were about four times more frequent than T_max or T_mean. Therefore, I decided to ignore them for an extension of my previous post, but after a further thought I felt that I should list all T_min inversions in Melbourne — based upon the previous criteria — since records began in 1855.

All T_min Seasonal Inversions in Melbourne Since 1855: 

		Tmin	Change
1859	August	6.87	-0.13
	September	6.74
1863	July	6.83	-0.52	Unusual inversion in that July was quite dry and August very wet (sixth-wettest in the records). This suggests very foggy conditions, but cloudiness data do not suggest exceptional gloominess
	August	5.09
	September	6.31
1866	October	9.35	-0.79	As noted previously, mean minimum for November cooler than for May, and was even so in Adelaide [52.8˚F or 11.56˚C in May; 52.4˚F or 11.33˚C in November]
	November	8.57
1870	May	6.34	-1.02	Almost certainly wettest year over Victoria — estimated state mean possibly greater than one metre — with particularly wet conditions in winter and spring. Very high cloudiness (7.7/10 in June versus mean of 6.6) and warm mornings explains large inversion
	June	7.36
1871	April	8.96	-0.03
	May	8.99
1872	May	7.25	-0.65	Another exceedingly wet winter throughout the state, with again very high cloud amount (7.5/10)
	June	7.90
1873	August	7.26	-0.08
	September	7.18
	October	9.49	-0.15	Very small compared to large Tmax inversion discussed in earlier post.
	November	9.35
1874	October	9.70	-0.02
	November	9.68
1875	May	7.32	-0.28
	June	7.61
	August	6.65	-0.07
	September	6.58
1877	October	8.45	-0.33	November mean minimum coolest on record. Like 1866, the mean was cooler than for May.
	November	8.11
1878	September	8.09	-0.35
	October	7.74
1880	September	8.26	-0.75	Third-wettest September on record in Melbourne after 1916 and 1870, with extreme flooding in Gippsland, where it was comparably wet to 1934–35, 1952 and 1978
	October	7.51
1881	August	7.19	-0.23
	September	6.96
1883	May	6.89	-1.90	Largest Tmin inversion on record in Melbourne. Although as I have noted Tmin inversions are much more common than Tmax, this inversion is smaller than the Tmax inversion between October and November 1940.
	June	8.79
1890	May	8.01	-0.87	The last two of three consecutive extremely wet Junes over Victoria, with consequent high cloud cover.
	June	8.89
1891	May	7.27	-0.29
	June	7.56
1894	August	6.74	-0.31
	September	6.43
1895	August	7.65	-0.45
	September	7.20
1898	May	6.45	-0.16	Notably cool and very blocked May followed by Australia’s ninth-wettest June since 1890 — very cool in Western Australia, but warm in east
	June	6.61
1899	September	8.46	-0.31
	October	8.15
1904	August	6.60	-0.34
	September	6.26
1905	March	11.32	-0.02	Extremely dry March virtually throughout Australia followed by very wet April in Murray–Darling Basin. Likely wettest on record in North Mallee.
	April	11.34
	August	6.11	-0.54	Record cool spell from 15 September to end of month with mean maximum of 12.225˚C — no day reaching 14˚C — and mean minimum of 5˚C.
	September	5.57
1911	April	9.44	-0.19	All these inversions were replicated throughout Victoria as a whole, though none are large. May 1912 is the driest May on record over the Murray–Darling Basin
	May	9.63
1912	May	6.52	-0.29
	June	6.81
1913	October	9.62	-0.01
	November	9.61
1915	September	8.70	-0.03	Coolest September on record in Perth, hottest in Brisbane, and wettest until 2016 in South Mallee and Wimmera districts
	October	8.67
1916	September	9.36	-0.40
	October	8.96
1920	May	7.51	-0.44	Coolest May of twentieth century followed by wet and windy June, beginning what would be Australia’s last big wet spell until 1939.
	June	7.95
1928	September	9.45	-0.72
	October	8.73
1931	April	8.86	-0.84	Notably large inversion due to warm, cyclonic May amidst a very wet spell widely noted in Every Game Ever Played.
	May	9.70
1932	September	7.78	-0.24	Unusual inversion between dry September and wet October, especially as not due to excessive fogginess (September 1932 cloud amount 6.1/10; similarly dry May 1932 7.1/10) and no Tmax inversion.
	October	7.54
1934	July	6.829	-0.446	Extremely cool September following warm July that saw 20˚C reached in the month for only the second time on record
	August	6.384
	September	6.383
1935	August	7.36	-0.44
	September	6.92
1936	July	6.15	-0.01	Extremely wet winter — third-wettest July on record over Melbourne — followed by cool September as noted in previous post
	August	7.04
	September	6.13
1942	April	10.12	-0.19	Record wet May in Melbourne and many other parts of Victoria and inland New South Wales. Fourth-wettest over Australia as a whole after 1921, 1955 and 1968.
	May	10.31
1945	August	7.62	-1.07	Fifth-largest Tmin inversion on record, and replicated all through Victoria. August was fairly wet — very much so in southwestern Australia and Tasmania — but September distinctly dry over all of Victoria outside south Gippsland.
	September	6.55
1946	July	7.29	-0.15	Extremely windy westerly July — very wet in Northeast, South Wimmera and West Coast, almost rainless in Queensland and New South Wales away from Southwest Slopes and Snowy Mountains — amidst long sequence of cool anticyclonic months. Total runoff into Perth’s dams in July 1946 alone greater than for the entire decade 2006 to 2015.
	August	6.40
	September	7.14
1948	March	10.37	-0.38	Extremely cool, dry southerly March followed by wet April in west and east — wettest ever in North Wimmera district
	April	10.75
1949	July	6.21	-0.07	Coolest year over Victoria since 1910 with what the New South Wales Yearbook called an “early spring” due to the less cool July — followed by one of Victoria’s driest Augusts on record with consequent cold mornings — though less cold than 1943 or 1944.
	August	5.35
	September	6.14
1952	May	7.64	-0.33
	June	7.97
1955	October	9.64	-0.13
	November	9.51
1957	May	8.02	-1.38	Record hot June throughout Victoria discussed previously, although Tmin inversion may not rival that of May and June 1883.
	June	9.39
1958	April	9.62	-0.39	Very dry April in Victoria — driest since 1923 in West Gippsland — followed by extremely wet and warm May throughout southeastern Australia and especially Tasmania where it rivals May 1923 as that state’s wettest month since 1890.
	May	10.02
	August	7.23	-0.62	Very wet August in Victoria followed by cool September with persistent anticyclones over Tasmania. Includes coolest V/AFL Grand Final Day on record (11.3˚C).
	September	6.61
1960	October	9.69	-0.47
	November	9.21
1961	May	7.91	-0.14
	June	8.05
1962	May	8.25	-0.08	Tmin inversion here very small, but part of a remarkably close pair of May-June Tmean inversions (two of three over 170 years in a five-year span)!
	June	8.32
1963	April	9.29	-0.32	Driest April since 1923 over southwestern Victoria followed by record gloomy May with only 1.6 hours of sunshine per day in Melbourne
	May	9.61
	October	12.22	-1.24	Hottest October until 2015 with very warm, humid northeasterly winds followed by southerly November with (near)-record dryness in Western Victoria and South Australia
	November	10.97
1965	October	11.09	-0.14
	November	10.95
1969	August	8.16	-0.49	Two of the major seasonal inversions over southeastern Australia since 1910.
	September	7.67
1977	August	8.48	-0.91
	September	7.58
1978	April	10.85	-0.06
	May	10.92
1981	September	10.14	-0.06
	October	10.09
1982	August	7.90	-0.62	Both of these are part of full Tmean inversions in Melbourne, though not replicated over Victoria as a whole.
	September	7.28
1984	August	8.67	-0.39
	September	8.28
1991	May	9.18	-0.50	Extremely dry May followed by record warm and wet June — sixth-wettest month over Victoria since 1890.
	June	9.68
	October	11.62	-0.43	Very hot and dry October — driest since 1914 over Mallee, North and alpine areas, and hottest since 1963 — followed by extremely cool summer beginning in November. Alongside 1914, only year when 30˚C was reached more often in October than in December.
	November	11.19
1992	July	7.64	-0.05	Record wet August to December spell — only case of four consecutive months over 100 millimetres in Melbourne, and only September that never reached 20˚C
	August	6.57
	September	7.60
1995	April	9.50	-0.04	Coolest April in Melbourne since 1951, and (Tmin) inversion extended to Victoria as a whole.
	May	9.54
	July	7.30	-0.19	Famously hot and dry August throughout southern mainland Australia preceded by wet westerly July and followed by cool September with heavy rain on the New South Wales coast but continuing dry conditions in Victoria away from East Gippsland.
	August	7.46
	September	7.27
1998	September	10.46	-0.39
	October	10.07
1999	April	10.32	-0.05	April extremely hot in southwestern Australia, but distinctly cool in the east.
	May	10.38
2007	April	12.31	-0.26	Record hot May, beating 141-year-old record in Melbourne.
	May	12.57
2008	May	9.04	-0.79	Unusual Tmin inversion during very dry, but foggy — I recall the long periods of still fog early in the month — June. Foggy, dry, warm anticyclonic easterly conditions widespread over Victoria.
	June	9.83
2013	September	11.18	-0.06
	October	11.12
2016	September	10.09	-0.05	Wettest September on record over eastern Australia — and wettest winter half-year month over Murray–Darling Basin — followed by coolest October over eastern Australia since 1982
	October	10.03

Conclusions:

1. In Melbourne since 1885 there have been about seventy T_min seasonal inversions between March and June or between August and November, or about two every five years.
• in contrast, there have been only 31 T_max or T_mean inversions over the same timespan
• six T_min seasonal inversions (in 1863, 1934, 1936, 1946, 1992 and 1995) extend from July to September
• seven years (1873, 1875, 1905, 1958, 1963, 1991 and 1995) had T_min inversions in both autumn and spring.
• Contrariwise, no year has ever had multiple T_max or T_mean inversions
2. Despite the much greater frequency of T_min inversions vis-à-vis either T_max or T_mean
• the greatest magnitude of a T_min inversion is nonetheless 0.65˚C smaller than for the T_max inversion between October and November 1940
• that greatest magnitude is still 0.75˚C greater than for the largest T_mean inversion between May and June 1957
3. There may be a possible reduction in magnitude of T_min inversions due to greenhouse gas emissions to enrich Gulf oil sheikhs and Australian coal barons:
• No T_min inversion (of eighteen) since 1963 has exceeded 1.0˚C in magnitude
• Contrariwise, up to 1963 there were five T_min inversions exceeding 1.0˚C in magnitude, or one every twenty-one years
4. It is possible that the shift in temperature and rainfall reporting station since 2015 could reduce the frequency of T_min inversions over Melbourne:
• There has been no T_min inversion over Melbourne since November 2016
• However, there has been two T_max [September-October 2023, August-September 2024] and one T_mean [September-October 2023] inversion in this timespan not replicated over Victoria as a whole
• It is possible that differences in location could make T_min inversions less likely, but I have not looked at how the change would do thus