Blooming Wonga-Wonga Vines
Despite more cloud, September was even more arid than August. Weekly temperatures remained normal until the last week, which was remarkably warm. There were some notable events. The 13th, the first 30°-day of the season, was followed by a day more than 16° cooler. Extremely low humidity early on the 20th made the dew point (-8.8°) almost as low as the record set last month. Among minimum overnight temperatures that were near zero, the one on the 24th (22.8°) set a record by being 14.7° higher than normal.
The number of frosts (below +2.2° in the screen) was 13 (a September record), almost as many as in August. Perhaps the frost on the 20th was the last of the season. That is the normal date for it.
There was 5.2 mm of rain on the 14th, and an estimated 0.3 mm on the 29th. (The automatic gauge at the Museum was down by then.)
Comparing September months
The mean daily maximum of 25.0° was rather high, fully 5° higher than last year. With a mean daily minimum (5.7°) that was rather low, the daily temperature range reached the record wide value of 19.3°.
Extremely dry air was shown by a mean early-morning dew point of 2.7°, the lowest September value, 8.1° below normal.
The total rainfall of 5.5 mm (estimated) was very far below the September average (41 mm), at the 8th percentile. That is a serious rainfall shortage. The current rainfall totals for four months (95 mm) and for six months (175 mm) are also serious rainfall shortages. Even worse are the totals for two months (19 mm) and for three months (33 mm): they are severe rainfall shortages.
Similar severe shortages occurred in October 2013, May 2008, and May 2005. Extreme shortages last occurred in the six-month drought of 2002.
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. The gauge last reported on 24 September 2017.
All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
A neighbour’s dam
The second cloudiest month of this century brought the warmest July night.
There were two very warm spells in the trace of weekly average temperature. Both were due mainly to warm nights. The second spell, coming in the third week, reached nearly six degrees above normal. On the morning of Saturday the 23rd, the minimum reading on the screen thermometer, 14.4°, was the highest July minimum in the record from 1999.
Up to the 25th, the weather was changeable, with some days overcast and rainy, and others fine and sunny. A very warm sunny day on the 17th, following a frost, had the unusually wide daily temperature range of 21.9°. From the 25th, the weather settled to what is normal for July. In the whole month, there were sixteen frosts, which is normal.
The highest rainfall reading was only 11.4 mm. Ten days had rainfall recorded, but three of these had 0.2 mm, on days when rain was not seen.
Comparing July months
The mean daily maximum temperature (16.9°) was normal. The mean daily minimum temperature (4.0°) was two degrees above normal, making the average temperature (10.5°) one degree above normal. Similarly, the subsoil temperature (14.7°) was one degree above normal.
The daily temperature range, normally 15.0°, was 12.9°, not quite as narrow as in 2010 (12.3°). The early morning dew point was normal. At 2.2°, it was so close the the daily minimum temperature (4.0°) that fogs were to be expected.
The month was extraordinarily cloudy. Cloud cover is assessed by the number of octas (eighths) of the sky seen to be covered by cloud at 9 am. I compare cloudiness of months by the percentage of “cloudy mornings”: those when I see more than four octas of cloud. This month, with 21 cloudy mornings, had 68%. July normally has only 35%. The only month in this century with a higher value was June 2013, with 73%.
The monthly rainfall total of 32.4 mm is below the average (41 mm), in the 47th percentile. The greatest rainfall “shortage” is now in the 48-month total (2221 mm) which is in the 14th percentile. Both Greenhatch Creek and Rushes Creek are just flowing.
Data. Rainfall figures for this month are from the automatic rain gauge at Manilla, published on the internet by the Bureau of Meteorology as Station 55031. All other data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.