Cool Dry April 2017

Pavonia blooms on a roadside

Roadside Pavonia

April began with cool days and nights, about three degrees below normal. However, the weather did not get any cooler until the last few days. In particular, ANZAC Day, at 27.4°, was the warmest day of the month – but that was more than a degree cooler than ANZAC Day 2002. (The average daily maximum temperature for ANZAC Day (from 2000) is 24.3°. The hottest was 28.7° (2002) and the coldest 16.8° (2012).)

Soaking rain of 10.6 mm, registered on the 26th, came with a remarkably warm night of 16.6°. Coming so late in autumn, this was 7.9° above normal, breaking the record of 7.1° above normal for an April night (20/04/06).
Further rain on the 27th (11.2 mm) fell as showers on a very cold day of 14.3°, that was 9.8° below normal. The final three nights were cold. The 30th, at 4.3°, was the coldest night of the month, but it was far from frosty.

Weather log for April 2017

Comparing April months

This month was cool, with a mean temperature of 17.0°, but not nearly as cool as April in 2008 (15.8°), 2006 (16.6°), or 1999 (15.6°). It was also rather low in moisture, with only 24 mm of rain, only 33% cloudy mornings, a daily temperature range as wide as 15.6°, and an early morning dew point of only 6.3°. What is unusual is the combination of low temperature values and low moisture values. Manilla’s climate generally swings between high temperature with low moisture (“droughts”) and low temperature with high moisture (“flooding rains”), as the poet said. (See these graphs.)
The total rainfall of 24.0 mm was at the 40th percentile, below the April average of 40 mm. There are no serious shortages of rainfall for groups of months to this date.

Climate for April 2017.


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.

3-year trends to April 2017

Parametric plots of smoothed climate variables at Manilla
“Cold-Arid ‘Glacial'”

Climate trends to April 2017

April raw anomaly data (orange)

In terms of anomalies, April 2017 was even cooler than March, but much more arid. Anomalies of both daily maximum and daily minimum temperature fell by more than three degrees from February values, (They plot near the margins of the lower left graph.)
On most of the graphs, raw anomaly values for April plot towards the top left corner. Rather than moving along the top-right-to-bottom-left axis of “Droughts and flooding rains”, they combine low temperature and aridity as happened in ice ages.

 Fully smoothed data (red)

The most recent fully-smoothed data is for October 2016. Following a winter that was cool and moist, October shows a climate becoming steadily warmer and drier.
The smoothed anomaly of daily minimum temperature, which had hit a record high value in May 2016, approached a minimum value that was near normal.
Subsoil temperature anomaly was still falling rapidly, and was certain to reach a new record low smoothed value in November.


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.

Rainy days in March 2017

March 2017 had 17 rain days. In 134 years, this was beaten only by June 1950, which had 18. [More about Manilla rain days here.]

Fronds of Acacia pendula

Weeping Myall

After the record high temperatures of February, day and night temperatures in March were normal, without extremes. On a weekly basis, the first half of the month was cooler than the second half. The subsoil temperature followed the weekly air temperature down, to be a degree below normal by the 20th.
The second week had mainly clear skies and low dew points, Then the skies became persistently cloudy and dew points were high. A number of afternoons had oppressive humidity, with minimum values over 70%.
Of the 17 rain days, only three were early in the month, and they had little rain. The highest daily reading of 15.0 mm came on the 22nd.

Weather log for March 2017

Comparing March months

March had been sunny and very warm in both 2016 and 2015. This March was like that of 2014 and 2013, but with even more moisture. The mean average temperature was normal but, due to the cloudiness (58% cloudy mornings), the mean daily maximum, 29.1° was low and the mean daily minimum, 16.4°, was high, yielding the record narrow daily temperature range for March of 12.7°. The mean early morning dew point, 13.7°, was the highest March value in a decade, and the mean afternoon humidity minimum, at 53%, was far above the usual value of 30%.
The total rainfall of 113.2 mm was at the 90th percentile, far above the March average of 54 mm. The previous month, February, had only 4.1 mm, at the 4th percentile for that month. Taken together the two-month total of 117.3 mm was well above normal, at the 63rd percentile.

Climate for March 2017


Data. In 2016, a Bureau of Meteorology automatic rain gauge (formerly used for flood prediction) was set up in the museum yard as the official Manilla rain gauge. From 23 May 2016, its daily readings were published as if from Manilla Post Office, Station 55031. The gauge ceased transmitting five months later, on 7 October 2016. This month, after repair, it came into operation again. From 17 March 2017, daily readings are now published as Manilla Museum, Station 55312.

In these reports,the rainfall data is from Station 55031 or Station 55312 when available. Otherwise, rainfall data is from 3 Monash Street, Manilla.  All other data, including subsoil at 750 mm, are also from there. 

3-year trends to March 2017

Parametric plots of smoothed climate variables at Manilla
“Very rainy and cloudy”

3-year trends to March 2017

March raw anomaly data (orange)

March 2017 was dramatically cooler and more moist than the extremely hot and dry February. March days were cooler than normal and both rainfall and cloud were very high. Dew point and daily temperature range moved to the moist side of normal.

 Fully smoothed data (red)

The most recent fully-smoothed data is for September 2016. Following a winter that was cool and moist, September days remained cool but the climate became drier.
The smoothed anomaly of daily minimum temperature, which had hit a record high value in May 2016, approached normal. Subsoil temperature fell rapidly to below normal.


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.

Summer 2016-17 the hottest

Young bearded dragon

Tiny Dragon

This summer, like summer 2013-14, was marked by repeated heat waves. The first, early in December, was brief. Another, in mid-January, led into one that was hotter, and persisted through the first half of February. On a weekly basis, temperatures did not fall below normal at any time in the season. Mid-February had the two hottest days of the new century, at 44.9° and 43.8°.
Although there were as many rain days as usual (22), only two days had rainfall exceeding 15 mm, and there was almost no rain in February.

Graphical log for summer 2016-17.

Comparing summer seasons

Mean temperatures set new records for the summer season: daily maximum 35.6°, average 27.6°, and daily minimum 19.7°. Each of these was more than a degree higher than the old record. Nearly all such figures for the months December, January, and February had also been records. However, the subsoil temperature for the summer (24.7°) was low.
Two indicators of moisture were a little low: mean early morning dew point (13.4°) was down 0.7°, and mean daily temperature range (15.9°) was 0.8° wider than usual.
The percentage of cloudy mornings (38%) was almost the same as in the last four summers, and lower than in the previous two. However, 38% is much more cloudy than the “normal” figure of 31% cloudy mornings that was set in the decade 1999-2008. Summers were more sunny then.
This summer’s rainfall was very low. The unofficial total of 101.4 mm would place it as the seventh driest on record. As shown on the graph, summer 2013-14 was drier (85 mm). Otherwise,  there has not been a drier summer in the half-century since 1964-65 (70 mm).

Climate for summer 2016-17


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 five months ago (8/10/16), and this month’s readings are from my non-standard gauge. All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

February 2017 had the hottest day

February 2017 was a month of extreme heat and hardly any rain.

Rainbow

No-rain Rainbow

The temperature rose to 44.9° on the 11th, the highest reading in this record from 1999. The next day, at 43.8°, was the next highest, beating readings of 43.7° on 3/01/2014 and 43.2° on 12/01/2013. These extremely hot days were part of a long heat-wave. Every day reached above 30° for 64 days up to the 19th, and the average weekly temperature was above 30° (4° above normal) from the 1st to the 15th.
Nights also remained warmer than normal until, abruptly, the temperature fell to 9.5° on the 20th: the 4th coldest February night! After that, day and night temperatures were normal.
Rain showers were seen frequently, but the only daily readings (unofficial) were 1.1 mm on the 20th and 3.0 mm on the 27th.

Weather log February 2017

Comparing February months

This was by far the hottest February of the new century, with highest values of all three temperatures: mean maximum temperature (36.8°), mean average temperature (28.4°) and mean minimum temperature (20.0°). Subsoil temperature was normal.
While cloudiness was normal, a rather low dew point and rather wide daily temperature range reflect low moisture, while the rainfall was very low indeed.
The estimated monthly rainfall total of 4.1 mm exceeds that of just a very few February months: 1901 (2 mm), 1932 (3 mm), and perhaps 1923 and 1938 (both 4 mm), but no others. However, this extremely low rainfall for the month has not brought any serious rainfall shortages for totals of more than one month. The four-month total of 123 mm is at the 17th percentile, which is not even as bad as the five-year total (2844 mm) which is at the 14th percentile.

Climate for February 2017.


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 four months ago (8/10/16), and this month’s readings are from my non-standard gauge. All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

3-year trends to February 2017

Parametric plots of smoothed climate variables at Manilla
“Extreme heat with little rain”

3-year trends to February 2017.

February raw anomaly data (orange)

In February 2017 days became extremely hot and rainfall very low. The subsoil temperature rose from low to normal.

 Fully smoothed data (red)

Fully-smoothed values are now available for the winter months (June, July, and August) of 2016. That winter, as daily maximum temperature fell through normal values, a maximum in moisture was shown by maxima in rainfall, cloudiness, and dew point, and a minimum in daily temperature range. None of the smoothed values was extreme; in fact, the dew point remained on the dry side of normal.
Not only daily maximum temperature anomaly fell during the summer. Both the daily minimum temperature anomaly and the subsoil temperature anomaly also fell. The smoothed daily minimum temperature anomaly had just reached a record high value in May, and was still above normal as the summer ended.


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.