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.

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Cool spring 2016

Photo of a wildflower

Nodding Chocolate Lilies

Through September, days were very cool, making for a narrow daily temperature range. Then, through October, both days and nights were very cool. In November, days and nights were nearer to normal but, in contrast to September, the daily temperature range was wide. The dew point failed to rise during the season, making the air very dry in November.
Rain fell frequently up to the middle of November, then ceased. There were 24 rain days, when there are normally 19 in spring. The highest reading was 28.8 mm on the 14th of September. The season total of 216.4 mm was rather high, in the 77th percentile.

Graphical log for spring 2016
All temperature measures were below normal by 1.5° to 2.0°. Only spring of 2001 had low values like that but in 2010 the mean daily maximum (only) was 2.5° below normal.
Measures of moisture were near normal, with cloud, rainfall, and daily temperature range on the moist side, and dew point on the dry side.

Climate for spring 2016


Data. Rainfall figures for this season began from the automatic rain gauge at Manilla, published on the internet by the Bureau of Meteorology as Station 55031. That gauge ceased reporting 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.

3-year trends to January 2016

Parametric plots of smoothed climate variables at Manilla
“January 2016: moist again”

Trends to January 2016

January raw anomaly data (orange)

In January 2016, raw values for nearly all anomalies moved well towards the cool and moist corner of the graphs.

 Fully smoothed data (red)

In the latest month with fully smoothed data (July 2015) anomalies were quite small, but were moving towards warm and dry. Partially smoothed data points for more recent months show that the warm and dry “El Nino” influence on values around October and November was smaller than it seemed at first. In particular, rainfall did not go below the “normal” range, but the anomaly of daily minimum temperature rose quite high.


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.

Very cloudy days in May 2015

Photo of a case moth

A case moth

While there were four frosts (usually 6) that came early in the month, a record number of eleven nights were warmer than 10°. Some were very warm. At 15.1°, the night of the 3rd was the 4th warmest May night. Although the night of the 31st was only 13.0°, since it came so late, that was 9.0° above normal for that date. By contrast, most days were cooler than normal.
The frostier times were sunny, but skies later became cloudy. Finally, days were chilly and overcast. Cloud blanketed the hills, but steady rain (16.5 mm) held off until the very end.

Weather log for May 2015

 Comparing May months

The most remarkable mean value for the month is the daily temperature range: at 12.9°, it is 2.4° below normal. The May months with the narrowest ranges to date, in 2001 and 2014, had ranges of 14.7°, only 0.6° below normal. The narrow temperature range is due to cloudy skies which, at 52%, equal the record for May.
Linked with these figures are a very cool mean daily maximum temperature of 20.2°, and a very warm mean daily minimum temperature of 7.3°. The mean early morning dew point (5.0°) is not high, but higher than in any May month since 2007.
The total rainfall of 30.8 mm is in the 51st percentile. (While the long-term May average is 40 mm, May rainfall in the 21st century has averaged only 21 mm.) Among rainfall totals for more than one month, there are no serious shortages. The lowest percentile value (14th) is for the 24-month total of 1019 mm.

Climate for May 2015


Data. All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.

Cool cloudy days in April 2015

Photo of labelled Saloop saltbush

Flourishing local Saloop saltbush

After 5 hot days in March (a record number), there were none in April. In fact, there were six days not reaching 20°, also a record number! On the 21st the temperature reached only 13.2°, making it the coldest April day of the century, 12.1° below normal. To get so cold, the temperature had fallen by 4° each day for four days. Many nights, however, were warm, and on four occasions the night was less than six degrees cooler than the day. As usual, there were no frosts.
There were eight rain days, with the highest reading 26.0 mm on the 4th.

Weather log for April 2015

Comparing April months

The average daily maximum temperature, at 23.9°, was colder than in any April since 1999 (23.5°). Night temperatures, while lower than last year’s record, were above normal, making the mean daily temperature range (12.7°) the narrowest for an April month, followed by April 2003 (13.6°). The percentage of cloudy mornings (more than 4/8 cloud) was a record 46.7%, equal with April 2012. The cloudiness and narrow daily temperature range, with high rainfall, make the climate this month like that on the coast.
The subsoil temperature (21.8°) and the early morning dew point (8.4°) were normal. (In March, the dew point had been almost the same (8.3°) but that was a record low value: in that month the normal dew point is much higher.)
The total rainfall of 70.9 mm is in the 84th percentile, far above the average of 40 mm. Among rainfall totals for more than one month, there are small increases. Even the 24-month total is now in the 12th percentile: not a serious shortage.

Climate for April 2015


Data. All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.
After 132 years of continuous record, rainfall readings are no longer taken at Manilla Post Office, Station 055031.

3-year trends to April 2015

Parametric plots of smoothed climate variables at Manilla
“April 2015: equable”

Trends to April 2015

  April raw anomaly data (orange)

In April, daily maximum temperature anomaly became very low (-2.1°) while daily minimum temperature anomaly remained high (+0.7°). Other anomalies, except subsoil temperature, moved down the graphs, showing moist conditions. The extremely low temperature range anomaly (-3.0°) shows that the climate was equable, as it had been in the spring of 2010 (a smoothed record value).

Fully smoothed data (red)

The latest fully-smoothed data anomalies (October 2014) moved little, being warm and slightly dry.

Loops in the subsoil anomaly graph

The parametric plot of subsoil temperature anomaly against that of daily maximum temperature (bottom right) shows several clockwise loops. That is, peaks or troughs of subsoil temperature precede those of daily maximum (air) temperature by a month or more. This is not what one would expect. Indeed, where graphs of these variables earlier in this sixteen-year record show such loops, they are always anti-clockwise. Subsoil temperature anmalies lag those of daily maximum air temperature. See the graphs for August 2002, August 2004, August 2006, August 2008, May 2010, and April 2012.

In the last mentioned graph, the three extreme points included show no lag between the two variables. That period, from early 2009 to late 2011 marks the transition from a stable regime of subsoil temperature lagging daily maximum air temperature to the current regime of subsoil temperature leading daily maximum air temperature.


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.

3-year trends to March 2013

Parametric plots of smoothed climate variables at Manilla

“Now cool and wet”Trends to March 2013.

While raw values of temperature anomalies were not as low as in February, March was further towards cool, moist conditions than December or January, or any months since July.

Fully-smoothed data points (red) for September 2012 continued to move towards drought. The dew point anomaly reached a seventh successive new record low: -3.37 degrees.

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.