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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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.

April 2016 also warm

Photo of red flowers

Red flowering gum

In the whole month, only one day and seven nights were cooler than normal. Days and nights warmed together. Weekly average temperature was 4.1° above normal early in the month, and again 3.5° above normal at the very end.
Rain was recorded only on the 10th (5.8 mm) and the 11th (13.0 mm). While the early morning dew point was high only when it rained, the afternoon humidity was always high, falling below 30% only once.

Weather log for April 2016

Comparing April months

Daily maximum, minimum, and mean temperatures were all very high but not record values for April. The mean of 20.5° was beaten by 20.6° in April 2005. In that month, this month’s daily maximum (29.0°) was also beaten (29.5°). This month’s daily minimum (12.1°) was beaten by the record value of 12.2° set in 2014.
The subsoil temperature, and other variables were near normal.
The total rainfall of 18.8 mm was well below the average of 40 mm, in the 32nd percentile. However, for the sixth month in a row, there are no serious rainfall shortages for totals for any number of months. Now, the greatest shortage is the 48-month total of 2191 mm, which is in the 12th percentile. Ponds persist in Greenhatch Creek.

Climate for April 2016


Data. 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.

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.

April Climate Anomalies Log

Heat Indicators log for April months

This post is the second in a set for the 12 calendar months. Graphs are sixteen-year logs of the monthly mean anomaly values of nine climate variables for Manilla, NSW, with fitted trend lines. I have explained the method in notes at the foot of the page.

Raw anomaly values for April

April anomalies had few extreme values in this period:
Daily Maximum Temperature anomaly +3.4°: April 2005;
Morning Dew Point Anomaly -3.3°: April 2008;
Morning Dew Point Anomaly -4.8°: April 2013;
Rainfall anomaly +79 mm: April 2003.

Trend lines for April

Heat Indicators

The trends of all three air temperature anomalies were almost the same. They began very low in 1999, reached a maximum in 2002-3 and a minimum in 2009-10. The trend of subsoil temperature began similarly, but with much less variation, and peaked in 2012.

Moisture Indicators log for April months

Continue reading

Warm humid nights in April 2014

The daily weather log

April-blooming Deane's wattle

April-blooming Deane’s wattle

After a cool wet week at the end of March, April began warm, especially at night. The night of the 5th, at 18.8°, was the second warmest April night. Rain fell overnight, and the dew point, 18.5°, was an April record. The third week was sunny but cool, and the fourth week nearly four degrees warmer than usual. The last day of the month was suddenly cold (16.9°) and overcast, with drizzle.Weather log April 2014

Comparing April months

The mean minimum temperature was a record 1.7° above normal for the month, warmer than in April 2005, and the mean maximum temperature was also slightly up. The subsoil, after more than two years above normal (by as much as 2.4° in winter 2013), finally cooled down in March and April.
Moisture was near normal, with low rainfall offset by cloudy skies.
Although the total rainfall of 13.0 mm was below the April average (40 mm), it was not unusually low but in the 28th percentile. Taking rainfall totals for more than one month, the greatest shortages are not serious (i.e. not below the 10th percentile). The nine month total (336 mm) is in the 14th percentile. Other totals have higher percentile values, and most totals for 30 months or more are above normal. Pools still survive in Greenhatch Creek.Climate April 2014


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.