Record warm nights

Two very warm nights

On two mornings this month, the 21st and 23rd, the minimum temperature in my thermometer screen was higher than it has ever been in July. That is, in the 17-year record that I began in March 1999.
These minimum readings were 14.3° and 14.4°. The highest July minimum had been 13.5° (31/07/2010), and only five readings had ever been above 12°. Such readings are more than ten degrees higher than normal in July.
In fact, one of the nights was much warmer than the minimum temperature indicates.

Minima not always at night

High minimum temperature readings are the usual evidence of warm nights. Unfortunately, they are not the same thing. Especially in the case of very high readings, they can be misleading.
The catch is that we expect daily maximum temperature to occur in daytime, when the sun is in the sky, and daily minimum temperature to occur at night, when it is not. In Manilla’s very sunny climate, the maximum is usually about fifteen degrees higher than the minimum. We can expect the maximum about 3 pm, and the minimum about 6 am.
When a thermometer is read at 9 am (as they are), the maximum reading recorded on it is usually that of the afternoon, and the minimum reading that of just before sunrise. Usually, but not always!
Times when nights are very warm are usually cloudy. The clouds form a blanket that keeps us warm. Because they also block the sun in daytime, the daily maximum temperature may be almost the same as the daily minimum. The times when maxima and minima occur may become vague. As a complication, warm nights tend to happen when warm air comes to us on the wind. Then much colder air often follows. If the cold air arrives before 9 am, it will lower the minimum temperature reading, destroying the evidence of a warm night.

Thermograph Traces

I do not have a thermograph that makes a continuous temperature trace. The trace for Tamworth Airport can be seen here. (Choose a date.)

For this month’s warmest night, the Tamworth thermograph trace shows that the daily minimum temperature value is misleading due to these factors. The night was much warmer.
Between 5:30 pm on the 22nd and 5:30 am on the 23rd, the lowest temperature, which came at 7:40 pm, was 17.8°. Most of the night, from midnight to 4:00 am, was above 20°! Yet the (Tamworth) minimum for the 24 hour period was 12.5°.
Earlier in the month, in the 24 hours to 9 am on the 6th, the conventional maximum and minimum values were highly misleading. The daily maximum was the very last reading (10.0°) and the daily minimum the very first, 24 hours earlier (6.5°). The afternoon maximum temperature was 8.0° and the pre-dawn minimum temperature was 8.2°. On that date, the day was 0.2° cooler than the night!

July 2015 cloudy and cool

Photo sequence of Wood Ducks and ducklings

Wood Ducks Predator Drill

After a week of fine weather, most of the month was overcast, with cool days and warm nights. One day was very cool, 7 degrees below normal. Later, to make up for that, one night was 7 degrees above normal. There were 13 frosts (usually 17).
The news was full of items about cold weather. In fact, the weekly average temperature was not low here.
It rained on ten days, but never more than 6 mm.

Weather log for July 2015

 Comparing July months

For monthly averages, the most remarkable was the cloudy mornings: 55%. Even that was not as high as in July 2010, which had 61%.
The mean daily maximum temperature was just one degree low and the mean daily minimum one degree high. That made the daily temperature range a narrow 13.2 degrees. This also was not quite as narrow as in July 2010.
The rainfall of 18.0 mm was in only the 21st percentile, but it was higher than in last July or in three other recent July months. This month, one rainfall total has fallen into the 9th percentile (a serious shortage): the 24-month total of 984 mm.

Climate for July 2015


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.

3-year trends to July 2015

Parametric plots of smoothed climate variables at Manilla
“July 2015: cooler, moister trend”

Trends to July 2015

July raw anomaly data (orange)

The near-normal values of June are now seen as merely interrupting a trend to cooler, moister climate. July had very low day temperature, very high cloudiness, and very low daily temperature range, but dew point was not extreme. Discordantly, rainfall, which had been very high in June, became very low in July.
Night-time and subsoil temperatures continued their trends towards higher values. (Relatively warm nights have now persisted for 17 months.)

Fully smoothed data (red)

January 2015 was relatively cooler by day than the previous month, but each of the other variables moved only slightly down the graphs.

El Niño

In this record, the last hot dry climate phase that matched an El Niño was in November-December 2009. At that time, the daily maximum temperature anomaly was very high, the rainfall anomaly was low, and the daily minimum temperature anomaly (lower left graph) was a record high.
Later, in November-December 2013, without an El Niño, Manilla had a more extreme hot dry climate phase. As seen on these graphs (marked in blue), 21st century records were set then for anomalies of high daily maximum temperature, high subsoil temperature, and low dew point.
Now, in July 2015, an El Niño is forecast, but these Manilla graphs show no movement as yet away from cool moist climate.


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.

July Climate Anomalies Log

Heat Indicators log for June months

This post is the fifth 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 July

Extreme values of July anomalies in this period were:

Subsoil Temperature anomaly +3.2 deg: July 2012;
Temperature range anomaly (minus) -3.2 deg: July 2002;
Dew Point Anomaly +3.3 deg: July 1999;
Dew Point Anomaly -3.8 deg: July 2002.

Trend lines for July

Heat Indicators

The trend of mean temperature anomalies fell below zero in 2003 then rose to +1 by 2014.
The trend of daily maximum temperature anomalies fell more slowly to -0.5 in 2007, then rose to meet the mean in 2014. The trend of minimum temperature anomaly reached an early minimum in 2002. It rose to a broad peak (+1.4) in 2010, then declined. The subsoil temperature anomaly trend was slightly low in 2004 and very high (+1.9) in 2013.Moisture Indicators log for July months

Continue reading

3-year trends to July 2014

Parametric plots of smoothed climate variables at Manilla
“July 2014 dry again”

Trends to July 2014

 July data (orange)

Most raw anomaly values for July have now moved back to be like the smoothed values during the summer drought. Very few of the partially-smoothed values during the last few months suggested a trend in this direction.

Fully smoothed data (red)

January 2014 is now the latest fully-smoothed data point. Through November, December and January all variables moved decisively away from drought, except for rainfall and daily minimum temperature. In those months, rainfall remained near a (drought) minimum. Daily minimum temperature (which has a cryptic relation to drought) increased, bringing very warm nights in autumn.


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.

 

Dry July 2014

The daily weather log

Photo of sunlit house interior

July sun heats the house

Normal sunny July weather was broken by two rainy days in mid-month and another “rainy” day later. With the first rain there was a very warm night of 11.0°, at the time when nights are usually at their coldest (1.8°).
Late in the month days and nights were two degrees warmer than usual.Weather log July 2014

 Comparing July months

Average temperatures were normal, but the rainfall was low and the humidity (Dew Point) was very low. Recent July months have been quite different. Last July was very warm, July 2012 was very wet (ninth wettest), and July 2010 was very cloudy and wet, with warm nights. This month was not as dry as July 2011, which was not as dry as July in the drought year: 2002.
The total rainfall of 11.4 mm is in the 15th percentile. Taking rainfall totals for more than one month, the 4-month total of 83 mm is now a serious shortage (6th percentile). There are also serious shortages in the totals for 12 months (6th percentile), 15 months (8th percentile), and 18 months (9th percentile), Other totals have higher percentile values, and most totals for 36 months or more are above normal. In the very long term, the 30-year rainfall total (19,314 mm) has just fallen below the median for the first time since August 2010.
(Note. Figures for 30-year totals begin in 1914. The lowest 30-year total rainfall was 18,026 mm (601 mm per year) in November 1940; the highest was 21,031 mm (701 mm per year) in December 1978.)Climate July 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.

Extremely warm July 2013

The daily weather logWeather log July 2013.

There were three warm spells and no cold spells in July. Fourteen days went over 20 degrees, instead of the usual four. There were only eleven frosts, the fewest in 15 July months (usually 17). In five rain days, two high rainfall figures came on the 20th (19.2mm) and the 21st (9.6mm).

Comparing July monthsClimate July 2013.

After June’s extreme cloudiness and rain, July was very near to normal in everything but temperature. The average values of daily maximum, daily minimum, and daily mean temperature were all just under two degrees above normal. The daily maximum and daily mean are 15-year record high values, but the daily minimum had been higher in July 2010: 2.4 degrees above normal.
(Note: My “normal” is the ten year average from March 1999. For the official normal period 1961-1990 there are no Manilla figures (except rainfall). This month’s very high temperatures would be (perhaps) just over 2 degrees above the 1961-1990 average.)
Rainfall, at 29.8 mm, is in the 43rd percentile, a bit below the average (41.1mm). Rainfall totals for 24 months and more are very high. This accounts for the rare appearance of water flowing locally in Greenhatch Creek.


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.