Winter 2010 wet, with few frosts

 An episode of maritime climate

I have posted this seasonal report for winter 2010 on the front page, as a sticky post, to show how the climate of that season was not normal. It was not the average temperature or the rainfall that were unusual. The sky was very cloudy, the humidity very high, and the daily temperature range very low. The climate was equable, as one would expect at a place near the sea: a maritime climate. More in the footnote*

Weather log winter 2010

Temperatures this winter changed little from month to month. June, July and August each had temperatures near the season averages: maximum 17.0°, mean 10.7° and minimum 4.5°. Warm days were rare: only 11 exceeded 20° (usually 25). This winter was even less frosty than the last, with only 32 frosts (usually 44). The lowest minimum was -3.1°.
There were 33 rain days, about twice the usual number.

In terms of daily mean temperature, this winter was normal, However, cool days and warm nights made the daily temperature range (12.5°) narrower than in any winter in the 12-year record. It was also the cloudiest, at 49% cloudy mornings. Manilla’s climate became much more cloudy three years ago, when the average number of cloudy mornings in a month jumped suddenly from nine to twelve (See also these other graphs.). Humidity, as shown by early morning Dew Point was also very high this winter. All these changes reflect a more maritime climate, as on the coast.
Each month would have had rainfall close to average, were it not for one reading of 34.2 mm at the end of July. The total of 160 mm is in the 70th percentile, like that of the wet winters of 2005 and 2007.

Climate winter 2010

*Footnote. The nature of this episode is clear on the 3-year graphs of climate trends, such as that for August 2011. The top left graph shows that, in June, July, and August 2010, rainfall was a little high and daily maximum temperature rather low. The bottom left graph shows the main anomaly: daily minimum temperature remained extremely high while daily maximum rapidly fell, reaching a record low value by October 2010. From July to November that year the difference between daily maximum and daily minimum temperature was some three degrees less than normal.
The middle graph on the right shows directly that the daily temperature range in those months was at record low (narrow) values.

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.

July 2010 Rain Twice Average

The daily weather logWeather log July 2010 Manilla

July began cold. The 2nd, with a maximum temperature of 9.1°, was the coldest July day in the record from 1999. The only two colder days were: 8/06/07 (8.8°), and 20/06/07 (8.3°).

Two warm spells followed, marked mainly by nights that were very warm for mid-winter. The minimum on the 12th (11.8°) was 10° above normal, and that on the 31st (13.5°) was 11.3° above normal. Colder nights included twelve mild frosts, the fewest on record.
There were 13 rain days spread through the month. The reading of 17.2 mm on the 29th was topped by 34.2 mm on the 31st.

“Normal Temperature”

Each Manilla monthly weather graph has dashed curves to show the temperatures that are normal for each day of the year. They are harmonic curves matching 10-year averages from March 1999. On this July graph, the lowest values are marked with a double “X”. Winter cold is due to lack of heat from the sun, which yields least heat on the 21st of June (the winter solstice). On that day the sun is lowest and shines the shortest time. However, it takes many days for the air to cool down. On average, the coldest day in Manilla comes 17 days later (July 8th) and the coldest night 22 days later (July 13th). Manilla’s coldest day and night follow the solstice with an unusually short lag time. (See Wikipedia: Seasonal lag.)

See the monthly weather report for January 2010 for the highest normal temperatures of the year. These relationships are shown on a graph here.

Comparing July monthsClimate July 2010 Manilla

Due to cloudy nights, the mean daily minimum temperature (4.6°) was by far the highest in the 12-year record for July, and 2.4° above the average. Because the mean maximum temperature was normal (16.9°), the mean average temperature was also high (10.8°). The mean daily temperature range (12.3°) was the narrowest in the July record.

Very high humidity was shown by a mean early morning Dew Point of 4.6°, higher than any since July 1999 (5.7°). The percentage of cloudy mornings (61%) was the highest, not only for July months, but for any month in this record. Nineteen mornings were completely overcast.
The rainfall of 79.8 mm is in the 90th percentile for July: only 12 July months have been wetter. It is close to double the long-term average of 41 mm. As a result, total rainfalls for the last two months and three months are now above the median. No serious rainfall shortages remain. The worst shortages are far from serious: the 15-month and the 9-year totals are both in the 14th percentile.

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.

June 2008 warm, with rain

The daily weather log

Weather log June 2008

Most of June was very warm. The 7-day average temperature stayed three degrees above normal for the first three weeks. All five rain days came during that time. The first, with 38.2 mm, was the wettest June day in a decade. By the 4th of the month the average rainfall for June (44 mm) had already been beaten. Sadly, the total rose only to 65.2 mm, the same as last year. Around the rainy days the nights were about 7° warmer than usual, and humidity was high (morning Dew Points near 10°). There were frequent fogs, including one on Saturday the 7th that was widespread and thick, and lasted a long time.

The fourth week saw a return to normal June temperatures, with sunny cloudless days. Frosts came back, but there were only eight altogether instead of the usual thirteen.

 Comparing June months

Climate June 2008

This June was warm and humid. However, due to the cool, dry change in the fourth week, it was no warmer or more humid than June of 2005. The graph shows that June 2005 had very high rainfall. It was the sixth wettest June on record.

While this month had more cloud than usual, June last year was much cloudier, and had bitterly cold days – nearly five degrees colder! By contrast, sunny June 2006 had very cold nights, including 21 frosts.
The rainfall total of 65 mm is high. It is in the 78th percentile for June, and nearly twice the median value (36 mm).
The rainfall total for this May and June together (79 mm) is in the 38th percentile of two-monthly totals, while the three-monthly total (99 mm) is in the 23rd percentile. Being above the tenth percentile, these do not count as “serious” shortages of rainfall. The four-month total (101 mm) is a serious shortage: it is only in the 9th percentile. The five-month total is much better (in the 35th percentile). Rainfall totals for longer periods are all normal, that is, near the median.

Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Dew point values before August 2005 are from Tamworth Airport 6 am data supplied by the Bureau of Meteorology. Temperature and other data are from 3 Monash Street, Manilla.


December 2007 cool, humid, cloudy, rainy

The daily weather logWeather log December 2007

Only four days, early in the month, had daily maximum temperatures warmer than normal. Decembers average five days over 35°, but there were none this month. The 22nd was nine degrees cooler than normal, at 24.2°. Daily minimum temperatures varied around the normal values (16°). The 7-day daily average temperature stayed below normal most of the time.

The graphs include the humidity of the air, using the Dew Point idea. All air contains moisture. If it cools to its Dew Point temperature, it gets so moist that cloud or fog forms, and dew appears. On humid days when the Dew Point is above 17°, most people find the weather unpleasantly sultry or sweaty. They find air with a low Dew Point, such as 5° or 10°, very pleasant and refreshing. The Dew Points shown on this graph are the early morning minimum values. Morning Dew Points this December were often between 15° and 18°: too humid for comfort. They never came below 10°.
Many mornings this month were overcast, and there were never two fine mornings together until the 29th.
There were fourteen rain days, with a total rainfall of 129.4 mm. The wettest day was the 4th, with 25.2 mm. There were only two runs of four days without rain, beginning on the 18th and 28th.

 Comparing December monthsClimate December 2007

The average daily maximum temperature this month, 29.4°, was far below the average for the last nine Decembers (31.7°). Only December 1999 had a slightly lower value (29.2°). The daily mean temperature (23.0°) was below average (24.0°), and the daily minimum temperature (16.6°) was near average (16.4°). As a result, the daily temperature range this month was only 12.8°.

The mean morning Dew Point for December 2007 is 14.2°. This high value, (meaning high humidity) seems to be about 2° above normal, but my record is short.
This was one of the three cloudiest months in nine years. The other two were also in 2007: November (50%) and June (60%).
The rainfall total of 129 mm makes this a very wet month. Only 14 Decembers since 1884 were wetter.
The year 2007 was wet: the total rainfall amounted to 741 mm. This is on the 68th percentile, meaning that higher rainfall has occurred roughly one year in three. The rainfall was 90 mm above the average (651 mm). It was the highest total since the strange wet year of 1998 (919 mm). That year nearly 400 mm more rain than usual fell in the six months that are normally the driest: from April to September.

Data. Rainfall data is from Manilla Post Office, courtesy of Phil Pinch. Dew point values before August 2005 are from Tamworth Airport 6 am data supplied by the Bureau of Meteorology. Temperature and other data are from 3 Monash Street, Manilla.