April 2008: fog and black frosts

The daily weather log

Weather log April 2008

Usually, the air cools and dries out quickly during April. This time only the daily maximum temperature came steadily down. The average temperature hovered near 16° until the last days.
At first, the air was very dry, with a Dew Point below 5°. Under a clear sky on the 4th the early morning temperature went down to 2.1° in the screen, which would be 0.1° of frost. Because the Dew Point (-3.8°) was much lower than that, there was no ice on the grass, which made it a “black frost”. It is said that frosts seldom occur in Manilla before ANZAC Day (April 25th).
As the month went on the air got moister. By the 24th the clouds in the overcast sky were down on the hills. On the 26th the town was blanketed in fog as the humidity hit 100%. (Temperature and Dew Point were both 8°.)
Evaporation was increased by strong winds on the 27th and 28th.
Dry southerly air made the last three days cool and sunny. Black frosts came back giving screen temperatures of 0.6° and 0.1° (around 2° of frost).
Practically no rain (3.6 mm) fell in more than seven weeks from 29 February to 21 April. After that, there were four rain days, including 12.8 mm on the 24th. In total, 20.2 mm fell in April, on five rain days.

 Comparing April months

Climate April 2008

The mean temperature this month was nearly as low as the coolest  April in ten years (1999). This was the fifth cool month in a row: December (1.0° down)  January (1.9° down) February (3.1° down) March (0.9° down) and April (2.1° down). As a 5-month average the temperature was 1.8° below normal. It is as if Manilla had been moved 400 km south (near Grenfell) or 150 metres higher (like Barraba). (Note added: This was a time of global low temperature.)

The month was as cloudy as usual, but less humid.
At 20 mm, this April’s total rainfall is about 20 mm below average, as in 2001 and 2004. It is much higher than in April 2005, when Manilla was in a rainfall  drought for several months.
The rainfall total for this March and April (22 mm) is in the 4th percentile of two-monthly totals: a severe shortage. However, the three-month total (138 mm) is just below the median, and the totals for 4, 5, 6, 9 and 12 months are all at the median or above it. In particular, the 6-month total (401 mm) is quite high, at the 75th percentile.


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.

 

Cold, cloudy wet February 2008

The daily weather logWeather log February 2008

Reading the 7-day mean temperatures, the month started near normal, but cooled to unusually low figures by the end of the first week – five degrees down! For a week from the 19th it was only two degrees below normal, then back to four degrees down at the end of the month.
Days were particularly cool, running about 29° instead of 33°.  However, the coolest days were not extreme.
The warmest day, Friday the 22nd, reached only 35.5°. The following morning was the warmest at 26.1°.
Dry air arrived from the south on the 24th, with a Dew Point of only 5.8°.
Rain fell frequently until the 19th, with the 6th being the wettest day (32 mm). The 29th was also very wet. There were nine rain days, totalling 115.6 mm. This is nearly twice the long-term February average of 66 mm.
Very few mornings were “Fine” (with no cloud).

 Comparing February months

Climate February 2008

This was by far the coldest of the last nine Februaries, by day and by night. The mean daily maximum of 28.8°, the mean daily mean of 22.2°, and the mean daily minimum of 15.6° were all well below average, by 3.7°, 3.1°, and 2.5° respectively.
The contrast with the last two years is stark: the days in February 2007 were 4.5° hotter, and those in February 2006, 5.2° hotter than this month. (Note added: This cooling was global.)
With 58% of mornings exceeding 4 octas of cloud, this February, along with December 2007 (58%) and June 2007 (60%) was one of the cloudiest months in nine years. Most months in Manilla have about 30% cloudy mornings.

This month’s rainfall of 116 mm is in the 81st percentile of February totals. (Last February’s 128 mm was the seventeenth wettest February on record.) Taking rainfall totals for more than one month, every total up to 12 months is very high: above the 70th percentile.


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.

 

Very cool January 2008

The daily weather logWeather log January 2008

The month began sunny and dry, but two degrees cooler than usual. Three rainy days beginning on the fifth brought high humidity and one daily maximum temperature as low as 24.4°. This is 9.2° below normal! Eight fine days followed, with normal January temperatures.

With a second rainy spell from the 17th to the 21st, days were again remarkably cool: five days were more than 8° below normal. In the dry fine weather that followed, all temperatures – maximum, minimum, and mean – were even lower than when the month began. They slowly rose to normal by the end of the month.
Humidity was normal for January: the morning Dew Point was 10° to 12° in the dry spells and 18° in wet spells, giving an average of 14.2°.
Rain fell on nine days. The wettest day, the 17th, had 17.2 mm, and the total was 65.8 mm.

 Comparing January monthsClimate January 2008

This January had the coolest days in nine years, and the second coolest mean temperature. This month’s mean daily maximum (31.0°) was 2.9° below the nine-year average (33.9°), and an astonishing 4.4° below last year’s figure (35.4°). Because the mean maximum was low and the mean minimum was not, the mean daily temperature range this month (13.7°) was also low.

Using Dew Point to measure humidity, January and February are Manilla’s most humid months. This month’s mean morning Dew Point of 15.3° is normal.

With 39% of mornings having more than 4 octas of cloud, this was a cloudy month, but not as cloudy as December (58%) or November (50%).
The total monthly rainfall of 65.8 mm is 21 mm short of the long-term January average. However, total rainfalls for the last 2, 3, and 4 months are all above the 80th percentile.


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.

 

Cold days in 2007 winter

Weather log winter 2007

The daily weather log

The temperature trends this winter look like a roller-coaster.
June had daily maximum temperatures about four degrees below normal. Two miserable days had maxima eight degrees below. Meanwhile, minimum temperatures were normal.
Maxima returned to normal in early July but, by that time, nightly minimum temperatures were well above normal. All temperatures then plummeted, losing 8°: by mid-July both maxima and minima were about 5° below normal.
By the end of July and early August maxima and minima had shot up again to well above normal. Next, maxima went up while minima went down, making the daily temperature range very large. This temperature range then collapsed to become very small. The winter ended with temperatures near normal.
The high ground in Manilla had 38 frosts* in June, July, and August. The nine-year average is 45. Seventeen nights went below zero and two nights below -4°.
There was quite a lot of rain, but not much fell in July. The amounts were 65 mm in June, 9 in July, and 81 in August. June was above average, July in the second decile, and August in the ninth decile.
There were ten rain days in June, seven in July, and five in August. One event was remarkable: rain fell continuously for more than 36 hours from the morning of 19th August, to a total of 55 mm.
Skies were overcast (8/8) around the periods of rain. In contrast, there were long sunny spells (0/8 or 1/8) in mid-July and the first half of August.

Comparing winter seasons

The average daily maximum temperature was the coldest in the last nine winters. At 16.6°, it was 1.6° below average.
Although the nights of 2005 were warmer, this winter also had warm nights. At 3.4°, they raised the daily mean temperature up to 10.0°, close to normal.
The daily temperature range in winter in Manilla is usually 15.4°. This winter’s cool days and warm nights made its daily range the lowest in these years. It was only 13.2°, typical of places nearer to the coast, such as Singleton.
The winter that stands out is 2002. With the warmest daily maxima (19.2°) and the coldest daily minima (1.7°) it had the remarkably high daily range of 17.5°. Such a range is found mainly in desert areas – which Manilla was at the time!.

Winter is the driest season in Manilla. The average winter rainfall, 125 mm, is just over half the average summer rainfall (227 mm).
This year’s winter rainfall (155 mm) was above average, and near that of 2005 (157 mm). None of the winters on the graph is far from the average except 2002.
The very dry winter of 2002, at 44 mm, was the ninth driest on the 124-year record. It was the driest since 1982 and 1972 (both 32 mm).
The graph just misses the very wet winter of 1998, nine years ago. Split Rock Dam suddenly filled up for the first time. At 304 mm, that was the second wettest winter on record. Only the winter of 1920 was wetter, with 318 mm.
The graph shows the peracentage of mornings with more than four octas of cloud. The winter average is 31%.
This winter, and winter 2000 were the cloudiest. The insulating blanket of cloud stopped the days from getting warm, and the nights from getting cold.
The winter of 2002 had the fewest cloudy days, another sign of how like a desert it was then.

Climate winter 2007

*Frost: A frost occurs when the temperature on the grass is below zero, causing water to freeze in the leaves. Not many stations measure grass temperature. My rule-of-thumb is to declare a frost if the temperature in the thermometer screen (at 1.5 metres) is below +2.2°.

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. Temperatures, including subsoil at 750 mm, and other data are from 3 Monash Street, Manilla.

Fine cold days in July 2007

The daily weather logWeather log July 2007

Most days in July were cooler than normal. The first chart shows cold days persisted for more than a fortnight. The coldest, on the 16th, reached only 10.5°, which is 5° below normal. However, the weather was mainly pleasant, with more fine days and fewer cloudy days than usual.

There were warm nights at each end of the month, including one 7° above normal. In the middle, there were thirteen frosty nights in a row (below +2.2 degrees in the thermometer screen). The lowest temperature for the month was minus 4.4°. There were 17 frosts in total; far fewer than the 28 frosts of July 2002. (Note added in 2014: Up to, and including 2011, minima have been below minus 4° only sixteen times:  June 2000 (5), June 2002 (1), July 2002 (6), July 2003 (2) and July 2007 (2).)

With both days and nights being so cold, the weekly average temperature went as low as 4.7° below normal on the 17th.

There were seven rain days, which is normal, but the highest reading (on the 1st) was only 4.2 mm.

 Comparing July monthsClimate July 2007

This July had colder daytime maximum temperatures than any July in the last seven. Night-time minimum temperatures were also a bit on the low side. July 2002 stands out from the others. It had by far the lowest night-time temperatures in these years: three degrees below the average. Cloudiness was low in both 2002 and 2007.

The month’s rainfall of 9.0 mm is quite low, in the 12th percentile for July. However, there have been few dry months recently, so no totals for more than one month are as low as the 20th percentile.


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.