Press Release February 2018

Meteorological data summary for February 2018 and the three months of summer (December to February) for the Blenheim Meteorological station located at the Grovetown Park campus of the Marlborough Research Centre.

 

Table 1: Weekly temperatures, rainfall and sunshine during February 2018

Mean Max

(°C)

Mean Min

(°C)

Mean

(°C)

Rainfall

(mm)

Sunshine

(hours)

1st – 7th 22.3     (-0.9) 14.6      (+2.2) 18.5    (+0.7) 8.8 58.0
8th – 14th 25.0     (+1.8) 13.8      (+1.4) 19.4    (+1.6) 39.4 59.2
15th – 21st 26.0     (+2.8) 15.6      (+3.2) 20.8    (+3.0) 108.0 62.1
22nd – 28th 20.9     (-2.3) 11.5      (-0.9) 16.2    (-1.6) 25.2 47.1
1st – 28th February 23.6    (+0.4°C ) 13.9   (+1.5°C) 18.8  (+1.0°C) 181.4   405% 226.4     99%
LTA 1986-2017 23.2 12.4 17.8 44.8 227.6

 

Temperature

February 2018 mean temperature of 18.8°C was 1.0°C above the long-term average temperature for February (1986-2017) of 17.8°C.

February 2017 mean temperature was 18.0°C.

February 2016 mean temperature was 20.0°C.  2nd warmest on record

February 1998 mean temperature was 20.7°C. Warmest on record

The second and third weeks of February were the warmest with well above average temperatures. However, the last week of the month was a lot cooler and much more like autumn weather.

The hottest day in Blenheim during February 2018 was the 13th with a maximum temperature of 31.6°C. There were a further 8 days when the maximum temperature was between 25 and 30°C.

The average daily maximum temperature for February 2018 of 23.6°C was 0.4°C above the long-term average.

The coolest overnight minimum temperature during February 2018 was 8.4°C on 8th February.

The average daily minimum temperature for February 2018 of 13.9°C was 1.5°C above the long-term average.

Summer temperatures

The summer of 2017/18 (December to February) will be remembered as one of the warmest on record for Blenheim.  For the 87 year period 1932 to 2018 only one other year (1934-35) has recorded a warmer summer (Table 2).

 Days of 30°C or greater this summer

In Blenheim there were six days that reached 30.0°C or greater this summer; (2 in Dec, 2 in Jan and 2 in Feb).

The summer of 2016-17 recorded no days of 30.0°C or greater.

The summer of 2015-16 recorded two days of 30.0°C or greater; (30.0°C and 32.2°C).

The summer of 2014-15 recorded one day of 30.0°C or greater; (30.8°C).

Table 2: Monthly mean temperatures over the summers of 2014-15, 2015-16, 2016-17 and 2017-18

Long-term

Average

°C

1934-35

Mean

°C

2014-15

Mean

°C

2015-16

Mean

°C

2016-17

Mean

°C

2017-18

Mean

°C

December 16.8 20.1 17.3 15.9 16.7 18.7
January 18.1 20.6 18.8 18.8 18.4 20.7
February 17.8 19.9 17.4 20.0 18.0 18.8
Mean

+/-LTA

17.6 20.2

+2.6

17.8

+0.3

18.2

+0.7

17.7

+0.2

19.4

+1.8

 Sunshine

226.4 hours sunshine for February is 99% of the long-term average for February of 227.6 hours (1986-2017).

February 2017 recorded 246.3 hours sunshine

February 2016 recorded 289.3 hours sunshine. 3rd highest Feb total on record

Table 3: Sunshine hours over the summers of 2014-15, 2015-16, 2016-17 and 2017/18

Long-term

Average

2014-15  % of

LTA

2015-16  % of

LTA

2016-17  % of

LTA

2017-18  % of

LTA

December 251.0 222.6         89% 294.8       117% 253.0       101% 319.1       127%
January 262.5 296.9        113% 232.4          89% 282.0       107% 243.6          93%
February 227.6 264.1        116% 289.3        127% 246.3       108% 226.4          99%
Total 741.1 783.6         106% 816.5        110% 781.3       105% 789.1         106%

 Total sunshine hours for the three months of summer (2017-18) were above average. However, this was entirely due to the fact that December 2017 recorded very high sunshine hours. With high rainfall in January and February 2018, sunshine hours were average to below average.

 Rainfall

Rainfall total of 181.4 mm is 405% of the long-term average for February of 44.8 mm (1986-2017).

The February 2018 rainfall total has entered the record books as the highest February total for the 89 years 1930 to 2018. The previous highest February total was 129.0 mm, recorded way back in 1936; i.e. February 2018 exceeded the previous highest February total by 52.4 mm.

February 2017 rainfall was 61.8 mm

February 2016 rainfall was 18.0 mm

February 2015 rainfall was 15.2 mm

Rain was recorded on 11 days in February 2018. Five of those days recorded greater than 10 mm rain:

11th = 35.0 mm, 19th = 15.0 mm, 20th = 75.2 mm, 21st = 17.8 mm, 26th = 12.4 mm.

19-21 Feb total from ex-tropical cyclone Gita was 108 mm.

Total rainfall for January and February 2018 is 261.8 mm. This is 41% of Blenheim’s long-term annual average rainfall total of 636 mm. This is the highest January/February total on record for the 89 years 1930-2018. In an average year it would take until half way through June for 262 mm rain to be received.

 Table 4: Rainfall for the summers of 2014-15, 2015-16, 2016-17 and 2017-18

Long-term

Average

2014-15  % of

mm          LTA

2015-16  % of

mm          LTA

2016-17  % of

mm          LTA

2017-18  % of

mm           LTA

December 46.5 31.8         68% 17.4          37% 20.2          43% 21.6           46%
January 44.6 4.4            10% 69.2         155% 27.2           61% 80.4           180%
February 44.8 15.2           34% 18.0            40% 61.8         138% 181.4         405%
Total 135.9 mm 51.4 mm    38% 104.6 mm   77% 109.2mm   80% 283.4mm    209%

 Total summer rainfall (Dec-Feb) in 2017-18 of 283.4 mm was 209% of the long-term average total. This is the third highest summer rainfall total for the 87 years 1930-31 to 2017-18. The highest summer rainfall total on record is 309 mm recorded in 1984-85.

 Wind Run

Average daily wind run for February was 236.9 km, 94% the long-term average (1996-2017) of 251.9 km.

The 13 years 2006-2018 have all recorded lower than average wind-run during February.

 Shallow Soil Moisture

Average shallow soil moisture (5–35 cm depth) at the Grovetown Park weather station for February was 27.7%. This is the highest average moisture level recorded for February for the 16 years 2003 to 2018.

Average soil moisture from 1 to 11 February was 20.0%

Average soil moisture from 12 to 28 February was 32.1%

 Potential Evapotranspiration

Potential evapotranspiration for February was 122.4 mm, 109% of February’s long-term average of 112 mm. Given the very high rainfall during February you may be wondering why the potential evapotranspiration was close to average, rather than well below average. However, temperature is a major driver of evapotranspiration, and February’s well above average mean temperature is in a large part responsible for the higher than average evapotranspiration.

It is interesting to note the differences in evapotranspiration for the three months December to February for the four seasons in Table 5, and how these compare with the long-term average. Evapotranspiration was very high in December 2017 due to well above average temperature and radiation (sunshine). Although January 2018 was very warm the evapotranspiration was below average, largely because wind-run was the lowest in 22 years; i.e. when it is calm there is little evaporative demand.

Table 5: Potential evapotranspiration for the summers of 2014-15, 2015-16 and 2016-17

Long-term

Average

2014-15    % of

mm            LTA

2015-16    % of

mm            LTA

2016-17      % of

mm             LTA

2017-18   % of

mm           LTA

December 141.4 126.6          90% 147.7        104% 153.7         109% 177.8        126%
January 142.2 143.8         102% 140.4         100% 181.5          129% 135.6           95%
February 112.0 117.1         105% 142.9         128% 121.9          109% 122.4          109%
Total 395.6 mm 387.5 mm    98% 431.0 mm   109% 457.1 mm   116% 435.8 mm    110%

 Potential Water Deficit

Potential water deficit (Table 6) is the difference between monthly rainfall received (Table 4) and potential monthly evapotranspiration lost (Table 5).

Potential water deficit for February 2018 was +59.0 mm, i.e. there was actually a water surplus in February, not a water deficit.

Potential water deficit for the three months December 2017 – February 2018 was -152.4 mm. This is the lowest potential water deficit for summer, for the 22 years 1996-97 to 2017-18. The long-term average water deficit for summer (Dec – Feb; 1996-2017) is 274 mm.

December 2017, the first month of summer, had very high potential water deficit (-156.2 mm). However, the high rainfall in January 2018 meant that the water deficit was low (-55.2 mm). With the extremely high rainfall in February 2018 (181.4 mm), there was actually a water surplus (+59 mm), rather than a water deficit.

In essence what this says is that there was a need for irrigation in December 2017 when it was very dry. However there was little need for irrigation in January and no need for irrigation in February 2018.

Table 6: Potential Water Deficit for the summers of 2014-15, 2015-16 and 2016-17

Long-term

Average

2014-15       % of

mm               LTA

2015-16       % of

mm               LTA

2016-17      % of

mm              LTA

2016-17      % of

mm              LTA

December -95.8 -94.8             99% -130.3         136% -133.5        139% -156.2          163%
January -99.7 -139.4          140% -71.2              71% -154.1         155% -55.2               55%
February -78.5 -101.9          130% -124.9           159% -60.1              77% +59.0
Total -274.0 mm -336.1 mm   123% -326.4 mm    119% -347.7 mm  127% -152.4 mm      56%

 Plant & Food Research / Marlborough Research Centre

rob.agnew@plantandfood.co.nz

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Filed under Blenheim Weather Data, Weather Press Releases.

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