Summary for April, 2007

=======================

HEADLINE: EXCEPTIONALLY WARM; ABSOLUTELY DRY MUCH OF MONTH

(last updated: 01/0900 MAY)

Location: Tawfield/Wooden Hill area of SW Bracknell, Berkshire, UK

Altitude 80 m (other location details see elsewhere on web site.)

(temperatures [standard screen] degC; rainfall/melted snowfall mm; snow depths cm; )

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TEMPERATURES ETC.

Highest day maximum (date):... 23.9(15)

Highest 24hr maximum (date):.. 23.9(15)

Lowest night minimum (date):... 00.6(05)

Lowest 24hr minimum (date):... 00.6(05)

Lowest overnight grass minimum (date):...-01.5(05)

[ number of days grass minimum < 0degC: ... 03 ]

[ Lowest day maximum (date):... 09.6(03)]

[ Highest night minimum (date):... 12.9(25)]

A. Mean Day (09-18Z) maximum: ... 18.0

A. Mean Night (18-09Z) minimum: ... 06.9

A. Mean of Day Max & Night min: ... 12.5

B. Mean 24hr maximum:... 18.0 [+5.1 anomaly wrt eLTA of 12.9degC]

B. Mean 24hr minimum:... 06.8 [+2.1 anomaly wrt eLTA of 4.7degC]

B. Mean of 24hr max & min:... 12.4 [+3.6 anomaly wrt eLTA of 8.8degC]

(data below relate to 24 hr day beginning 09Z on date given)

Nr of days minimum at 09UTC <0.0degC:00

Nr of days maximum at 09UTC >=21degC:05

Nr of days maximum at 09UTC >=25degC:00

Nr of days maximum at 09UTC >=30degC:00

(Notes relating to temperature & allied observations:

none)

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PRECIPITATION (PPN/mm)

Total rainfall/melted snow etc:... 01.9 [04% of eLTA of 52mm]

Highest 24hr total:............... 01.3(26)

No. days PPN total >= 0.2:02

No. days PPN total >= 1.0:01

No. days PPN total >=10.0:00

No. days PPN total >=25.0:00

(Notes relating to precipitation & allied observations:

3rd: id(very light) ~0850Z, probably dying out during morning (away in Poole);

22nd: ir(scattered/well-separated droplets) between 1520 & 1530Z;

23rd: ir(very light) from 07Z, becoming persistent (isol near-moderate) between 1130 & 12Z, then ir(slight), ceased by 13Z;

24th: ir(slight) from early hours, petering out through second-half of morning; ir(very few droplets) ~1750Z for about 10-15 minutes;

25th: pr(slight/Ac cast) ~0845Z; ir(slight) AM & early PM;

26th: pr(slight)/r(slight), short-period r, between 1215Z & 1515Z;)

=================================

OTHER TOTALS

Number of days thunder heard: (dates).. 00

Number of days hail < 0.5cm diameter:.. 00

Number of days hail >=0.5cm diameter:.. 00

Number of days snow/rain & snow:....... 00

Number of days snow lying at 09UTC:.... 00

Deepest snow cover (date,s):........... -

Number of days fog (visibility < 1km @ 09UTC).. 00

=================================

Additional comments on the weather in April, 2007

(none)

[thunder]

Nil

[snow]

Nil

... these data can also be viewed at:-

http://homepage.ntlworld.com/booty.weather/metinfo/wxdata/climintro.htm

Tn Tx Tg RR Tn Tx RR RR24hr Remark code (below)

(09Z) (09Z) (09Z)(18-09Z) (18Z) (18Z) (09-18Z) (from 09Z today)

01 06.1 12.2 03.7 - 09.0 16.2 - - -

02 05.4 13.9 02.2 - 09.1 17.5 - tr

03 04.9 15.3 02.3 tr 06.9 09.6 tr tr

04 02.6 (06.7)-00.6 - 06.4 11.4 - - A

05 00.6 09.9 -01.5 - 07.4 17.7 - -

06 04.1 16.4 00.7 - 10.8 16.5 - -

07 02.9 14.9 00.4 - 09.9 14.9 - -

08 03.2 14.0 -00.3 - 10.3 17.6 - -

09 05.2 16.1 01.9 - 09.5 17.1 - - B

10 10.6 15.4 09.2 - 14.0 19.1 - -

11 08.7 17.6 05.7 - 13.6 18.0 - -

12 06.0 17.0 03.1 - 11.7 18.3 - -

13 07.8 16.6 06.0 - 12.2 18.0 - -

14 07.2 16.6 04.8 - 11.2 22.5 - -

15 07.8 21.6 04.9 - 14.3 23.9 - -

16 10.6 22.5 07.9 - 16.0 22.3 - -

17 10.5 20.1 08.6 - 12.3 17.3 - -

18 04.2 15.3 01.8 - 10.7 15.7 - -

19 04.5 14.5 01.8 - 12.2 19.7 - -

20 06.8 18.0 03.6 - 12.1 17.0 - -

21 04.1 15.6 01.6 - 12.2 19.0 - -

22 04.8 15.9 02.1 - 15.2 21.0 tr tr

23 09.2 19.2 06.4 tr 13.0 16.5 00.2 00.6

24 11.4 15.8 10.8 00.4 14.2 20.2 tr tr

25 12.9 18.6 09.9 tr 15.6 18.5 tr tr C

26 09.4 17.0 05.7 - 13.2 16.7 01.3 01.3

27 09.5 13.2 08.3 - 11.1 16.4 - -

28 07.8 15.4 05.6 - 13.1 21.8 - -

29 08.4 21.0 07.4 - 12.0 19.8 - -

30 08.4 19.8 06.2 - 13.5 19.7 - -

Readings taken at 0900 and 1800 UTC. Where the NIGHT maximum or DAY minimum are significantly different from 24hr values, this will be noted in the listing against a 'Remarks' letter. There are two mean temperatures shown: the first is the mean of the average day maximum and average night minimum (A), and the second is the average of the 24hr maximum and 24hr minimum (B) .. the anomalies are shown for this latter figure from 1971-2000 estimated Long Term Averages. Rainfall is credited to the 24hr day beginning 0900 UTC.

Remarks:

A. night data for period 21-09Z (away in Poole): night min a 'true' value, night max is the value at 21Z/3rd

B. day min.(9.5), also 24hr min 10th, occurred 09/09Z

C. grass min.(9.9) might be too low / resetting error?

Number of occasions (24hr periods) THIS YEAR (2007)

maximum temperature >= 21degC (70degF) = 05

minimum temperature >= 16degC (61degF) = 00

Rolling 12 month temperature anomaly: +2.2 (was +2.0 end last month)

Dry Aprils

==========

In a composite local record (since 1971), there have been 6 Aprils under half the average (1971-2000) rainfall for the month:

1974: 20 mm (part of a sequence of dry March, April & May)

1976: 12 mm (a notably dry winter, spring & summer)

1980: 20 mm (part of a sequence of dry April & May)

1982: 16 mm (on its own)

1984: 3 mm (on its own)

1997: 11 mm (part of a sequence of dry March, April & May)

All of the above had positive MAXIMUM temperature anomalies (wrt 71-00 mean), exceeding +0.5C, with the last three (1982, 1984 & 1997) >= +1.0C. However, unlike the current month, the 24hr MINIMUM anomalies were *all* negative, with 5 out of the 6 having anomalies >= -0.5C and 4 (1974, 1976, 1982 & 1984) ended up with an anomaly >= -1.0C (1984 –1.9C).

and this year (2007)

2007: total rainfall 2 mm [1.9 mm] would have been part of a sequence of dry March & April, but for the wet first week of March (which effectively marked the end of the rather wet winter).

The total rainfall over the past 8 weeks (6th March onwards) was just 16 mm with most rainfall 'events' below 2 mm in any 24hr period. As a consequence of both the lack of rainfall, the often strong sunshine and the periods of brisk wind with moderate or low relative humidity, the soil both on the surface and to at least 10 cm is notably dry at the date of this summary.

A notable difference from previous dry Aprils (at least over the past 36 years – see above) is that the * minima * were notably above average with an anomaly of +2.1 C, probably reflecting the general increase in average temperatures in recent times: these are the average 24hr temperatures over the last 3 decades (and last 6 years) –

1971-1980: 7.5degC

1981-1990: 7.7degC

1991-2000: 8.8degC (sharp increase over previous)

2001-2006(last 6 years): 8.9degC.

As well as being the driest April in the 1971-2007 dataset, this April (2007) also ties (with October 1978) as THE driest 'any-month' in that series.

The warmth this month has been *consistent*, rather than spectacular on a day-to-day basis. On only 2 days (3rd & 4th) were the maxima below the long-term mean 24hr maximum, all the other 28 daily maxima being comfortably in excess of the mean maximum temperature.

Over the past 12 months, half of them have been either the warmest, or second-warmest months in the 1971-current dataset. There were four 'record-breakers' (July, September, January & April), and all four exceeded the previous 'high' by at least 0.5C.

Martin.