Summary for February 2005

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

HEADLINE:DRY OVERALL: MILD START, COLDER FROM MID-MONTH: SNOW LAST WEEK

(last updated: 03/0900 MARCH-correction to days with small hail)

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; ) Readings taken at 0900 and 1800 UTC. Where the NIGHT maximum

or DAY minimum are significantly different from figures hereunder, this will be noted in the accompanying text summary. There are now two mean daily 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 .. as kept formerly) .. 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.

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TEMPERATURES ETC.

Highest day maximum (date):... 12.3(12)

Highest 24hr maximum (date):.. 12.3(12)

Lowest night minimum (date):...-06.4(28)

Lowest 24hr minimum (date):...-06.4(28)

Lowest overnight grass minimum (date):...-07.6(28)

[ number of days grass minimum < 0degC: ... 13 ]

[ Lowest day maximum (date):... 02.0(24)]

[ Highest night minimum (date):... 10.5(12)]

A. Mean Day (09-18Z) maximum: ... 06.6

A. Mean Night (18-09Z) minimum: ... 02.3

A. Mean of Day Max & Night min: ... 04.5

B. Mean 24hr maximum:... 06.6

B. Mean 24hr minimum:... 02.0

B. Mean of 24hr max & min:... 04.3 [ 0.0 anomaly on eLTA of 4.3degC]

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

Nr of days minimum at 09UTC <0.0degC:08[dates: 17,20-21,23,25-28]

Nr of days maximum at 09UTC >=21degC:00

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:... 22.3 [51% of eLTA of 44mm]

Highest 24hr total:............... 05.2(24)

No. days PPN total >= 0.2:13

No. days PPN total >= 1.0:07

No. days PPN total >=10.0:00

No. days PPN total >=25.0:00

(Notes relating to precipitation & allied observations:

1st: dr(slight)/d(slight) from 0645Z .. credited to 31st January; further light rain 09-10Z; ocnl light rain remainder of day (to 18Z); further idr(slight) early evening;

3rd: very light r (showers?) 08-12Z;

5th/6th: dr(slight) evening/overnight, csd by 06Z;

7th/8th: ir(slight) o/night;

9th: id(slight) morning, csd by 0930Z;

10th: v.light d early hours; ocnl r(mainly slight) during day/evening;

10th/11th: r(slight), ocnl r overnight, csd by ~ 0730Z;

11th: d(slight), ocnl d and/or r(slight) most of day;

11th/12th: r(slight), ocnl r overnight; csd by 12/0630Z;

12th: couple of very light rain showers PM;

12th/13th: light rain showers overnight;

13th: prs(slight), temporarily prs 0825Z to 0900: further very light rain/snow showers through day, but 95% day dry/fine;

15th: ps(slight)>prs(slight)>pr(slight) all within 0915-0925Z; no snow cover, surface damp temporarily only;

17th: r/d(all light) off/on 0930Z-1715Z;

17th/18th: ocnl r overnight;

18th: ir(slight) 14Z onwards, with r short-period 1645/1655Z, csd by 1715Z;

20th: pr(very slight) 1630-1650Z

21st: prs(slight) ~05Z; ps(slight) 0850Z; further light prs/ph[snow pellets]/ps through day, but long dry/fine periods too;

21st/22nd: ocnl s(slight) overnight: further light snow 06Z-0845Z: accumulation by 09Z = 3cm/max 4cm;

22nd: prs/s during day – all light/no impact on surface;

23rd: s(light) ~07-0810Z, ps(v.slight) just before 09Z; further ps(very slight) through day;

24th: rs(slight), ocnl s(slight) since ~0530Z: no effect on surfaces: further rs(slight), ocnl s(slight) most of day/no impact on surface;

24th/25th: s(slight/moderate) late evening, then is(slight) rest of night, with continuous/light snow until 09Z at least: depth = 4cm/max 6cm; light snow slowly easing through morning, with good melt setting in by midday;

25th: further is(light) early afternoon, ceased by ~15Z: rapid melting most surfaces;

26th: rs/s(all slight) from ~0030-0715Z: light/patchy snow cover by 09Z, 1cm over grass, nil/melting elsewhere; ir(slight) between 13 & 14Z: r(slight) 1615Z onwards, continuous at 18Z, csd by 1930Z;

26th/27th: light shower snow/snow pellets ~01Z;

27th: light snow/snow-pellet showers through day: no effect on surfaces;

28th: is(very light) from ~ 1505Z, becoming steadier from 1745Z: light snow (or sleet) off & on through night/see March summary.)

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OTHER TOTALS

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

Number of days hail < 0.5cm diameter:.. 02

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

Number of days snow/rain & snow:....... 10

Number of days snow lying at 09UTC:.... 03

Deepest snow cover (date,s):........... 04 (25)

Number of days fog (visibility < 1km @ 09UTC).. 01

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Additional comments on the weather in February, 2005

13th: 'sleet' showers hardly impacting on weather;

17th: f (~800/900m) 1615-1715Z;

19th: exceptional visibility all day, well in excess of 50km (Arctic-origin airmass);

22nd: average snow depth (09Z) = 3cm, maximum 4cm, but many road/paved surfaces either clear or only patchy cover; by 15Z, all snow gone (apart from very isol clumps);

25th: average snow depth (09Z) = 4cm, maximum 6cm, with all road/paved surfaces covered/ 1 to 2 cm, perhaps a shade more; snow melted through day, with rapid melt all hard/paved surfaces afternoon, only patchy cover grass by 18Z;

26th: irregular snow cover at 09Z after overnight light snow: grass average 1cm; hard/paved surfaces virtually nil (but at 07Z, around 0.5cm in some spots); all snow gone by 15Z;

27th: remarkably dry air for several hours during day with RH <<50%;

... 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 07.4 09.9 06.9 00.1 07.5 08.6 00.1 00.2 -

02 05.5 08.9 04.9 00.1 06.0 08.0 - - A

03 02.9 07.0 -00.7 tr 06.5 10.1 tr tr B

04 06.6 08.8 06.0 - 07.0 09.3 - -

05 03.4 07.7 00.3 - 04.8 07.1 - 00.5

06 04.8 05.8 04.0 00.5 05.6 09.1 - -

07 01.0 06.9 -01.4 - 02.8 07.1 - tr

08 01.7 04.5 -00.6 tr 04.5 08.6 - tr

09 04.4 07.7 02.2 tr 07.6 09.8 tr tr C

10 08.3 10.1 07.2 tr 09.6 11.2 00.8 04.4 D

11 05.5 09.7 05.4 03.6 05.9 10.5 00.6 02.4 E

12 10.5 11.7 10.5 01.8 08.0 12.3 tr 00.7 F

13 02.1 08.0 00.7 00.7 02.1 06.4 tr tr

14 01.8 06.0 00.1 - 02.8 06.0 - -

15 01.6 04.9 00.0 - 02.1 06.1 tr tr

16 01.2 03.5 -00.7 - 02.6 04.4 - -

17 -00.3 03.0 -02.7 - 02.3 06.0 00.4 01.0

18 03.5 06.0 00.1 00.6 04.4 08.7 00.6 00.6

19 02.5 06.7 00.7 - 02.8 05.4 - -

20 -01.4 03.6 -03.0 - -00.3 04.3 tr tr G

21 00.6 03.3 -01.5 tr 01.2 04.6 00.1 04.0

22 00.2 01.6 -01.5 03.9 01.1 03.1 00.1 00.1 H

23 -01.1 01.4 -02.9 tr 00.5 02.9 tr 00.4

24 00.6 01.6 00.2 00.4 01.1 02.0 01.9 05.2

25 -01.3 01.8 -03.7 03.3 -00.6 02.2 00.5 01.2 I

26 -01.0 01.9 -05.0 00.7 01.9 04.6 00.9 01.0 J

27 -00.5 04.4 -02.1 00.1 00.4 02.6 tr tr

28 -06.4 00.4 -07.6 - -03.1 02.9 tr 00.6 K

Remarks:

A. night max.(8.9) was also the 24hr max for the 1st

B. day min.(6.5), also 24hr min 4th, occurred 03/09Z

C. day min.(7.6), also 24hr min 10th, occurred 09/09Z

D. night max.(10.1), also 24hr max 9th, occurred 10/09Z

E. day min.(5.9), also 24hr min 12th, occurred 11/09Z

F. night max.(11.7), also 24hr max 11th, occurred around dawn 12th

G. day min.(-0.3), also 24hr min 21st, occurred 20/09Z

H. PPN at 09Z on 22nd all from melted snow overnight

I. PPN at 09Z on 25th all from snow 24/22Z to 25/09Z

J. night max.(1.9) occurred 26/09Z

K. day min.(-3.1), also 24hr min 1st March, occurred 28/09Z

Number of occasions (24hr periods) THIS YEAR (2005)

maximum temperature >= 21degC (70degF) = 00

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

Summary re: February 2005

TEMPERATURE:

A month when the overall mean temperature is pretty meaningless! The final figure for us gives an anomaly of 0.0C on the whole-month eLTA.

This of course masks the fact that the first half of the month was notably mild, with estimated anomaly at least +2C (day max. 12.3degC on the 12th).

The colder weather really set in around the 20th: the last week's depressed temperatures dragging the overall mean down dramatically. We had to wait until the night of the 16th/17th for the first air frost of the month (breaking a long frost-free period: previous air frost 25th/26th January, the only one for that month), but even then, temperatures on most 'frosty' nights in February were not dramatically low (-1.4degC/20th), until of course the last night, when –6.4degC was recorded, our lowest since January 2002.

RAINFALL:

Total precipitation for the month = 22.3mm (51%), with a significant proportion of that coming from the sleet/snow events of the last week (12.5mm, or just under half of the total).

Summary re: Winter 2004/05

TEMPERATURE:

MEAN MAX(ANOMALY) MEAN MIN(ANOMALY) 24HR MEAN

DEC: 7.9 (+0.3) 2.4 (-0.6) 5.1 (-0.2)

JAN: 8.7 (+1.9) 3.5 (+1.9) 6.1 (+1.9)

FEB: 6.6 (-0.7) 2.0 (+0.7) 4.3 ( 0.0)

Interesting to note that the chill in February was primarily a daytime phenomenon.

PRECIPITATION:

The total precipitation (all types) for the three 'standard' winter months = 98.3mm (55% eLTA). In a composite Easthampstead Park / Tawfield series (1971-2004), the driest such period was that of 1991/92 (42mm): our total this season places us roughly in the 'top-6' of dry winters locally (date order): 1975/76, 1980/81, 1988/89, 1991/92, 1996/97 & 2004/05.

For an extended period including November (total = 139mm), the anomaly is 57%. It is perhaps the extended dry weather, rather than individual monthly anomalies, that is the interesting point here, coming across a period when we would normally expect beneficial rainfall. Other dry Nov-Feb periods locally (since 1971) are:-

1991/92 (106mm)

1988/89 (109mm)

1980/81 (118mm)

1975/76 (128mm)

(November 1996 was wet, so doesn't figure in this list)

RUNNING 12-MONTH ANOMALY (March 2004-February 2005)

+1.0 C

Martin.