July 2015: average, wet and dull

The title of this monthly review is probably very misleading as July was a month that blew hot and cold.

The Casella 'check' thermometer registered 35.8C on July 1st - 0.3C lower than the AWS reading, within the contraints
The Casella ‘check’ thermometer registered 35.8C on July 1st – 0.3C lower than the AWS reading, within the contraints

The start of the month began with the July all-time record being set: 36.1C. The month ended with a couple of very chilly nights: 6.9C in the early hours of 31st with a grass minimum of 4.5C. I haven’t yet been able to go through my records but, according to the Met Office, temperatures in southern England on the same night that fell to 1C represent an all-time low July record.

There were ten occasions when the maximum exceeded 25C. Mean temperature for the month was 18.6C, 0.1C above the 1981-2010 mean and the coolest July since 2012. Rainfall of 70.4mm was 162% of average though it is worth noting that three quarters of this was recorded on two days.

There were 174 hours of sunshine recorded in this area which is 91% of what we can expect to see during an average July. The wettest day occurred on the 24th with 32.4mm of rain. There were two days of thunder recorded.

IMG_3877So what has August got in store weatherwise? The models this morning (August 1st) suggest very little change in the overall pattern of things. The jet stream is still well south across the Atlantic and is likely to remain so for the forseeable future. However, because we are on the eastern side of the troughed flow across the eastern Atlantic this allows the potential for some very warm or even hot conditions to be drawn up across the UK in the coming five days and possibly beyond. However, the longer projections turns the flow more west to east across the south of the UK again returning cooler air to the SE as well in week two.

This means a continuation of changeable conditions as low pressure remains anchored in the north-west or north of the UK. Thunder could be likely.

In contrast to the models my long range method suggests that we are in for a rather cool August, about 1C below average, at 41% probability. The next highest probability is for something average at 27% probability. So an average to rather cool August works out at 68% probability.

Rainfall is uncertain. There is the same probability for dry (50% average) and very wet (175% average): 23% probability. However, the next highest probability is for average at 18%.

This grainy image shows distant lightning illuminating a cloud. The storm was centred over St Albans
This grainy image shows distant lightning illuminating a cloud. The storm was centred over St Albans on July 16th

My data for sunshine only stretches back to 1878. There is a 73% chance of a duller than average August.

My July outlook was very poor, I predicted a rather warm to warm month – but it was nothing like last year’s or the 2013 classic. My rainfall and sunshine predictions were also hopelessly out. However, it was the first month since January that my temperature forecast has been wide of the mark. It’s just weather – in that it frequently doesn’t do what you think it’s going to do.

Here follows the full weather diary for July…Full stats for the month here:http://1drv.ms/1rSfT7Y

1st: Sunny until after midday when cloud bubbled up and took edge of temperature. Hottest July day ever was set at 5pm. Breeze made it feel bearable.
2nd: Sunny start though cloud quickly built with rain at midday. Just 0.3mm fell which evaporated on impact with the hot ground.
3rd: Sunny, clear day though humidity began to build from mid afternoon with the appearance of cloud. Still sunny spells till late into the evening. Big thunderstorm from around midnight for an hour.
4th: Sunny and muggy start. Long sunny spells, hardly a cloud in the sky until later. Sunny dawn but rain arrived at 9am.
5th: Light rain to start. This cleared late morning to sunny spells. Feeling muggy.
6th: Sunny start though lots of fair weather cumulus bubbled up.
7th: Cloudy start with light patchy rain around 11.30am, clearing to sunny spells. Some rain after 9am.
8th Cloudy and blustery with rain in the air. A few showers around.
9th: Sunny with just a few clouds, low humidity. Sky completely cleared after 3pm for a gorgeous evening.
10th: Sunny start. Some cloud bubbling up as jetstream neared – lots of cirrus and then cirrocumulus forming. Turned sunnier late afternoon. Also dawned clear and sunny.
11th: Long sunny spells with just a few cirrus and cumulus at times. Feeling warm and humid. Some light rain around midnight but not amounting to much.
12th: Cloudy and comparatively cool compared with recently. Light rain at 5pm with drizzle in wind through evening. More rain at 7.30am that fell intermittently up to obs time.
13th: Light rain to start with bursts through morning to 10.45am. Further bursts of light rain into early afternoon then overcast and muggy all night. More drizzle early am.
14th: Drizzly start – this continued into late morning. Then overcast and muggy. More drizzly burst overnight into the early hours – drizzle was persistent from 8.30am to 9am.
15th: Sunny intervals after light drizzle.
16th: Bright and sunny spells tending to turn more cloudy after midday. Big electrical storm around midnight with 67 flashes per minute seen to the north-west.
17th: Light drizzle to start turned to bright spells and a pleasant summer’s day.
18th: Sunny start with cloud bubbling up late afternoon. Light rain shower at 8.30 at end of Music in Wanstead Park and again in early hours at 6am.
19th: Sunny morning tended to cloud in at midday before cold front cleared to leave sunny evening. Mackerel sky at dusk with light rain at 8.15am.
20th: Showery rain to start.
21st: Sunny start but clouds bubbled up through the day for long sunny spells. Warm with a breeze.
22nd: Sunny start, cloud bubbling up during the day with spots of rain at 5pm – heavy shower in Wanstead.
23rd: Cloudy with occasional bright spells, feeling humid.
24th: Drizzly start. rain started falling at 11am. Outbreaks of prolonged rain through the day, heaviest between 5pm and 6pm. More rain after 8pm but then a drier interlude before more rain at midnight as occluded front came back. Last tip of the gauge just before 4am.
25th: Sunny and breezy though much cooler. A pleasant evening at John’s party though. Cloudy spells overnight before rain moved in at 9am.
26th: Rain to start with heavy outbreaks up to 1pm. Further outbreaks of rain through the day and into the evening.
27th: Drizzly bursts of rain to 11am. Then dry and bright.
28th: Bright and breezy to start. A light shower in evening then cool and clear – sunny start.
29th: Bright start but cloud filling in. Burst of rain at 8.30pm then variable cloud overnight.
30th: Bright but a burst of rain just after 10am. Then mostly cloudy with a few bright breaks.
31st: Sunny start but cloud filled in.


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