Heat: A tale of two airflows

The past few days have offered a couple of perfect examples of how wind direction can have a massive effect on the resulting maximum temperature at this time of year.

Friday, August 12th and Monday, August 15th, were both very similar in that any morning cloud completely cleared by 11am. But while the wind blew from a SW’ly direction on Friday, nudging Wanstead up to a very warm 28.1C, by Monday the high pressure had drifted north, drawing in a cool NE’ly flow off the North Sea. The high temperature in Wanstead on Monday was nearly four degrees cooler at 24.4C.

Under these conditions temperatures will be warmer the further west you go, as the graphs below show.

Highs to 6pm on 12th were: Wanstead 28.1C with Northolt reaching 27C


Highs to 6pm on 15th were Northolt at 25C. Gravesend, being furthest east and most influenced by the cooling North Sea breeze reached 22.6C



July 2016: rather warm and very dry

There was plenty of interest in the weather last month even though the overall stats suggest July 2016 wasn’t that remarkable.

july 9 sky
The sunset on July 9th was spectacular

Most notable was temperature: the warmest minimum on record for this area (21.1C) was recorded during the early hours of the 20th – coming hours after the hottest day of the year: 33.5C – the 14th hottest day on record. The mean temperature of 19.5C  was a degree warmer than average, the 18th warmest July since 1797.

Rainfall was very sparse. A total of 17.3mm fell during the month, that’s 40 per cent of average, the driest for six years and the 19th driest in the series going back to 1797.

After a very dull start to the month sunshine was always going to struggle: just under 172 hours were recorded – that’s 89 per cent of average and marginally down on last July.

Air frosts: 0, Ground frosts: 0

record warm min
The temperature didn’t fall below 21.1C on the night of 19th July, making it the warmest minimum on record in this area back to 1959

So what has August in store weatherwise? The models on the 1st suggest the month will start with a mixture of sunshine and showers. At the end of this week there are indications of a change to warm and later very warm weather.

Beyond the grasp of the models my long range outlook method is hampered this month because of the very dry July. However, the data I do have suggests a rather warm month at 50 per cent probability. The ‘worst case’ scenario suggests something average, a contrast to  the past couple of Augusts which have been poor. Perhaps we can look forward to another reasonable summer month, defined by plenty of fine, at times hot, weather – though anyone looking for unending days of 30C and higher will be disappointed.

A dryer than average month (possibly very dry) looks most likely at 50% probability. A very sunny month looks most probable.

So to sum up: mean 19C (0.8C above average), rainfall 30.3mm (60%), sunshine 239 hours (123%).

hottest dayMy July outlook for temperature was good. I predicted a mean of 18.8C (outcome: 19.5C). Rainfall was very poor: 50mm (outcome: 17.3mm). Sunshine not badr: 171.9 hours (outcome: 190 hours).

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

1st: Cloudy with sunny intervals. Some sharp showers.
2nd: Bright start though breezy. Very heavy shower at 1740.
3rd: Sunny though with lots of cumulus.
4th: Sunny, gin clear start though cumulus rolled in at 1.30pm.
5th: Cloudy start with very brief, very light drizzle though with sunny breaks developing.
6th: Hazy mix of cirrus and cumulus gradually decreased to a clear sky by 1pm. More cumulus bubbled up later but still mostly sunny and low humidity.
7th: Sunny start with lots of cumulus, cirrus and stratus around. Sunny spells through the day.
8th: Cloudy and breezy start.hants
9th: Bright start with sunny spells but also lots of cloud. Amazing sunset with fronts coming in.
1oth: Cloudy start with light rain spreading in but only lasting for 40 minutes. Some sunshine in the afternoon though was breezy.
11th: Cloudy start with heavy showers early afternoon.
12th: Sunny start though with plenty of cloud which bubbled up and gave heavy showers from 11.30am. More showers in the afternoon – miserable.
13th: Bright and sunny to start that cloud gradually built before heavy showers hit at 2pm, these lighter over Aldersbrook.
14th: Sunny, bright start with sunny spells, tending to turn cloudier.
15th: Bright start but cloud piled in and breeze picked up.
16th: Sunny start with lots of cirro-cumulus. Cloud tended to build at times and a front passed over at 4pm. Warm evening and night.
17th: Bright start though with lots of heavy cumulus around. This tended to break up at intervals during the day, making it feel hot in the sun because of the high humidity.
18th: Sunny start with patchy cirrus and cumulus. This decreased as day wore on leaving a hot day. Felt almost airless with variable cloud.
19th: Sunny with decreasing cirrus to start to leave a gin clear day. Breeze picked up at noon meaning it wasn’t as warm as it could have been.
20th: Sunny but hazy start but with more of a breeze than yesterday. Cloud tended to fill in but then burnt off to leave another hot day.
21st: Sunny but cooler start than yesterday with lots of milky cumulus around.
22nd: Cloudy start after overnight rain. Sun breaking through at 12.30pm.
23rd: Cloudy start with spots of drizzle at 11am then slowy getting brighter with evening sunshine.
24th: Cloudy start with early showers breaking to sunny spells.
25th: Sunny start with variable amounts of cloud through the day. Feeling cooler.
26th: Sunny start though with cloud bubbling up through the morning. Overcast by 2pm.
27th: Cloudy and damp with light rain before and after obs time.
28th: Sunny periods with variable cumulus
29th: Cloudy start with brief rain showers in Chigwell. Sky broke to allow long sunny spells before it clouded over again. Rain shower at 9pm.
30th: Cloudy and overcast start. Long sunny spells into the afternoon.
31st: Sunny start though more cloud tending to bubble up in the afternoon.