The coldest and wettest days of June

Looking out the window on a cold and miserable June afternoon yesterday reminded me of similar such days during the Seventies and Eighties.

But the mind plays tricks and I wondered if these kind of days were that common in the past.

To weed out the also-rans qualifying days had to be sunless with an anomaly that was at least 4C cooler than the daily average and rainfall of at least 12mm.

This gave the following list.

24hrd

So, in the last 60 years there have been only 12 days similar to June 10th 2019. That would give a probability of less than 1% (0.00743)

Looking elsewhere it would appear that there was much more rain to the north, south and west of Wanstead.

rain all

 

 

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The curse of June 13th

1 Jun 21 Jun 16 Jun 77

June can be a strange month weatherwise. Scorching temperatures as well as washout, cold weather, perhaps epitomised by the Queen’s Diamond Jubilee pageant on the river Thames in 2012, can feature prominently.

The month can also throw up some striking anomalies, none more so than the fact that the 13th is the only day in the month where the temperature has ever reached or exceeded 30C anywhere in the British Isles.

According to TORRO the highest daily maximum recorded in the UK is 28.3C at Earls Colne, Essex, in 1948; at Brixton, south London, in 1896 and Aboyne in 1994. Yet either side of this date has records comfortably above 31C, as the table below shows.

torro.PNG

The closest we’ve got locally to 30C in the last 60 years was in 1989 when 27C was recorded.

So why is the 13th ‘cursed’ with traditionally being the coolest day of the month? The best explaination perhaps is the fact that the date occurs more or less during the middle of the North-west European monsoon.

According to Philip Eden’s list of singularities the June monsoon can strike any time between the 1st and 21st but normally peaks on the 16th with a 77 per cent frequency.

As well as cool temperatures the phenomenon can also bring copious amounts of rain, as happened in 1903 when large parts of Redbridge were inundated following a 59-hour deluge that started on… the 13th.

Will we see a repeat this Thursday? Unlikely, though the general pattern is not that different to what led to events over a hundred years ago.

13th

 

 

May 2019: average but dry

May finished average though the final figure, like April, masked cool warm spells.

The mean temperature finished 13.2C that’s 0.1C above average and nearly 2C cooler than last May.

Only 28.3mm of precipitation were recorded, 55.3 per cent of the 1981-2010 average.

Some 175.8 hours of sunshine were recorded, that’s 96.8 per cent of average..

To view full stats follow this link:http://1drv.ms/1kiTuzv

may tmax.PNG
‘Feels like’ maxima.
may 2019 feels like.PNG
May 1981-2019 maximum anomalies
may since.PNG

 

The 12 month rolling rainfall total has fallen below 470mm for the first time since July 2017.

12 month.PNG

Summary for May 2019

Temperature (°C):
Mean (1 minute)  13.3
Mean (min+max)   13.2
Mean Minimum     8.1
Mean Maximum     18.4
Minimum          2.5 day 11
Maximum          25.3 day 23
Highest Minimum  16.0 day 25
Lowest Maximum   10.9 day 04
Air frosts       0
Rainfall (mm):
Total for month  28.3
Wettest day      7.3 day 07
High rain rate   52.3 day 26
Rain days        11
Dry days         20
Wind (mph):
Highest Gust     20.6 day 04
Average Speed    1.9
Wind Run         1637 miles
Gale days        0
Pressure (mb):
Maximum          1041.8 day 13
Minimum          991.6 day 08
Days with snow falling         0
Days with snow lying at 0900   0
Total hours of sunshine        0.0

Front loaded rainfall months

Since February most of this region’s rainfall has been falling during the first half of the month.

feb

February: 86%

march

March: 134%

april

April 28%

may

May (to 26th) 54%

With only one of these months wetter than average the long-term, rolling trend continues to head downwards.

rolling

Considering past rainfall patterns it can only be a matter of time before the graph heads upwards again. Looking further back at rainfall data to 1961 reveals the extremes were higher and that the jump from dry to wet can be sudden.

The wettest 12-month rolling period ended mid way through May 1975 with a total of 873mm. However, just 16 months later, at the end of the hot summer of 1976, the rolling 12-month average was just 302mm, that’s less than half of our average annual rainfall!

average rain

 

The climatology of Zermatt

Zermatt and the surrounding Valais area in Switzerland has a varied Alpine climate. But a study of weather data back to the beginning of 2011 reveals distinct seasonal patterns in terms of air pressure and precipitation.

Although these patterns can’t be relied on completely in terms of planning a wintersport or summer climbing trip awareness of the extremes can be a big help. Knowing when pressure is usually highest can help mountaineers pick that ideal week in summer to tackle 4,000m peaks. Similarly pinpointing weeks with lowest pressure and highest precipitation is the holy grail for those hunting for powder snow.

Looking at the averages pressure is highest on December 23rd. Further scrutiny of rolling weekly averages shows this date coincides with the week commencing December 20th. Anyone who’s been to the Alps at Christmas time will know that this period can be very unreliable for deep snow cover. In terms of summer pressure is highest on August 21st.

Pressure is lowest on February 2nd. Again this date often coincides when the deepest snowfalls often arrive after weeks of dry weather. Despite the unsettled pattern at this time annual precipitation is usually greatest at the end of October / beginning of November. I’ve lost count of the number of times the press interpret these early snowfalls to be a sign of a bumper season ahead only for the skies to clear at the end of November and, sometimes, the arrival of unseasonably warm weather.

The second wettest period is usually the end of April / beginning of May. Again, this past week has seen some parts of the Alps record the best snowfalls this season.

zermatt pressure

zermatt rainfall

April 2019: average and dry

April finished average though the final figure masked cool and warm spells.

The mean temperature finished 9.7C that’s 0.1C below average and 2C cooler than last April.

Only 11.9mm of precipitation were recorded,  28 per cent of the 1981-2010 average and almost as dry as April 2017.

Some 170 hours of sunshine were recorded, that’s 106 per cent of average.

Four air frosts were recorded.

To view full stats follow this link:http://1drv.ms/1kiTuzv

april2019max
‘Feels like’ maxima.
april 2019
April 1981-2019 maximum anomalies
april 1981-2019

Where’s east London’s rain coming from?

April 2019 was yet another dry month. Just under 12mm was recorded, that’s 28 per cent of average.

There has been rain around but the prevailing wind has not been conducive for great amounts to fall here. Last weekend, over a period of 5 days, just 0.9mm fall. Yet Capel Curig in Snowdonia, 200 miles northwest as the crow flies, recorded 130mm thanks to a NW’ly regime.

A look at rainfall in Wanstead back to July 2013 shows that of the 3,550mm recorded just 17 per cent has fallen when the wind was NW’ly.

Because of the topography of the area most of our rain falls when the wind is blowing between SE’ly and SW’ly, a total of 43 per cent.

A westerly is usually reliable for rainfall, however because this area is in the lee of high ground areas such as Hampstead westerlies have delivered just under 8 per cent of that 6-year total.

rain rose

How April has warmed in London since 1980

april 1981-2019

The above graphic shows maxima recorded in the month of April with shading to represent the anomaly of each day relative to the 1981-2010 average.

The last two years show the warm spells experienced in the second half of the month. The overall impression is that warming seems to have accelerated since 2011.

 

March 2019: mild and wet

March was mild, particularly compared with last year. And wet though, like February, the rain fell at the start of the month, leaving a dry end.

The mean temperature finished 9.4C that’s 1.7C above average and over 3C warmer than last March.

Some 54.5mm of precipitation was recorded,  134 per cent of the 1981-2010 average.

Some  109 hours of sunshine were recorded, that’s  precisely average.

Just one air frost was recorded.

To view full stats follow this link:http://1drv.ms/1kiTuzv

march 2019
‘Feels like’ maxima.
march 2019 feels like
key

Is it warm, cold or just normal?

Saying how warm or cold a day feels is subjective; one person’s hot day in spring is another’s ‘on the warm side’. Similarly when someone says the temperature on any given day is ‘normal for the time of year’ others will be exclaiming how cold they’re feeling.

The ‘heatwave’ in February was a case in point. Though many places recorded their warmest February maxima on record many were saying it was just a nice, warmer than normal spell of weather.

Some years ago the Met Office issued guidance on how warm or cold a day was relative to the anomaly. Earlier this month the table was posted on Twitter and I have plotted a graph for the spring period.

Today’s (March 22nd) maximum of 11.1C is therefore described as ‘normal’.

temp feel

cold hot warm

 

Meteorology-based musings about east London and beyond

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