Category Archives: Uncategorized

Diurnal temps present a clothing challenge

The erratic onset of spring in some years often presents that problem of what to wear every morning. During the current warm spell I’ve seen all manner of attire on the school run; everything from T-shirt and shorts to full winter regalia topped off with hat and gloves.

The position of the sun is now bringing in to range the season when the gap in temperature between day and night can be at its greatest.

On Saturday (23/2), virtually unbroken sunshine and ‘thick’ air saw the temperature in Wanstead peak at 16.1C before clear conditions overnight saw the minimum plunge to just 0.2C. The gap of 15.9C represents the fourth highest diurnal temperature range for February in this area back to 1959.

feb diurnal
Top 10 February diurnal temp ranges

 

Looking at the year as a whole the greatest range is 20.8C with the months of May and June the most likely to see the condition.

top 10 diunrals
Top 10 diurnal temperature ranges since 1959

 

Advertisements

An erratic season for snow in the Alps

Earlier this winter there were many reports on how good snowfall had been in Austria. But on closer inspection it was clear that the weather pattern at that time only favoured certain resorts.

In contrast with last year the totals I’ve used in my cross section of the range don’t look that exciting; Bourg-St-Maurice, the jumping off point for Savoie resorts including Les Arcs and Val d’Isere, has recorded 96mm of precipitation this season, in stark contrast to the 433mm it recorded last season between Christmas Day and February 5th.

In Switzerland Arosa, a resort well placed to pick up snow from any direction, has recorded the same this season as last. Totals in Davos are well down on last season. Similarly San Bernardino has recorded about half the amount of precipitation than it did last season. Its location toward the southern side of the range has been sheltered from the prevailing winds this year. That said it did enjoy a big dump last week.

Going further south and east St Vallentin in Italy has recorded about a third what it did at this stage last season.

Mean temperatures overall are about 2C to 3C lower than they were last season.

snowmap update
30-day precipitation totals reveal that Bourg St Maurice recorded just 96mm, compared with last year’s 433mm while Obertauern in the east recorded 77mm, compared with 106mm the same period last year

 

Winter 2017/18: average, cold start and end

The winter of 2017/18 will probably be remembered as much colder that it actually was – the exceptionally severe spell right at the end was only at its halfway point by the time the meteorological winter was over.

pathfinder
Like a scene from the Pathfinder movie

The mean temperature for the season finished 5C, that’s 0.5C below average and the coldest for five years.

Rainfall was above average: 180.8mm fell, that’s 124 per cent of average and the wettest for four years.

Sunshine was just over average: 174.4 hrs is 104 per cent over average and the sunniest for tree years.

As so often with winters at this latitude the average for three months makes it look a non-descript season – it is only when you look at the detail that compelling facts emerge.

The coldest day of the season occurred on the last day of February when the maximum failed to rise above -1C, the first ‘ice day’ for five years and the coldest day since 2010. It was also the seventh equal coldest February day in a local record going back to 1959.

perch
Perch pond, being deeper, took longer to ice over

The coldest night of the winter was in the early hours of the 28th when a low of -6.9C was recorded. The temperature would have been far lower were it not for a shower that moved in at 3am.

The warmest day of the winter occurred on December 30th with 14.2C recorded. The warmest night was on January 28th when the temperature fell to just 10.8C.
The wettest day of the winter occurred on January 2nd when 15.3mm was recorded.

Snow arrived at the start of winter and at the very end: seven days of snow falling and four days of snow lying over the three months is below average.

 

This slideshow requires JavaScript.

Screen Shot 2018-03-04 at 23.14.20
The daily mean temp yo-yo’d throughout December, January and February

There were 30 air frosts during the three months, eight above the 1981-2010 average.

air frosts

There were 11,680 minutes of frost over the winter, less than last year, though 66 per cent of those were recorded in February. Considering the past 6 Februaries this year’s frost hours were 170 per cent greater than the next highest, February 2016!.

frost minutes

A full weather diary is available for the months of DecemberJanuary and February. To view full stats for each month follow this link:http://1drv.ms/1kiTuzv

Summary for period 01/12/2017 to 28/02/2018

Temperature (°C):
Mean (1 minute) 5.2
Mean (min+max) 5.0
Mean Minimum 2.0
Mean Maximum 8.0
Minimum -6.9 on 27/02/2018
Maximum 14.2 on 30/12/2017
Highest Minimum 10.8 on 28/01/2018
Lowest Maximum -1.0 on 28/02/2018
Air frosts 30

Rainfall (mm):
Total for period 182.2
Wettest day 15.3 on 02/01/2018
High rain rate 28.2 day 02/01/2018
Rain days 52
Dry days 38

Wind (mph):
Highest Gust 45.0 on 02/01/2018
Average Speed 3.7
Wind Run 8059.5 miles
Gale days 0

Pressure (mb):
Maximum 1036.4 on 22/12/2017
Minimum 970.3 on 10/12/2017

Days with snow falling 7
Days with snow lying at 0900 4

 

 

Best Alpine snow for 30 years?

There’s been countless reports about amazing amounts of snow falling across the French, Swiss and Italian Alps to the point where some agencies have been proclaiming that it has been the best season for the white stuff in 30 years.

Extraordinary totals have fallen in some areas. Bourg-St-Maurice, the jumping off point for Savoie resorts including Les Arcs and Val d’Isere, has recorded over 400mm of precipitation over the past 30 days, equating to around 4m of snow at the resort summits.

In Switzerland, large amounts of snow in a short period caused chaos in Zermatt, stranding tourists after the area’s rail services suffered disruption.

Away from the north and west side of the Alps, however, snowfall, while good, has been less impressive the further south and east you look.

alps arrow
30-day precipitation totals reveal that Bourg St Maurice recorded 422mm while Obertauern in the east recorded 99mm. 

It is a far cry from last year where some resorts on the southern side of the range were particularly dry. San Bernardino, during the last 30-days, has recorded 179mm of precipitation. During the same period last year just 14.6mm fell!

The outlook for the Alps continues to look unsettled with snow forecast to fall at resorts that are in deficit to the Valais and Savoie areas.

snow

 

 

Snow for day after Boxing Day?

The models are showing another knife-edge situation for snow – similar to the ‘rain turning to snow’ event earlier this month. But there are a number of factors working against it this time round, at least for most of us who live between sea level and 30 metres.

Screen Shot 2017-12-26 at 08.43.38
The highest resolution model AROME shows snowfall rate but I would expect that only high ground (100m +) will see any accumulation

The low level supply of air off the continent is much milder this time round. Hamburg and northern Germany on the 9th was some 5C colder than currently.

The air pressure, crucial to bringing that snow line down lower, is forecast to be around 10mb higher this time.

And even if we see settling the soil temps, after the recent mild spell, are still 5C – 10C down to 10cm… Screen Shot 2017-12-26 at 11.46.19

wet bulb

chilterns

September 2017: average temps, rain. Dull

The first month of autumn continued in the same vein as the last month of summer .

The mean temperature finished 14.8C, 0.6C below average and very similar overall to September 2013.Screen Shot 2017-10-02 at 09.34.34

Some 53.5mm of rainfall was recorded, 103% of the 1981-2010 average. Some 114 hours of sunshine were recorded, 81 per cent of average, so on the dull side.

Overall the month was typical for early autumn – though possibly felt more autumnal because it was around 3C cooler than September 2016 and much wetter and duller than that month.

As usual at this time of year there is already much speculation about how cold the coming winter may, or may not, be. Winter has arrived over Siberia and early season snow cover is predicted to increase over the next week. However, the factor of early snow over Siberia being a sign of a cold winter to come in NW Europe is is only one piece of the jigsaw and I have seen it proved wrong a few times.

 

Summary for September 2017
Temperature (°C):
Mean (1 minute)  14.4
Mean (min+max)   14.8
Mean Minimum     10.7
Mean Maximum     18.9
Minimum          5.3 day 21
Maximum          22.7 day 04
Highest Minimum  16.7 day 04
Lowest Maximum   15.2 day 19
Air frosts       0

Rainfall (mm):
Total for month  53.5
Wettest day      16.1 day 27
High rain rate   16.1 day 13
Rain days        19
Dry days         11

Wind (mph):
Highest Gust     28.9 day 12
Average Speed    2.3
Wind Run         1670.8 miles
Gale days        0

Pressure (mb):
Maximum          1022.7 day 01
Minimum          989.1 day 12

Total hours of sunshine        114 (81%)

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

Screen Shot 2017-10-02 at 09.01.01

 

Is this the last remaining snow of winter?

I spent last weekend in the Lake District, on Saturday ascending both Scafell and the Pike, England’s two highest mountains.

The 964m Scafell, though lower than the Pike, is a much more technical ascent with hard to negotiate gullies, among them Lord’s Rake, where I discovered three lumps of icy snow. My findings, that I later Tweeted, attracted the attention of Iain Cameron, who, with a team of volunteers, maps and measures all British snow patches that survive through the summer.

Screen Shot 2017-05-05 at 18.26.12.pngI’ve read about Iain’s findings in the Royal Meteorological Society‘s journal Weather but to find one of these surviving patches myself enabled me to empathise just why he and others find the task of mapping and measuring them fascinating, a sort of first-hand insight into how the UK’s climate varies from year to year.

On descending from Scafell I thought I’d seen further patches lower down but these turned out to be melted puddles on the moorland that were reflecting white against the bright sky.

It was a cracking weekend weatherwise. Though the wind on Sunday was fairly brisk at the top of Hellvellyn it didn’t impact much on the conditions. Two dry days in a row with excellent visibility are rare at any time of year in the Lakes. I can’t wait to return.

 

What is happening to Wanstead Park’s lakes?

Lack of rainfall and a broken pump have been cited by City of London Corporation as the main reason for the shocking levels of the ponds through the park.

Screen Shot 2017-04-26 at 22.46.07
The Ornamental Water by the Grotto is virtually dry. Images courtesy of Ralph Potter

The plight of the water courses has been well documented of late; a press release from the Corporation explains the catalogue of issues hampering efforts to address the problem. Closer scrutiny of these reasons, however, suggest that too much is being blamed on the weather.

A study of local rainfall back to 1981 suggests that though the ground water replenishing season (October 1st – April 24th) has been dry it is by no means out of the ordinary.

Screen Shot 2017-04-26 at 14.11.29

As you can see from the graph the rainfall here has gone up and down like a yo-yo and 2016-17 is only the fourth driest period: 1991-92, 1995-96, 1996-97 and 2011-12 were drier.

The Corporation’s press release states: “2015-16 was a helpfully wet period for us…”

Wrong. 2015-16 was average. And if you consider annual rainfall 2015 saw 92 per cent of average rainfall recorded; 2016 was 93 per cent – placing 58th and 66th in driest years since 1797. Nothing out of the ordinary.

“2016-17 has, however, been an especially dry period with below average rainfall since Spring 2016.”

Wrong. See above detail. There have been three drier periods since 1981. And since March 2016, only half of the months have been notably dry, a period that included the third wettest June since 1797.

“January to March 2017 has seen roughly 50% less rainfall than average”

Wrong. January to March rainfall was 94% of the 1981-2010 average

April has been dry, and could be among the top 5 driest back to 1797, but it seems the Corporation are trying to blame nature instead of years of neglect on their part.

Screen Shot 2017-04-26 at 22.45.51
The past months have seen much of Heronry Pond dry out. Image by Ralph Potter

 

The situation is in stark contrast to CoL’s other open space, Hampstead Heath, which has recently seen the completion of a £23m project to make safe the ponds there. CoL has deep pockets yet they have dithered for years over spending £25,000 to renovate the Coronation Bridge – and offer the people of Ilford a route into the park.
Figures released by CoL show it has only invested £1.23m in Wanstead Park over the last five years, compared with £50m spent in Hampstead Heath.

We are constantly told that problems in the park are ‘in hand’ yet progress on anything is painfully slow – and action to repair the pump has sadly come too late for much of the wildlife on Heronry Pond.

People from far and wide use Wanstead Park – they really deserve better!

Screen Shot 2017-04-26 at 22.42.10
You can view City of London Corporation’s press release here

 

Christmas 1810: stormy then very cold

Earthquakes in Italy and early season snow cover in Siberia have been well documented in 2016.

They were also mentioned by Luke Howard in his publication The Climate of London in 1810.

screen-shot-2016-12-16-at-18-57-08

He also mentions winter thunderstorms over the Yuletide period, from Christmas Eve to Boxing Day – the amount of rain overflowing the Thames.

24th: Very windy night with heavy rain. 25th: Wind high all day with rain frequent lightning in the evening from SE. 26th: Wind very boisterous early in the morning day fine the rain of the last three or four days being impeded in its passage to the Thames by the spring tides overflowed the banks and filled the marshes.

Within two days of this wild and wet spell, complete with strong north-westerlies, the wind swung north and then north-easterly to usher in 1811 with a 12-day cold spell.

screen-shot-2016-12-17-at-20-55-36

The conditions of the cold spell were not severe, the coldest night was -8C, it was a pretty standard cold spell for the time and one that the south-east used to experience with fair regularity in the early to mid 1980s.

screen-shot-2016-12-17-at-20-48-37

Models currently show a (fairly) narrow chance of a stormy Christmas period. It would be interesting if it were followed with a cold spell in January – just like the ones we used to get in 1980s.

* The Booty website also contains the following on that notable month…
What is thought to be Britain’s strongest tornado occurred in December 1810. A category of “T8” (on a ten-point scale) occurred on the 14th at Old Portsmouth. The TORRO website says it:  “tracked from Old Portsmouth to Southsea Common causing immense damage – although no deaths, it is believed. Some houses completely levelled and many others were so badly damaged that they had to be demolished; chimneys were blown down and the lead on a bank roof was ‘rolled up like a piece of canvas and blown from its situation’.”

September 2016: very warm, very dry

Last month was the second warmest September in a local record going back to 1797! The monthly mean finished 17.8C, 2.4C above average. Despite being an ‘autumn’ month September was actually a full degree warmer than June!

screen-shot-2016-10-01-at-11-55-19
September 2016 was the second warmest in a local record back to 1797, though we’re talking by fewer than tenths of a degree.

The hottest September day since 1959 was recorded on the 13th when 33.1C was reached, the sixth equal hottest in the local daily record back to 1848.

The month also saw the warmest minimum recorded since 1959 when the mercury failed to fall below 18.7C on the 6th.

It was another very dry month, the third much drier than average month in a row: just 27.7mm fell, 24 per cent of average, making it the driest September since since 2007 and the 12th driest in the local record.

Like August, the month only falls down in terms of impressiveness when sunshine hours are considered. Some 119 hours were recorded, that’s 85 per cent of average, making it the dullest September for 15 years.

Air frosts: 0, Ground frosts: 0

So what has September got in store weatherwise? The models on the 1st suggest that a large Scandinavian high will become established to our NE bringing lots of settled weather and showers on coasts. There’s obviously the chance of trough disruption as the month progresses if the anticyclone’s influence declines.

Beyond the grasp of the models my usual long range outlook method falls down this month due to September’s warmth and dryness – there is nothing within  +/- 10% of September’s statistics. I would guess, however, that we are looking at another drier than average month with frost becoming a risk as the month progresses where skies clear. There is also the chance of more pleasant autumn days where skies are clear during the day.

My September outlook for temperature was poor. I predicted a mean of 15.3C (outcome: 17.8C). It was much, much drier than I thought: 300mm (outcome: 27.7mm). Sunshine was poor: 140 hours (outcome: 119 hours).

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

1st: Sunny start but cloud gradually increased until it was overcast by 6pm. Clear spells overnight but warmer than previous nights.
2nd: Cloudy though some brighter intervals.
3rd: Sunny start, cloud began to pile in at 12.30pm with rain arriving at 5.30pm, this fell through the evening with some showers in the early hours.
4th: Bright, breezy start but rapidly turning cloudy and dull. Some rain overnight.
5th: Light rain and dull to start – this quickly clearing to cloud by 3pm. Things remained cloudy with a muggy night.
6th: Cloudy, dull and muggy start after warmest September night on record. Another warm night though muggy.screen-shot-2016-10-01-at-12-22-03
7th: Cloudy to 11am though sun breaking through as drier air arrived. Feeling humid.
8th: Sunny start but with plenty of cumulus, this quickly decreasing to leave clear sky.
9th: Cloudy morning though sky seemed to periodically clear of low cumulus before becoming overcast and very breezy in the afternoon. Some rain overnight and just before obs time.
10th: Cloudy start with patchy light rain, this briefly turning  heavy at 1pm  before turning occasionally moderate. Dreadful afternoon after recently. Clearing overnight to leave a sunny start.
11th: A glorious sunny day with only the odd patch of cirrus.
12th: Bright start with some sunshine, clouding over with a few splodges of rain with warm front. Then sunny and very warm.
13th: Sunny start with a few cirrus and castalanus around. Breezy at times with the thermals. The warmest September day since 1959 and 6th equal warmest since 1848.screen-shot-2016-10-01-at-12-13-54
14th: Sunny start with a few cirrus. A few patches of alto-cumulus later. Very warm but not as hot as yesterday. Warm, pleasant evening.
15th: Sunny with a few wispy cumulus, clearing to hot sunshine. Some alto-cumulus developed at 2pm and towering cumulus could be seen in distance. Thunderstorms reporting to NW of London. Cloudy and warm overnight with eight peals of thunder in the early hours and heavy rain.
16th: Light to moderate rain through the morning, petering out at 1.30pm.
17th: Cloudy, cool and breezy all day, at times dull.
18th: Cloudy all day, a bit warmer than the previous two days.
19th: Cloudy start though with sun breaking through briefly at 11am until 1pm then cloudy again. Rain at 1am that didn’t last long enough to register.
20th: Cloudy and fairly calm – a nothing day with odd very light drizzle.
21st: Bright start with cloud breaking to long spells of sunshine before more cloud moved in. Warmer than of late.
22nd: Cloudy but  sun broke through giving pleasant afternoon and cool overnight.
23rd: Sunny, gin clear and cold start. Just a few fair weather cumulus through the day.
24th: Sunny start with cloud decreasing. Very warm in sun but cloud and breeze built through the day. Overnight light rain between 6am and 9am.
25th: Bright start after overnight light rain.
26th: Bright start with a few cloud breaks here and there. Heavy shower at 12.15pm with further threat of rain but stayed dry.
27th: Bright start with signs of a cold front moving in from south then cloudy.
28th: Sunny start with patchy cirrus, this tending to thicken at lunchtime to turn mostly overcast with humidity increasing. Breeze also picked up with reappearance of sun mid afternoon. Cloudy, very mild and breezy rest of the day.
29th: Cold front and brief heavy rain swept in at 10.03am. Then intermittent falls until 11.23am.
30th: Sunny, gin-clear start, patchy cumulus bubbling up at 10.30am. Cloud grew thicker around 12 noon with brief shower at 1pm. Then sunny spells and cloudier periods. Another shower just after nightfall then clear. Cloud moved in after 2am with another shower. Early sunshine  gave way to moderate showers around 9.45am.