Muggy air

Relative Humidity [%] for Mon, 6 Jun 2016 at 1500 UTC
Relative Humidity [%] for Mon, 6 Jun 2016 at 1500 UTC (excuse the contouring)

Inland by day I wouldn’t say that it’s been that muggy today, in fact if this was back in the old days of manual weather observations (SYNOPs), then at many sites across the UK observers would have had to add the Beaufort letter ‘y’ to their observations to signify dry air (<60% relative humidity) this afternoon. Dewpoints were certainly higher in the west especially over Ireland (16-17°C) but for the bulk of the country 10 to 13°C more or less covered it.

Relative Humidity [%] for Mon, 6 Jun 2016 at 1500 UTC
Relative Humidity [%] for Mon, 6 Jun 2016 at 1500 UTC

Of course overnight things do get a little bit sticky as the humidity rises. Here are the humidities in the early hours of this morning across the country.

Relative Humidity [%] for Mon, 6 Jun 2016 at 0300 UTC
Relative Humidity [%] for Mon, 6 Jun 2016 at 0300 UTC (excuse the contouring)
I think the meteogram for Exeter during the past week might be fairly typical of overnight humidity levels across a lot of the country. There used to be something called a comfort index, which might be a useful way of quantifying how difficult it is to sleep – without air conditioning of course.

03839 Exeter Airport - United Kingdom  31 AMSL 30 May-5 June 2016
03839 Exeter Airport – United Kingdom 31 AMSL 30 May-5 June 2016

If you think it’s muggy here then spare a thought for areas around the Gulf of Mexico as Tropical Storm Colin tracks towards Florida, dew points in coastal regions there are in the range 20 to 27.8°C (Nassau).

Dew Point [°C] for Mon, 6 Jun 2016 at 1200 UTC
Dew Point [°C] for Mon, 6 Jun 2016 at 1200 UTC

May Pressure Patterns

When statistics can be misleading

I’ve always liked monthly mean pressure maps they can be very useful at summing up the weather of a month at a glance. But sometimes they can be very misleading and not at all helpful, take a look at the anomaly chart for May 2016 below as a perfect example:

Mean Sea Level Pressure & Anomalies 01 May to 31 May 2016
Mean Sea Level Pressure & Anomalies 01 May to 31 May 2016

As you can see the central north Atlantic had anomalously higher pressure than average (+2 hPa) in the month of May, with a lower than average pressures (-4 hPa) between Portugal and the Azores and across the bulk of southern Europe. Higher than average pressure to the SW of the Azores produced an intense high pressure cell in the southern Atlantic, but they were few isobars across the bulk of the central Atlantic, British Isles  and most of central Europe. Now look at the month in little more detail and broken down into three parts, early, mid and late:

Mean MSLP & Anomalies Monthly (3x3) May 2016
Mean MSLP & Anomalies Monthly (3×3) May 2016

And as you can see from the above charts, splitting the month into three separate periods show you why there is a distinct lack of isobars in the monthly mean. The first chart shows that for the first 10 days of the month fairly strong and warm south or southeasterlies predominated (and hence the record CET values), but from the 10th to the 20th the flow reversed, and the pressure anomalies instead of being above average over southern Sweden (+9 hPa) flipped to below average (-8 hPa) effectively cancelling out the southerly flow of the first ten days. During the last 11 days of the month negative anomalies (-3 hPa) continued across Germany and France, whilst higher than average pressure persisted to the northwest of the British Isles maintaining the NE’ly flow, and the cloudy cool weather in the east and heavy rain over the continent right through to the end of the month.

So what have I learnt – don’t rely on monthly charts – well not entirely at any rate. Perhaps ten days is the maximum period that a mean pressure charts can be relied on to identify trends, before those trends and features are distorted, smoothed or cancelled out by a distinct change of type part way through the month.

North Atlantic MSLP [UKMO] May 2016 (courtesy of the Met Office)
North Atlantic MSLP [UKMO] May 2016 (courtesy of the Met Office)

(todo: fix those dates in the titles 1-10, 11-20 & 21-31)

West still best!

The BBC weather presenters have had a really bad week, for day after day London and the southeast has been stubbornly cloudy and very cool, so much so that none of the usual London weather stations never featured in the top twenty of warmest or sunniest places in the British Isles, let alone top the table. Yesterday (Saturday) was supposed to be start of the return to normal for the southeast, but yet again the low cloud clung on for a good part of the day. Never mind, in steps Nick Miller to redress the balance in the forecast on Saturday night, and announces that at 1600 BST on Sunday things will have been put right with the world and London as usual will be the (joint) warmest place with 26°C.

Temperature at 1600 on 5 June 2016 (courtesy of BBC)
Temperature at 1600 on 5 June 2016 (courtesy of BBC)

Here’s how it looked in reality at 1600 BST:

Air Temperature [°C] for Sun, 5 Jun 2016 at 1500 UTC
Air Temperature [°C] for Sun, 5 Jun 2016 at 1500 UTC

It’s obvious really that any western coastal site would have been warmer today than London, even with the massive heat island effect that London has, and even will all the concrete that there is at Heathrow airport it could only make 22.9°C by 1600, and fell 3°C short of the forecast 26°C. I am nitpicking I know, but I see this happen far too many times over the course of the spring and summer in BBC forecasts. They don’t make it easy to check what they forecast and rarely if ever apologise for a bad forecast because the general public have such short memories and it’s only ‘the weather’.

Highest Air Temperature 1500 UTC on Sunday, 5 June 2016 In WMO Block 03
Highest Air Temperature 1500 UTC on Sunday, 5 June 2016 In WMO Block 03

The cloud and precipitation didn’t seem to go according to plan either I’m afraid, and at 1600 the showers forecast for the south of Wales, southwest and central southern England hadn’t materialised, in fact there none further south of 53°N, but well done for those that fired off over the high ground of the Lake District, southwest Scotland and the central Highlands though.

Temperature at 1600 on 5 June 2016 (courtesy of BBC)
Cloud & Rain at 1600 on 5 June 2016 (courtesy of BBC)

PS One thing that irritates the hell out of me is how they use the temperature at Plymouth as representative of the whole of the southwest of England. Not only that but they stick the label right on top of mid-Devon, which obscures the colour filled contours and gives the impression that the temperature will be 19°C (2°C warmer than it actually was at Plymouth by the way) there, incidentally the temperature here in mid-Devon was 23.3°C at 1600. The graphic below is how I think it should be done, which surely can’t be that difficult to achieve, it’s now obvious that the temperature is for Plymouth, and for not the rest of Devon. The line connecting the label with the site might be a step too far but a lot of the time it’s impossible to decide what temperature goes with what location, the chart below for example has a temperature over Manchester but a label for Birmingham with no apparent temperature. It’s it for Birmingham or have they labeled it incorrectly and it’s for Manchester?

IMG_2745

May Temperature Anomalies

Here is a chart of the reanalysis surface temperature anomalies for May 2016 using reanalysis data from NOAA. As you can see in May the bulk of the central Atlantic remained slightly cooler than average (-1°C), but the Arctic around Baffin bay and the Barents sea is anomalously warm (+5°C) as were northeast Russia and eastern Scandinavia. The recent heat wave over northern Pakistan and Afghanistan are clear to see (+5°C), as are the very warm conditions in central Canada (+4°C).

Air Temperature Anomalies 01 May to 31 May 2016
Air Temperature Anomalies 01 May to 31 May 2016

From what I can see, I would hazard a guess that when the global surface temperatures for May are released, although well above average, may not be quite at the record levels of previous months. Incidentally I’ve changed the mapping component that I use in my application, and there are some issues with it at the moment, one of the major ones being I can’t see much further south than the equator! I’ll have to get my programmer to pull his finger out and sort this out tout suite.

Arctic meltdown

How low can it go?

With the suspension of the normal sea ice index, here are some of the images from the provisional F18 data of the ASINA site. To be honest the Americans couldn’t have picked a better year to update the way that they measure sea ice, because as you can see from the chart below, Arctic sea ice totals are in meltdown – well in summer they always are I suppose but this time it’s a doozy. There seem to be holes appearing in the ice sheet where they just shouldn’t be holes at this time of the year.  The coast of eastern Greenland looks stripped bare of sea ice, and there are long gaps all along the Alaskan coast with no ice, not to mention the frontal lobotomy that has existed right through the winter in the Barents sea area. It looks odd on that summer 2016 is going to set a new extreme low record for Arctic sea ice, the only question is how low will it get? This story is not going to away and is going to big news the closer we get to September.N_stddev_timeseries N_daily_extent_hires

Antarctic

Things are looking a little more healthy in the Antarctic, but having said that the gains that the sea ice made in the early Autumn now seemed to have vanished, and the graph of the total sea ice extent has shifted to the other side of average during the last month or so. Looking at the map the sea ice seems to have exploded out of the Weddell sea, but the sea ice edge has been trimmed back to the NNE and WSW (best I can do without a better map!). Hopefully the NSIDC sea ice index will make a swift return in the next month or so.

S_stddev_timeseries S_daily_extent_hires

All images courtesy of the NSIDC.

Dry Devon

Precipitation 03839 Exeter Airport - United Kingdom  31 AMSL 3 April - 3 June 2016
Precipitation 03839 Exeter Airport – United Kingdom 31 AMSL 3 April – 3 June 2016

Only 68.4 mm of rainfall in the last two months at Exeter Airport in Devon. I make that total approximately 57% of the long-term average (119.3 mm) going by this useful table of statistics from the Met Office. Interestingly just 6.63 miles to the north we have collected even less, around 58.3 mm in the same period – I calculated the distance between two locations using this useful site.

Exeter Rainfall Statistics (courtesy of Met Office)
Exeter Rainfall Statistics (courtesy of Met Office)

Here comes the sun

0630-1045 on Fri, 3 Jun 2016
0630-1045 on Fri, 3 Jun 2016

It’s took it all morning, but we’ve finally started to clear the low stratus that invaded southern parts of Devon overnight, and the sun has burst through. It’s kept temperatures at around 8°C at places like nearby Dunkeswell, I was beginning to feel how someone who lives in the east of England has been feeling in the last week. Apologies for the small animation, but my programmer chappie is having problems with the scaling of animated GIF’s, but it’s interesting to see how the edge of the stratus is running ENE/WSW across central Devon with very little movement, all I can think is the low-level flow must have backed a little and there is slightly more of a northerly component to the flow than there was earlier.

Synop Grid - 03840 Dunkeswell
Synop Grid – 03840 Dunkeswell

Tri weather data sets

A bit of a strange title I know, but I’ve recently written an application that displays climate data for the UK from three separate daily data sets for atmospheric circulation, temperature and precipitation, and hence the tri.

  • Daily Central England Temperature [CET]
  • Objective Lamb Weather Type [LWT]
  • UK regional precipitation series [HadUKP]

It’s not the first time I’ve merged weather data sets in a single application, but this is probably the first time I’ve managed to finish it and publish the results that it generates. The essential requirement of course is a source of regular daily weather data, and so the CET and LWT series were the ideal (and only) choice because they are both updated on a daily or weekly basis. The other daily weather set that fits was the HadUKP series that the Met Office maintain, but there are a couple of problems with this series, one being that is only updated on a monthly basis, and the other is that the series isn’t very long and only extends back to 1931, and not 1772 and 1861 as in the case of CET and LWT. The big plus for anyone interested in the climate of the British Isles is that you can explore the climate of a particular day, week, month or season very easily and quickly. Here is a screenshot of the application as it stands now:

LWT-CET-UKP application
LWT-CET-UKP application

Below are a few examples of some particular well-known periods and spells of weather from the past, starting with a look at last Autumn and Winter.

27 Sep 2015 - 20 Mar 2016
27 Sep 2015 – 20 Mar 2016

You can certainly see the lovely anticyclonic spell that we had in September 2015, and the record mild November and December that followed, in this six month overview. Next a four-month window and a look at the Winter of 1946-47, you can clearly see how the cold started with an anticyclonic spell in the second half of January 1947, with the snow following along at the start of February.

1 Dec 1946 - 23 Mar 1947
1 Dec 1946 – 23 Mar 1947

Here’s the summer of 1976 and the record warmth of late June and early July, notice also the preponderance of anticyclonic types up until the start of September, then the breakdown into more cyclonic weather and the rains that brought an end to the drought.

18 Apr 1976 - 17 Oct 1976
18 Apr 1976 – 17 Oct 1976

Here’s the great winter of 1962-63, in comparison to 1946-47 it’s clear that winter 1962-63 started much earlier (before Christmas) and finished earlier, but was also drier and more anticyclonic.

16 Dec 1962 - 24 Mar 1963
16 Dec 1962 – 24 Mar 1963

Improvements

I could maybe add an extra chart in the shape of a ‘barograph’ because I hold all the mean pressure points in the LWT data. I could present that as a scatter graph of all the 16 MSLP grid values for 12 UTC and then plot a moving average. I could also highlight with a star the named storms, but that would only work for the very latest years. I could also colour the precipitation bar chart blue to indicate snow rather than rain when the CET was less than 1 or 2 °C (I have in fact now implemented that idea as you can see if you look at the screenshot of the application!). I do plan to add functionality to show a grid of archived weather charts for the selected period from Wetterzentrale. The one element that I think it does miss is daily sunshine data, but there is no source that I know of for daily sunshine values for a region, let alone for a single station, so that’s a non-starter. I must say that this really is an excellent tool for any climatologist with an interest into the weather of the British Isles over the last 150 years or so.

East-West split continues

The awful cold and cloudy conditions are continuing again today down the east coast of England, and the infamous east-west split coined by Michael Fish has been called into play again today by weather presenters at the BBC.

Satellite Image 12 UTC on Thu, 2 June 2016
Satellite Image 12 UTC on Thu, 2 June 2016

Philip Avery was very agitated about the storms over France when he presented the BBC weather this lunchtime, and proceeded to show us a couple of days worth of satellite images in a loop, and his arms went round and round as he described the “storm” that had been causing all the flooding problems in France and Germany. He then muttered something about “a bit of an east-west split going on” and showed this graphic.

BBC Weather 1356 UTC 2 June 2016
BBC Weather 1356 UTC 2 June 2016

All I can say to Philip is, yes you’re quite right there is most definitely an “east-west split” going on, and yes, to use another tired old cliché “west is best”. In fact it’s been going on for several days now and has suppressed temperatures across the eastern and central parts of England, have a look at these thermograph traces that illustrate the temperature differences between east and west. Approximately around +4°C warmer in the SW than the SE, and still no appreciable rain west of Yeovilton for almost a fortnight.

03827 Plymouth - United Kingdom 50 AMSL 26 May-2 June 2016
03827 Plymouth – United Kingdom 50 AMSL 26 May-2 June 2016
03772 London Heathrow - United Kingdom 24 AMSL 26 May-1 June 2016
03772 London Heathrow – United Kingdom 24 AMSL 26 May-2 June 2016

He then went onto present another graphic of the forecast situation at 1600 BST. But looking at the spread of temperatures along the south coast you would be forgiven for thinking that it was the SW of England that had been covered in cloud all day and not the SE.

BBC Weather 1357 UTC 2 June 2016
BBC Weather 1357 UTC 2 June 2016

Plymouth is not a great site to use as a representative temperature for the whole of Devon and Cornwall, and at the moment here in mid-Devon at 1500 BST it’s 19.7°C, and it could even be a little higher by 1600 BST under these blues skies. I am skeptical that the low cloud in the SE will break up as much as is indicated in the above graphic, and allow temperatures to rise to 18°C, but of course it may do, but I notice that it didn’t yesterday or the day before.

Latest Update  1830 BST

Just for completeness and complete “I told you so” here is what the cloud and temperatures were at 1600 BST.

Satellite Image 1500 UTC on Thu, 2 June 2016
Satellite Image 1500 UTC on Thu, 2 June 2016

The cloud remained solid down the east coast and across London and most of Sussex, which of course reflected in lower temperatures than forecast, in other words a poor forecast for the southeast even though it was for less than three hours in the future! I may be that the presenters don’t have any way of modifying model cloud amounts, but surely they can inject a few more temperatures to reflect reality. It’s a great shame that the BBC presenters can’t display thermograms or meteograms for the last week temperatures from locations in the east to compare them with those in the west, like I have done. Incidentally the maximum here in mid-Devon was 19.8°C at 1429 UTC.

Air Temperature [°C] for Thu, 2 Jun 2016 at 1500 UTC
Air Temperature [°C] for Thu, 2 Jun 2016 at 1500 UTC

Final update (I promise) 10000 BST on 3 June 2016

I’ll let the graphics do the talking…

Maximum Temperature Anomaly [06-18] UTC on Thursday, 2 June 2016
Maximum Temperature Anomaly [06-18] UTC on Thursday, 2 June 2016