April 1-23 northern hemisphere temperature anomalies

The recent cold weather seems to have cancelled out the earlier warmth in the month of April, because temperature anomalies up until the 23rd are quite close to average across most of Europe, although Iberia has been unusually warm. The Arctic has been its exceptional mild self once again, and is probably one of the reasons why this recent ‘Arctic blast’ has been so relatively innocuous.

Figure 1

Cold spell gone before it started

I have a theory that northerlies don’t last as long as they did in the past, the general life expectancy of one is probably no more than 48 hours tops. The cold from the current ‘Arctic blast’, has already moved south to allow warmer temperatures to come down from of all places the Arctic. It’s not evident until you run a comparison of temperatures differences that are 24 hours apart that you’re ever likely to notice it though (fig 1). I’m not saying that temperatures aren’t several degrees below average for this time of year, but it’s warmer 2 or 3°C warmer than it was at the same time yesterday over much of the north, and conversely it’s up to 7°C colder across many central  and southern areas.

Figure 1

Liscombe top of the shop

Figure 1

It’s not very often that you’ll see Liscombe in Somerset (and not in Devon as I had always thought) as the warmest place in the British Isles, but it happened today with a temperature of 15.0°C at 15 UTC (fig 1), in fact it was a southwest one two with Exeter Airport second in the table (fig 2), but I bet you won’t hear about that on the BBC weather.

Figure 2

You can’t even call Liscombe a village in all honesty, there is a Liscombe Farm, but the AWS is a little way to the east up what looks a very lonely lane on Exmoor at a height of 348 M (fig 3), so it might be getting a little help from the northwesterly wind.

Figure 3 – Liscombe courtesy of Google Maps

April snow for Cairngorms

Figure 1 – Cairngorm from Loch Morlich courtesy of © Winterhighland Limited

It’s proving to be a cold and showery Easter over Northern Scotland this year, and the showers affecting the area on Saturday afternoon look like they are putting snow down to ~3000 feet if this webcam image is anything to go by (fig 1). That’s because the cold air over Scotland is holding the air temperature on Cairngorm at a very cold -2.9°C (13 UTC) at the moment. The heatmap of air temperatures on the summit since the start of March shows that until this last week, it had been relatively mild since around the 24th of March (fig 2). It looks like the high ground might get a bit more snow overnight, but it might be a bit late to extend the skiing season from what I can see from the other webcams in the area.

Figure 2

At the same time it’s been quite a benign Spring as far as gales and storm force winds are concerned on the summit (fig 3).

Figure 3

Just a tad cooler across the country today…

Figure 1

I noticed that there were a number of places in Eastern England, that were 10°C or colder this afternoon at 15 UTC,  than they were just 24 hours earlier on Sunday afternoon.

Look back at Sunday’s maximum temperatures

I thought that I would look back at yesterday’s (9th April 2017) maximum temperatures forecast by the BBC. This is not a moan about the temperature contrast across the south of the country, their most certainly was a good contrast, it’s more to do with the sites that the BBC choose as representative of their region and label in their graphics. The one that infuriates me the most is Plymouth in the southwest. There is a method in their madness though, because the Met Office bonus is dependent on how these extreme temperatures are scored in verification, choosing a coastal site (which is difficult not to do on an Island) can pay dividends, because the extremes, and therefore any potential misses are not as large. I believe that yesterday’s maximum temperature of 20.0°C at Exeter was more representative for the whole of Cornwall, Devon, Somerset and Dorset, than a forecast maximum of 14°C was for Plymouth, and even here the temperature reached 16.8°C. Rather oddly many of the temperatures on the chart don’t reflect the colour filled temperature contours that they are overlaid on, for example, a forecast maximum of just 16°C at Birmingham was always going to be wrong but the background colour is a mid-orange colour.

I think that I would have the full support of the South West Tourist board if the BBC put a little more thought into how they forecast regional temperatures.

Figure 1 – Courtesy of the BBC

I couldn’t help myself and resist scoring the maximum temperatures on the chart, if anything it underlines the fact that the Met Office model seems to have as many problems underestimating maximum temperatures as it does overestimating low cloud at the moment.

Figure 2

Where would you go to catch the sun?

Figure 1 – Courtesy of the BBC

Where would you go for a day out and catch the sun? It’s a simple enough question, but I bet the majority of the people who saw this chart wouldn’t say the southwest of England.

I don’t know why this surprises me because I moan about it every time spring and summer come around. The BBC presenters in past years have done irreparable damage to the tourist industry of the southwest with misleading charts like this. It doesn’t matter how many times that you complain that a maximum temperature for Plymouth Hoe is just not representative for the whole of the southwest peninsula (especially in a SE’ly) it has absolutely no effect in the slightest.

To be fair weather presenters must feel a little left out and neglected once the named storm season and all that gesticulating and arm waving that goes with it have finished, so they return to their first love, extreme temperatures, and if they are occurring in the southeast of England so much the better!

Bradninch top of the shop

The temperature at 11 UTC was 16.3°C here in Bradninch Devon from my trusty Vantage Pro. I notice that it had reached 16.9°C just before 12 UTC. The sea breeze that’s keeping it cooler at Exeter airport, hasn’t quite made it this far north as of yet.

April 2011 – warmest on record*

Figure 1 – Image and data courtesy of the Met Office, CRU & Wetterzentrale

April 2011 – warmest on record*

*Or what you can do with a load of climate and weather data

Figure 2 – Data courtesy of the Met Office

It seems that we have incredibly short memories when it comes to weather across the country, well at least I know that I have, and that’s why I never noticed that April 2011 was, and still is the warmest April on record since at least 1659 in Central England (figs 2, 3 & 4). The mean CET temperature for the month was +3.91°C above the 1961-1990 long-term average, and 0.6°C warmer than the second warmest April in the list 2007. I’ve just put together a blog that consists of a number of tables, charts and graphs of climate data for the month that I’ve constructed from data or images that I’ve downloaded from the Internet.

Figure 3  – Data courtesy of the Met Office

Here’s a more detailed of daily temperatures, in what was a very mild Spring in Central England, particularly in March and April (fig 4).

Figure 4 – Data courtesy of the Met Office

The monthly mean 12 UTC temperature anomaly of +5°C sits across northeast France and dominates most of western Europe by its influence (fig 5).

Figure 5  – Data courtesy of NCEP/NOAA

The mean pressure field for the month of April was ideal for warm and dry weather with plenty of sunshine. An anomaly of +6 hPa over the North Sea enabled a cut-off anticyclonic cell over England and Wales, although the weather was more southwesterly in the northwest (figs 6 & 7).

Figure 6 & 7 – Data courtesy of NCEP/NOAA

Here’s a chart of daily rainfall from the EWP series (fig 8), apart from a wet start, the month was predominantly dry in all areas of the UK except the northwest of Scotland.

Figure  8 – Data courtesy of the Met Office

And here are the 12 UTC plotted SYNOP observations for Northolt  in London for each day of that April (fig 9).

Figure 9 – Images courtesy of OGIMET

And finally here are anomaly charts of rainfall, temperature and sunshine for the month courtesy of the Met Office (fig 10). The thing is I can produce maps, charts and graphs easier than I can write the text that glues them all altogether.

Figure 10 – Images courtesy of the Met Office

April 1938 – probably the most anticyclonic month on record

Figure 1 – Data and Images courtesy of The Met Office, CRU & Wetterzentrale

There’s no doubt about it April 1938 was quite an extraordinary month across the British Isles. Not only was it the most anticyclonic April on record, it was also the most anticyclonic* of any month in the objective LWT series that started in 1871 (fig 4). Mean anomalies for the month were in excess of +16 hPa above the 1918-1947 long-term average across northwest Ireland (fig 2 & 3), and according to the MWR for the month :

Mean pressure markedly exceeded the average throughout the British Isles, the excess at 7h. ranging from 10.6 mb. at Lerwick to 16.7 mb. at Malin Head. The mean pressure over Scotland as a whole was the highest recorded in the month of April for at least 80 years. At Oxford the mean pressure was the highest for April since 1881 and at Southport the mean pressure was the highest in April since record were first taken in 1871.

(Courtesy of the Met Office © Crown Copyright)

I’m so pleased that the anomalies I generated for the month from the NCEP reanalysis data match the anomalies reported in the April 1938 MWR. NOAA doesn’t make things easy with their 6 hourly MSLP reanalysis data which is on a 2.5° x 2.5° grid back to 1948, but before then (from the 20th Century Reanalysis project) is on a finer 2° x 2° grid. This makes the file sizes much larger to download (~35 mb), and required changes to the code to handle both grid sizes, it also explains the strange LTA period of 1918-1947 that I’ve used in the anomaly chart (fig 3).

*I calculate a simple anticyclonicity index for the month by scoring the LWT for each day. Pure anticyclonic scores 1, while a hybrid anticyclonic type scores 0.5, add them and calculate a percentage of the maximum possible, and hey presto you have a simple anticyclonic index. You could of course have used the mean daily vorticity for the month that the objective LWT data series also produces.

Figure 2 – Data Courtesy of NCEP/NOAA Reanalysis

Figure 3 – Data Courtesy of NCEP/NOAA Reanalysis

I’m slightly concerned about the number of pure ‘A’ types in the objective LWT series from the CRU (fig 4). A few of the days look like they may have been better classified as more of a hybrid anticyclonic type rather than a pure anticyclonic type, take the 30th for example. Should that be an AE or ANE type perhaps rather than pure anticyclonic? Of course it’s impossible to be definitive about this though, because the objective LWT is derived from 12 UTC reanalysis data and the Wetterzentrale charts are generated using 00 UTC data. Going back to the original ‘subjective’ LWT data that Hubert Lamb developed, and who was the final arbiter on, and that scores an anticyclonicity index of 68.3. Who knows perhaps Lamb was being a bit hard on April 1938, especially in the first week. I will investigate this a little more.

Figure 4 – Data courtesy of CRU

It goes without saying that such an anticyclonic month was also very dry across the whole of the British Isles. Using the UK gridded rainfall data it was the driest April in the whole series that started in 1910 (fig 5).

Figure 5 – Data courtesy of the Met Office

Using the EWP series it was the driest April since at least 1766 when the series started (fig 6).

Figure 6 – Data courtesy of the Met Office

Sunshine was well above average in all western regions, but closer to average in eastern areas and the North of Scotland. The MWR says that Valentia Observatory had a total of 262 hours, the largest total for April in a record which started in 1880. It goes on to say that at Mallaranny, in County Mayo (notice how we didn’t exclude the Irish Republic back in 1938), they recorded 129.6 hours from the 8th-18th inclusive which is a daily mean of 11.8 hours for 11 consecutive days.

Temperatures were also above average in the west, but closer to average in eastern districts. Because I use the very warm 1981-2010 LTA to generate the anomalies for the April 1938 graphic (fig 1), all regions look rather cold, which just goes to show you just how misleading statistics can sometimes be.