For the UK, spring (March) started very cold and moderated as the month progressed and became increasingly wet (wettest since 1981 for England). The month averaged slightly below temperature-wise.

April is seeing a mild, dry north, cooler, wetter south and is likely to wind up near to slightly below average temperature-wise and perhaps near average for rainfall overall. That being said.

The below temperature anomaly of warmer (& drier) north, cooler (wetter) south is thanks to what may have turned out to be the deepest April negative North Atlantic Oscillation since 1995 with strong blocking over Scandinavia extending across Scotland with lower heights and storm track further south.

The strong -NAO this April may be linked directly to two key factors, the hangover effects of the major SSW back in February as well as the strong phase 8 into 1 MJO which tends to promote high-latitude blocking and southward displaced storm track.

https://twitter.com/WorldClimateSvc/status/1648697175944175618

https://twitter.com/WorldClimateSvc/status/1649111192546181125

Through the first 10 days of the month, it was fairly wet in southern UK, the period between 10-20th saw a strengthening block to the north which aided milder, drier conditions for Scotland, fresher conditions further south with strong east winds, those winds veered more southerly in Scotland and this allowed the warmest temperatures to focus across the north. Aided by the foehn effect, Kinlochewe in NW Highland has observed the UK’s warmest temperature of the year with 21.2C at the same time coastal Aberdeenshire only mustered 8C.

Between the 18-23rd, cold northerlies returned bringing a 10-15C drop in daytime temperatures across Scotland, nearer 5 to 8C further south. Places such as Aviemore which topped close to 19C last week only managed 5C this week.

Thanks to clear, calm and cold air in place, a low of -7.4C was achieved at Tulloch Bridge (Fersit), Highland on the 25th and -7.3C at Loch Glascarnoch the following morning.

A gradual return of the southerly flow through the final days of the month will allow day and night temperatures to rise back to average or above average. If the UK maximum remains below that of 21.2C reached at Kinlochewe last week then the UK will have witnessed it’s coolest April maximum since 2016.

It’s been colder & warmer in April’s gone by

Despite seeing ‘late April’ maximums of 4C in the north and 8C in the south and overnight lows of -2 to -6C, the chill isn’t particularly unusual.

Here are the multiple recent examples of cold and snowy spells during April.

2015

2016

Big contrasts north to south 9th April 2017 with heavy snow and sub freezing wind chill in the Highlands at the same time London topped 25C!

The hot spot was Cambridge which hit 25.5C.

2018 was pretty remarkable with wintry conditions and significant snowfall early month. Tulloch Bridge only managed a maximum of 0.8C on the 3rd. Beyond mid-month and it suddenly felt like mid-summer, particulalrly in the south and east with the UK witnessing it’s warmest April day since 1949.

https://twitter.com/MarkVogan/status/981417723891765253?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E981417723891765253%7Ctwgr%5E48a894927327242349ae1ed24265782569102ee2%7Ctwcon%5Es1_&ref_url=http%3A%2F%2Fwww.markvoganweather.com%2F2018%2F04%2F05%2Fa-very-snowy-april-3-4th-shall-be-followed-by-spring-warmth-late-week-weekend%2F

4 April, 2018

https://twitter.com/SeanBattyTV/status/981849155655143430?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E981849155655143430%7Ctwgr%5Eb32f9ae75bbd357b77c1f23da1f950d8af414dfe%7Ctwcon%5Es1_&ref_url=http%3A%2F%2Fwww.markvoganweather.com%2F2018%2F04%2F06%2Fedinburgh-has-coldest-april-day-in-80-years-following-snowiest-march-day-since-1979%2F

https://twitter.com/MarkVogan/status/981585884955971586?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E981585884955971586%7Ctwgr%5E48a894927327242349ae1ed24265782569102ee2%7Ctwcon%5Es1_&ref_url=http%3A%2F%2Fwww.markvoganweather.com%2F2018%2F04%2F05%2Fa-very-snowy-april-3-4th-shall-be-followed-by-spring-warmth-late-week-weekend%2F

Just after the mid-point of the month, a hot southerly flow took over allowing London’s St James Park to achieve the UK’s highest April temperature since 1949 with 29.1C. Kenley Airfield, Greater London recorded a minimum of 15.9C, a new UK April warmest minimum. Temperatures as warm as 25C were achieved as far north as Whitby, North Yorkshire.

UK APRIL WARMEST/LOWEST TEMPS

2013: 23.1C (Faversham, Kent, 25th), -11.2C (Braemar, Aberdeenshire, 2nd)

2014: 22.0C (Aviemore, Inverness-shire, 28th), -5.2C (Aboyne, Aberdeenshire, 20th)

2015: 25.6C (Faversham, Kent, 15th), -8.0C (Katesbridge, Co Down, 27th)

2016: 20.3C (Porthmadog, Wales 21st), -5.6C (Kinbrace, Sutherland, 28th)

2017: 25.5C (Cambridge, Cambridgeshire, 9th), -6.2C (Cromdale, Moray, 18th)

2018: 29.1C (St James Pk, London 19th), -8.8C (Tulloch Bridge, Inverness-shire, 1st)

2019: 25.8C (Treknow, Cornwall 19th), -6.8C (Braemar, Aberdeenshire, 10th)

2020: 26.0C (Treknow, Cornwall, 10th), -6.9C (Aboyne, Aberdeenshire, 19th)

2021: 21.4C (Treknow, Cornwall, 1st), -9.4C (Tulloch Bridge, Inverness-shire, 12th)

2022: 23.4C (St James Park, London, 15th), -8.0C (Tulloch Bridge, Inverness-shire, 1st)

2023: 21.2C (Kinlochewe, Ross-shire), -7.4C (Tulloch Bridge, Highland)

Cool theme to continue?

The negative AO/NAO appears to linger into May, the suggestion would be for the continuation of warm north, cool south UK but the month starts with cool north, warm south.

Mid-month onwards, I expect the AO/NAO to flip positive and therefore a warming trend in which we could suddenly flip from anemic spring to sudden summer…

With a UK max of only 21.2C, there’s only been one cooler April max in the past decade and so we await some proper warmth.

May looks to see the continuation of a Scandinavian blocking high through the first half of the month with a naturally weakening storm track suppressed to the south.

Low pressure in the means looks to hang just west or southwest of Ireland and UK. This supports enhanced showers or longer spells of rain west and south.

Warmer and drier than average is likely to be (like April) further north across Scotland, possibly Northern Ireland and Scandinavia.

RAINFALL has been 200% of normal in parts of the southern UK (& Ireland) during the March-April period and it wouldn’t surprise me if this ‘unusual compared to recent years’ WET theme continued for the final meteorological month of spring…

CFSv2 weekly

Wk 1

Wk 2

Wk 3

MAY COMPARED TO AVERAGE: Slightly above average temperature & rainfall for UK and Ireland… Cooler north, warmer south Europe with average to above average rainfall for central areas, drier for Iberia but wetter France and Low Countries.

featured image credit: Stephen Cheatley @Stephencheatley

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