Mid-spring snow to very warm, from the E or SE

[Summer8906]

It's fairly well known that at this time of year, the temperature can suddenly drop as an anticyclone, which has remained in situ over the UK for days leading to increasing temps (often into the 20s) is suddenly displaced by a northerly plunge. Good examples include April 9 1988, April 2-4 1989, around April 16 1991, April 18 1995, or April 5 2008. Another example I much less clearly remember occurred just after mid-month in 1985. On such occasions it can literally go from 21C to snow overnight.

However I'm struggling to think of examples of the reverse, in which cold and snow can be suddenly replaced by seriously warm air. I can think of a synoptic when this could, in theory, occur. A strong northerly is present over the UK with low pressure over the Low Countries, associated with a warm front. To the east of this low pressure is deep warm air from far south. The warm front moves into the cold northerly, producing possibly heavy snow, which turns to rain and then stops. The cloud breaks, and the warm SE-lies behind the warm front spread westwards across the UK. Temps rapidly rise as a result, in theory perhaps producing 21C maxima just two days after heavy snow.

As I said I cannot think of a single example of this synoptic; warm fronts from the E can occur at this time of year but I can't think of one in which a warm front moved W-wards into seriously cold air, followed by seriously warm air behind. Can anyone think of any historical examples?

Edited April 9, 2023 by Summer8906

[Metwatch]

Closest I can think of is April 2003. On the 10th -7.5°C in Hawarden, light snow for parts of southern England. 6 days later, 27.4°C in a spot just south of Reading.

That was the 3rd highest temperature recorded in April, and the highest since 1949. 27.2°C for Inverailort, Scotland - highest April Scotland temperature on record. Turned colder again from the 18th. 

I imagine @Weather-historymay have a better example. 

Edited April 9, 2023 by Metwatch

[MP-R]

Another slightly later example is May 2001. Chilly northeasterlies followed by thunderstorms on the 09th/10th,  then a warm southeasterly.

 

 

[Andy Bown]

4 hours ago, Summer8906 said:

However I'm struggling to think of examples of the reverse, in which cold and snow can be suddenly replaced by seriously warm air. I can think of a synoptic when this could, in theory, occur.

I cannot remember which year though it was definitely in the 90s.

There was 2 inches of snow on the Saturday morning, the Sunday reached 19c.

[Weather-history]

4 hours ago, Summer8906 said:

It's fairly well known that at this time of year, the temperature can suddenly drop as an anticyclone, which has remained in situ over the UK for days leading to increasing temps (often into the 20s) is suddenly displaced by a northerly plunge. Good examples include April 9 1988, April 2-4 1989, around April 16 1991, April 18 1995, or April 5 2008. Another example I much less clearly remember occurred just after mid-month in 1985. On such occasions it can literally go from 21C to snow overnight.

However I'm struggling to think of examples of the reverse, in which cold and snow can be suddenly replaced by seriously warm air. I can think of a synoptic when this could, in theory, occur. A strong northerly is present over the UK with low pressure over the Low Countries, associated with a warm front. To the east of this low pressure is deep warm air from far south. The warm front moves into the cold northerly, producing possibly heavy snow, which turns to rain and then stops. The cloud breaks, and the warm SE-lies behind the warm front spread westwards across the UK. Temps rapidly rise as a result, in theory perhaps producing 21C maxima just two days after heavy snow.

As I said I cannot think of a single example of this synoptic; warm fronts from the E can occur at this time of year but I can't think of one in which a warm front moved W-wards into seriously cold air, followed by seriously warm air behind. Can anyone think of any historical examples?

As WWII was coming to an end in Europe

[Frigid]

May 2020 is a perfect example, cold north-easterly winds with frosts to heatwave conditions

 

 

 

[Summer8906]

3 hours ago, MP-R said:

Another slightly later example is May 2001. Chilly northeasterlies followed by thunderstorms on the 09th/10th,  then a warm southeasterly.

 

 

True, and indeed this has come up on the other thread.

However, I am specifically thinking of examples in which it was properly wintry - cold enough for snow - ahead of the front and then properly warm (ideally 20C+) behind.

2 hours ago, Weather-history said:

As WWII was coming to an end in Europe

Thanks, will try and look that one up. Assuming that low did move east to west and drew up warm air behind it, that would be a perfect example.

[Summer8906]

2 hours ago, Frigid said:

May 2020 is a perfect example, cold north-easterly winds with frosts to heatwave conditions

 

 

 

True, though I think this was a gradual warm up rather than the sudden arrival of very warm air behind a warm front.

[Weather-history]

18 hours ago, Summer8906 said:

It's fairly well known that at this time of year, the temperature can suddenly drop as an anticyclone, which has remained in situ over the UK for days leading to increasing temps (often into the 20s) is suddenly displaced by a northerly plunge. Good examples include April 9 1988, April 2-4 1989, around April 16 1991, April 18 1995, or April 5 2008. Another example I much less clearly remember occurred just after mid-month in 1985. On such occasions it can literally go from 21C to snow overnight.

However I'm struggling to think of examples of the reverse, in which cold and snow can be suddenly replaced by seriously warm air. I can think of a synoptic when this could, in theory, occur. A strong northerly is present over the UK with low pressure over the Low Countries, associated with a warm front. To the east of this low pressure is deep warm air from far south. The warm front moves into the cold northerly, producing possibly heavy snow, which turns to rain and then stops. The cloud breaks, and the warm SE-lies behind the warm front spread westwards across the UK. Temps rapidly rise as a result, in theory perhaps producing 21C maxima just two days after heavy snow.

As I said I cannot think of a single example of this synoptic; warm fronts from the E can occur at this time of year but I can't think of one in which a warm front moved W-wards into seriously cold air, followed by seriously warm air behind. Can anyone think of any historical examples?

I think you are going to find it a struggle, there are a number of examples of it going from very cold to very mild during the winter radpidly, even the autumn season but going from cold to very warm dramatically is pretty rare. Most cases. the process goes through stages.

June 1975 started off with snow falling in places then it rapidly transition to very warm weather but that happened not even in the meteorological spring

[Summer8906]

3 hours ago, Weather-history said:

I think you are going to find it a struggle, there are a number of examples of it going from very cold to very mild during the winter radpidly, even the autumn season but going from cold to very warm dramatically is pretty rare. Most cases. the process goes through stages.

June 1975 started off with snow falling in places then it rapidly transition to very warm weather but that happened not even in the meteorological spring

Ah ok, thanks.

In that case it's quite a contrast to the converse (very warm to cold) - as I stated in my original post there are plenty of examples of that.

I'm just surprised that the theoretical progression of a warm front moving westwards into very cold air, to be followed by very warm SElies, occurs so rarely if at all - given that westwards-moving warm fronts do occur not infrequently this time of year (but not directly into really cold air).

I did look at that 1945 progression btw - even that was not a "clean" conversion from cold to warm.

Edited April 10, 2023 by Summer8906

[MP-R]

I think your struggle will be finding such cold air beforehand as that’s very much an exception rather than a rule in spring. There are plenty of examples of rapid switcharounds but not from the setup you’re looking for.

[Metwatch]

I still think April 2003 is the closest example there could be, with light snow to mid to high 20s in essentially the same areas in under a week.

Infact looking at the reanalysis, the proper warm airmass arrived in just 4 days after the cold airmass was over the country (10-14th.) Almost that warm front you're looking for after pretty chilly air.

[Summer8906]

23 minutes ago, Metwatch said:

I still think April 2003 is the closest example there could be, with light snow to mid to high 20s in essentially the same areas in under a week.

Infact looking at the reanalysis, the proper warm airmass arrived in just 4 days after the cold airmass was over the country (10-14th.) Almost that warm front you're looking for after pretty chilly air.

Ah, ok thanks.

The fact that this has slipped under the radar could be explained by the fact that I was out of the UK from the 12th to the 27th and actually missed the warm spell. (I was in California but the max temp I experienced there was about 20!)

I remember early April, up to the 12th as being sunny and seem to remember a cold-ish spell though don't recall it being notably cold here. After a sunny week the 12th was more hazy with some medium-level cloud but not sure exactly how things developed after that.

If I remember right the breakdown of the warm air was also unusual. First cool and cloudy air from the NE displaced the warm weather over the Easter weekend, and then, some days after the cool and cloudy conditions arrived, a full on breakdown from France arrived with heavy rain, the Atlantic was then unleashed, and the rest of the month was very dull and wet with a low-latitude depression track (and these were the conditions I arrived back home into on the 27th... oh joy). May was then mostly awful apart from the last week though thankfully the summer was better!

(EDIT: just looked at the archives. It does indeed appear that the warm air arrived directly from the east on Sunday 13th, though I can't remember how warm or cold Friday 11th was. It then appears the cool cloudy air arrived on Easter Saturday and the heavy rain from the south on Easter Sunday or Monday, though there was then a further slack easterly interlude before the Atlantic went into overdrive on the following Saturday. But slightly unfortunate timing for Easter with only Good Friday producing decent weather, by the looks of things).

Edited April 10, 2023 by Summer8906

[SummerShower]

20 hours ago, MP-R said:

Another slightly later example is May 2001. Chilly northeasterlies followed by thunderstorms on the 09th/10th,  then a warm southeasterly.

 

 

https://community.netweather.tv/topic/98627-warm-front-thunderstorms-may-2001/?do=getNewComment

 

[SummerShower]

Agreed this didn't start off with air cold enough for snow, but found it fascinating to have such an increase in temperature after such a violent storm.

I've always dreamed of the scenario 'late season beast from the east meets early season spanish plume' though!

[MP-R]

Here are my temps from the April 2003 period - quite an interesting one really. Cold to very warm to pretty cold again. Notably low and high minima for April. Thereafter, it warmed up once more then, as said above, ended wet and thundery.

 

09th: 09.1 / -00.3

10th: 07.5 / -01.7

11th: 10.6 / -02.0

12th: 13.5 / 01.0

13th: 15.2 / 08.0

14th: 18.4 / 13.1

15th: 23.1 / 09.5

16th: 25.0 / 07.8

17th: 25.4 / 09.2

18th: 23.3 / 09.5

19th: 10.7 / 06.7

[Summer8906]

3 hours ago, MP-R said:

Here are my temps from the April 2003 period - quite an interesting one really. Cold to very warm to pretty cold again. Notably low and high minima for April. Thereafter, it warmed up once more then, as said above, ended wet and thundery.

 

09th: 09.1 / -00.3

10th: 07.5 / -01.7

11th: 10.6 / -02.0

12th: 13.5 / 01.0

13th: 15.2 / 08.0

14th: 18.4 / 13.1

15th: 23.1 / 09.5

16th: 25.0 / 07.8

17th: 25.4 / 09.2

18th: 23.3 / 09.5

19th: 10.7 / 06.7

Interesting. The drop on the 19th was considerably more than I thought though! (As I said I was out of the country during this spell).

Would hazard a guess that the 13th and 14th were quite heavily encumbered by cloud given the low diurnal range. From the synoptics it looks like there was a low just to the west, so places in the SE might have been sunnier and might have seen a really dramatic rise.

[Weather-history]

24th April 1908

Manchester max: 5.6°C

1st May 1908

Manchester Max: 20.3°C

[Summer8906]

3 hours ago, Weather-history said:

24th April 1908

Manchester max: 5.6°C

1st May 1908

Manchester Max: 20.3°C

Perhaps this is the closest match. Late April 1908 had notable heavy snow, remarkably on the exact same date as 1981 and also 1950. Extraordinary to have three separate incidences of heavy snow on the same date so late in the year on three entirely separate occasions in the 20th century. In another curious coincidence the calendars of 1908 and 1981 were identical, and Easter occurred on April 19th in both years.

From the Monthly Weather Report of April 1908, regarding the late snow: "On the morning of the 25th it was 14 ins. deep in Southampton and over 10 ins. at Totland Bay, Isle of Wight" and on the morning of the 26th it was "11 ins. deep at Marlborough, 16 ins. at Oxford and 19 ins. at Bucklebury Palace" followed by this description of the closing days: "with a low pressure beyond Ireland, a southerly to southeasterly type prevailed", though it looks like this was dull and damp until the end of the month.

MWR_1908_04 | Met Office UA

DIGITAL.NMLA.METOFFICE.GOV.UK

And from the May MWR: "A sudden and rapid rise of the thermometer took place on the first day of May" including "77 degrees [F] at Maidenhead". So for the Thames Valley, heavy snow to 25C in just five days.

MWR_1908_05 | Met Office UA

DIGITAL.NMLA.METOFFICE.GOV.UK

So it looks like this is a very good match to the sort of synoptic I was looking for, though the really warm air took a few days to get in.

Edited April 10, 2023 by Summer8906

[Metwatch]

18 minutes ago, Summer8906 said:

Perhaps this is the closest match. Late April 1908 had notable heavy snow, remarkably on the exact same date as 1981 and also 1950. Extraordinary to have three separate incidences of heavy snow on the same date so late in the year on three entirely separate occasions in the 20th century. In another curious coincidence the calendars of 1908 and 1981 were identical, and Easter occurred on April 19th in both years.

From the Monthly Weather Report of April 1908, regarding the late snow: "On the morning of the 25th it was 14 ins. deep in Southampton and over 10 ins. at Totland Bay, Isle of Wight" and on the morning of the 26th it was "11 ins. deep at Marlborough, 16 ins. at Oxford and 19 ins. at Bucklebury Palace" followed by this description of the closing days: "with a low pressure beyond Ireland, a southerly to southeasterly type prevailed", though it looks like this was dull and damp until the end of the month.

MWR_1908_04 | Met Office UA

DIGITAL.NMLA.METOFFICE.GOV.UK

And from the May MWR: "A sudden and rapid rise of the thermometer took place on the first day of May" including "77 degrees [F] at Maidenhead". So for the Thames Valley, heavy snow to 25C in just five days.

MWR_1908_05 | Met Office UA

DIGITAL.NMLA.METOFFICE.GOV.UK

So it looks like this is a very good match to the sort of synoptic I was looking for, though the really warm air took a few days to get in.

April 1908 Brought 22cm of snow on the 26th to Coventry, this is way above any highest snow records in March, (unless something major occurred in the 1920s-1950s during no data) which hasn't even got above 13cm at most.  

Interestingly the same date in 1981 got 15cm. Both melting very quick under that very strong sun though. 

[Weather-history]

End of April/early May 1838

Cambridge

29th Apr

Max: 46°F, min: 32°F   Snow am light rain in evening

30th Apr

Max: 51°F, min: 36°F  Cloudy, rain, much milder

1st May

Max: 60°F, min: 36°F  Rain am, afterwards fine 

2nd May

Max: 70°F.. min: 48°F  Fine but often cloudy. Brilliant display of sheet lightning in the SE, SW, NW and N horizons successively with distant thunder in the SW. Oprresively warm all day

 

 

[Summer8906]

Interesting, I'd guess that this was an instance of a warm front moving east-west into an Arctic outbreak with warm southerlies behind, but still with low pressure.

[B87]

 Weather-history How can a 21c high with a 9c low be considered oppressively warm all day, in May?

[Weather-history]

 B87

Compare to the previous spring.........

Don't forget this is 1838

[B87]

 Weather-history London averaged just above 18c in May in the mid to late 1800s, and Cambridge probably not too different. I can't imagine anyone would have considered 21c oppressive, even then. 

Edited April 28 by B87