HARD SPRING FROSTS

[iapennell]

There is a real possibility (according to my Spring 2016 forecast) of an Arctic blast at the end of April or beginning of May that will bring a short spell of unseasonably cold weather following which, with night skies clearing, air frosts will be widespread and temperatures could go down to -3C in lowland Scotland and the North of England.

Given the right conditions, with dry ground, a sustained flow of air from the central Arctic for several days and with a dry clear night and winds falling calm in a ridge of high-pressure following such Arctic airstreams some surprisingly low temperatures can occur just about anywhere in the country (even as late as May).  In mid-May 1935 an exceptionally cold Arctic airstream affected Britain which brought snow-showers as far south as London and Wiltshire. Clear skies occurred at night with the northerly airstream falling light and the air temperature fell to a garden-devastating -8C at Rickmansworth in Hertfordshire (this is on the outskirts of London).

This could happen again, possibly this spring: If a strong high-pressure forms over Greenland following the passage of a depression into Scandinavia the northerly winds could be strong and come from a long way north bringing an airmass which is close to freezing point even at sea-level across the English Midlands and South in early May (the Central Arctic remains a source of some surprisingly cold air until early May when its mean temperature is still around -10C). If skies clear and winds fall light as a ridge moves in from the west (a likely scenario following a spell of northerlies) air temperatures near the surface would fall a further several degrees (and more than 10C colder in some favoured frost hollows). This means that severe air frosts with minima of -5C or colder remain a small possibility across most of the country until surprisingly late in the spring.

At my home at just over 400 metres' elevation in the North Pennines I have recorded a minimum temperature of -9C in April (in 1990) and -5C in May (1984). Moreover, as recently as last year I recorded -5C overnight 26th/27th April and one local gardener lost the entire contents of his Polly-tunnel! 

[MP-R]

Interesting read there! Not particularly pleasing but not without interest. I think I've only actually seen frost twice in May because it tends to have disappeared before most people have even got up, that was in May 2005 and May 2010. I guess the lowest temperatures will depend no dryness of the ground as you say which, going by long range forecasts, doesn't look like it'll be the case.

[reef]

There's been a few unusually cold nights in early-May in recent years. Last year was 0.0C on the 1st May coming after 0.1C on 11th May 2010, 0.0C on 4th May 2011, -0.1C on 7th May 2012 and 0.9C on 3rd May 2014.

You could be forgiven for thinking its actually quite normal, but the temperature only dropped below 1C in May on two other occasions here between 1982 and 2010.

Edited April 6, 2016 by reef

[Liam J]

Interesting, no good for gardeners with tender spring plants! Frost at this time of year disappears rapidly once the sun rises, a week or so ago Altnaharra recorded -8°C at dawn and 2/3 hours later the temperature had risen to +6°C in the ever strengthening sun. There would be some large temperature contrasts if we got a clear high following a cold northerly (for the time of year) into May with some frosts possible, and into the afternoon temps could be heading towards double figures. I'll take anything if it's dry and sunny! Nearly managed two weeks with little or no rain last month with plenty of sunny days, it was great! 

[iapennell]

1 hour ago, reef said:

There's been a few unusually cold nights in early-May in recent years. Last year was 0.0C on the 1st May coming after 0.1C on 11th May 2010, 0.0C on 4th May 2011, -0.1C on 7th May 2012 and 0.9C on 3rd May 2014.

You could be forgiven for thinking its actually quite normal, but the temperature only dropped below 1C in May on two other occasions here between 1982 and 2010.

We have of course had a run of quite wet Mays over recent years, that does of course mitigate frost risk. Do you live near the East Yorkshire coast, if so that would explain the limited amount of frost that you might have compared to places further inland?  Coastal locations and hillside locations can escape frost when adjacent areas inland  and in valley-bottoms can endure really hard frosts that wipe out flowers and kill blossoms. 

I live at just over 400 metres above sea level in the North Pennines but my AWS is on a little hillock (i.e. NOT in a frost hollow), even so extreme minima for three of the last four Mays have been -2C or colder and last year the temperature overnight 26th/27th April fell to -5C; which leaves one to wonder what decimating air and ground frosts might have occurred in the nearby South Tyne and West/East Allen Valley bottoms!

We had a really sharp air frost mid May 2008 when the air temperature at my weather station fell to -3C, in nearby Alston a AWS in the valley bottom recorded -6C (and yes, that was mid-May).  May 2008 was a dry month and cold north-easterly airstreams prevailed for a time mid-month, unsurprisingly when night skies cleared temperatures fell dramatically.

[Interitus]

2 hours ago, iapennell said:

There is a real possibility (according to my Spring 2016 forecast) of an Arctic blast at the end of April or beginning of May that will bring a short spell of unseasonably cold weather following which, with night skies clearing, air frosts will be widespread and temperatures could go down to -3C in lowland Scotland and the North of England.

Given the right conditions, with dry ground, a sustained flow of air from the central Arctic for several days and with a dry clear night and winds falling calm in a ridge of high-pressure following such Arctic airstreams some surprisingly low temperatures can occur just about anywhere in the country (even as late as May).  In mid-May 1935 an exceptionally cold Arctic airstream affected Britain which brought snow-showers as far south as London and Wiltshire. Clear skies occurred at night with the northerly airstream falling light and the air temperature fell to a garden-devastating -8C at Rickmansworth in Hertfordshire (this is on the outskirts of London).

This could happen again, possibly this spring: If a strong high-pressure forms over Greenland following the passage of a depression into Scandinavia the northerly winds could be strong and come from a long way north bringing an airmass which is close to freezing point even at sea-level across the English Midlands and South in early May (the Central Arctic remains a source of some surprisingly cold air until early May when its mean temperature is still around -10C). If skies clear and winds fall light as a ridge moves in from the west (a likely scenario following a spell of northerlies) air temperatures near the surface would fall a further several degrees (and more than 10C colder in some favoured frost hollows). This means that severe air frosts with minima of -5C or colder remain a small possibility across most of the country until surprisingly late in the spring.

At my home at just over 400 metres' elevation in the North Pennines I have recorded a minimum temperature of -9C in April (in 1990) and -5C in May (1984). Moreover, as recently as last year I recorded -5C overnight 26th/27th April and one local gardener lost the entire contents of his Polly-tunnel! 

A couple of observations, Rickmansworth is a renowned frost hollow which has been suggested may have been aided by early land use developments to help cold air pooling. However, subsequent urbanisation has meant that a similarly cold temperature as -8°C would be less likely now, as discussed some time back in a two part article in the journal Weather -

http://onlinelibrary.wiley.com/doi/10.1256/wea.53.04/pdf

http://onlinelibrary.wiley.com/doi/10.1256/wea.54.04/pdf

Regarding polytunnels, if the plastic film covering is not opaque to infrared then the interior air is able to cool more effectively than outside because of lack of air movement. Assuming lack of insulation, supplementary artificial heat or sufficient daytime insolation this can surprisingly result in the inside being colder than the external environment.

[Scorcher]

On 4/6/2016 at 5:28 PM, iapennell said:

There is a real possibility (according to my Spring 2016 forecast) of an Arctic blast at the end of April or beginning of May that will bring a short spell of unseasonably cold weather following which, with night skies clearing, air frosts will be widespread and temperatures could go down to -3C in lowland Scotland and the North of England.

Given the right conditions, with dry ground, a sustained flow of air from the central Arctic for several days and with a dry clear night and winds falling calm in a ridge of high-pressure following such Arctic airstreams some surprisingly low temperatures can occur just about anywhere in the country (even as late as May).  In mid-May 1935 an exceptionally cold Arctic airstream affected Britain which brought snow-showers as far south as London and Wiltshire. Clear skies occurred at night with the northerly airstream falling light and the air temperature fell to a garden-devastating -8C at Rickmansworth in Hertfordshire (this is on the outskirts of London).

This could happen again, possibly this spring: If a strong high-pressure forms over Greenland following the passage of a depression into Scandinavia the northerly winds could be strong and come from a long way north bringing an airmass which is close to freezing point even at sea-level across the English Midlands and South in early May (the Central Arctic remains a source of some surprisingly cold air until early May when its mean temperature is still around -10C). If skies clear and winds fall light as a ridge moves in from the west (a likely scenario following a spell of northerlies) air temperatures near the surface would fall a further several degrees (and more than 10C colder in some favoured frost hollows). This means that severe air frosts with minima of -5C or colder remain a small possibility across most of the country until surprisingly late in the spring.

At my home at just over 400 metres' elevation in the North Pennines I have recorded a minimum temperature of -9C in April (in 1990) and -5C in May (1984). Moreover, as recently as last year I recorded -5C overnight 26th/27th April and one local gardener lost the entire contents of his Polly-tunnel! 

It may well be possible, but we haven't had a particularly hard frost here all winter/spring- there have been very few nights below -3C even at Manchester Airport which is more prone to frost than urban Manchester with its semi-rural location. I believe there has only been one night which has dipped below -3C there since last winter, and virtually all the frosts that have occurred have been only slightly below 0C. I imagine frosts have been even rarer closer to the coast in NW England and further south.

So with the nights shortening all the time, as much as it is still possible to get 'hard frosts' well into April, the odds are strongly against it. Touching 0C is another matter.

[damianslaw]

Charts shown today by ECM and GFS would enable such a set up to take hold.

[iapennell]

Interesting conditions in parts of the country with the recent Arctic spell: Subzero temperatures have been quite widespread particularly across the North and Scotland.  At my home near Alston in the North Pennines I have recorded three nights with air temperature down to -3C all within the last fortnight. This might be expected at just over 400 metres above sea-level in the North of England but my weather station is on a hillside so colder conditions are bound to have occurred in the nearby Nent and South Tyne valleys.

It would be interesting to see what temperatures some of you have recorded in the last fortnight and what effect such freezing temperatures have had on your garden flowers and blossoms!!

[March]

I had my coldest night last night at -1.2C, but that's the only air frost since April 17 which was only -0.2C. April 1 and 10 are the only other days of air front, both reaching -1C. 

[MP-R]

Managed -0.9C yesterday morning and frost was still evident when I left the house for work at 8 - that is unusual for so late in the season.

I remember May 2010 and May 2005 had a few ground frosts but never air frosts. I wonder if this May will produce one.

[hillbilly]

There have been plenty times here with late cold spells.Last night was the biggest snowfall this season here with 4 to 5 inches on high ground drifting in places.It has probably been the coldest late April since the 80s.1986 was the coldest april and there has not been a colder one in almost 100 years.1981 gave the most snow late in April that has no comparison with enormous drifts a month later than any comparative snow event.Both 1995 and 1996 had snow and frost in May particularly 1996 and there has not been a colder one since,it certainly felt cold as I was living at 340m at the time and worked at 365m .

[hillbilly]

APRIL

 CF 

1-11.711West Linton (Borders) etc 1917; Braemar (Aberdeenshire) 1922; Buddon Ness (Angus) 1967

2-15.05Newton Rigg (Cumbria) 1917

3-12.210Newton Rigg (Cumbria) 1917

4-11.211.8Glenlivet (Moray) 1961

5-9.015.8Grendon Underwood (Bucks) 1990

6-12.210Wolfelee (Borders) 1917

7-8.916Balmoral (Grampian) 1935

8-9.415Caldecott (Leics) 1968

9-8.317Leadhills (Borders) 1923; -7.8/18 Alwen (Conwy) 1968

10-10.113.8Grantown-on-Spey (Highland) 1978

11-13.38Braemar (Aberdeenshire) 1917

12-9.415Alwen (Conwy) 1958

13-9.215.4Lednathie (Perth and Kinross) 1890

14-10.613Achnagoichan (Highland) 1966

15-10.014Newton Rigg (Cumbria) 1892

16-11.711Braemar (Aberdeenshire) 1892

17-10.014Braemar and Balmoral (Aberdeenshire) 1966

18-10.014Lagganlia (High1and) 1986

19-8.117.5Inverdruie (Highland) 1969

20-7.818Alwen (Conwy) 1969

21-10.014Dalwhinnie (Highland) 1981

22-10.712.7Kingussie (Highland) 1899

23-10.612.9Dalwhinnie (Highland)1981

24-12.89Garforth (W Yorks) and Perth (Perth and Kinross) 1908

25-12.210Corstophine (Edinburgh) 1908

26-8.317Kincraig (Highland) 1957

27-6.121Glenlivet (Moray) 1956

28-7.818Glenlivet (Moray) 1956

29-9.914.2Eskdalemuir (Dumfries and Galloway) 1973

30-7.917.8Kindrogan (Perth and Kinross) 1973

 

This is the list of the coldest recorded temperatures for every day of April.

[Snowyowl9]

Today max has been colder than any day December gave 6.2c today and its currently 4.5c

Had a -2c in may back in 2005

Edited April 29, 2016 by Snowyowl9

[iapennell]

On 4/29/2016 at 2:36 PM, hillbilly said:

APRIL

 CF 

1-11.711West Linton (Borders) etc 1917; Braemar (Aberdeenshire) 1922; Buddon Ness (Angus) 1967

2-15.05Newton Rigg (Cumbria) 1917

3-12.210Newton Rigg (Cumbria) 1917

4-11.211.8Glenlivet (Moray) 1961

5-9.015.8Grendon Underwood (Bucks) 1990

6-12.210Wolfelee (Borders) 1917

7-8.916Balmoral (Grampian) 1935

8-9.415Caldecott (Leics) 1968

9-8.317Leadhills (Borders) 1923; -7.8/18 Alwen (Conwy) 1968

10-10.113.8Grantown-on-Spey (Highland) 1978

11-13.38Braemar (Aberdeenshire) 1917

12-9.415Alwen (Conwy) 1958

13-9.215.4Lednathie (Perth and Kinross) 1890

14-10.613Achnagoichan (Highland) 1966

15-10.014Newton Rigg (Cumbria) 1892

16-11.711Braemar (Aberdeenshire) 1892

17-10.014Braemar and Balmoral (Aberdeenshire) 1966

18-10.014Lagganlia (High1and) 1986

19-8.117.5Inverdruie (Highland) 1969

20-7.818Alwen (Conwy) 1969

21-10.014Dalwhinnie (Highland) 1981

22-10.712.7Kingussie (Highland) 1899

23-10.612.9Dalwhinnie (Highland)1981

24-12.89Garforth (W Yorks) and Perth (Perth and Kinross) 1908

25-12.210Corstophine (Edinburgh) 1908

26-8.317Kincraig (Highland) 1957

27-6.121Glenlivet (Moray) 1956

28-7.818Glenlivet (Moray) 1956

29-9.914.2Eskdalemuir (Dumfries and Galloway) 1973

30-7.917.8Kindrogan (Perth and Kinross) 1973

 

This is the list of the coldest recorded temperatures for every day of April.

Certainly interesting to note the frequency of temperatures below -10C in April in some parts of the country during the 20th Century!

Although none of these records have been surpassed since 2000 that is not to say really hard frosts in April (or indeed May) are not possible.

A temperature of -6C was recorded in mid-May just a few miles from my home as recently as 2008. The location was in the bottom of the South Tyne Valley near Alston (Cumbria) just over 300 metres above sea level!