First Air Frost watch season 2016-2017

[damianslaw]

I've started this topic a bit later than normal..

As per usual please use this thread to post your thoughts on when the first air frost in the UK will be recorded and where.

I think one or two spots in the Highlands may have recorded 1 or 2 degrees in August, but I class the start of the new season as September.

There is very limited prospect of even single digit mins in England over the next week..

I will say Tulloch Bridge on 24 September.

England and Wales 6 October - Redesdale or Shap

Suspect it will be a slow start to the season for frost this year.

Here we usually see our first ground frost by late September, and first air frost by about the 3rd week of October. 2012 delivered an early air frost around the 23 Sept when we went down to -3 degrees. Hoping for much more frost this season than last year.

[NorthYorksWeather]

Usually October here for ground frost, often end of September in nearby frost hollows if conditions are right! Air frosts have occurred in October here but more likely in November.

[Turnedoutniceagain]

I gather Scotland have had a few already?

[iapennell]

Looking at the recently-changed patterns of sea-surface temperatures, QBO and from my prediction to where Autumn 2016 is now likely to go I am not now holding out much hope of air-frost before November for the great majority of us, not even for where I live at over 400 metres up in the North Pennines. And that is saying something!

[Weather-history]

2 hours ago, iapennell said:

Looking at the recently-changed patterns of sea-surface temperatures, QBO and from my prediction to where Autumn 2016 is now likely to go I am not now holding out much hope of air-frost before November for the great majority of us, not even for where I live at over 400 metres up in the North Pennines. And that is saying something!

associate early season air frosts with valleys/glens/prone cold spots such as Benson rather than high places. So I'm not sure you are say something that you are not expecting an air frost until November for your location given your altitude. Remember cold air sinks.

Edited September 5, 2016 by Weather-history
,..

[Frost HoIIow]

19 minutes ago, Weather-history said:

I associate early season air frosts with valleys/glens/prone cold spots such as Benson rather than high places. So I'm not sure you are say something that you are not expecting an air frost until November for your location given your altitude. Remember cold air sinks.

Indeed. During cold spells I always record much colder night and morning temps than a relative who lives in Saddleworth over 100m higher up than here. I think the confusion comes because very high up areas do generally get more snow so this gives an impression of that area being a lot colder. The reason higher up areas get more snow is because of orographic lifting and having a lower dew point, not always because of the actual air temp. During clear calm nights valleys/glens are almost always a good deal colder. What puzzles a lot of people is when I tell them that the weather station at Altnaharra is 88m asl & close to a river. Yet that place recorded -27.2C. People think Altnaharra is on top of a mountain or something.

Edited September 5, 2016 by Frost HoIIow

[Jo Farrow]

11 hours ago, Turnedoutniceagain said:

I gather Scotland have had a few already?

Lowest min   -1.5 C  Kindrogan ( Perthshire)10th August, we'll ignore that one.  Starting from NOW

[Frosty hollows]

Well, I shall let you know as soon as I record one being so favourably placed! The coldest I've recorded was - 17.1 C in 2010. Yet, we get very little in the way of snow

[NorthYorksWeather]

3 hours ago, Weather-history said:

associate early season air frosts with valleys/glens/prone cold spots such as Benson rather than high places. So I'm not sure you are say something that you are not expecting an air frost until November for your location given your altitude. Remember cold air sinks.

 

5 hours ago, iapennell said:

Looking at the recently-changed patterns of sea-surface temperatures, QBO and from my prediction to where Autumn 2016 is now likely to go I am not now holding out much hope of air-frost before November for the great majority of us, not even for where I live at over 400 metres up in the North Pennines. And that is saying something!

Even though Alston is 400m asl, it is actually in a valley, surrounded by hills somewhat 100-200m higher than the village, so therefore I would imagine it is a very good frost hollow even at that altitude.

 

 

[iapennell]

7 hours ago, Weather-history said:

associate early season air frosts with valleys/glens/prone cold spots such as Benson rather than high places. So I'm not sure you are say something that you are not expecting an air frost until November for your location given your altitude. Remember cold air sinks.

@WeatherHistory ; I am aware that cold air sinks, particularly on cold clear nights. My AWS is on a hillside just over 400 metres above sea-level and air temperatures in the valley below are often 4C colder on a cold clear night. 

That said, at the altitude where I live the temperature of the atmosphere well above the surface (I.e.100 or more metres up) is on average about 3C colder than for the free atmosphere at sea-level. So although near-surface air may only cool 6 or 7C at my location on a clear still winter night the air has (clearly) a lower temperature to fall from and could therefore fall lower than the lowland plains and valleys despite the steeper nighttime drops in temperature in the latter areas (due, as you point out, to the ponding of rapidly-cooling air on the same clear still winter night). 

With regards to having to wait until November for the first air-frost to occur,  this has happened in just four of the last 35 years where I live; 1989, 2001, 2004 and 2013. If I have reason to believe that Autumn 2016 will follow suit in being similarly devoid of any air-frosts it means that there will be a remarkable absence of cold airstreams reaching Northern Britain and an absence of clear nights following them, throughout both September and October. That is unusual when compared to the average for Autumn over the last 40 years. 

[lassie23]

21c here at the moment.

[iapennell]

3 hours ago, vizzy2004 said:

 

Even though Alston is 400m asl, it is actually in a valley, surrounded by hills somewhat 100-200m higher than the village, so therefore I would imagine it is a very good frost hollow even at that altitude.

 

 

@vizzy2004, Alston is just over 300 metres above sea-level and as it sits in the South Tyne Valley it can get some very low temperatures on clear still winter nights. It's elevation above sea-level actually means it can get colder than the adjacent lowland valleys of the Tyne and Eden because the atmosphere above Alston (being at higher elevations) is colder than the corresponding atmosphere above the lowland valleys. Notwithstanding that the very cold air can drain from upland valleys to the lowlands (and the effect is slow with a valley which has a slow incline and with extensive catchment to collect cold air from surrounding hillsides) upland valley locations can get colder than lowland valleys. 

I actually live about four miles south-east of Alston and another 100 metres higher than Alston on a hillside. Rapidly cooling air drains away from my home location on a clear still night so it is very rare (though not unknown) for minimum night temperatures to drop to more than 8C below the ambient airmass temperature 100 metres up. Alston , as well as the Nent Valley below where I live can get much colder. 

[cheese]

12 hours ago, Weather-history said:

associate early season air frosts with valleys/glens/prone cold spots such as Benson rather than high places. So I'm not sure you are say something that you are not expecting an air frost until November for your location given your altitude. Remember cold air sinks.

High-elevation areas receive more air frosts on average. Areas in valley bottoms get colder, but not necessarily more often.

Great Dun Fell receives 125.5 air frosts a year on average, and all months bar July have an average air frost figure - even though in August it's only 0.1 days, so one every ten years.

Benson gets 57.7 air frosts a year on average. There are many stations in England with a higher figure than that - including Shap with 74.5, Topcliffe with 58.8, Buxton with 59.0, Ambleside with 62.8, Redesdape Camp with 78.9, Malham Tarn with 73.0, and Santon Downham with 76.5. Areas of Norfolk and Suffolk are probably the most continental in the UK - although Santon Downham is an extreme frost hollow and is not representative of anywhere other than itself.

Altnaharra gets 77.7 air frosts a year on average so is actually less frost prone than England's frostiest (non-mountain) weather station. Braemar, on the other hand, gets 101.7 air frosts a year on average, and is located at 339m ASL. It is the most frost-prone weather station in the UK that isn't on a mountain.

Edited September 6, 2016 by cheese

[B87]

We usually don't see our first frost here until the end of November, though rarely it happens in October.

We get a frost night maybe once every 3-4 years in October, and twice per November, with the average first date being 20-25th November.

Edited September 6, 2016 by B87

[damianslaw]

On 06/09/2016 at 00:25, iapennell said:

@WeatherHistory ; I am aware that cold air sinks, particularly on cold clear nights. My AWS is on a hillside just over 400 metres above sea-level and air temperatures in the valley below are often 4C colder on a cold clear night. 

That said, at the altitude where I live the temperature of the atmosphere well above the surface (I.e.100 or more metres up) is on average about 3C colder than for the free atmosphere at sea-level. So although near-surface air may only cool 6 or 7C at my location on a clear still winter night the air has (clearly) a lower temperature to fall from and could therefore fall lower than the lowland plains and valleys despite the steeper nighttime drops in temperature in the latter areas (due, as you point out, to the ponding of rapidly-cooling air on the same clear still winter night). 

With regards to having to wait until November for the first air-frost to occur,  this has happened in just four of the last 35 years where I live; 1989, 2001, 2004 and 2013. If I have reason to believe that Autumn 2016 will follow suit in being similarly devoid of any air-frosts it means that there will be a remarkable absence of cold airstreams reaching Northern Britain and an absence of clear nights following them, throughout both September and October. That is unusual when compared to the average for Autumn over the last 40 years. 

There was also very little frost before November in 2006 and 2011, perhaps a rogue air frost only - those autumns were especially warm.

It only takes a relatively cool airmass and clear skies and no winds to produce an air frost in sheltered northern valleys in October - so I never the rule the chances of an air frost out once we get into October, a polar maritime airflow can easily do it, even when faced by what looks like an inpenetrable atlantic onslaught - you don't need high pressure, just a calm still relatively cool night in the cold sector between frontal systems.

Edited September 7, 2016 by damianslaw

[iapennell]

2 hours ago, damianslaw said:

 

I never the rule the chances of an air frost out once we get into October, a polar maritime airflow can easily do it, even when faced by what looks like an inpenetrable atlantic onslaught - you don't need high pressure, just a calm still relatively cool night in the cold sector between frontal systems.

I like your optimism! If we have a persistent West or south-westerly type pattern in October it is rare, very rare, for the wind to remain below 6 to 8 mph for more than a few hours (even during ridges of high-pressure following cold fronts), I live on a hillside just over 400 metres above sea-level so it is a relatively exposed location. Furthermore, and this often happens in the North Pennines with moist Westerly airstreams, nocturnal cooling with some mixing of the air results in the formation of stratus or stratocumulus cloud-cover (which often persists under an inversion associated with the said ridge of high-pressure). The formation of such cloud-cover can follow a chilly bright day with Maritime Polar air crossing the district from the west or north-west, this quickly nips any potential frost in the bud.

For there to be any guarantee of air frost before November on the hillside where I live in the North Pennines, winds would have to reach Britain from well within the Arctic Circle for a couple of days and be followed by the Greenland High delivering it moving south-eastwards over Britain. Because of our location, there is almost always a breeze and one is lucky to get continually clear night skies for more than a few hours. Hence for the guarantee of an air frost we would need an airmass with ambient temperature 100 metres above the surface at dusk of no more than 5C with a ridge of high-pressure moving in on north-westerly (not backing south-westerly!) winds. And personally I would also want as small a number of Praying Mantris asking God to protect their precious dahlias on such evenings as possible (preferably none!).

The chance of that happening in the next six weeks, given the manner in which the general circulation is shaping up over the foreseeable future, is not that great. 

Edited September 7, 2016 by iapennell

[MP-R]

Other than 2004-2007, I've tended to record my first air frost of the autumn every other October:

2014 came close on the 05th, instead I had to wait for a whole month for the actual first air frost early on 06th November

2013 - 19th November

2012 - 27th October

2011 - 10th December!

2010 - 21st October

2009 - 01st December

2008 - 29th October

2007 - 12th November

2006 - 01st November

2005 - 14th November

2004 - 11th November

2003 - 24th October

2002 - 19th October

[Norrona2015]

Last frost was 11-08-2016.

[damianslaw]

Aboyne got down to 0.9 degrees last night. Somewhere may go a bit lower tonight, but doubtful of an air frost, so we still await the first one of the season. Sunday night looks quite chilly but again doubt anywhere will see an air frost, so my guess of 24 Sept very unlikely (Saturday night looks mild everywhere). However, there indications that come the following weekend air frost could be on the cards for a few, so I'm hopeful this thread will see a bit more activity in the next couple of weeks. Even Met office long range forecast is mentioning air frosts in October.

[Frost HoIIow]

Had 2 air frosts here in September 2005 on the 17th & 24th both at -1C. I doubt we will this month at all. October looking more seasonal though as said above. Last time we had an air frost here in September was 2012 on the 22nd. Like 2005 we got down to -1C.

 

[NorthYorksWeather]

Few spots in the Yorkshire Dales and North York Moors currently at 5c at 21.30pm, so a chance of a ground frost in places. Depends on cloud cover as the night progresses.

[lassie23]

26 minutes ago, vizzy2004 said:

Few spots in the Yorkshire Dales and North York Moors currently at 5c at 21.30pm, so a chance of a ground frost in places. Depends on cloud cover as the night progresses.

Feels cold out, but it's 13c lol

[reef]

Still haven't dropped below 10C here yet this month, so its a long time before we can think of even a ground frost, let alone an air frost! Tonight might finally manage a sub-10C min though, down to 10.9C already.

[4wd]

https://www.wunderground.com/personal-weather-station/dashboard?ID=IUNITEDK529

This is in Farndale North York Moors, they got below 3C early this morning - really good frost hollow there.

[NorthYorksWeather]

2.4c early doors there Colin, 5c colder than yourself

4 minutes ago, 4wd said:

https://www.wunderground.com/personal-weather-station/dashboard?ID=IUNITEDK529

This is in Farndale North York Moors, they got below 3C early this morning - really good frost hollow there.