First sign of Winter

[Isolated Frost]

most recent -5C or below 850hpa event (since August 2010):

12 April (Scotland)

18 March (England, Northern Ireland and ROI)

11 March (Wales)

most recent -10C or below 850hpa event (since August 2010):

7 January (Scotland)

20 December (England)

17 December (Northern Ireland and ROI)

3 December (Wales)

-------------------------

latest -5C or below 850hpa event (August 2009-2010):

25 May (Scotland)

13 May (England)

12 May (Wales and Northern Ireland)

4 April (ROI)

latest -10C or below 850hpa event (since August 2009-2010):

11 February (England)

29 January (Scotland)

10 January (Wales, ROI and Northern Ireland)

This is using information where the -5 or -10C line can be in just part of the nation.

Edited August 24, 2011 by Isolated Frost

[A Winter's Tale]

most recent -5C or below 850hpa event (since August 2010):

12 April (Scotland)

18 March (England, Northern Ireland and ROI)

11 March (Wales)

most recent -10C or below 850hpa event (since August 2010):

7 January (Scotland)

20 December (England)

17 December (Northern Ireland and ROI)

3 December (Wales)

-------------------------

latest -5C or below 850hpa event (August 2009-2010):

25 May (Scotland)

13 May (England)

12 May (Wales and Northern Ireland)

4 April (ROI)

latest -10C or below 850hpa event (since August 2009-2010):

11 February (England)

29 January (Scotland)

10 January (Wales, ROI and Northern Ireland)

This is using information where the -5 or -10C line can be in just part of the nation.

When was the first time we saw the -5c or -10c after August 2010. There was pretty cold period in September and October if I remember correctly.

[Isolated Frost]

20 October 2010: -5C 850hpa air in Scotland

25 November 2010: -10C 850hpa air hits Shetlands

27 November 2010: -10C 850hpa air hits Scotland

01 December 2010: Much of UK under -10C 850hpa air

[A Winter's Tale]

20 October 2010: -5C 850hpa air in Scotland

25 November 2010: -10C 850hpa air hits Shetlands

27 November 2010: -10C 850hpa air hits Scotland

01 December 2010: Much of UK under -10C 850hpa air

I would imagine that the -5C line in Winter would be a good signal for cold and snowy weather. So at low level, what is the signficance between the 0c, -5c and -10c lines.

[Radiating Dendrite]

I would imagine that the -5C line in Winter would be a good signal for cold and snowy weather. So at low level, what is the signficance between the 0c, -5c and -10c lines.

-5 is usually cold enough for snow at low levels, though there are a number of other important factors too.

850hpa is the temperature at roughly 1500m. A 0c 850hpa in the highlands would usually lead to wintriness on the mountain tops (1200m and up). -2 850s and the snowline would be lower, probably getting down to around 650-700m in that instance.

Remember though, cold 850s do not always mean snow. I would recommend that you look at the "will it snow" guide on netweather, should be in the learners section.

[summer blizzard]

Quick question - if the dewpoint is under 0C, will it definitely snow, regardless of 850's, dam levels, temperatures etc.?

First ground frost on Friday morning according to 18Z - enjoy!

You do not always get snow with a dewpoint below 0C. The breakdown on the 27th December 2010 actually saw a dewpoint of -0.6C, but heavy rain/sleet. There are a number of factors which need to come together.

[Aaron]

On a few model runs the 0C isotherm reached northern Scotland. There's a few cold nights to come soon, with temperatures in frost hollows down to around 3c this August, so the first ground frost for many could be in September, with air frost in the usual locations (Shap, Braemar etc) seems likely too.

[Isolated Frost]

Loch Glascarnoch got down to 1.4C on 25th morning. Altnaharra was at 1.9C at 0600 today.

[A Winter's Tale]

Loch Glascarnoch got down to 1.4C on 25th morning. Altnaharra was at 1.9C at 0600 today.

Good news.

I'll keep an eye out for tonight.

[Isolated Frost]

Unless conditions improve dramatically, there will be no frosts tonight - just drizzle and cloud in the Pennines, North Wales and Highlands. I'll have a go at 5.7C at Altnaharra (0500).

Sunday night/Monday morning and the next night however is a whole different story, with a fresher slack NW/N wind in Scotland, frost and snow will be something to look for.

However, tomorrow we do bring in the N'ly flow and by evening we will be looking at 850's nearer 0C. They are currently 4-6C in the Highlands and above in other areas of Britain.

[Geordiesnow]

Saying that though Isolated Frost, tomorrow night over the highlands, it will be wet and very windy so it would prevent any frost despite the uppers being down to 0C. Sunday night may see a touch of ground frost over Northern Ireland in rural areas with city centre temperatures could get down to a chilly 5 or 6C with light winds.

Parts of the highlands may see a touch of ground frost also on Sunday night but it will probably still be too breezy for temperatures to drop down too much. Early part of next week looks a good bet for ground frost across the highlands, even dare I say, an slight air frost by Tuesday morning!?

Regarding snowfall across the highest top of the highlands, I think you are getting carried away with that one, the Northerly flow is a dry and slack one with pressure rising pretty quickly and it probably won't be cold enough for snowfall anyways. Still too early in the season for that, get a moist NW'ly flow with uppers of -5 nearby, then snowfall across the highlands would be a better bet.

[Isolated Frost]

GS - yeah, I agree, winds do look a bit strong but in some sheltered places around Highland and Borders, we could get some frosty evenings, esp. in valleys. Regarding snowfall, on Monday morning, we have -2C uppers in the Highlands and usually that should give wintry showers and snow at the top - snow and mountain forecast have forecasted snow on Monday. However I do understand as it's source is more northerly but is definitely from a west HP source so it certainly won't be potent - but yeah it's definitely no moist NWly - however I wouldn't really rule out a few wintry showers with snowy periods on Cairngorm top and Ptarmigan bar at 1000m. But yeah I would agree I was probably a tad carried away We had a similar spell last year with a cool end to August - but the HP was right next door to us and we had warm days and cool nights then - I think parts of the Highlands got snow then aswell?

[damianslaw]

You do not always get snow with a dewpoint below 0C. The breakdown on the 27th December 2010 actually saw a dewpoint of -0.6C, but heavy rain/sleet. There are a number of factors which need to come together.

Yes lots of factors need to be take into account when predicting likelihood of snow. The dewpoint is a good indicator, but intensity of precipitation, altitude also come into play. Other factors include wind direction and how saturated the air is and is source. The 27th december showed how important these factors played in the events of that day. Here in Windermere we had a few hours of moderate but very wet snow during the early hours of the morning with favourable dewpoints, however, as the precipitation eased in intensity the snow gradually became sleetier in nature and we began to see a rise in temps above 0 degrees as winds swung more into the SW off the Irish Sea as opposed to the S/SE. The front dissipated in its intensity as it reached the pennines and thus without the aid of evaporative cooling, dewpoints rose rapidly thus giving only sleet to many low level parts and limited light snowfalls to western parts.

An example of much more favourable conditions for long lasting snow occured on the 5/6 feb 96 in these parts. On that occasion we had a very stubborn high pressure block to our east which although had given a cold week of weather nothing on the scale of the build up to last christmas. But on this occasion the front became slow-moving as it hit the block and aligned itself on a NW-SE axis maintaining winds from a SE direction off a cold land source only veru slowly weakening in situ, thus the milder uppers and high dewpoints never got a look in on that occasion. Altitude made little difference due to the air source and wind direction, coastal districts of Cumbria so more snow than even here.

[Aaron]

Sunday is forecast to be sunny with a high of 17c and a low of 9c. The BBC always over-estimate the temperatures, and on many occasions I record temperatures at night 4c lower than the forecast, due to my more rural and sheltered location. Frost is unlikely at a low level area like mine but I'm sure it's gonna be chilly the next few nights!

[Isolated Frost]

Regardless of what you's say - I'll take this! Cairngorm summit is in frost territory!

Cairngorm summit

1400: 0.5C

1500: 0.3C

1600: 0.2C

1700: -0.1C

1800: -0.2C

1900: -0.4C

2000: -0.5C

[NorthernRab]

There we have it then, I'll take that! First frost

[A Winter's Tale]

Currently around 7c in many settlements in the Highlands. We may see temps drop below 3c and any shower in the area could bring snow down to quite low levels.

Keep an eye out for an outside bet of first settlement snowfall of the winter!

6.6c in Aviemore at 8pm.

Hopefully below 3c or 2c by morning are really hopefully below freezing with a wee shower of snow!

From the Scotland Regional Discussion Thread:

Doctormog "I see that Altnaharra was reporting sleet at 7pm . Surely some mistake?"

If there was sleet in Altnaharra there would surely have to be some snow flakes. Therefore, if that's the case, we are looking at the first Snowfall of the Winter in Any Settlement on August 28th 2011.

Last year it was around September 27th when I started my first topic on how snow was reported in Altnaharra. There's still time to see if we do get a confirmed snowfall so fingers crossed for a definite First Snowfall of the Winter!

[A Winter's Tale]

http://www.metoffice.gov.uk/weather/uk/he/altnaharra_latest_weather.html

Take a look at Altnaharra at 7pm. Sleet was reported!!!!!!!

If a single snow flake had fallen then we are looking at the first Snowfall of the Winter in any UK Town.

Last year I joined Netweather and posted about how the first snow arrived in Altnaharra on September 27th.

If it had snowed or a single wet flake had fallen then we should celebrate.

First Snow, First ramp for a cold and snow winter!

[Aaron]

To think, Altnaharra is at a same elevation as me... how unfair!

[Aaron]

The skies will need to clear first in Scotland, If it's still raining up there. Currently 10 °C at Leeds Airport station, so if skies clear more, a chilly night for us.. hopefully our first ground frost won't be too long.

[A Winter's Tale]

An incredibly cold day up in Altnaharra with temps failing to rise above 9c!.

With night time still to come perhaps there could be more in the way of sleet and snow in either Altnaharra or Aviemore that currently sits at 7c!

I'll check the met office observations tomorrow morning to see if snow has fallen up there.

Aviemore is still at 6.6c and many other places are at 7c. Temperatures should drop in the 4c region (or below) and there is still some preciptation in the region. I would say the Aviemore is still the best bet for snow during the night as the low pressure leaves Altnaharra and Aviemore is already at a distinctly chilly 6.6c. It really has been more of a November day up there rather than late August!

Autumn has well and truly begun and so has the snow season!

[Geordiesnow]

"I see that Altnaharra was reporting sleet at 7pm . Surely some mistake?"

If there was sleet in Altnaharra there would surely have to be some snow flakes. Therefore, if that's the case, we are looking at the first Snowfall of the Winter in Any Settlement on August 28th 2011.

Yeah it was an error seeing as Altnaharra is reporting 8C and heavy rain on its 8PM update.

Impressive too see Aberdeenshire is 7C with a 5C dewpoint with drizzle being reported, just shows that the airmass is quite cool and that temperatures have falling despite strong winds and rain.

Looks like it been a miserable day in Scotland today with temperatures barely getting into double figures. What was Aberdeen's highest temp today? Did it scrap into 10C or was it single figures all day?

Regarding first frosts, it depends how much the cloud breaks but even on Monday night, there is still an noticetable airflow across Scotland which would surely keep temperatures up if not by the wind, then by any cloud that would probably appear?

[Staffordshire]

If it is only 81m ASL then surely it's snowing on the mountains?

[Aaron]

Sleet in Altnaharra at 7C is possible. It's unlikely but it can happen, so we should wait and see.

[Optimus Prime]

It really has been more of a November day up there rather than late August!

Looks like the highest maximum today was 11.0c at 1 AM this morning. But it certainly has been an exceptionally cold day for Altnahara. The average maximum is 17.1c.

Looks likely to be the lowest maximum since 1993 when on the 22nd the maximum was 10.2c (and 10.8c on the 23rd)