Dave J
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Some very low maxes today in the SE/ E Anglia:
Charlwood, Surrey -2.9C
Marham, Norfolk -2.6C
Andrewsfield, Essex -2.5C
Wattisham, Suffolk -2.5C
Kenley, Gtr London -2.4C
Farnborough, Hampshire -2.0C
London Heathrow AP -1.9C
Northolt, Gtr London -1.9C
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IT's probably in some way related to the recent cold weather and subsequent thaw. There were balcony railings falling off buildings in Plymouth on the local news yesterday.
http://www.thisisplymouth.co.uk/news/Cold-...il/article.html
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Hey DaveJ, Wattisham being the main Ipswich weather recording site, I can confirm dense freezing fog all day of 100m below visibilty, they have 200m now but where I am its a lot thicker. No respite all day, and now a chilly -1oC
Yeah it seems to be thickening again, they've gone down to 100m on their latest ob and -2C!
EGUW 081650Z 00000KT 0100 FZFG VV/// M02/M02 Q1028 RED NOSIG
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Feels quite warm here today despite it being only +4C and cloudy with thick stratus all day. Light winds. I can see a break in the St out over West Dorset heading towards us, so it looks like we'll get another air frost tonight - then some sharper ones to come on Friday and Saturday night as we pick up a drier continental feed.
Noticed that Wattisham has been in freezing fog all day!
Currently -1C already there: METAR EGUW 081550Z 00000KT 0200 FZFG SCT200 M01/M01 Q1029 RED NOSIG=
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Mean temperature for the first 7 days of the month at home in Suffolk was -1.1C! :wacko:
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Weather stats from Leavenheath, Suffolk (~60m AMSL)
(Departures from mean are from the 1971-2000 mean at Wattisham airfield in Suffolk which is ~10 miles northeast of the site)
A cold and dry month, the coldest December for 7 years - and even drier than that December which recorded 17.4mm of rainfall.
December 2008
Mean temperature: 3.7C (Lowest since 2001 which recorded a mean of 3.0C)
Mean maximum: 5.7C (-1.4C)
Mean minimum: 1.6C (-0.3C)
Highest maximum: 12.5C (20th December)
Lowest maximum: 1.5C (29th December)
Lowest minimum: -4.2C (12th December)
Highest minimum: 8.5C (22nd December)
No. of air frosts: 12
Total rainfall: 12.0mm (23%)
Wettest day: 6.8mm (13th December)
Days with rain >=1mm: 3 (-8 )
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Ok this is something thats confused me for a while
What is the Highest temperature that snow can fall at?
someone tells me is 2c
someone else tells me its 3c
Well it could theoretically snow with an air temperatures as high as 8C, but you would need a dew point of -23C (RH: 11%) and this is extremely unlikely! In reality it's more like around 4C as an absolute limit in the UK (which still requires a dew point of -8C) and is likely to occur in Spring when you get a cold northerly outbreak with strong sunshine able to heat the air at the surface very quickly drying it out - then a heavy shower with a strong downdraft passing over which will lead to very strong evaporative cooling occurring reducing the air temperature to the wet bulb temperature (in this case around 0C) and snow to fall to the surface.
Edit - what TWS said basically.
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Typical of OON to show off his 4 inches on national television. Sophie Raworth does look very impressed however.
Well done and that..
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Following on from this, what exactly determines/sets the dewpoint at a particular place and time? I understand dewpoint being "the temperature to which air must cool to reach 100% relative humidity"- but why do some airmasses have higher dewpoints than others, and why looking at maps can dewpoint vary by 3-5C over a few dozen miles, when the same air mass is present everywhere? (I have seen this phenomenon this week).
The dew point is effectively a measure of how moist an airmass is, this will vary considerably within a particular airmass particularly over the UK because of the variations between drier inland observation sites and those that are near lakes or by the coast where there are significant moistures sources. Airmasses that originate over the warm Azores (Tm/Tropical maritime) pick up the characteristics of where they are formed and therefore have high moisture content (typically in the summer as high as 15C) whereas those that form over the dry continent of eastern Europe/Russia such as our current Pc/Polar continental airmass, have low moisture content which can be as low as MS10C. Dew points will also fall at night at varying rates as moisture is deposited on surfaces as hoar frost. The dew point can also vary with pressure though this effect is only really noticeable with altitude rather than over distances at the surface, where the variations are an order of magnitude higher.
I can understand why it rains with a dewpoint 1C and temp 1C as it can't cool below freezing before precip occurs, but why do higher dewpoints stop snow settling?The dew point is the temperature at which evaporation and condensation of water vapour is in equilibrium - it has a very high positive correlation with snowmelt such that the higher the dew point the faster the melting/evaporation of snowcover. This is because the vapour pressure of the snow (frozen water) becomes increasing less than that of air (water vapor) and therefore condensation occurs, which releases latent heat melting the snow (a process which in itself takes latent heat).
This is often observed in the form of low stratus and/or fog developing (depending on surface flow) as positive dew points advect over snow fields.
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A Tephigram for yesterday will probably illustrate it best.
Below is Albemarle's midnight ascent for the night just gone. Ok it's not exactly Lancashire but it's the nearest one we have..
As you can see, at the surface the air temp is 0.2C and dew point -1.2C which you would expect to produce precipitation in the form of snow- however in the profile between approx. 1000ft and 3000ft AMSL there is a wedge of relatively warmer and moist air which acts to melt the snowflakes as they fall through that relatively warmer layer on their way to the surface. The melting snowflakes will fall to the surface as either a mix of raindrops and big snowflakes (that survive the warm layer) or if the cold surface layer is deep and cold enough, result in ice pellets or even the very hazardous and relatively rare freezing rain!
There are other complications such as evaporative cooling which can, over time and with little mixing, cause the profile in the lowest few thousand feet to became isothermal along the 0C line and bring the freezing level to the surface - and with it rain changing over to snow!
It all adds up to make snow forecasting a total nightmare...
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December 2001 Cet was 3.6c
So looks like 3.5c, the coldest for 12 years.
We are really on a cooling trend this year. :o
I meant the year, not the month - though it is quite possibly the second coldest recorded CET for a month this millennium. :o
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9.75°C
Global warming rolled back a decade as Met Office says 2008 coldest since 1996.
That's not what the Met Office wants to happen. So they are just waiting a few more days before they release the results that they already know.
1996!? It definitely won't be colder than 2001.
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Slight rise on Hadley to the 5th
CET 01/01/09-05/01/09 -0.2C
Goes to show that with such a low starting point, it needs to be really cold for falls to occur, although the 6th should see a fall.
They have last nights minimum as -5.6C, coldest CET night since 3 March 2006 (-5.9C).
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Kentimetres! I love it. :blush:
Speaking of which, Kent was actually the last place that I saw a 'proper' snowfall on 10th April 2006. 10cm of wet and completely unforecasted snow fell close to Tunbridge Wells during the night.
... and that was in the year that became the warmest on record for England and Wales!
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14.0C - mostly cool and unsettled later but some prolonged warm, settled periods in first and second week. Think we're overdue a cool(average) June..
The 61-90 and 71-00 average for June is 14.1C, here are the values from the past 10 years:
1996: 14.4C
1997: 14.1C
1998: 14.2C
1999: 13.9C
2000: 15.1C
2001: 14.3C
2002: 14.4C
2003: 16.0C
2004: 15.3C
2005: 15.7C
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To get total rainfall expected over the next few days you might find these charts useful:
http://www.wetterzentrale.de/pics/Rmgfs24sum.gif (T+24hours)
http://www.wetterzentrale.de/pics/Rmgfs48sum.gif (T+48hours)
http://www.wetterzentrale.de/pics/Rmgfs72sum.gif (T+72hours)
http://www.wetterzentrale.de/pics/Rmgfs96sum.gif (T+96hours)
http://www.wetterzentrale.de/pics/Rmgfs120sum.gif (T+120hours)
http://www.wetterzentrale.de/pics/Rmgfs144sum.gif (T+144hours)
They show accumulated rainfall from the initiation of the run until T+24, 48hours etc...
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I don't think we should still be discussing whether GW is going to have a major impact or not as we seem to enter a neverending debate whereby the pro-AGW people put forward more and more evidence from well-funded research which the anti-AGW instantly dismiss. To put it another way, there is no amount of evidence that will persuade the anti-AGW people that it isn't happening... until of course it's too late.
I try to keep an open mind on the matter- having recently studied Climate Change as part of my degree I understand the atmospheric chemistry and physics behind AGW and the problems encountered with trying to model a complex atmosphere and to understand what impact we may or may not be having.
There are many uncertainties (cloud feedbacks, aerosol feedbacks, future emissions), and we don't even know how sensitive the climate system is to the forcing induced by increased well-mixed greenhouse gases. When looking at global temperatures and how they have changed, there are few reliable observations before 1900 and those that do go back further have undergone change in instrumentation, the change from Fahrenheit to Celcius, changes in site exposure (more urbanised) etc.
We cannot continue to use resources at the rate we currently are (as we're beginning to find out with Petrol prices rising to record levels) and funding needs to be spent on creating a more sustainable society. New buildings should have solar panels, efficient recycling, better public transport, more local produce - instead of getting your strawberries from thousands of miles away- go to the local farm and pick your own, or buy the ones picked from the farm...
There ends my lecture.
The only thing that's confusing is that I thought water/water vapour is the biggest warming agent playing a bigger role in warming than CO2 or is that not right.Yeah you're right but CO2 has increased much more (percentage-wise, from 275ppm to 380ppm) than H20. A doubling in CO2 will have a greater "radiative forcing" on the climate system than the comparatively small increase in water vapour.
Water vapour could be a positive feedback mechanism because in a warmer world there is more evaporation from the land and sea water stores leading to a greater H20-concentration in the atmosphere (which will then warm the climate further- and lead to more evaporation etc...)
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Here are the maxima I recorded from the 6th- 11th August 2003; my station at the time tended to underestimate the max by around 0.5C - 1C due to a very slow lag-time but in general the maxima were close to that of nearby Wattisham in Suffolk.
6th: 33.0C
7th: 29.7C
8th: 29.3C
9th: 33.2C
10th: 34.6C
11th: 31.8C
The 6th, 9th and 10th are the 3 hottest days I've ever recorded (with records only going back to July 2000)- and on the 10th it passed 30C at around 10.30am!
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Yesterday the max at Connaught Airport, Ireland was just 6.5C, some 8C below average.
For the past 8 or so days, daytime maxima have been below average across much of England and Wales, it's just that overnight minima have been much above average for sometime which has skewed the CET.
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Appreciate the work you've put into this Ian. Makes very interesting reading.
Not surprised that ECMWF has come out top dog- I've always considered it the best model when looking at the medium range (4 days+) and this goes some way to support that. The forecasters at the Met Office take a great deal of consideration over its output often and it has a much bigger ensemble!
Very interesting also that GFS model just pips UKMet, although the difference is negligible and because the judgement is subjective it probably isn't worth reading into.
Thanks again.
--P.S. would be interesting to see the standard deviation/variance of each model (I think it's quite simple to do in Excel?) to see how "wobbly" each model is.
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Quite right Scorcher!
I'm still going for between 13C and 14C, although at the start of the month I guessed 12.6C. I see no way it will drop as low as some on here are suggesting. It's May not January! And with the second half coming up, notwithstanding the changeable scenario for a week or so I can't see it dropping much if at all from here.
Hey Richard- did you notice the extreme heat across SE Spain today?
850hPa temps circa. +24,+25C and surface temps up to +40C. Many station temperature records have fallen today for May.
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Cheers Steve for putting the summer forecast together.
Sounds great- Convective storms, prolonged warmth and no exceptional heatwaves. Great stuff! :blink:
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Rain is likely in all areas at times during the week ahead, however, in the south there should also be some drier and brighter weather at times.
During the day temperatures will be quite warm, but will fall at night. Sunlight will also decrease at night, and when it's not windy it's expected to be relatively calm. Clouds are expected to form at times but skies will otherwise be cloud-free.
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I reckon (looking at recent model output and trends) that the month will end up around 1C above average (12.3C) by the end due to a significantly colder and wetter 2nd half.
Scottish Met Office
in Spring Weather Discussion
Posted
The Aberdeen office forecast minimum temperatures for Scotland, due to their local knowledge/expertise...