Temperature

Fri 8 Jan 2010, 16:08

I also recorded a minimum temperature of -8.3 C on Thursday morning and this is the lowest in January since my daily record began in 1990.
This reading was taken at the standard meteorological height of 4 feet above ground level, although at the moment it is effectively about 9 inches lower than that with respect to the top of the lying snow.
However, the minimum temperature on the surface of the snow was -16.7 C (2 F). This difference in temperature in a little over 3 feet illustrates the sort of variation that can occur over snow cover on a clear night, and why there is this need for a standard height when comparing temperature readings.
It also explains why frost hollows, like Benson, attain such low temperature because the dense and very cold air near the snow surface flows downhill and eventually accumulates to a height of more than 4 feet at the bottom of an enclosed valley.

Fri 8 Jan 2010, 12:23

Readers may recall that I produce maximum and minimum temperatures for the Charlbury Chronicle. I have been keeping daily records since 1st January 1989.
The temperature on my thermometer dropped to 17°F (about -8.3°C) during the night of 6th/7th January. This is a little higher than John Dora recorded (16°F) and confirms what Hamish Nicholl suspects about there being considerable differences depending on where you are in Charlbury.
As to whether this 17°F was a record, it certainly was for a January night during the 22 year period that I have been keeping these records. The previous January record low was 18°F, set in 1997 and equalled only a year ago, also on 6th/7th. The lowest temperature recorded since 1989 was 15°F (-9.4°C) in December 1991.
Just to put this into perspective, the lowest temperature that I have ever recorded since aquiring my maximum/minimum thermometer in 1980 was in January 1982 when the temperature plummeted to -1°F (-18.3°C). That winter, we had two cold spells, one in December, the other in January.

Thu 7 Jan 2010, 20:03

Do have a look at my other weather page: www.dora.abelgratis.com/assets/Charlbury_Weather.html

Thu 7 Jan 2010, 19:46

Thanks for the explanation Tony. I should have realised it was Relative Humidity.

Thu 7 Jan 2010, 19:16

I understand that this mornings minimum temperature recorded in Wychwood Paddocks was the coldest since 1990
To answer Mike's point about the humidity. It is not so that 'all the moisture has been frozen out'. Air can still hold a proportion of water vapour (a colourless gas) at temperatures below zero. Relative Humidity is the proportion of water vapour present compared to the maximum it could hold at the ambient temperature (expressed as a percentage).
On a more controversial point (but please don't quote me!) Since the recordings were automated and instruments moved to a different site in the 1990s,minimum temperatures recorded at Benson have been consistently lower than those recorded before and compared with others around. It seems the 'new' is something of a frost hollow and not altogether representative of the general area.

Thu 7 Jan 2010, 17:25

Agree it is a great site!
John, may I ask (roughly) where in Charlbury is your weather station situated? Walking around Charlbury and the surrounding fields in the evenings it is quite noticable how much the temperature varies. For example walking from Sturt road down past Wellington cottages towards the Cornbury gatehouse the temperature sometimes feels like it's plummeting!
However, there's no doubt it's bl@@dy cold outside, but absolutely beautiful as well. It's great to see in these cold temperature that people's warmth to everyone else, whether friend or stranger appears to increase exponentially and more than make up for the abundant snow and ice - is this just because work/school is cancelled for the day??!

Thu 7 Jan 2010, 17:05

Great site! I'm puzzled about humidity though. Is it an outdoor reading? If so, with the air temperature below zero, I'd expect humidity also to be zero (all the moisture having frozen and lying as frost on the ground). Or is it an indoor reading ? Thanks.

Thu 7 Jan 2010, 16:55

Congratulations John on a great website. I will put it in my favorites.

Thu 7 Jan 2010, 16:37

I'll own up to the website....and the weather station that feeds it.

The 'all time records' relate to the data held on the database and it's been running only since 2006 so that's 'all time' to the machine!

Sadly it doesn't record snow depth and the raingauge can become frozen - I notice that today the sun did melt some of the snow which shows up as 'rain'!!

The indoor temperature is high not because I'm wasteful on heating but because the indoor sensor is conveniently situated near the PC which is running continuously. It'd be great to have microprocessors that don't generate so much heat. Perhaps one day the Government will introduce a scrappage scheme for steam powered coal fired PCs...?

Thu 7 Jan 2010, 11:20

What I can't understand is how that webite knows the indoor temperature of 22.4C. If that in my living room temperature I had better turn the thermostat down a notch!

Thu 7 Jan 2010, 11:17

Thanks all. I expect he will think -9 C (give or take 2 degrees!) is pretty good.

Thu 7 Jan 2010, 11:06

According to my (aging, slightly temperamental) max and min thermometer, the minimum temperature last night in Crawborough was -7 C. If that's right, then your son might like to know that it's been around that every night recently, and certainly no lower.

Thu 7 Jan 2010, 11:04

If you click the Records button you will see that the lowest temperature was -9 deg C at 06:51 today in Charlbury. if you click All Time Records, you will see that it appears to be an all time record. Is it true though?

Thu 7 Jan 2010, 10:45

Fabulous though the site is (and we will be using it from now on), am I right in thinking it only shows you the current temperature, not what it was last night?

Thu 7 Jan 2010, 10:35

Fabulous website - thank you Graham!

Thu 7 Jan 2010, 10:19

Have a look at www.dora.abelgratis.com/assets/CharlburyWDL.html for current and recent Charlbury weather information. I can not always vouch for its accuracy but it does give a pretty good guide to conditions. The site used to be listed on the Charlbury website but I'm not sure if the link is still there.
Graham

Thu 7 Jan 2010, 10:03

To help my son compete with his cousins in the Netherlands in the field of worst (=best) winter, can anyone tell me what the temperature was last night in Charlbury? On the bbc oxfordshire website it said that temperatures of -18 C have been recorded but was it as low as this here?