Temp/humidity differences between Farnborough and Reading

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Temp/humidity differences between Farnborough and Reading

Postby greg_gruner » 2014 Dec 02, 12:17

I always compare my readings with those at Reading University (http://www.met.reading.ac.uk/weatherdat ... eport.html)

At 1200 today, there were some interesting differences:

My station:
Temp = 6.5C
Dew point = 5.4C
RH = 93%

Temp = 7.1C
Dew point = 4.4C
RH = 83%

The differences are slight, but usually the values are closer than that, as the university site is only 18km NW of here. Especially on an overcast day like this, one would expect a close fit.

However, the wind is NNE both here and at Reading (and over most of SE England). Looking at the trajectory of the air, it would appear that the path to Farnborough is over the Wash, while that to Reading crosses the coast at the Humber estuary, giving a significantly longer path over land. I am speculating, but maybe that accounts for the drier but slightly warmer air over Reading?
Greg Gruner
Farnborough, Hampshire
Posts: 224
Joined: 2012 Feb 04, 17:28

Re: Temp/humidity differences between Farnborough and Readin

Postby Stephen Burt » 2014 Dec 06, 19:11

... much more likely to be due to more local influences and/or sensor differences, I suspect.

Assuming you're using a Davis AWS (I think I saw this from previous postings?), the Davis RH sensor is quite slow to respond. Most capacitative sensors are sluggish in the higher ranges, and will 'stick' there for some while after a spell of high humidity, as it was earlier that day. For what it's worth, my readings at 1200z were:

Screen temperature (PRT) 7.4°C
Davis VP2 7.2°C
AWS screen (PRT) 6.9°C
Aspirated (PRT) 6.9°C

RH (screen, from dry and wet bulb PRTs) 83%
RH (from Vaisala capacitative sensor) 84%
RH (from Davis VP2) 83%

Wind (10 m anemo) was 360°, 10 kn, gusting 21 kn in the previous hour. Although there was no sunshine here (10 km SW of the university site), it was slightly brighter in the preceding half-hour, and it could also have been that slightly thinner cloud that caused the slightly higher temperature and lower RH in the Reading area. On other days, you'd just as likely find differences in the opposite direction, I'm sure.

Stratfield Mortimer, Berkshire - central southern England
51.4°N, 1.0°W, 60 m AMSL, station grade A - AAAA47R
Records commenced here 1987 - local records available back to 1862
The Weather Observer's Handbook: www.measuringtheweather.com
Stephen Burt
Posts: 247
Joined: 2011 Dec 02, 19:36
Location: Stratfield Mortimer, Berkshire; a well-exposed rural site, 10 km SW of Reading

Re: Temp/humidity differences between Farnborough and Readin

Postby greg_gruner » 2014 Dec 07, 20:34

Thank you, Stephen, for shedding some light on this! I am sure you are right both about the sensor (I use a David Vantage Vue) and the local differences. Although Reading didn't report any sunshine, I think that thinner cloud may also have made a difference, as you suggest. It was a low, thick overcast here.
Greg Gruner
Farnborough, Hampshire
Posts: 224
Joined: 2012 Feb 04, 17:28

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