On 31/12/2015 11:34, Norman Lynagh wrote:
It does make sense if you use manual instrumentation rather than electronic. In
particular, the rain gauges in automatic weather stations, such as the various
Davis instruments, are a bit flaky. I find that mine under-reads by a variable
factor, usually in the range 10-20%, compared to what I measure with a standard
5" manual gauge.

If you use the standard 09z-09z recording period tonight's minimum temperature
will be credited to 1st Jan. As far as the daily minimum temperature is
concerned December ended at 0900z today. For the daily maximum temperature
December ends at 0900z tomorrow.

I agree Norman, even though my Davis TBR sits next to my 5" copper gauge
with both rims at 30 cm above the grass, it still under-records by
around 10%.

The difference with my TBR is that the under-recording is quite
consistent and if you times the TBR readings by 1.1 then you get a
result that is almost the same as the manual recordings.

This is even with the TBR being calibrated.

For example, in November my manual gauge gave a total of 68.8 mm whilst
the TBR result (x1.1) gave 66.7 mm. This is pretty typical of most months.

--
Nick Gardner
Otter Valley, Devon
20 m amsl
http://www.ottervalley.co.uk